Browsing by Person "Sauerborn, Joachim"

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Agrobiodiversity and its use in Naban River Watershed National Nature Reserve : implications for bio-cultural diversity conservation
(2012) Ghorbani Dahaneh, Abdolbaset; Sauerborn, Joachim
This study was conducted in the Naban River Watershed National Nature Reserve (NRWNNR), Xishuangbanna Dai Prefecture, SW China and aimed at identifying the diversity of medicinal and food plants used by local people living in NRWNNR and documenting their applications. NRWNNR is diverse biologically and culturally and people living in its territories get benefits from their diverse natural environment. However the extension of cash crops such as rubber (Hevea brasilliens (Willd. ex A. Juss.) Müll. Arg.) plantations and fragmentation of natural habitats including forests resulted in decreasing biological diversity which could be used by the local people. This also put more pressure on the remaining forests and plant resources. In order to find sustainable alternatives to conserve biodiversity and at the same time helping the development of the area it is necessary to know the available resources in the area. Among important plant resources in the area are non-timber forest products with economic and cultural importance including medicinal and food plants. Therefore, using ethnobotanical methods this study intended to document wild medicinal and food plant resources used by ethnic groups and their use details including their collection practices, preparation methods and habitat preferences. Data on useful plant resources was used to identify the main land use sources of useful plants for local people. The study also intended to understand the role of these plants in local people?s livelihood by identifying economically important medicinal and food plants traded in the area. Vulnerability of plant species to resource exploitation and harvest sustainability for selected species were assessed. To achieve above mentioned objectives, an ethnobotanical inventory of useful wild plant resources was conducted in the area to collect data on wild plant resources and uses. Semi-structured, freelisting, and household interviews were conducted from January 2008 to January 2010. Informants from Dai, Hani, Lahu and Mountain Han ethnic groups were selected randomly for freelisting and semi-structured interviews and key informants by the snowball method. Household interviews were conducted in six villages. Interviews were also conducted with harvesters and traders. All interviews were supplemented with plant sample collection for botanical identification. Plant specimens were prepared, dried, and identified with the help of local botanists. To address the vulnerability and sustainability of plant harvest, strip-transects were used to estimate the density and distribution of selected species in natural populations. Results showed that 480 plant species (25% of recorded flora) from 117 families and 334 genera are used by the local population. From these, 378 species (19%) belonging to 102 families and 277 genera are used as medicine and 161 species (8%) representing 68 families and 116 genera are used as food plants. Concerning livelihood contribution, most of these plants are used at the subsistence level and not for income generation. However some households can get from 1.1% up to 25.4% of their total annual income from sale of few medicinal species. Among food plants only bamboo shoots and mushrooms contribute to the cash income of households with the highest share in BenGang Hani village (1.1%). Knowledge of medicinal plant use and folk medicine still exists in the area and there are local healers and practitioners who are active in some villages. However this knowledge shows some differences among ethnic groups. Number of medicinal plants used by Lahu and Hani is different and some species are solely known and used by only one ethnic group. Since these ethnic groups live in neighboring villages, it was expected that a large proportion of their medicinal plant knowledge is shared. However, the diversity of medicinal species utilized by the two ethnic groups show 30% overlap. Medicinal plants are grouped into different categories based on frequency of use. 1- Frequently used medicinal plants which are few in number. 2- A large number of medicinal species are only known and collected by traditional healers or some knowledgeable elderly people. 3- A few numbers of medicinal plants are frequently and in high amounts harvested by locale people for commercial purposes and not for self consumption. Examples of these species include Asparagus subscandens F.T. Wang & S.C. Chen, Asparagus filicinus Buch.-Ham. ex D. Don, Stemona tuberosa Lour. and Paris polyphylla var. yunnanensis (Franch) Hand -Mazz. Although use of these medicinal plants is known to traditional healers, majority of the villagers which are involved in harvesting of these species are not knowledgeable about their medicinal applications. In fact harvest is driven by market demand which is brought to the area by middlemen and retailers visiting the villages. Wild food plants are also grouped based on harvest and use frequency into different categories. The first group includes species with high frequency of use which have a very common distribution range in the area. Second group includes bamboo shoots and mushrooms which are traded to some extent. The last group includes a large number of species which are not used frequently but are potential food plants used only by a small proportion of the local population or during famine or crop failure periods. Based on vulnerability assessment of marketed species in the area, most of the important plants are in danger of overexploitation. However frequently used food plants are not threatened with overharvesting since they are very common in the area. Among the wild food resources bamboo shoots and mushrooms are exploited without sustainability measures. Collection of high economically valuable medicinal plants is also not sustainable as subterranean parts are harvested and collection is fatal for the plant. Sustainable harvest and management strategies should be implemented to prevent overexploitation of these species. Findings also highlight plant species which can be proper candidates for cultivation especially in agroforestry systems. There is already a good potential on the improvement of economic gains from some forest products such as mushrooms with value adding by improving drying methods and establishment of village based enterprises. Cultivation of economically important medicinal plants in herbal gardens or agroforestry systems are recommended since it can reduce pressure on natural population and at the same time diversify and secure the economic gain of villagers.
Biodiversity and arthropod abundance in the upland of Leyte, Philippines
(2005) Szinicz, Gundula; Sauerborn, Joachim
In the humid tropics of SE-Asia the last primary forests are dwindling at an alarming rate. In many regions cultivated and degraded land outnumbers by far natural ecosystems. In the upland of Leyte island this is due to commercial and illegal logging activities and intensive slash-and-burn agriculture. The loss of the natural vegetation cover is accompanied by a decrease in diversity of fauna and flora, consequently also in ecosystem services and interactions, thus destabilizing the system and finally leading to degradation. To further preserve and restore natural biodiversity landscapes dominated by man need to be included in an overall research strategy. So far only few studies focus on the biodiversity of cleared and converted land adjacent to natural areas in the tropics. This study was conducted in a Philippine upland area and focused on interchanges of insects between the natural and the managed landscape. Two questions were approached. (1) Which structures and components of the cultural landscape are of significance for conserving arthropod biodiversity, and (2) are there species which originate from the natural forest and are able to become resident in the man-made systems? In order to answer these questions insect- and plant surveys as well as the movement patterns of selected insect species were examined along a gradient from the natural forest through the agricultural land. So as to define the effects of habitat destruction on the arthropod community of the research area arthropod communities of different habitats between the natural and agricultural ecosystems with increasing distance to the forest, in relation to the vegetation were compared. Insect sampling was carried out using modified Malaise traps, whereby four habitats were considered: (a) forest interior, (b) forest margin, (c) vegetable fields and (d) chayote ((Sechium edule (Jacq.) Sw. (Cucurbitaceae); the only perennial vegetable of the area) fields. These traps allowed a separate catch for each of the two arrival sides, whereby the one was always opened to the forest and the other to the field. Trapping was set up for a total of 18 months in 2001 and 2002 at three sites with the four habitats each. Arthropod diversity, composition of the arthropod community and trophic guild composition at habitats were determined for each habitat and arrival side. Obtained results are presented and discussed with regard to first: arthropod diversity and community composition along the transect from natural through agricultural systems; second: abundance patterns of selected species in natural and agricultural systems and third: abundance patterns of selected species within the agricultural land. It was found that plant diversity, vegetation structure and taxonomic composition as well as differences in the turnover of the vegetation at habitats (productivity of vegetation) influence arthropod groups and species in the study area in different ways which could not be generalised. Further, the relationships of insects between the natural forest and the open agricultural land were considered. In order to identify species that occur in the forest as well as in the open country, first, insects at sites of the forest interior, the forest margin and the agricultural land, were recorded using modified Malaise traps. Then, movement patterns of selected species were determined based on their abundances at the different habitats and arrival sides. In addition it was tried to find out whether major pest species of the cultivated crops show any relationship to the adjacent natural forest, and whether species originating from the forest (non-pest species) are able to colonize open country. The results indicate that the habitat of the pest species considered is limited to the cultivated land and does not include the forest. None of the non-pest species recorded in this study would be able to exist permanently in the agricultural area. They all depend on a closed forest habitat and therefore will become extinct as the forest disappears with proceeding slash-and-burn agriculture. However, some but not all of the pest and forest species were regularly recorded from the forest margin. Finally it was focused on relationships of insects between perennial and consecutive changing vegetable crops. Two kinds of habitats were distinguished: (i) frequently disturbed and rotational changing vegetables with simple architecture; (ii) rarely disturbed stands of chayote, with complex architecture. The impact of changing crop and weed species composition and the agricultural practices (soil preparation, planting, weeding, harvest) applied on the abundance of selected insect species and the question whether stands of chayote are used as refuge as long as conditions in the seasonal vegetables become unfavourable due to agroecosystem management applied were analysed. The insect species investigated include phytophagous specialists and generalists as well as beneficials (predators and pollinators). It only was possible to generalize movement patterns regarding significance of abundance variations at habitats and at opposite arrival sides of the traps in each habitat. With respect to the population development of the species in relation to cropping patterns and agricultural practices applied no common patterns could be determined. The results contribute to the assessment of the effects of man-made habitat conversion on the arthropod fauna in tropical ecosystems. The identification and classification of habitats and their interactions might enhance the understanding of ecosystems in order to make aware the need to preserve and restore biodiversity.
