Browsing by Subject "Kohlenstoff"

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Biological regulation of subsoil C-cycling
(2019) Preußer, Sebastian; Kandeler, Ellen
Soils are the largest terrestrial reservoir of organic carbon (OC). Substantial proportions of the stored OC are found in stabilized form in deeper soil layers. Beside the quality and quantity of C input from plant biomass, C storage in soil is primarily controlled by the microbial decomposition capacity. Various physical, chemical and biological factors (e.g., substrate availability, temperature, water content, pH, texture) vary within soil profiles and directly or indirectly influence the abundance, composition and activity of microbial communities and thus the microbial C turnover. While soil microbiological research has so far focused mainly on processes in topsoil, the mechanisms of C storage and turnover in subsoil are largely unknown. The objective of the present thesis was therefore to investigate the specific influence of substrate availability and different environmental factors as well as their interactions on microbial communities and their regulatory function in subsoil C-cycling. This objective was addressed in three studies. In the first and second study, one-year field experiments were established in which microbial communities from different soil depths were exposed to altered habitat conditions to identify crucial factors influencing the spatial and temporal development of microbial abundance and substrate utilization within soil profiles. This was achieved by reciprocal translocation of soils between subsoil horizons (first study) and topsoil and subsoil horizons (second study) in combination with addition of 13C-labelled substrates and different sampling dates. In the third study, a flow cascade experiment with soil columns from topsoil and subsoil horizons and soil minerals (goethite) coated with 13C-labelled organic matter (OM) was established. This laboratory experiment investigated the importance of exchange processes of OM with reactive soil minerals for the quality and quantity of dissolved OM and the influence of these soil micro-habitats on microbial abundance and community composition with increasing soil depth. In the first study, the reciprocal translocation of subsoils from different soil depths revealed that due to comparable micro-climatic conditions and soil textures within the subsoil profile, no changes in microbial biomass, community composition and activity occurred. Moreover, increasing microbial substrate utilization in relation to the quantity of added substrate indicated that deep soil layers exhibit high potential for microbial C turnover. However, this potential was constrained by low soil moisture in interplay with the coarse soil texture and the resulting micro-scale fragmentation of the subsoil environment. The bacterial substrate utilization was more affected by this spatial separation between microorganisms and potentially available substrate than that of fungi, which was further confirmed by the translocation experiment with topsoil and subsoil in the second study. While the absolute substrate utilization capacity of bacteria decreased from the more moist topsoil to the drier subsoil, fungi were able to increase their substrate utilization and thus to partially compensate the decrease in C input from other sources. Furthermore, the addition of root litter as a preferential C source of fungal decomposer communities led to a pronounced fungal growth in subsoil. The third study demonstrated the high importance of reactive soil minerals both in topsoil and in subsoil for microbial growth due to extensive exchange processes of OM and the associated high availability of labile C. In particular copiotrophic bacteria such as Betaproteobacteria benefited from the increased C availability under non-limiting water conditions leading to a pronounced increase in bacterial dominance in the microbial communities of these soil micro-habitats. In conclusion, this thesis showed that subsoil exhibits great potential for both bacterial and fungal C turnover, albeit this potential is limited by various factors. This thesis, however, allowed to determine the specific effects of these factors on bacteria and fungi and their function in subsoil C-cycling and thus to identify those factors of critical importance. The micro-climate in subsoil, in particular soil moisture, was the primary factor limiting bacterial growth and activity, whereas fungi were more strongly restricted by substrate limitations.
