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Experimental evidence shows that grassland plant diversity enhances ecosystem functioning. Yet, the transfer of results from controlled biodiversity experiments to naturally assembled 'real world' ecosystems remains challenging due to environmental variation among sites, confounding biodiversity ecosystem functioning relations in observational studies. To bridge the gap between classical biodiversity‐ecosystem functioning experiments and observational studies of naturally assembled and managed ecosystems, we created regionally replicated, within‐site gradients of species richness by seeding across agricultural grasslands differing in land‐use intensity (LUI) and abiotic site conditions.Within each of 73 grassland sites, we established a full‐factorial experiment with high‐diversity seeding and topsoil disturbance and measured 12 ecosystem functions related to productivity, and carbon and nutrient cycling after 4 years. We then analysed the effects of plant diversity (seeded richness as well as realized richness), functional community composition, land use and abiotic conditions on the ecosystem functions within (local scale) as well as among grassland sites (landscape scale).Despite the successful creation of a within‐site gradient in plant diversity (average increase in species richness in seeding treatments by 10%–35%), we found that only one to two of the 12 ecosystem functions responded to realized species richness, resulting in more closed nitrogen cycles in more diverse plant communities. Similar results were found when analysing the effect of the seeding treatment instead of realized species richness. Among sites, ecosystem functioning was mostly driven by environmental conditions and LUI. Also here, the only functions related to plant species richness were those associated with a more closed nitrogen cycle under increased diversity.The minor effects of species enrichment we found suggest that the functionally‐relevant niche space is largely saturated in naturally assembled grasslands, and that competitive, high‐functioning species are already present.Synthesis: While nature conservation and cultural ecosystem services can certainly benefit from plant species enrichment, our study indicates that restoration of plant diversity in naturally assembled communities may deliver only relatively weak increases in ecosystem functioning, such as a more closed nitrogen cycle, within the extensively to moderate intensively managed agricultural grasslands of our study. [ABSTRACT FROM AUTHOR]

Spatial and temporal processes shaping microbial communities are inseparably linked but rarely studied together. By Illumina 16S rRNA sequencing, we monitored soil bacteria in 360 stations on a 100 square meter plot distributed across six intra-annual samplings in a rarely managed, temperate grassland. Using a multi-tiered approach, we tested the extent to which stochastic or deterministic processes influenced the composition of local communities. A combination of phylogenetic turnover analysis and null modeling demonstrated that either homogenization by unlimited stochastic dispersal or scenarios, in which neither stochastic processes nor deterministic forces dominated, explained local assembly processes. Thus, the majority of all sampled communities (82%) was rather homogeneous with no significant changes in abundance-weighted composition. However, we detected strong and uniform taxonomic shifts within just nine samples in early summer. Thus, community snapshots sampled from single points in time or space do not necessarily reflect a representative community state. The potential for change despite the overall homogeneity was further demonstrated when the focus shifted to the rare biosphere. Rare OTU turnover, rather than nestedness, characterized abundance-independent β-diversity. Accordingly, boosted generalized additive models encompassing spatial, temporal and environmental variables revealed strong and highly diverse effects of space on OTU abundance, even within the same genus. This pure spatial effect increased with decreasing OTU abundance and frequency, whereas soil moisture – the most important environmental variable – had an opposite effect by impacting abundant OTUs more than the rare ones. These results indicate that – despite considerable oscillation in space and time – the abundant and resident OTUs provide a community backbone that supports much higher β-diversity of a dynamic rare biosphere. Our findings reveal complex interactions among space, time, and environmental filters within bacterial communities in a long-established temperate grassland. [ABSTRACT FROM AUTHOR]