Biological control of Striga hermonthica (Del.) Benth. using formulated mycoherbicides under Sudan field conditions
(2008) Zahran, Eldur; Sauerborn, Joachim
Striga hermonthica is a parasitic flowering plant belonging to the family Orobanchaceae. It is a root parasite that attacks sorghum, maize, millet and several grass weeds in the semi-arid Tropics. In Sudan, Striga is widespread in irrigated and rainfed areas and considered the main biotic constraint in production of sorghum, the main staple food for the majority of Sudanese people. More than 500,000 hectares under rainfed cultivation are heavily infested with Striga, which commonly results in significant yield losses of 70 ? 100%. It has become obvious that there is no simple, fast and inexpensive solution to the Striga problem in Africa. Biological control is considered a potential cost-effective and environmentally safe means for reducing weed populations in crops, forests, or rangelands where low profit margins prevent large herbicide expenditure. Biological control using microorganisms (especially phytopathogenic fungi) showed a high efficacy in controlling S. hermonthica under controlled and field conditions. However, so far it did not come to practical field application. This could be attributed to environmental obstacles or due to the lack of appropriate delivery systems. The pathogenicity of two fungal isolates indigenous to Sudan (Fusarium nygamai [FN] and F. ?Abuharaz? [FA] isolate) against Striga has been studied using infected sorghum grains or a spore suspension as inoculum. These formulations were very effective in controlling Striga under controlled and natural conditions; however, a high level of fungal inoculum (approximately 800 kg ha-1 for the grain inoculum) would be required for effective control, which arises a lot of problems e.g. concerning sterilization and transportation. Such problems can be overcome by adopting an appropriate formulation technology. Granular formulations such as ?Pesta? and alginate pellets were found to be suitable delivery systems for controlling weeds. ?Pesta? granules are made by encapsulating bioagents in a gluten matrix. Alginate formulations are prepared by incorporating the biocontrol agent?s propagules in a sodium alginate solution, which is dripped to a calcium chloride or calcium gluconate solution. Alginate pellets are then formed by ionotrophic gelation. The main objectives of this study were: (a) to study the efficacy of the two Fusarium species in controlling Striga under field conditions using ?Pesta? and alginate formulations, (b) evaluate the effect on sorghum yield, (c) determine the optimum dose of the formulated material, (d) investigate the persistence of the formulated fungal isolates in the soil, and (e) study the efficacy of seed treatments as an alternative delivery system. Furthermore, for environmental safety reasons the newly isolated F. ?Abuharaz? isolate was tested for its ability to produce some of the most important mycotoxins. Harvested sorghum seeds out of the fungus-treated plots were also investigated for their mycotoxins content. A prerequisite to be able to formulate biocontrol fungi is the development of an inexpensive method of inoculum production that yields sufficient biomass containing viable, highly virulent propagules. Chlamydospores are the soil-persisting propagules of many Fusarium species and considered as ideal propagules to be used in granular formulations. For this reason, finding a medium suitable for the production of chlamydospores by the two Fusarium isolates was one of the specific objectives of this study. Different media were tested among them Special Nutrient-poor Broth (SNB) + yeast gave the highest number of chlamydospores (105 ml-1) in both isolates throughout the incubation period. However, both isolates generally did not form sufficient chlamydospores to be used within a bioherbicide formulation. Richard?s solution gave the highest number of microconidia (108 ml-1) after five days of incubation and hence it was selected as growth medium for formulation purposes throughout this study. FN and FA were successfully formulated in ?Pesta? and alginate granules amended either with 10% wheat flour or 6% sorghum flour or yeast extract. Alginate granules generally gave higher numbers of colony forming units (cfu) per g of formulated material compared to ?Pesta?. Alginate preparations amended with 6% sorghum flour or yeast extract had significantly higher cfu compared to the alginate formulation using 10% wheat flour. Yeast extract amendment further increased the number of cfu by about 38 and 32% for FN and FA, respectively, compared to sorghum amendment. In the first field experiment (2003/04), a screening for the suitable dose of ?Pesta? granules per planting hole to control Striga was conducted together with the investigation of a seed coating treatment as an alternative delivery system of the biocontrol agents. The ?Pesta? technology showed a potential to be used as a delivery system to control S. hermonthica under field conditions. Both ?Pesta?-formulated Fusarium isolates were able to delay Striga emergence, reduce the total number of Striga shoots and induce disease symptoms on all growth stages of Striga plants, irrespective to the dose and method of application used. The highest control efficacy was achieved by applying FA at 1.5g, which reduced the total number of parasite shoots by 82 % and the number of healthy Striga shoots by 88% compared to the untreated control. As a consequence, sorghum biomass and sorghum 100-seed weight were increased by 86 and 110%, respectively. FN and the combination of the fungal isolates were slightly less efficient in controlling the parasites. 1.5 g ?Pesta? granules per planting hole was found to be the optimum dosage for Striga management since increasing the dosage did not result in a significant improvement of control. In the second season (2004/05), the efficacy of alginate formulations amended with 10% wheat flour applied at 1.5g/planting hole was evaluated in addition to the ?Pesta? formulation for controlling Striga under field conditions. Alginate granules were able to delay Striga incidence significantly and reduce the total number of Striga shoots by 64 ? 78 % compared to the control early in the season. In contrast to the first season, fungal isolates formulated in ?Pesta? granules had no pronounced effect on delaying Striga emergence, however, ?Pesta?-granulated Fusarium species were able to reduce the total number of Striga shoots by 42 ? 