Compound-specific 13C fingerprinting for sediment source allocationin intensely cultivated catchments
(2018) Brandt, Christian; Cadisch, Georg
The loss of fertile topsoil due to soil degradation and erosion not only threatens crop productivity, but also induces sedimentation of aquatic systems and leads to social-, economical-, and environmental problems in many regions of the world. The abandonment of shifting cultivation in favor of intensive mono-cultural cropping systems on sloping land accompanied by rainfall detachment and surface runoff induced soil erosion is one of the most pressing environmental and agricultural problems in the highlands of Southeast Asia. Informed soil management strategies require knowledge on the main sediment sources in a catchment. Compound-specific stable isotope (CSSI) fingerprinting, based on δ13C values of fatty acid methyl ester (FAME), allows identifying hot-spots of soil erosion, particularly with regard to assigning sediment sources to actual land uses. In this regard, we assessed the potential of the CSSI – fingerprinting approach to assign sediment sources to specific land use types in various intensely cultivated catchments. In a first step we improved the statistical procedure to identify sediment sources in a heterogeneous agricultural catchment in the mountainous northwestern region of Vietnam. In a next step we tested the CSSI-fingerprinting under different agro-ecological conditions to evaluate its global applicability, using an aligned protocol. Finally, we integrated CSSI-fingerprinting and fallout radio nuclide (FRN, 210Pbex, 137Cs) analysis to estimate past net erosion rates linked to land use types. In conclusion, the integrated Bayesian SIAR-CSSI approach was an appropriate tool to identify and assign sediment sources to actual land uses in small and heterogeneous catchments. This methodology was also suitable to identify hot-spots of soil erosion in contrasting catchments of different sizes and agro-ecological zones. Integrating CSSI-fingerprinting and fallout radio nuclide analysis to determine past sediment budgets provided insight into the impact of specific land use changes on soil retrogression and degradation. Such knowledge is of great value for informed and effective soil conservation through evidence-based land management and decision making.
Constraints on microbial pesticide degradation in soils
(2023) Wirsching, Johannes; Kandeler, Ellen
Pesticides are an essential component of intensified agriculture and have contributed significantly to the increase in food production observed in recent decades. Since 1960, pesticide use has increased by a factor of fifteen to twenty, representing a market value of $40 billion in 2016. Soil monitoring campaigns to track pesticide contamination of croplands across Europe are quantifying pesticide residues whose residence times in soils exceed expected values. Diffuse contamination by pesticide residues raises concerns about soil functions, soil biodiversity, and food safety, as well as the transport of contaminants by wind and water to surface waters or to adjacent, organically managed croplands. Data on the frequency of occurrence and concentrations of pesticide residues in soil demonstrate a discrepancy between the determination of persistence and subsequent approval and their actual fate in soil. This raises the question of whether degradability of individual organic compounds has been adequately studied. Microbiological degradation is the most important process for reducing pesticide loads in soils. A reliable estimate of pesticide residence time requires an expanded understanding of the factors limiting microbial degradation. Degradation of anthropogenic organic chemicals in soils occurs much more slowly than would be expected based on their physicochemical properties. While processes that determine the fate of pesticides in soil have often been studied at different spatial and temporal scales, reasons for discrepancies between the observed complete degradation of pesticides under laboratory conditions and their persistence in the field remain unclear. This thesis addresses this challenge by focusing on the central question of why inherently biodegradable compounds in soils display increased persistence under field conditions. Organic contaminants in low but detectable and environmentally significant concentrations could remain in the soil once available concentrations fall below a threshold where bioenergetic growth restrictions come into play. In addition, potential microbial and biophysical limitations and environmental factors such as soil temperature and soil moisture are often examined separately in current degradation studies. Combinations of temperature and soil moisture changes associated with different concentration levels have been less well examined, resulting in an incomplete understanding of the degradation process. Another key factor in the demonstrated discrepancy between predicted and actual persistence in the field could be due to laboratory experiments that cannot account for field-scale processes. Therefore, degradation rates determined in laboratory experiments cannot be confidently extrapolated to the field scale. . This thesis identified further important regulatory mechanisms for microbially mediated pesticide degradation. The previously unknown concentration-dependent degradation dynamics and the concentration-dependent influence of limiting environmental conditions on microbial degradation emphasize the importance of studies using a realistic concentration range. Evidence of deep transport of a highly sorptive pesticide such as glyphosate primarily via preferential flow pathways into the subsoil with lower degradation dynamics underscores the need to include processes that can only be verified in field studies as part of risk assessments. The results of this thesis suggest that the biodegradation rates of pesticides are not homogeneous at field scales and may account in part for the discrepancy between complete degradation of pesticides under laboratory conditions and their persistence in the field. Laboratory studies in which soil samples are pooled and mixed to obtain a single "representative" sample can provide a simplified understanding of the process, but the complexity, particularly that of soil heterogeneity, of pesticide distribution and microbial degradation associated with prevailing climatic conditions, requires calibration of previously used methods in field studies and possibly at landscape, watershed, or regional scales. The scale-dependent degradation aspect will become even more important in the future; as soil properties and processes that control the toxicological aspects of contaminants include temperature and moisture, and changes associated with climate change will lead to an increase in extreme precipitation, longer dry periods, and soil erosion.
