Browsing by Person "Keil, Daniel"

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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.