55 % compared to the control early in the season. By the end of the season, the effect of both formulations on the total number of Striga shoots became negligible, but they significantly increased disease incidence on Striga shoots compared to the untreated control. FA formulated in ?Pesta? or alginate pellets was especially effective in this regard, causing disease in 74 and 80% of the Striga plants and reducing the total number of healthy Striga shoots by 55 and 60% compared to the control, respectively. FA applied as ?Pesta? granules was the most effective treatment in reducing Striga biomass by 58 % compared to the control which was positively reflected in an increased sorghum grain yield (63%) and sorghum straw yield (73%) compared to the control. The reduction of the efficacy of the ?Pesta? formulation in controlling Striga in the second season compared to the first season can probably be attributed to three reasons. These include a) climatic conditions, which differed from the first season in higher temperatures coupled with lower rainfall and low relative humidity, b) sodicity problems in the fields which might have affected the proliferation of the fungi in the soil and c) an inhibitory effect of the metabolites of the applied insecticide Sevin (active ingredient Carbaryl (1-naphthyl N-methylcarbamate)) on the virulence of soil fungi. Furthermore, an outdoor pot experiment was conducted to study the efficacy of alginate formulations with different amendments (wheat flour, sorghum flour and yeast extract) in comparison to the ?Pesta? formulation and seed treatments on controlling Striga. In this experiment, FA formulated as ?Pesta? granules was the most effective treatment and successfully inhibited Striga emergence until the end of the season. This was reflected in a significantly increased sorghum plant height (by 80%) and sorghum shoot dry weight (400%) compared to the negative control. Fusarium species in alginate granules also delayed Striga emergence and reduced the total number of Striga throughout the growing season. The best efficacy was obtained by FA, which reduced the total number of Striga shoots by 71% (using 10% wheat flour) and 84% (6% sorghum flour or yeast extract) compared to the control. Likewise, it reduced the proportion of healthy Striga shoots by 71%, 88% and 84%, respectively, and Striga biomass by 50%, 81%, and 89%, respectively. Alginate formulations generally also significantly increased sorghum plant height by up to 80% and sorghum shoot dry weight by 200 to 400% compared to the control. It can therefore be summarized that of the investigated fungal isolates and granular formulations FA formulated in ?Pesta? granules showed the best efficacy in controlling Striga under field and controlled conditions. The ability of FA to produce trichothecene mycotoxins that could be a hazard to humans or animals was assessed from samples of the fungus growing on autoclaved wheat grains. Additionally, samples of harvested sorghum seeds from various plots inoculated with the biocontrol agents were investigated for the content of trichothecene mycotoxins. None of the following toxins were either produced by FA or translocated to harvested sorghum seeds under field conditions: nivalenol, fusarenon X, deoxynivalenol, 15-actetyldeoxynivalenol, scirpentriol, monoacetoxyscirpenol, diacetoxyscirpenol, T-2 triol, HT-2 toxin, T-2 toxin and neosolaniol. A simple seed coating treatment using fine ?Pesta? granules and gum Arabic as adhesive material also showed a potential to control Striga in the first season experiment. It was able to reduce the total number of Striga shoots by more than 55% compared to the control. Consequently, sorghum biomass was increased by 54 ? 67% and sorghum100-seed weight by 70%. The effects were comparable to that caused by chemical control using 2,4-D. To improve the efficacy of seed coating under field conditions for the second season experiments, the effect of five types of adhesive materials (2 types of cellulose, 2 types of organic polymers and a clay) on growth and sporulation of FA and FN were tested in solid and liquid media. Cellulose 1 and 2 were found to enhance radial growth of both isolates but did not increase sporulation in liquid media. Organic polymer 2 was found to retard both radial growth and sporulation of the two isolates. Organic polymer 1 and clay significantly enhanced the production of chlamydospores, especially by FA, compared to Richard?s solution alone or amended with the other tested materials. For this reason one of them was suggested to be used for seed coating in addition to Arabic gum. Sorghum seeds were coated by a private company (SUET Saat- und Erntetechnik GmbH, Eschwege, Germany), using air-dried fungal propagules fermented on 1.5 % (w/v) sorghum straw. Arabic gum was observed to give a better coverage of sorghum seeds and higher cfu per seed (4 x 104 [FA] and 19 x104 cfu [FN]) compared to the second adhesive material. Coating sorghum seeds with the biocontrol agents did generally not result in a significant reduction of Striga shoots in the field, but some of the seed-coating treatments were very efficient in inducing disease symptoms on Striga shoots. Especially FN coated with Arabic gum and FA applied to the seeds in fine ?Pesta? granules increased the proportion of diseased Striga shoots significantly compared to the control by 79%. In the pot experiment, the fungal isolates applied as a seed coating neither resulted in a significant reduction of Striga shoots. Nevertheless, FA applied to sorghum seeds using the adhesive material provided by SUET reduced the total number of Striga plants by 52% compared to the control at the end of the season. FN in the same treatment significantly increased the proportion of diseased Striga by 77% at the end of the season. The effect of seed coating on increasing sorghum plant height and dry matter was lower than that caused by the granular formulations and not statistically significant compared to the control. From the obtained results it can be concluded that both granular formulations applied to the planting holes and seed coating can be used as effective delivery systems for biocontrol fungi and can be adopted under field conditions to reduce Striga infestation. However, the granular formulations showed a higher efficacy in controlling Striga. Inoculum type and concentration as well as nutritional amendments to the formulations should be further optimized in future investigations.