Drivers of ecosystem stability have been a major topic in ecology for decades. Most studies have focused on the influence of species richness on ecosystem stability and found positive diversity‐stability relationships. However, land use and abiotic factors shape species richness and functional composition of plant communities and may override species richness‐stability relations in managed grasslands.We analysed the relative importance of land‐use intensity (LUI), resident plant species richness and functional composition for recovery of plant communities (plant species richness, plant cover, above‐ and below‐ground biomass) and release of soil nutrients after a severe mechanical disturbance. Experimental sward disturbance was applied to 73 grassland sites along a LUI gradient in three German regions. We considered relative (ln(disturbance/control)) and absolute (disturbance − control) treatment effects. Using structural equation modelling, we disentangled direct effects of LUI and resident species richness on recovery and indirect effects via changes in functional richness.Community‐weighted‐mean traits rarely mattered for recovery or nutrient release, while functional richness especially increased relative recovery of plant communities but also relative release of NO3‐N and NH4‐N. These effects were enhanced by increasing resident plant species richness and decreasing LUI. Next to these indirect influences of LUI and resident plant species richness via functional community composition, grasslands of high compared with grasslands of low resident plant species richness generally showed decreased recovery of plant communities. In grasslands of high LUI, absolute recovery of some aspects of plant communities was decreased. We did not find consistent differences between the relative importance of the different drivers of recovery after the first and the second season. Overall, resident species richness seemed most important for relative recovery and less important for absolute recovery, where direct effects of LUI were more common.Synthesis. The stability of ecosystems in managed grasslands depends on more than species richness. Thus, drivers that directly affect species richness and functional community composition have to be considered when studying the stability of real‐world ecosystems. More specifically, in managed grasslands high resident species richness but also high land‐use intensity (LUI) decreased the stability of ecosystem functions, which was partially buffered by increases in functional richness. [ABSTRACT FROM AUTHOR]

Soil protists are increasingly appreciated as essential components of soil foodwebs; however, there is a dearth of information on the factors structuring their communities. Here we investigate the importance of different biotic and abiotic factors as key drivers of spatial and seasonal distribution of protistan communities. We conducted an intensive survey of a 10 m2 grassland plot in Germany, focusing on a major group of protists, the Cercozoa. From 177 soil samples, collected from April to November, we obtained 694 Operational Taxonomy Units representing >6 million Illumina reads. All major cercozoan taxonomic and functional groups were present, dominated by the small flagellates of the Glissomonadida. We found evidence of environmental selection structuring the cercozoan communities both spatially and seasonally. Spatial analyses indicated that communities were correlated within a range of 3.5 m. Seasonal variations in the abundance of bacterivores and bacteria, followed by that of omnivores suggested a dynamic prey-predator succession. The most influential edaphic properties were moisture and clay content, which differentially affected each functional group. Our study is based on an intense sampling of protists at a small scale, thus providing a detailed description of the biodiversity of different taxa/functional groups and the ecological processes involved in shaping their distribution. [ABSTRACT FROM AUTHOR]

Abstract: Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium‐nitrate fertilizer solution, in which either ammonium ( NH 4 +) or nitrate ( NO 3 −) was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than twofold higher than under aCO2. The tracing model results indicated that plant uptake of NH 4 + did not differ between treatments, but uptake of NO 3 − was significantly reduced under eCO2. However, the NH 4 + and NO 3 − availability increased slightly under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8,407 μg N2O–N/m2 during the first 58 days after labelling, were associated with NO 3 − reduction (+2.0%), NH 4 + oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N2O:N2 emission ratio, explains the doubling of N2O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change. [ABSTRACT FROM AUTHOR]

Increased warming in spring and prolonged summer drought may alter soil microbial denitrification. We measured potential denitrification activity and denitrifier marker gene abundances (nirK, nirS, nosZ) in grasslands soils in three geographic regions characterized by site-specific land-use indices (LUI) after warming in spring, at an intermediate sampling and after summer drought. Potential denitrification was significantly increased by warming, but did not persist over the intermediate sampling. At the intermediate sampling, the relevance of grassland land-use intensity was reflected by increased potential N2O production at sites with higher LUI. Abundances of total bacteria did not respond to experimental warming or drought treatments, displaying resilience to minor and short-term effects of climate change. In contrast, nirS- and nirK-type denitrifiers were more influenced by drought in combination with LUI and pH, while the nosZ abundance responded to the summer drought manipulation. Land-use was a strong driver for potential denitrification as grasslands with higher LUI also had greater potentials for N2O emissions. We conclude that both warming and drought affected the denitrifying communities and the potential denitrification in grassland soils. However, these effects are overruled by regional and site-specific differences in soil chemical and physical properties which are also related to grassland land-use intensity. [ABSTRACT FROM AUTHOR]