Effects of elevated soil temperature and altered precipitation patterns on N-cycling and production of N2O and CO2 in an agricultural soil
(2016) Latt, Yadana Khin; Kandeler, Ellen
Both temperature and precipitation regimes are expected to change with climate change and are, at the same time, major environmental factors regulating biogeochemical cycles in terrestrial ecosystems. Therefore, crop water availability, soil nitrogen transformations, losses, and uptake by plants as well as CO2 emissions from soil are likely to be changed by climate change. Agriculture is known to be one of the most important human activities for releasing significant amounts of N2O and CO2 to the atmosphere. Due to global concern about the changing climate, there has been a great interest in reducing emissions of N2O and CO2 from agricultural soils. CO2 and N2O are produced in soil primarily by microbial processes. Their production and emissions from the soil are controlled by a number of environmental variables including inorganic N availability, soil temperature and water content. Agricultural management practices, such as irrigation, affect these environmental variables and thus have the potential to dramatically alter N2O and CO2 emissions from the soil. The present study is titled "Effects of elevated soil temperature and altered precipitation patterns on N cycling and production of N2O and CO2 in an agricultural soil". The objectives of this study were: to determine the effects of elevated soil temperature on N cycling in a winter wheat cropping system, to investigate the short-term response of N2O and CO2 fluxes during rewetting of soils after extended dry periods in summer, and to determine the effects of different degrees of rewetting on the CO2 emission peaks after rewetting in laboratory incubations. In the 1st experiment, we used the Hohenheim Climate Change (HoCC) experiment in Stuttgart, Germany, to test the hypothesis that elevated soil temperature will increase microbial N cycling, plant N uptake and wheat growth. In the HoCC experiment, soil temperature is elevated by 2.5°C at 4 cm depth. This experiment was conducted at non-roofed plots (1m x 1m) with ambient (Ta) and elevated (Te) soil temperature and with ambient precipitation. In 2012, winter wheat (Triticum aestivum) was planted. C and N concentrations in soil and aboveground plant fractions, soil microbial biomass C and N (Cmic and Nmic), mineral N content (NH4+ - N and NO3- - N), potential nitrification and enzymes involved in nitrogen cycling were analyzed at soil depths of 0-15 and 15-30 cm at five sampling dates. The plants were rated weekly for their phenological development and senescence behavior. We found that an increase in soil temperature by 2.5oC did not have a persistent effect on mineral N content and the activity of potential nitrification within the soil. Plant growth development also did not respond to increased soil temperature. However microbial biomass C and N, and some enzyme activities involved in N-cycling, tended to increase under elevated soil temperature. Overall, the results of this study suggested that soil warming by 2.5oC slightly stimulates soil N cycling but does not alter plant growth development. In the 2nd experiment, in 2013, the effects of a change in the amount and frequency of precipitation patterns on N2O and CO2 emissions were studied after the two dry periods in summer in the HoCC experiment. N2O and CO2 gas samples were taken from four subplots (1m x 1m) of each roofed plot exposed to ambient (Ta) or elevated (Te) soil temperature and four precipitation manipulations (ambient plot, reduced precipitation amount, reduced precipitation frequency, and reduced precipitation amount and frequency). We found that CO2 emissions were affected only by temperature, but not by precipitation pattern. It can be said that N2O and CO2 emissions after rewetting of dry soil were not altered by changing precipitation patterns during dry periods in summer. In the year 2014, using laboratory incubations, we also measured the short-term response of CO2 production to a rewetting of dry soil to different volumetric water contents for 24 hours. This study was conducted by manipulating microcosms with agricultural soil from the HoCC experimental site, which had been exposed to severe drought conditions of three months duration for each of the last six years. The results showed that CO2 production increased with increases in the water content of soils by rewetting at 5%, 15%, 25%, 35% and 45% VWC. With increasing water additions more peaks in CO2 production were detected and different temporal patterns of CO2 emission were affected by adding different amounts of water. It might be due to the fact that with greater water additions successively larger pore sizes were water filled and therefore different bacterial groups located in different pore size classes might have contributed to CO2 production. In summary, the results from field study suggested that climate warming will affect N cycling in soils in an agricultural cropping system. The results from both field and microcosm rewetting experiments contribute to a better understanding of C and N dynamics in soil by investigating the effect of varying soil water content on the emission of N2O and CO2.