Developing a biodiversity evaluation tool and scenario design methods for the Greater Mekong Subregion
(2011) Cotter, Marc; Sauerborn, Joachim
The Xishuangbanna Prefecture in Yunnan Province (PR China) is facing increasing conflicts between rural development and nature conservation because of an ongoing expansion and commercialization of farming. The rapid development of large-scale farming and the improvement of infrastructure throughout the region are posing serious threats to the conservation of endemic species of flora and fauna, while also offering possibilities for enhancing the livelihood of rural populations to an extend never seen before. The expansion of rubber (Hevea brasiliensis Willd Ex A. Juss) has caused a reduction and fragmentation of natural and secondary forest cover, thereby decreasing structural and species diversity as well as the loss of valuable ecosystem services. The establishment of intensified agriculture, especially plantations on sloping terrain, often leads to an increased erosion risk, nutrient run-off and sedimentation in water courses. Thus, large scale deforestation is not just a problem for nature conservation but also one for the rural economies. Rural development and simultaneous environment conservation often face trade-offs, especially in regions that host an exceptionally high biodiversity, such as many tropical areas. In order to adequately consider and evaluate these interactions, tools and methods have to be developed that allow decision makers to assess the impacts of different management and infrastructure options on the environment. The aim of the work presented in this thesis was to analyze and evaluate the effect of large-scale rubber cultivation on local and regional biodiversity by developing methods to integrate field studies from various disciplines into a comprehensive assessment model. This model was then used to highlight key aspects of anthropogenic influence on the plant species composition within the research area and to identify possible impacts of alternative land use decisions. Furthermore, the development of an interdisciplinary approach to scientific scenario design methods has been supplemented with a study on the acceptance of 3D-visualization as communication tool for land use planning in the background of nature conservation sciences. In order to achieve this, an overview of the agronomical and ecological aspects of rubber cultivation was provided. Literature sources referring to the impact of different cultivation systems on natural biodiversity were discussed and an introduction to the effect of rubber cultivation on Ecosystem Services was given. A method for projection of regionally adapted carbon capture properties of rubber cultivation under suboptimal growth conditions was presented and a comparative assessment of greenhouse gas emissions during the establishment of rubber plantations in regard to the preexisting vegetation was made. A biodiversity evaluation tool based on the combination of approaches from landscape ecology and empirical data within a Geographic Information System was developed. Detailed data on plant species diversity and distribution were combined with quality criteria like endemism or invasiveness to form spatially explicit biodiversity indices for different land use types in various elevation classes. Up-scaling in accordance to the land use distribution observed allowed the estimation of overall plant diversity and the evaluation of the effect of possible future land use scenarios. Habitat characteristics and spatial distribution were included into the analysis of the land use map derived from remote sensing information to allow for the assessment of fragmentation and landscape matrix structure. The methodology was tested with an array of possible present and future land use maps. It was possible not only to evaluate the different land use classes within and their distribution throughout the research area, but we were also able to compare distinct sub-regions based on topography or administrative status. The challenges stakeholders and nature conservation face in the different elevation zones of Nabanhe were highlighted and related to the findings of our partner workgroups from economy and social sciences. The feasibility of this approach to administration staff with limited experience in ecological modeling was one of the main goals in designing the methods. Given a reasonable data set on species diversity and distribution within any given tropical research area, this approach will enable planners and nature park administration to quickly project possible consequences on species diversity indices deriving from land use change within their respective research area. Using this approach, the importance of natural tropical forests for the maintenance of species diversity in tropical cultivated landscapes was highlighted. With the information gained from constructing this evaluation tool, the design and development process for a land use scenario based on the integration of multidisciplinary assessments and iterative scenario refinement with repeated stakeholder inclusion was promoted. By combining stricter conservation rules with alternative sources of income for the rural population in order to offer an alternative to monoculture rubber farming, the economic models and the land use allocation model predicted a stop in rubber and agriculture related deforestation, and the establishment of a considerable amount of reforested area. This was achieved by introducing an innovative land use type that is closely related to traditional local home garden agroforestry systems. By coupling reforestation efforts with the economic gain derived from intercropping Traditional Chinese Medicinal plants into degraded secondary forests, this scenario was, at least theoretically, able to remove deforestation pressure from the natural forest types and to offer an economic alternative to rubber cultivation. The methods used for this assignment can serve as guideline for future projects that want to implement scenario design procedures based on the combination of social sciences, economics, ecology and landscape planning. The acceptance and comprehensibility of computer based 3D visualization models for the communication of possible future land use scenarios was also tested. Two alternative scenarios were visualized and compared to the status quo, with questionnaires and guided interviews covering the acceptability and adaptability of such techniques for professionals from various fields of nature conservation. This thesis presents an overview over agronomic, economic and ecological aspects of rubber cultivation and highlights its implications on biodiversity and nature conservation. The methods discussed here can serve as a guideline for the integration of ecological indicators in land use planning and decision making processes. Although the concepts and topics introduced herein are closely interlinked within the framework of the Living Landscapes China (LILAC) research project, the methods and approaches can easily be applied to other areas in the Greater Mekong Subregion and beyond, be it the expansion of oil palm plantations in the Malayan Archipelago or the fragmentation of forests due to increased population pressure in Central Africa. Nature conservation is facing similar problems all over the developing world, and adaptable approaches such as the ones presented here are needed to support decision making processes in order to secure the preservation and long-term survival of the worlds? diversity in species and natural habitats.
Ecophysiological and agronomic response of Abaca (Musa textilis) to different resource conditions in Leyte Island, Philippines
(2012) Bande, Marlito M.; Sauerborn, Joachim
Abaca (Musa textilis Née) is closely related to edible bananas (Musa acuminata Colla and M. balbisiana Colla). Abaca usually thrives in the shade beneath tall trees, especially important for protecting the young plants from the sun and the older, taller plants from wind breakage. However, there is still disagreement on the need for shade trees in abaca cultivation. Hence, this study was conducted to ascertain the ecophysiological and agronomic response of abaca grown in different shade conditions, water and nutrient management systems in Leyte Island, Philippines. The objectives of the study were to: (a) explore the influence of shade and irrigation-fertilization on the morphological and physiological performance of abaca; (b) investigate the effect of reducing light intensities by 30%, 40% and 50% of full sunlight on fiber yield and fiber quality; (c) determine the optimum light requirement of abaca plants to attain the optimum yield without affecting the quality of the fiber for industrial use; (d) examine the effect of shade and irrigation-fertilization on biomass production and allocation as well as on NPK absorption and distribution among abaca organs; and (e) find out if irrigation and fertilization could offset the effect of shade on biomass production, NPK absorption and fiber yield of abaca. Field trials were established where light infiltration was reduced by 30%, 40%, and 50% of full sunlight using polypropylene shade nets. Irrigation was applied at a rate of 5 liters plant-1 application-1 day-1. The frequency of irrigation was applied two times per day at seedling stage (1-3 months after planting), three times at the early vegetative stage (4-6 MAP), four times at the late vegetative stage (7-9 MAP), and five times at flagleaf stage (10-12 MAP). On the other hand, placement application of N, P2O5, K2O using complete fertilizer was done at 14 g plant-1 in every three months for the first six months and was increased to 40 g plant-1 in every three months for the next six months after planting. The results of this study showed that plant height, cumulative leaf area, pseudostem length and base girth of abaca significantly improved when the light was further reduced to 50%. The application of NPK fertilizer and combination of irrigation-fertilization further enhanced the growth performance of abaca. Statistical analysis showed that shade, NPK fertilization and combination of irrigation-fertilization positively affected dry matter production, crop growth rate, leaf area ratio and net assimilation rate from seedling to flagleaf stage. Furthermore, biomass allocation and NPK distribution among abaca organs was significantly affected by high radiation and/or temperature at seedling and early vegetative stages, and differential leaf senescence at flagleaf stage where shade plays a considerable function. The amount of NPK absorbed by each organ was influenced by the growth made during the different stages of crop development. Meanwhile, irrigation and fertilizer application further improved biomass allocation that considerably increased NPK absorption and distribution among plant parts. With regards to agronomic response, the abaca planted under different light regimes showed that 50% shade had significantly higher fiber yield compared to those that were under other light treatments since the plants pseudostem under such treatment were longer, bigger and heavier. The combination of irrigation and fertilization could further enhance fiber yield to as much as 141% (compared to the control) but this was not enough to offset the effects of shade on the physiological performance of the plant which significantly increased fiber yield to as much as 265% (compared to the control). Statistical analysis showed that shade and irrigation-fertilizer application had no significant effect on fiber fineness and tensile strength. The superior productivity of abaca in response to shade was due to the avoidance of photoinhibition and photooxidative damage that negatively affected the abaca grown under full sunlight at seedling and early vegetative stage. Likewise, the detrimental effect of photoinhibition on the photosynthetic capacity of abaca grown in full sunlight significantly decreased biomass production and allocation among abaca organs. The amount of NPK absorbed by each organ was influenced by high radiation causing photooxidative damage at seedling stage and differential leaf senescence at flagleaf stage. This significantly affected the pattern of biomass allocation and NPK distribution among abaca plant organs. On the other hand, the application of fertilizer considerably enhanced biomass production but did not change the usual pattern of biomass and NPK distribution. The results showed that irrigation and fertilizer application cannot offset or equalize the positive effect of shade on the vegetative growth, physiological performance, and NPK absorption among plant organs.
