Browsing by Subject "Land use"

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Coupling pyrolysis with mid-infrared spectroscopy for the characterization of soil organic matter
(2021) Nkwain Funkuin, Yvonne; Cadisch, Georg
Soil organic matter (SOM) is known to play an important role in the global carbon cycle due to its ability to sequester atmospheric carbon dioxide (CO2) and maintenance of soil physical, chemical, and biological properties. Due to the growing need to enhance the understanding of SOM composition and dynamics as influenced by natural and anthropogenic factors, in addition to the limited ability to exist analytical techniques to provide in-depth knowledge into the constituents of SOM, a lot of research is currently focused on the development of new techniques to address the aforementioned concerns. In this study, a novel analytical technique, pyrolysis coupled with mid-infrared spectroscopy (Py-MIRS) was developed and applied to study SOM bulk chemistry in soils by measuring certain mid-infrared organic functional groups. Secondly, the developed Py-MIRS technique was applied to soil samples from different long term experiments to investigate the effects of agricultural management practices and land uses by monitoring the different functional groups. Lastly, the implications of methodological considerations of diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) on specific mid-infrared functional groups and quality indices were investigated on soils from a number of long-term field experiments. Py-MIRS was developed by testing critical experimental conditions like pyrolysis temperature, heating rate, and time using a range of reference standard compounds varying in chemical and structural composition and bulk soils. As a next step in the methodological development, the suitability of the newly developed Py-MIRS was further evaluated by testing the effect of long-term management and land use on the molecular composition of SOM in bulk soils taken from long-term field experiments in Ultuna, Sweden, and Lusignan, France. The newly developed Py-MIRS technique and the evaluation of the effect of drying temperatures on peak areas obtained with DRIFTS demonstrate progress in the use of pyrolytic and spectroscopic techniques in the domain of SOM characterization. Py-MIRS revealed its potential as a rapid, reproducible, and effective technique to yield information on SOM molecular composition with minimal constraints due to mineral interferences and secondary thermal reactions. Py-MIRS also provided some insights into sustainable practices that improve SOM quality. However, the technique requires further development and testing on different clay mineralogies and land uses.
Effects of farmland conversion to orchard or agroforestry on soil organic carbon fractions in an arid desert oasis area
(2022) Wang, Weixia; Ingwersen, Joachim; Yang, Guang; Wang, Zhenxi; Alimu, Aliya
In southern Xinjiang province, northwest China, farmland is undergoing rapid conversion to orchards or agroforestry. This has improved land-use efficiency but has also caused drastic ecological changes in this region. This study investigated the effects of farmland conversion to orchard or agroforestry on soil total organic carbon (TOC) and several soil labile fractions: readily oxidizable carbon (ROC), light fraction organic carbon (LFOC), and dissolved organic carbon (DOC). Soil samples were collected from seven cropping treatments: a monocultured wheat field (Mono), a 5-year-old jujube orchard (5 J), a 5-year-old jujube/wheat alley cropping system (5 JW), a 10-year-old jujube orchard (10 J), a 10-year-old jujube/wheat alley cropping system (10 JW), a 15-year-old jujube orchard (15 J), and a 15-year-old jujube/wheat alley cropping system (15 JW). The results show that the ROC concentrations varied from 0.17 ± 0.09 g/kg to 2.35 ± 0.05 g/kg across all land-use types and soil depths studied. It was higher in the 0–10 cm and 10–20 cm layers of treatment 10 JW than in other treatments and significantly greater than in the Mono treatment. The highest value of DOC was reached at 593.04 mg/kg in the 15 JW treatment at 0–10 cm. Labile organic carbon decreased with increasing depth in all treatments. The proportion of ROC and LFOC to TOC decreased with increasing soil depth. In all treatments, the ratio of DOC to TOC generally decreased initially and then increased again with increasing depth. Correlation analysis showed that ROC, LFOC, and DOC were closely correlated with TOC (p < 0.01). The ROC, LFOC, and DOC concentrations were significantly correlated with each other (p < 0.01). Following conversion of farmland to jujube orchard or agroforestry, the content and activity of soil organic carbon tended to increase due to augmentation of plant residues. Thus, jujube orchards and agroforestry systems are effective methods to restore soil organic carbon.