Measuring and modelling carbon stocks in rubber (Hevea brasiliensis) dominated landscapes in Subtropical China
(2019) Yang, Xueqing; Cadisch, Georg
Rubber plantation has been rapidly expanded in Montane Mainland South East Asia in past decades. Limited by long-term monitoring data availability, the impacts of environmental change on rubber trees carbon stock development still not fully understood. Against global warming background, in order to better facilitate regional forest management, we applied synergetic approach combining field survey and modelling tools to improve predictions of dynamic carbon stock changes. The trade-off analysis regarding to rubber carbon stock and latex production optimization was further discussed in view of sustainable rubber cultivation. The first study explored the impact of regional land-use changes on landscape carbon balances. The Naban River Watershed National Nature Reserve (NRWNNR), Xishuangbanna, China, was selected as a case study location. Carbon stocks were evaluated using the Rapid Carbon Stock Appraisal (RaCSA) method based on tree, plot, land use and landscape level assessments of carbon stocks, integrating field sampling with remote sensing and GIS technology. The results showed that rubber plantations had larger time-averaged carbon stocks than non-forest land use types (agricultural crops, bush and grassland) but much lower than natural forest. During 23 years (1989-2012), the whole landscape of the nature reserve (26574 ha) gained 0.644 Tg C. Despite rubber expansion, the reforestation activities conducted in NRWNNR were able to enhance the carbon stocks. Regional evaluation of the carbon sequestration potential of rubber trees depends largely on the selection of suitable allometric equations and the biomass-to-carbon conversion factor. The second study developed generic allometric equations for rubber trees, covering rotation lengths of 4-35 years, within elevation gradient of 621-1,127 m, and locally used rubber tree clones (GT1, PRIM600, Yunyan77-4) in mountainous South Western China. Allometric equations for aboveground biomass (AGB) estimations considering diameter at breast height (DBH), tree height, and wood density were superior to other equations. We also tested goodness of fit for the recently proposed pan-tropical forest model. The results displayed that prediction of AGB by the model calibrated with the harvested rubber tree biomass and wood density was more accurate than the results produced by the pan-tropical forest model adjusted to local conditions. The relationships between DBH and height and between DBH and biomass were influenced by tapping, therefore biomass and C stock calculations for rubber have to be done using species-specific allometric equations. Based on the analysis of environmental factors acting at the landscape level, we noticed that above- and belowground carbon stocks were mostly affected by stand age, soil clay content, aspect, and planting density. The results of this study provide reference for reliable carbon accounting in other rubber-cultivated regions. In the last study, we explored how rubber trees growth and production response to climate change and regional management strategies (cultivation elevation, planting density). We applied the process-based Land Use Change Impact Assessment tool (LUCIA) calibrated with detailed ground survey data to model tree biomass development and latex yield in rubber plantations at the tree, plot and landscape level. Model simulation showed that during a 40-year rotation, lowland rubber plantations (< 900m) grew quicker and had larger latex yield than highland rubber (≧900m). High planting density rubber plantations showed 5% higher above ground biomass than those at low- and medium-planting density. The mean total biomass and cumulative latex yield per tree over 40 years increased by 28% and 48%, respectively, when climate change scenarios were modelled from baseline to highest CO2 emission scenario (RCP 8.5). The same trend of biomass and latex yield increase with climate change was observed at plot level. Denser plantations had larger biomass, but the cumulative latex production decreased dramatically. The spatially explicit output maps produced during modelling could help maximize carbon stock and latex production of regional rubber plantations. Overall, rubber-based system required for appropriate monitoring scale in both temporal aspect (daily-, monthly-, and yearly-level) and in spatial aspect (pixel-, land use-, watershed-, and landscape- level). The findings from present study highlighted the important application of ecological modelling tools in nature resources management. The lessons learned here could be applicable for other rubber-cultivated regions, by updating with site-specific environmental variables. The significant role of rubber tree not limited in its nature latex production, it also lies in its great carbon sequestration potential. Our results here provided entry point for future developing comprehensive climate change adaption and mitigation strategies in South East Asia. By making use of interdisplinary cooperation, the sustainable rubber cultivation in Great Mekong Regions could be well realized.