Human urine as a crop fertilizer under saline conditions
(2013) Boh, Michael Yongha; Sauerborn, Joachim
Soil salinity and nutrients deficiency are jointly responsible for low agricultural production in many parts of the world. With a still growing world population and a continuing pressure on arable land, there is need to increase the productivity of salt affected soils. It is known that the application of N fertilizer can mitigate the deleterious effects of salinity on crop growth but this beneficial effect depends on the source of nitrogen and the extent of soil salinity. Whereas commercial inorganic fertilizers are expensive and often inaccessible to poor farmers especially in developing countries, human urine is an alternative low-cost fertilizer which, if collected and used, can replace up to 20% of current world fertilizer consumption. Its efficacy to increase crop productivity has been validated in scientific experiments. However, the high concentration of soluble salts (especially Na and Cl) in urine may impose a restriction on its use under saline and/or sodic conditions. The research presented in this thesis investigates the extent to which urine can be used as a fertilizer under saline/sodic conditions. It compares the effect of urine and ammonium nitrate-N sources on nutrients accumulation and growth of maize and sorghum plants in NaCl-saline substrate under controlled environmental conditions. Additionally, the effect of urine fertilization on changes in substrate chemical composition was investigated. Due to the high content of K, Ca and Mg in wood ash which can improve the soil cationic balance in salt affected soils, it was further investigated whether or not supplemental wood ash application can enhance salt- and Na-tolerance of urine-fertilized maize plants. Regardless of NaCl salinity treatment, no significant difference in investigated growth factors (height, leaf area and shoot biomass accumulation) of maize plants was measured when N was supplied at 180 mg kg-1 cultivation substrate as urine or ammonium nitrate. Meanwhile, urine treated maize plants produced comparatively less shoot biomass following the application of 380 mg N kg-1 of cultivation substrate and at NaCl salinities of 4.6 and 7.6 dS m-1. As expected, sorghum plants were more tolerant to salinity than maize and produced more biomass under urine than ammonium nitrate fertilization. Though there was a positive relationship between biomass yield and tissue nitrogen concentration regardless of salinity treatment level, this relationship was stronger for ammonium nitrate than urine treatments. Ca and Mg concentration in the tissue of urine-fed maize and sorghum plants was higher than those treated with ammonium nitrate which can be explained by the inherent content of these nutrients in urine. However, there was no direct relationship with biomass yield of maize plants of either nutrient. Additionally, urine fertilization significantly increased substrate salinity by 2 to 3-fold. Substrate sodium concentration and a tendency towards mounting sodicity with an increase in urine fertilization were also observed. At a NaCl-salinity of ECe 4.2 dS m-1, the application of wood ash (150 mg kg-1 soil) alone or in combination with 75 mg urine-N kg-1 soil fostered Na and salinity tolerance of maize which can be explained by the dilution effect of K and Ca supplied through wood ash. However, at a higher urine-N dosage (150 mg kg-1 soil) with or without wood ash enrichment growth inhibition occurred indicating that the tolerance threshold had been exceeded assumingly due to urine-induced increase in Na and salinity. It was demonstrated that urine can substitute ammonium nitrate as a source of nitrogen for maize and sorghum and can be considered for fertilization if salinity does not exceed ECe 4.0 dS m-1. Due to urine-induced increase in salinity and Na concentration in the growing medium, regular monitoring for salt build up and the use of salt-tolerant crop varieties should be included in urine fertilizer planning. It was further demonstrated that supplemental wood ash enhances Na and salinity tolerance and where necessary should be incorporated in urine-fertilizer programs.
Impact of rubber tree dominated land-use on biodiversity and ecosystem services in the Greater Mekong Subregion
(2017) Häuser, Inga; Sauerborn, Joachim
The present dissertation analyzes the impact of rubber tree (Hevea brasiliensis) dominated land-use on biodiversity and ecosystem services (ESS) in the Greater Mekong Subregion (GMS). Although originating from South-America natural rubber is mainly cultivated in South-East Asia. This expansion of rubber plantations affects different ESS such as carbon storage, availability and quality of water and threatens biodiversity in this highly biodiverse region. In order to analyze these impacts the first task was to give a comprehensive overview about publications concerning ESS and biodiversity in rubber cultivation systems. A thorough literature review showed that the majority of publications concentrated on single or few ESS, which does not match the demands of decision-makers. In order to make sound decisions for land-use planning or developing Payments for Ecosystem Services Schemes a holistic view including multiple services. In order to fill this knowledge gap, the second task was to analyze the impacts of rubber on the ESS carbon storage, soil erosion, water availability and water quality and economically and socially related ESS, such as income and livelihood security. Although there are still great uncertainties about carbon storage in different land-use systems there are hints that the carbon storage in rubber plantations is lower than in natural forests. Concerning erodibility, rubber plantations increase the soil erosion risk compared to natural forests. Rubber cultivation also affects the local and regional water balance. Since rubber production in monocultures requires the use of huge amounts of pesticides and chemical fertilizers which enter the aquatic system by rainfall-induced run-off, water quality for humans and aquatic organisms is as well threatened. Undoubtedly, from an economic point of view the introduction of rubber resulted in significant increases in household income and is hence a possibility to move households and communities out of poverty. However, by deciding to grow rubber, farmers are committing themselves for decades to come and are thus dependent on a single product, which exposes them to further risks. In addition, there are ecological hazards due to crop diseases, pests, unfavorable weather conditions or changes in climate. The review of studies clearly indicates that increasing rubber cultivation in the GMS is accompanied by various problems and threats to farmers and the environment. Therefore, the development of more sustainable land-use concepts is required. Concordantly, suggestions for land-use change are based on system diversification and forest restoration, which both require economic incentives for farmers. The next part of this dissertation deals with the development of a biodiversity indicator (based on selected flora and fauna species) that can be included in existing biodiversity models to show the impact that different rubber cultivation scenarios will have on various species groups. A combination of multi-species data supplemented with literature data was used and included flora, vertebrates and invertebrates. The resulting indicator was used as input into an established ESS assessment framework. Finally, a current land-use map from 2007 was compared with two scenarios. In order to get a more detailed picture, sub-groups of biodiversity were analyzed as well. First, a sub-group of “human use species” category was assessed which included only species which are directly used by humans. Second, the sub-group “red list species”, consisting of red list plants and mammals was analyzed separately to include the conservational aspect. The results showed that when considering the indices from the category “human use species” there is less of an impact between the scenarios, because medicinal plants for example are still commonly distributed within rubber plantations, albeit with different species (generalists, ruderal flora). This leads to an important conclusion: not only the decision on “what” is analyzed (biodiversity), but also “how” it is analyzed (groups of different species) considerably influences the results. To complete this dissertation the transferability of this place-based research to other regions of the world was tested to assess the relevance beyond the study area. To do this the system of land archetypes was used, which utilizes a wide range of land-use intensity metrics and incorporates simultaneously environmental and socio-economic conditions. In a first step, the ‘project archetype’ was defined, based on a synthesis of global land system indicators. For the project Sustainable Rubber Cultivation in the Mekong Region, only few of the 32 global indicators did not closely match the local reality. The transferability potential for the GMS was quite high and therefore emphasizes the importance of the project results for this huge region.