Influence of land use on abundance, function and spatial distribution of N-cycling microorganisms in grassland soils
(2015) Keil, Daniel; Kandeler, Ellen
This thesis focuses on the influence of land use on the abundance, function and spatial distribution of N-cycling microorganisms in grassland soils, but also on soil biogeochemical properties, as well as on enzyme activities involved in the carbon-, nitrogen-, and phosphorous cycle. The objective of this thesis was tackled in three studies. All study sites that were investigated as part of this thesis were preselected and assigned according to study region and land use within the framework of the “Exploratories for Functional Biodiversity Research – The Biodiversity Exploratories” of the Deutsche Forschungsgemeinschaft priority program 1374. The first study addressed the question whether land-use intensity influences soil biogeochemical properties, as well as the abundance and spatial distributions of ammonia-oxidizing and denitrifying microorganisms in grasslands of the Schwäbische Alb. To this end, a geostatistical approach on replicated grassland sites (10 m × 10 m), belonging to either unfertilized pastures (n = 3) or fertilized mown meadows (n = 3), representing low and high land-use intensity, was applied. Results of this study revealed that land-use intensity changed spatial patterns of both soil biogeochemical properties and N-cycling microorganisms at the plot scale. For soil biogeochemical properties, spatial heterogeneity decreased with higher land-use intensity, but increased for ammonia oxidizers and nirS-type denitrifiers. This suggests that other factors, both biotic and abiotic than those measured, are driving the spatial distribution of these microorganisms at the plot scale. Furterhmore, the geostatistical analysis indicated spatial coexistence for ammonia oxidizers (amoA ammonia-oxidizing archaea and amoA ammonia-oxidizing bacteria) and nitrate reducers (napA and narG), but niche partitioning between nirK- and nirS-type denitrifiers. The second study aimed at whether land-use intensity contributes to spatial variation in microbial abundance and function in grassland ecosystems of the Schwäbische Alb assigned to either low (unfertilized pastures, n = 3), intermediate (fertilized mown pastures, n = 3), or high (fertilized mown meadows, n = 3) land-use intensity. Plot-scale (10 m × 10 m) spatial heterogeneity and autocorrelation of soil biogeochemical properties, microbial biomass and enzymes involved in C, N, and P cycle were investigated using a geostatistical approach. Geostatistics revealed spatial autocorrelations (p-Range) of chemical soil properties within the maximum sampling distance of the investigated plots, while greater variations of p-Ranges of soil microbiological properties indicated spatial heterogeneity at multiple scales. An expected decrease in small-scale spatial heterogeneity in high land-use intensity could not be confirmed for microbiological soil properties. Finding smaller spatial autocorrelations for most of the investigated properties indicated increased habitat heterogeneity at smaller scales under high land-use intensity. In the third study, the effects of warming and drought on the abundance of denitrifier marker genes, the potential denitrification activity and the N2O emission potential from grassland ecosystems located in the Schwäbische Alb, the Hainich, and the Schorfheide region were investigated. Land use was defined individually for each grassland site by a land-use index that integrated mowing, grazing and fertilization at the sites over the last three years before sampling of the soil. It was tested if the microbial community response to warming and drought depended on more static site properties (soil organic carbon, water holding capacity, pH) in interaction with land use, the study region and the climate change treatment. It was further tested to which extent the N2O emission potential was influenced by more dynamic properties, e.g. the actual water content, the availability of organic carbon and nitrate, or the size of the denitrifier community. Warming effects in enhanced the potential denitrification of denitrifying microorganisms. While differences among the study regions were mainly related to soil chemical and physical properties, the land-use index was a stronger driver for potential denitrification, and grasslands with higher land use also had greater potentials for N2O emissions. The total bacterial community did not respond to experimental treatments, displaying resilience to minor and short-term effects of climate change. In contrast, the denitrifier community tended to be influenced by the experimental treatments and particularly the nosZ abundance was influenced by drought. The results indicate that warming and drought affected the denitrifying communities and the potential denitrification, but these effects are overruled by study region and site-specific land-use index. This thesis gives novel insights into the performance of N-cycling microorganisms in grassland ecosystems. The spatial distribution of soil biogeochemical properties is strongly dependent on land-use intensity, as in return is the spatial distribution of nitrifying and denitrifying microorganisms and the ecosystem services they perform. Yet, future work will be necessary to fully understand the interrelating factors and seasonal variability, which influence the ecosystem functioning and ecosystem services that are provided by N-cycling soil microorganisms at multiple scales.
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.
Small-mammal abundance and species diversity: Land use and seasonal influences in the Serengeti Ecosystem, Tanzania
(2023) Shilereyo, Monica T.; Magige, Flora J.; Ogutu, Joseph O.; Røskaft, Eivin
Land use, habitat suitability, and seasonality can fundamentally shape small-mammal abundance, species richness, diversity, evenness, and composition. However, how these characteristics of small mammals are determined by land use, habitat type, and rainfall seasonality is still poorly understood for most ecosystems. We analyze how land use (protection in a national park, pastoralism, and crop agriculture), habitat type, and rainfall seasonality influence small-mammal relative abundance, species richness, and diversity in the Tanzania Serengeti Ecosystem. We used 141 live traps to capture 612 small mammals in the wet and dry seasons of 2017 and 2018. Relative abundance was higher in the pastoral land than in the park or agricultural land and in the dry season in all the three land use types. Species richness and diversity were highest in the park, middling in the agricultural land, and lowest in the pastoral land. The high relative abundance in the pastoral land was primarily due to the numerical dominance of two generalist species in the shrubland (grass rat Arvicanthis niloticus) and cropland (multimammate rat Mastomys natalensis), resulting in low species richness and diversity. High species richness and diversity in the park indicate high habitat heterogeneity, whereas high species diversity in the agricultural land during the dry season reflects high food availability during and soon after harvests. Thus, human activities apparently exert deleterious effects on some specialist small mammals as a result of reduced habitat heterogeneity while promoting the abundance of some generalist species in African savanna ecosystems. However, increased abundance of generalist species reduces small mammal species diversity while increasing the risk of human–small mammal conflicts. We offer several testable hypotheses motivated by our results.