Die Rolle des Porenraums im Kohlenstoffhaushalt anthropogen beeinflusster Niedermoore des Donaurieds
(2007) Höll, Bettina; Stahr, Karl
The use of peatlands in Central Europe for hundreds of years has led to their degradation (loss of organic matter) due to intensive mineralisation. Re-wetting of formerly drained peat aereas has been a popular method of retaining existing peatlands. The effect of re-wetting of degraded fens on their C-pools and C-fluxes is unknown. The protection of these natural resources combined with the creation of biological C-sinks might render the protection and conservation of peatland ecosystems more attractive. Water-logging leads to the accumulation of water in previously air-filled soil pores, something that might increase the C-pool of the soil. It is unknown whether the pore space, which possibly accounts for up to 90% of peatlands, contains carbon components that are similar to those found in the solid soil substance. It is also unknown how much the utilisation of peatlands affects the composition of C-components of the pore space. The major objectives of the present study were (1) to assess the temporal and spatial variability of the C-components in the pore space in fens undergoing different anthropogenic use (drainage, re-wetting) and (2) to assess the role of the pore space in the C-budget. In a Southern German area known as the Schwäbisches Donaumoos, carbon components of the gaseous phase (CO2, CH4) and the liquid phase (CO2/DIC, CH4, DOC, POC) were collected at different depths (5, 10, 20, 40, 60, 80 cm) from different drained (deep, moderately) fen sites and from a long-term re-wetted fen site. Sampling was done at weekly intervals between April 2004 and April 2006. The samples of the water phase and gas phase were collected at the respective sites using slotted PVC tubes and soil-air probes. Gas was analysed using a gas chromatograph and dissolved organic carbon was analysed using a TC water analyser. The fen sites were characterised by selected static parameters of the solid substance and dynamic parameters such as redox potentials, temperature, water level, soil-moisture tension and pH value. The specific use of the fens, which is closely related to the water budget of the area, was a decisive determinant of the amounts of carbon in pore space. Although the solid soil substance in fen sites accounted for less of 10% of the total substance (solid + pores), it still contained a higher amount of carbon (60 -152 kg C m-3) than the pore space. Furthermore the amount of time that the carbon remains is eventually longer in the solid soil substance than in the pore water. Assuming the pore water works only as a short time reservoir. Filling of the pore space with either air or water had a decisive effect on the amount of C. The investigations showed that the amount of C in the air-filled pore space contained an annual average of 15 g C m-3 (deep-drained area), whereas the water-filled pore space contained on average 263 g C m-3 (re-wetted area). The variable anthropogenic effects on fens led to area-specific situations (e.g. groundwater level) that not only affected the amount of C but also had a significant effect on the composition of C components. Dissolved inorganic carbon (DIC), with an average proportion of 55-72%, accounted for the largest proportion of dissolved carbon. Particulate organic carbon (POC) had similar concentrations to dissolved organic carbon (DOC), whereas dissolved methane (CH4) only accounted for a minor proportion (< 0.1%) of the entire carbon of the liquid phase. The DIC concentration was highest in the water from the pores of re-wetted fen. Independent from the use of the fens, different DIC isotope signatures of the ground, karst and spring waters (-11.7‰ to -14.3‰) in comparison to the pore waters (-16.7‰ to -18.4‰) were observed. The further differentiation into the 13C ratios of CO2 contained in the gaseous phase (-23.0‰ to -26.6‰) suggests that DIC ‘accumulated’ in the pore water by way of biogenic CO2. DOC concentrations were lowest in the re-wetted fen. The temporal variability of DOC was related to changes in the bioavailability of DOC. This was also observed in the moderately drained area. The low degree of aromatisation (= higher bioavailability) associated with higher DOC concentrations led to significantly lower values in the re-wetted area compared to the moderately drained area. The microbially easily available DOC proportion was not only temporally but also spatially limited and had a significant effect on the CO2 and CH4 concentrations. At similar depths, CO2 values 10- to 1000-fold higher than CH4 levels could be measured in the gaseous phase (2.7-67 mg CO2-C l-1 vs. < 5.3 mg CH4-C l-1). The highest concentrations were measured in the re-wetted fen. The CO2-C/CH4-C ratios rarely achieved ratios of below 100:1. Due to the higher concentrations of CO2, it can be assumed that the carbon dioxide could compensate for the effect of methane on the climate, on the condition that comparable CO2-C/CH4-C ratios are found in the emissions. The protection of fens as natural resources could be related to carbon uptake (results of the gas exchange to the atmosphere) and higher carbon amounts in the pore space. The amount of time that the carbon remains in the pore waters is correlated to carbon turnover and hydrological conditions. The latter are also important when assessing the indirect emissions, playing an important role in drained fens and rounding out carbon balances.