Mitigate habitat degradation in the semiarid Brazil : potential and limitation of the endemic tree Spondias tuberosa Arruda
(2017) Mertens, Jan Heiko; Sauerborn, Joachim
Semiarid regions cover 15 % of the global land mass and are inhabited by approximately one billion people. Due to the strong rural character of these regions the well-being of 13 % of the world’s population relying directly or indirectly on their ecosystem services. One of the most densely populated semiarid region is the Caatinga biome, that is located in the Brazilian Northeast. Its climate is hot semiarid (BSh) with little, erratic, and seasonal precipitation, ranging from 250 to 900 mm per year. The average annual temperatures range from 23°C to 27°C. An evapotranspiration above 2000 mm per year results in a negative water balance during 7 to 11 months. The deciduous natural Caatinga vegetation ranges from tropical dry forest to open shrubby vegetation, with a seasonal herbaceous layer. Loss of its natural vegetation due to wood extraction, pasturing, and inappropriate land-use led to habitat degradation in up to 80 % of the area of the Caatinga biome. A degraded habitat jeopardizes the ecosystem services of the biome and poses a direct threat to its dwellers. In order to mitigate further habitat degradation an alternative land-use strategy is necessary to substitute or cut back prevailing land-use. The agro-industrial utilization of the fructiferous multipurpose tree Spondias tuberosa Arruda (Anacardiaceae), endemic to the Caatinga, has the potential to be a viable alternative to current irrigation farming and extensive animal husbandry. The current utilization of S. tuberosa is limited to extractivism of its fruits that lacks sustainability and appears to be a finite resource. The natural population of S. tuberosa presents a weakening natural regeneration with a resultant over aged S. tuberosa population. Poor natural regeneration results from a multifactorial problem. At this juncture, S. tuberosa is not considered endangered based on the criteria of the International Union for Conservation of Nature, due to lacking information for a Red List of Threatened Species threat assessment. However, the combination of expected changing environmental conditions within the Caatinga and restricted natural regeneration of S. tuberosa, both discussed in literature, provides a strong evidence, that the S. tuberosa faces a high risk to become extinct. This work aims to provide a first basis for a scientifically-backed, extensive cropping system for S. tuberosa on disturbed Caatinga sites meliorated by the use of biochar, clay substrate, and goat manure. The effect of biochar, clay substrate, and goat manure with or without additional mineral fertilization as soil conditioner in planting holes were tested in a 23-months field experiment in a marginal Arenosol. Further, it was studied, whether changed soil physical conditions support establishment and development of one-year-old S. tuberosa seedlings. At given application rates neither biochar nor clay substrate significantly affected soil physical parameters of the experimental soil. The application rate of 10 % v/v clay substrate, chosen from literature, seems to be too little to be affective on the experimental Arenosol, that was poor in fine particles (< 0.02 mm). The utilized biochar were proven hydrophobic and presumingly little porous duo to a low pyrolysis temperature. Both combined could explain the absence of a significant biochar‑mediated change of soil physical parameters. Goat manure significantly increased total porosity, and significantly reduced soil bulk density. The water content at permanent wilting point, and volumetric water content within the planting holes during the experiment were significantly increased owing to melioration with goat manure. Due to a strong correlation (R2 = 0.75) of water content at field capacity and water content at permanent wilting point, the available water capacity, an important target parameter for plant production, remained unchanged. Neither stem growth nor seedling survival was significantly affected by initial nutrient supplies or melioration. Conversely, fine root growth and root tuber growth were significantly affected by melioration. Goat manure in the planting holes led to significantly reduced fine root dry matter. Since fine root dry matter showed a weak but significant negative correlation with soil water content, the fine root reduction was evidently caused by increased soil water content resulting from goat manure application. The goat manure application also affected tuber growth significantly, and led to larger tubers. In contrast to the fine roots, root tuber growth did not respond to soil water content but showed a significant correlation with soil bulk density and total porosity. Reduced soil bulk density and increased soil porosity after goat manure addition application led to higher tuber volume.
Pathogenitätsfaktoren und induzierte Resistenz in der Interaktion von Orobanche ramosa L. und Nicotiana tabacum L.
(2005) Gonsior, Guido; Sauerborn, Joachim
Parasitic weeds of the genus Orobanche, cause severe damage to vegetables, legumes and sunflower in Europe, the Middle East and North Africa. Recently there is evidence for increasing occurrence of branched broomrape (Orobanche ramosa L.) in rape and tobacco cultivars in France and Germany. This research concerns on biology and pathogenicity of O. ramosa with special focus on the interactions with the host plant. In addition mechanisms of induced resistance of the host plant against the parasite were considered. The results showed genetic differences between the populations of O. ramosa in Germany, which partially parasitize different hosts. As possible factors of pathogenicity the accumulation of reactive oxygen species and a high peroxidase activity together with a high antioxidative capacity caused by the phenylpropanoids Verbascosid and Oraposid were identified. The control of branched broomrape was possible by application of agents, which are described to induce disease resistance. Control of branched broomrape could be based on systemic acquired resistance (SAR) as well as on induced systemic resistance (ISR). As defense mechanisms in tobacco roots against O. ramosa the biosynthesis of the hydroxycoumarin scopoletin and a significant increase of soluble and bound phenolics was discussed. This is underlined by a high activity and an increased expression of phenylalanine ammonia-lyase (PAL) the key enzyme of the phenylpropanoid pathway. Beside phytoalexin production we recognized an increased activity of peroxidases in Orobanche ramosa infected tobacco roots. Further it could be shown that the plant hormone Ethylene as well as the regulation of the sugar metabolism have importance for the resistance of the host plant.
