Browsing by Subject "Enzymaktivität"

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Community Structure and Activity of Nitrate-Reducing Microorganisms in Soils under Global Climate Change
(2006) Deiglmayr, Kathrin; Kandeler, Ellen
Since the beginning of the Industrial Revolution, atmospheric carbon dioxide concentrations have been steadily increasing and, thus, contributed to a warming of the climate and altered biogeochemical cycles. To study the response of soil microorganisms to altered environmental conditions under global climate change, the nitrate-reducing community was regarded as a model community in the present thesis. This functional group, which performs the first step in the denitrification pathway, was selected because it is phylogenetically very diverse. In particular rising levels of atmospheric carbon dioxide as the most important catalyst of temperature rise and the retreat of glaciers in the Alps as one of the most evident consequences of climate change were investigated. The behaviour of nitrate reducers was investigated in a biphasic approach: (i) at the level of its enzyme activity of the nitrate reductase and (ii) at the level of community structure, which was characterised by RFLP (Restriction Fragment Length Polymorphism)-fingerprints using the functional gene narG. The effect of elevated atmospheric carbon dioxide concentrations on nitrate-reducing micro-organisms was studied in the Swiss FACE (Free Air Carbon dioxide Enrichment) experiment including the rhizosphere of two functional plant types (Lolium perenne and Trifolium repens), two N fertilisation levels and two sampling dates (June and October 2002). Whereas in June no significant treatment effect was observed, the nitrate reductase activity proved to be significantly reduced under elevated atmospheric carbon dioxide at the autumn sampling date. Simultaneously, elevated enzyme activities were recorded under Trifolium repens and high N fertilisation pointing to a control of nitrate reductase activity by nitrate availability at the time of sampling. The community structure of nitrate reducers, however, showed a different response pattern with sampling date and the strongly varying pH of the different experimental plots constituting the main driving factors. With respect to the three experimental factors atmospheric carbon dioxide, plant type and N fertilisation the composition of the nitrate reducers revealed a high stability. The microbial succession of nitrate-reducing microorganisms was studied in the rhizosphere of Poa alpina across the glacier foreland of the Rotmoosferner/Oetz valley. Sampling was performed in August and at the end of the short period of vegetation in September. The nitrate reductase activity increased significantly with progressing successional age, whereas organic carbon together with nitrate concentrations in the soils explained the major part of this effect. The microbial community of nitrate reducers revealed a significant shift across the glacier foreland, with pH and organic carbon representing the most important environmental factors inducing this shift. A detailed analysis of the clone libraries that were constructed for the youngest and the oldest site in the glacier foreland pointed to the tendency of lower diversity in the late succession compared to the young succession. Possibly an increasing selective pressure due to higher densities of microorganisms and, hence, a higher competition for limited resources contributed to the decline in diversity. In conclusion, the functional group of nitrate reducers responded to changing environmental conditions under global climate change particularly through altered enzyme activities. The amount and the direction of this response depended strongly on the nitrate availability and the organic carbon content in soils. The community structure of nitrate-reducing microorganisms, however, proved to be resilient towards short-term substrate fluctuations. This indicates that the genetic pool of this group of soil microorganisms possesses a high functional stability characterized by a relatively persistent composition and an independent modulation of enzyme activity.
Effect of reduced nitrogen deposition on microbial activity, abundance and diversity in forest soils
(2012) Enowashu, Esther Eneckeh; Kandeler, Ellen
The deposition of nitrogen has increased many-fold due to anthropogenic activities. Since forest ecosystems are often limited by N availability, elevated N inputs from the atmosphere can have a fertilization effect but in the long-term, excess N can influence above- and below-ground production. One of the consequences of N deposition and increased N inputs is a shift in microbial community structure and function as ecosystems move towards N saturation. Soil microorganisms through the action of enzymes play an important role in N dynamics. Thus, the availability and turnover of N depends strongly on microbial abundance, diversity and activity which are in turn influenced by soil properties. Studies on the effects of high nitrogen inputs and the response of forest ecosystems to nitrogen saturation are many and well understood. However, the reversibility of N-induced shifts in forest ecosystem processes is largely unknown. This thesis was therefore designed to study the response of soil microorganisms to reduced N deposition. A biphasic approach was employed to look into (i) the general microbial functional status of the Solling forest site as well as (ii) the microbial community structure which may be a key regulator of two important processes of N transformation: denitrification and proteolysis. The goal of the present thesis was addressed in three studies. Denitrification is considered sensitive to environmental changes and the response of nitrate-reducers and denitrifiers to reduced N deposition was determined in the first study. The goal of the second study was to investigate the overall microbial activity of the Solling forest profiles especially focussing on enzymes involved in the N cycle. This revealed a pronounced activity of peptidases whereby a set of novel pepN primers encoding alanine aminopeptidase enzyme was designed in the third study to determine the group of bacteria involved in proteolysis in forest as well as agricultural and grassland soils. The Solling experimental station was established more than two decades ago and it gave the opportunity to study the N cycle in a natural forest ecosystem at different sampling dates and depths. A combination of classical biological methods and modern molecular techniques were used in the studies. Soil physico-chemical parameters (OC, Nt, NO3-, NH4+, pH, % Water content) were analysed to gain more information on mineralization and immobilization of N in the soil profiles. The analysis of microbial biomass, ergosterol content and the activity of several enzymes of the N, C and P cycles as well as enzyme activity of nitrate reducers was determined in order to interpret microbial functions. The abundance of nitrate reducers and denitrifiers were determined by quantitative PCR of 16S