Untersuchung der Energie- und Nährstoffflüsse mikrobieller Gemeinschaften
(2017) Starke, Robert; Seifert, Jana
The activity of microorganisms was heavily investigated using the incorporation of stabile isotopes in the last decade. Here, all biomolecules but predominantly DNA, RNA, proteins and phospholipid derived fatty acids are used to trace the label in the biomass of active microbes. Thereby, the phylogenetic information decreases from DNA and RNA to proteins whereas the latter allow to describe the actual phenotype. In this work, protein stable isotope probing (protein-SIP) was applied to two different microbial systems: (a) the anaerobic mineralization of benzene and (b) the assimilation of plant-derived organic matter in soil. Labeling of the secondary metabolism of the benzene-mineralizing and sulfate-reducing community using 13C2-acetate: The well-described microbial community enriched from the Zeitz aquifer was fed with the postulated and fully 13C-labeled intermediate of syntrophic benzene fermentation, acetate, to unveil detailed secondary utilization processes. Additional acetate amended to the ongoing benzene mineralization showed no influence on sulfide produced by sulfate reduction. Instead, labeled acetate was incorporated by Campylobacterales, Syntrophobacterales, Archaeoglobales, Clostridiales and Desulfobacterales in descending order. The epsilonproteobacterial Campylobacterales featured the fastest and the highest 13C-incorporation to confirm previous metagenome-based studies and to assign a physiological role to this phylotype of the community for the first time. Metagenome based labeling of the secondary metabolism of the benzene-mineralizing and sulfate-reducing community: In this study, the population genome of the primary acetate utilizer was reconstructed from the metagenome of the benzene mineralizing community obtained by whole-genome shotgun sequencing. Genomic DNA originated from a starvation enrichment culture previously metabolizing m-xylen and enriched in the identical epsilonproteobacterial phylotype of this community. The presence of the sulfide quinone oxidoreductase (sqr) and the polysulfide reductase (psr) suggested a key role in sulfur cycling. Hence, the epsilonproteobacterial phylotype is able to oxidize otherwise toxic sulfid produced by sulfate reduction to polysulfide via SQR and its subsequent reduction to sulfide via PSR. Further, the detection of an acetate transporter (actP) and the acetyl-CoA synthetase (acsA) for acetate activation approved direct assimilation as shown in the previous study. Short-term assimilation of plant-derived organic matter in soil: In this protein-SIP study, the short-term assimilation of plant-derived organic matter in soil was demonstrated using 15N-labeled tobacco for the first time. In contrast to the postulated model in which fungi degrade plant-derived complex compounds and secrete low molecular weight compounds which are then degraded by bacteria, our study demonstrated the dominance of bacteria over fungi during the short-term assimilation of plant-derived organic matter. Bacteria outcompete fungi for the easy available plant-derived compounds until complex compounds such as cellulose and lignin are enriched and degraded by slow growing fungi. The use of multiOMIC techniques resulted in a multidimensional scheme to easily group and categorize different behaviours of microorganisms.