Rainforestation farming on Leyte island, Philippines - aspects of soil fertility and carbon sequestration potential
(2007) Marohn, Carsten; Sauerborn, Joachim
This study aimed at investigating rainforestation systems in Leyte, Philippines, under different aspects: Characterisation of typical soils in Leyte with respect to physical, chemical and biological parameters relevant for tree growth, possible contributions of rainforestation to restoring soil fertility, performance of a recently planted rainforestation system under different microclimatic and soil conditions, potential of the rainforestation approach for projects under the umbrella of the Clean Development Mechanism (CDM). Soils in Leyte can be grouped into a volcanic and a calcareous category. The latter were formed on coralline limestone and are high in pH and Ca2+ and Mg2+. Contents of organic matter are high while concentrations of plant available PBray are low. Volcanic soils are characterised by low pH and CEC as well as extremely low PBray contents. Organic matter levels are below those of the calcareous soils but still moderate. In any analysed soil, N would not limit tree growth. Pore volume and water infiltration were propitious for all sites, which is relevant in the context of erosion. For calcareous soils, drought and reduced rootability due to clayey subsoil posed the most relevant constraints. The frequently claimed role of rainforestation in the rehabilitation of degraded soils was assessed in a paired plot approach. Chemical and biological soil parameters under 10 year old rainforestation were contrasted with adjacent fallow or Gmelina sp. Clear tendencies across all seven sampled sites were lower available Mg2+ and pH under rainforestation. Other differences were less distinct. Generally, a depletion of soil reserves e.g. in basic cations can be explained by uptake into the plants. A feed-back of these elements to the topsoil via leaf litter, however, could be observed only for available P. In conclusion, plant uptake of single elements can reach orders of magnitudethat reduce soil stocks. At the same time, generally lower pH under rainforestation may have contributed to elevated losses, especially of basic cations. A general improvement of the sampled soils in terms of chemical or biological characteristics through rainforestation could not be observed. To evaluate plant performance six timber and four fruit species, most native, were interplanted on a 1ha plot. Rainforestation, commonly understood as high-density closed canopy system was modified to a less dense 5x5m grid, interplanted with Musa textilis. The plot varied strongly on a small scale due to heterogeneous canopy closure and relief. Methodologically, the entire area was divided into 10 subplots in representative positions to be sampled. Soil physical and chemical properties, microbial activity, PAR and root length density were determined and correlated to plant survival and growth at consecutive inventories. For Musa textilis, the most sensitive species, which was used as an indicator, logistic regressions were calculated to determine the influence of all relevant parameters on survival rates. The most important predictors for survival were organic matter contents, parameters related to biological activity and leaf litter production, which resembled canopy closure and thus indirectly light intensity and soil moisture. To assess growth, multiple regressions were formulated for biomass at five inventories. Corg and NLOM were the most relevant variables determining the regressions used for biomass and growth of abaca. Assessing the potential of rainforestation for Clean Development Mechanism (CDM) measures, amounts of sequestered CO2 during 10 and 20 years, respectively, were estimated under different management options using the WaNuLCAS model. Despite all given uncertainty associated with modelling, one very obvious finding was the dominant role of soil carbon for the plot balance: Appropriate soil management, especially during land preparation (e.g. clearing vs. enrichment planting) is of paramount importance. Looking at the modelled contribution of various tree species to the carbon balance, Musa textilis had a significant influence only during the very first years; later on, the principal share of carbon was bound in the tree component. Here, exotic Gmelina arborea built up biomass more quickly than a rainforestation plot composed of native Shorea contorta and Durio zibethinus, but was then overtaken. In absolute quantities of CO2 sequestration, magnitudes matched inventory and modelled data given in various literature sources for Leyte and the Philippines. Relative to earlier inventory data from two rainforestation sites, modelled values overestimated growth.
Rubber production in Continental Southeast Asia : its potentialities and limitations
(2019) Golbon, Reza; Sauerborn, Joachim
This thesis focuses on three climate-related aspects of Para rubber (Hevea brasiliensis) cultivation in areas where altitudes and latitudes higher than its endemic range create conditions which are labeled nontraditional, suboptimal or marginal for rubber cultivation: 1. rubber yield in relation to the meteorological conditions preceding harvest events, 2. potential geographical shifts in rubber cultivation through climate change and 3. assessment of climate driven susceptibility to South American leaf blight (Pseudocercospora ulei) of rubber.
Spatial undergrowth species composition in oil palm (Elaeis guineensis Jacq.) in West Sumatra
(2003) Germer, Jörn Uwe; Sauerborn, Joachim
The area planted to oil palm expanded during the last decades substantially, making it become the world's second most important oil crop. Despite its economic significance the oil palm remains remarkably unknown. Little attention is paid also to the oil palm undergrowth, though important in stabilizing the agro-ecosystem in plantations. Comprehensive knowledge of undergrowth species adapted to specific ecological niches in oil palm plantations is essential to investigate their function in and potential benefit to the oil palm agro-ecosystem. The objectives of the conducted research were to develop a reproducible approach for phytosociological investigation in oil palm plantations and to accomplish a general inventory of the vascular plants associated with oil palm in a plantation in West Sumatra. Additionally it was aimed to study the undergrowth heterogeneity within the fields and the distribution of species in the plantation in response to solar radiation below the palm canopy, soil type and physical and chemical soil parameters. A rich diversity of 298 species, 186 dicotyledonae, 77 monocotyledonae and 35 pteridophyta (ferns and allies), representing 81 families was identified in the research area. Similar to rainforests, plants with a high consistency were few, while most of the species occurred only sporadically in the oil palm undergrowth. In average 36 species were found in each of the 100 sampled relevés. The 8 most frequent species were identified as an abstract plant community: Mikania micrantha H.B.&K., Pouzolzia zeylanica Benn., Ageratum conyzoides L., Sporobolus diander Beauv., Nephrolepis biserrata (Sw.) Schott., Pityrogramma calomelanos (L.) Link, Lygodium microphyllum (Cav.) R.Br. and Stenochlaena palustris Bedd. Due to particular management practice, oil palm fields can be zoned in harvesting path, palm circle and inter-row. Species that were mainly found in the inter-row were: Diplazium esculentum (Retz.) Sw, Cyclosorus interruptus (Willd.) H.Ito, Nephrolepis biserrata and Christella dentate (Forssk.) Brownsey & Jermy. Plants that were found primarily in the other zones were small herb species such as Hedyotis corymbosa Lam., Limnophila rugosa Merrill, Borreria setidens (Miq.) Boldingh and Peperomia pellucida H.B.&K., the sedges Fimbristylis miliacea Vahl and Cyperus kyllingia Endl. as well as the grass Sporobolus diander. It was found that the palm canopies developed slower on histosol than on fluvisol and assumed that the main reason for this difference was the lower nutrient pool in low-density organic soil. Melliferous species, which are often important as hosts for pest antagonists, were infrequent where less light was available. In the inter-row a distinct shift from a creeper and grass to a fern and non-creeper dicotyledonae dominated undergrowth was observed with falling levels of solar radiation. Species consistently more frequent in less shaded sampling sites throughout the research area were: Basella alba Linn., Calopogonium muconoides Desv., Commelina diffusa Brum.f., Imperata cylindrica Beauv., Pueraria phaseoloides Benth. and Sporobolus diander whereas Ageratum conyzoides, Christella dentata, Diplazium esculentum, Peperomia pellucida, Phyllanthus debilis Willd., Pouzolzia zeylanica and Sparganophorus villantii Crantz preferred more shaded environments. The soil analyses revealed that the soil carbon content was not only distinctly different between histosol and fluvisol, but also between individual sites on the two soil types. Next to the carbon content the effective cation exchange capacity varied largely between sites. The physical soil properties were stable within the sites, while the chemical properties were significantly influenced by fertilization. Species abundance per relevé was significantly higher on fluvisol than on histosol, while the difference in the total number of species between the soil types was small. 11 species showed a preference towards low soil carbon content: Ceratopteris thalictroides (L.) Brongn., Christella dentata, Christella parasitica (L.) Lev., Diplazium esculentum, Eleusine indica (L.) Gaertn., Hedyotis corymbosa, Pleocnemia irregularis (C.Presl) Holtt., Polygonum barbatum L., Selaginella plana Hieron., Sphaerostephanos polycarpus (Bl.) Copel. and Stachytarpheta indica Vahl. Accordingly the presence of two species: Borreria latifolia (Aubl.) K. Schum. and Dicranopteris linearis J. Underw. augmented with increasing soil carbon content. In the sampling sites marked by high ECEC ferns were dominant. On fluvisol 11 out of 18 species that occurred more frequently where the ECEC was higher were ferns and on histosol 3 out of 12 species respectively. The distinct difference of soil carbon content blanketed, apart form the ECEC possible effects of other soil properties on the undergrowth species composition.