rRNA, nitrate reductase (narG and napA) and denitrification (nirK, nirS and nosZ) genes. The diversity of peptide degrading bacteria was analysed by PCR, cloning and sequencing and the construction of pepN gene libraries. The results of the first study indicated that time and space were the main drivers influencing the abundance and activity of the nitrate reducers and denitrifier communities in the forest soil profiles. Reduced N deposition had a of minimal effect. Interestingly, the ratios of nosZ to16S rRNA gene and nosZ to nirK increased with soil depth thereby tempting to conclude that the size of denitriﬁers capable of reducing N2O into N2 might be bigger in the mineral horizons. In the second study, a stronger response of N cycling enzymes to reduced N deposition could be seen. However, these responses especially that of specific peptidases differed in magnitude which could be indicative of a modification of the reaction rates of the different N cycling enzymes. Correlation of nutrients (N, C, P) with microbial biomass and enzyme activities in the soil profiles revealed that substrate availability was the main factor influencing microbial activity. In the third study, analyses of gene libraries from extracted DNA from forest, agricultural and glacier soil samples revealed a high diversity of pepN sequences related to mainly α-Proteobacteria. A majority of the sequences showed similarity to published data revealing that the amplified region of pepN might be conserved. Linking diversity and enzymatic data, lowest diversity was observed in the agricultural soil where activity levels of alanine aminopeptidase were lowest indicating the importance of diversity studies for ecosystem functioning. In conclusion, this thesis offers valuable contributions to understanding the impact of N deposition. The approach used was suitable to assess the response of the different microbial communities to reduced N deposition. The magnitude of the response depended strongly on space, time and substrate availability in soils as well as their interactions.
Spatial and temporal variations of microorganisms in grassland soils : influences of land-use intensity, plants and soil properties
(2019) Boeddinghaus, Runa S.; Kandeler, Ellen
Grassland ecosystems provide a wide range of services to human societies (Allan et al., 2015) and plants and soil microorganisms have been identified as key drivers of ecosystem functioning (Soliveres et al., 2016). Therefore, understanding soil microbial distributions and processes in agricultural grassland soils is crucial for characterizing these ecosystems and for predicting how they may shift in a changing environment. Yet we are only beginning to understand these complex ecosystems, which account for about 26% of the world’s terrestrial surface (FAOSTATS, 2018), making it especially urgent to gain better insights into the effects of land-use intensity on soil microbial properties and plant-microbe interactions. This thesis was conducted to evaluate the impact land-use intensity has on soil microbial biogeography of grasslands with respect to both spatial patterns and temporal changes in soil microbial abundance, function (in terms of enzyme activities), and community composition. It also investigated the relationships between plants and the spatial and temporal distributions of soil microorganisms. Thereby both, land-use intensity effects and plant-microbe interactions, were assessed in light of ecological niche and neutral theory. This thesis is based on three observational studies conducted on from one to 150 continuously farmed, un-manipulated grassland sites in three regions of Germany within the Biodiversity Exploratories project (DFG priority program 1374). The first study assessed the effects of land-use intensity and physico-chemical soil properties on the spatial biogeography of soil microbial abundance and function in 18 grasslands sites from two of the three regions, sampled at one time point. The second study analyzed spatial and temporal distributions of alpha- and beta-diversity of arbuscular mycorrhizal fungi in a low land-use intensity grassland with six sampling time points across one season. The third study investigated both legacy and short-term change effects of land-use intensity, soil physico-chemical properties, plant functional traits, and plant biomass properties on temporal changes in soil microbial abundance, function, and community composition in 150 grassland sites across three regions, with particular regard to direct and indirect land-use intensity effects. Although the three studies used different approaches and assessed different soil microbial properties, general patterns were detectable. Abiotic soil properties, namely pH, nitrogen content, texture, and bulk density played fundamental roles for spatial and temporal microbial biogeography. Since these factors were specific and unique for each investigated site, they formed the background based on which other processes occurred. In addition to abiotic soil properties, impacts of land-use intensity and plants were detected, though to various degrees in the three studies. Land-use intensity played a much smaller role than anticipated in the first and third study. No influence on the spatial distribution of soil microbial abundance and function could be detected in the first study. In the third study, short-term changes in and legacy effects of land-use intensity played a minor role with respect to short-term changes in soil microbial abundance, function, and community composition. Where detected, changes in land-use intensity had a direct and negative effect on soil microbial properties in structural equation modelling; i.e., increases in land-use intensity reduced, e.g., soil microbial enzyme activities, while legacy effects of land-use intensity were shown to act both directly and indirectly on soil microbial properties. Thereby indirect legacy effects were mediated via plant functional traits. Only one of the three studies detected minor plant diversity effects on soil microbial properties. Instead, functional properties of the plant communities, i.e., plant functional traits, biomass, and nutritional quality, were significantly related to spatial and temporal distributions of soil microorganisms. Finally, the findings of the three studies suggest that processes related to niche and neutral theory both drive spatial and temporal patterns of soil microbial properties at the investigated plot scale (up to 50 m × 50 m). This thesis concluded that in order to gain deeper insights into the complex functions and processes occurring in grassland ecosystems, a multidisciplinary approach investigating fundamental physico-chemical site characteristics, microbial soil properties, and plants is necessary. The results of the thesis suggest that focus be turned to functional properties of plant and microbial communities, as they are closely intermingled, provide more detailed insights into plant-microbe interactions, and are able to reflect effects of human impacts on grassland soils better than diversity measures.