Understanding the role of plant growth promoting bacteria on sorghum growth and biotic suppression of striga infestation
(2014) Mounde, Lenard Gichana; Sauerborn, Joachim
Witchweeds (Striga sp.) are parasitic weeds of great agricultural significance, parasitizing the roots of their hosts. Striga, like all other root parasitic weeds, drain essential organic and inorganic resources from their hosts leading to poor crop development and low yield. In Africa, about 50 million ha in over 30 countries are infested by Striga spp. causing grain loss of cereals. Estimated yield losses of maize, sorghum, millets and upland rice are between 30 and 90%. The parasite, therefore, is ranked as the leading biotic constraint to cereal production in the continent. Plant growth promoting rhizobacteria (PGPR) are promising components for integrated solutions to agro-environmental problems because inoculants possess the capacity to promote crop growth and reduce the population of deleterious microbes in the rhizosphere. Although there are numerous studies on crop growth promotion and biological control of diseases, weeds, nematodes and parasitic weeds using PGPR, little is known about the potential of some Bacillus subtilis, B. amyloliquefaciens and Burkholderia phytofirmans strains in sorghum growth promotion and resistance against Striga infection. The main objective of the study was to assess the effect of B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN on growth promotion of sorghum crop and suppression of Striga development, thus providing a basic understanding on the sorghum-PGPR-Striga interaction. This study opens with an elaborate review of the state-of-the-art knowledge on the tripartite interactions between Striga, sorghum and different species of PGPR. Prior to this, bipartite relationship between sorghum and Striga, PGPR-sorghum and PGPR-Striga are reviewed with a focus on understanding Striga impact on sorghum, sorghum defence responses to infection, plant growth and disease suppression benefits by PGPR on sorghum, and the effect of PGPR on Striga development. Knowledge gaps in both bipartite and tripartite relationships are described, and future research recommendations given. A key recommendation from the review is to conduct experiments under controlled environmental conditions using Bacillus subtilis, B. amyloliquefaciens and Burkhoderia phytofirmans strains in order to understand their relationship with sorghum and Striga at bipartite and tripartite levels. Petri dish bioassays and root chamber experiments under controlled conditions were conducted at the Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim between 2012 and 2014. B. subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans strain PsJN inocula and their corresponding cell culture supernatants were evaluated for their growth promotion potential on sorghum and suppressiveness on Striga development. Sorghum root exudates and synthetic stimulant GR24 were used to induce Striga seed germination. Bacillus subtilis Bsn5 supernatant, which showed the greatest inhibitory activity on Striga germination and radicle elongation, was separated by ethyl acetate into lipophilic and hydrophilic phases. The purpose of this extraction was to try and identify the polarity of the inhibitor. Protein composition by mass spectrometry (MS) was also done on the supernatant with a view of establishing the presence of peptides because peptides have been associated with Orobancheceae germination and radicle inhibition in previous studies. In addition, determination of plant growth hormones in bacteria supernatants was also conducted using Radio-Immuno-Assay (RIA) in order to relate PGPR hormone production and sorghum growth enhancement. Burkholderia phytofirmans PsJN significantly (<0.05) induced a higher vigor index (VI) on sorghum seedlings (>18,000) compared to other PGPR and control treatments. The lowest VI (7626) was recorded in seeds inoculated with Bacillus amyloliquefaciens FZB42. Complete Striga germination inhibition (0% germination) occurred in seeds exposed to all PGPR inocula suspended while the highest germination (>60%) occurred in control treatments (10% Luria Bertani (LB) + GR24 and sterile distilled water (SDW) + GR24). The effect of bacterial supernatants on the germination percentage and radicle length of Striga seeds was also significantly (<0.05) different among treatments. The least germination (7.4 %) was observed in Bacillus subtilis Bsn5 + GR24 while the highest (66 %) was observed in SDW + GR24 control. Bacillus subtilis Bsn5 supernatant produced the lowest mean radicle lengths (0.1 mm) while the highest radicle lengths were observed in SDW + GR24 (2.2 mm). Therefore, Bacillus subtilis Bsn5 supernatant was selected for further investigation of compounds causing inhibition of Striga germination and preventing radicle elongation. The supernatant was separated into hydrophilic and hydrophobic fractions using ethyl acetate. Each fraction was then prepared in 1%, 25%, 50%, 75% and 100% concentrations before being evaluated for their inhibitory activity in Striga germination and radicle elongation. The highest germination percentage (63%) and radical length (2.9 mm) was observed in SDW + GR24 control treatment. The ethyl acetate (lipophilic) fraction at both 100% and 1% concentration + GR24 produced a germination percentage of >40% which was similar to 10% LB + GR24 and ethyl acetate + GR24 controls. There was complete inhibition of Striga seed germination after exposure to either Bacillus subtilis Bsn5 supernatant + GR24 or 100% hydrophilic fraction of the supernatant + GR24. However, at 25% and 1% concentration + GR24, Striga germination percentage increased to 34% and 49%, respectively. Light microscopy examination of Striga radicles exposed to Bacillus subtilis Bsn5 supernatant + GR24 revealed that stunting of the radicles was due to reduction in cell sizes at the radicle elongation zone. Extended agar gel assays (EAGA) experiments showed a similar trend of results with B. subtilis Bsn5 showing the highest inhibitory activity on Striga germination and radicle elongation compared to other PGPR and control treatments. Results from root chamber experiments demonstrated significant (p<0.05) differences in biomass production between Striga-free and Striga-infected sorghum. Total biomass yield in uninoculated Striga-free plants was 40% higher than uninoculated Striga-infected sorghum plants. Bacillus amyloliquefaciens FZB42, B. subtilis GBO3 and Burkholderia phytofirmans PsJN inoculated Striga-free sorghum showed a 75%; 142% and 158% increase in biomass yield, respectively, compared to uninoculated Striga-free sorghum. There were no significant differences in biomass yield observed between inoculated and uninoculated Striga-infected plants. All PGPR supernatants and 10% LB media showed production of phytohormones cytokinin, IAA, GAs and ABA. Cytokinin content in PGPR supernatants was significantly (>0.05) higher than blank 10% LB control media. There was a significant negative correlation (r= -0.96) between IAA and cytokinins. However, there was no significant positive correlation between any phytohormone and sorghum plant height, SPAD values, biomass production, Striga germination, attachment and tubercle death. Finally, this study shows that Bacillus subtilis Bsn5, B. subtilis GBO3, B. amyloliquefaciens FZB42 and Burkholderia phytofirmans PsJN might accelerate sorghum growth and suppress key stages of Striga development under laboratory conditions. Greenhouse and field experiments are recommended to better understand these interactions under natural conditions where other biotic and abiotic factors come into play. These findings could contribute to a better understanding of sorghum and beneficial bacteria interactions and provide novel information of the long-term effects of a PGPR on sorghum development, opening new avenues for Striga control and sustainable, ecofriendly sorghum production.