Understanding factors driving the ecology of N cycling microbial communities is of central importance for sustainable land use. In this study we report changes of abundance of denitrifiers, nitrifiers and nitrogen-fixing microorganisms (based on qPCR data for selected functional genes) in response to different land use intensity levels and the consequences for potential turnover rates. We investigated selected grassland sites being comparable with respect to soil type and climatic conditions, which have been continuously treated for many years as intensely used meadows (IM), intensely used mown pastures (IP) and extensively used pastures (EP), respectively. The obtained data were linked to above ground biodiversity pattern as well as water extractable fractions of nitrogen and carbon in soil. Shifts in land use intensity changed plant community composition from systems dominated by s-strategists in extensive managed grasslands to c-strategist dominated communities in intensive managed grasslands. Along the different types of land use intensity, the availability of inorganic nitrogen regulated the abundance of bacterial and archaeal ammonia oxidizers. In contrast, the amount of dissolved organic nitrogen determined the abundance of denitrifiers (nirS and nirK). The high abundance of nifH carrying bacteria at intensive managed sites gave evidence that the amounts of substrates as energy source outcompete the high availability of inorganic nitrogen in these sites. Overall, we revealed that abundance and function of microorganisms involved in key processes of inorganic N cycling (nitrification, denitrification and N fixation) might be independently regulated by different abiotic and biotic factors in response to land use intensity. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to underpin the capability of diffuse reflectance Fourier transform mid-infrared spectroscopy (midDRIFTS)-based partial least squares regression (PLSR) analyses to accurately predict soil microbiological properties across six temperate grassland ecosystems differing in their land-use intensity; three sites of low land-use intensity (low LUI) and three fertilized mown meadows (high LUI). In addition, the potential of midDRIFTS-PLSR analyses for spatial studies between soils of contrasting grassland ecosystems was evaluated. 304 samples were subjected to midDRIFTS-PLSR-based predictions of soil microbial biomass, activities of beta-d-glucosidase, xylosidase and urease, as well as bacterial abundance based on 16S rRNA gene quantification. Accuracies of midDRIFTS-PLSR-based predictions across both LUI were, on basis of the residual prediction deviation (RPD), ‘acceptable’ for all soil microbiological properties, in particular soil microbial biomass (coefficient of determination (R 2) = 0.92; RPD = 3.55), urease (0.91; 3.42) and beta-d-glucosidase (0.89; 3.01). Predictions of ‘moderately successful’ accuracy were developed for 16S rRNA gene copies (0.88; 2.93) and xylosidase (0.84; 2.55). Spatial midDRIFTS-PLSR-based predictions between grassland ecosystems were only ‘acceptable’ for soil microbial biomass, while the other studied soil microbiological properties revealed only ‘moderately successful’ predictions. The potential of midDRIFTS-PLSR to predict a range of soil microbiological properties including molecular data with ‘acceptable’ accuracies across the two investigated grassland ecosystems with contrasting land-use intensities was substantiated. However, the prevailing ‘moderately successful’ prediction accuracies between grassland ecosystems were probably due to the dependence on land use-specific data sets for calibration and validation. For prospective application of cost- and time-efficient midDRIFTS-PLSR-based approaches, predictions of soil microbiological properties considering particularly, but not yet ‘acceptable’ molecular data will greatly advance the understanding on the abundance and functional dynamics of soil microbial communities across spatial and temporal scales of contrasting ecosystems. [Copyright &y& Elsevier]

Very few principles have been unraveled that explain the relationship between soil properties and soil biota across large spatial scales and different land-use types. Here, we seek these general relationships using data from 52 differently managed grassland and forest soils in three study regions spanning a latitudinal gradient in Germany. We hypothesize that, after extraction of variation that is explained by location and land-use type, soil properties still explain significant proportions of variation in the abundance and diversity of soil biota. If the relationships between predictors and soil organisms were analyzed individually for each predictor group, soil properties explained the highest amount of variation in soil biota abundance and diversity, followed by land-use type and sampling location. After extraction of variation that originated from location or land-use, abiotic soil properties explained significant amounts of variation in fungal, meso- and macrofauna, but not in yeast or bacterial biomass or diversity. Nitrate or nitrogen concentration and fungal biomass were positively related, but nitrate concentration was negatively related to the abundances of Collembola and mites and to the myriapod species richness across a range of forest and grassland soils. The species richness of earthworms was positively correlated with clay content of soils independent of sample location and land-use type. Our study indicates that after accounting for heterogeneity resulting from large scale differences among sampling locations and land-use types, soil properties still explain significant proportions of variation in fungal and soil fauna abundance or diversity. However, soil biota was also related to processes that act at larger spatial scales and bacteria or soil yeasts only showed weak relationships to soil properties. We therefore argue that more general relationships between soil properties and soil biota can only be derived from future studies that consider larger spatial scales and different land-use types. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present study was to investigate whether land-use intensity (LUI) contributes to spatial variation in microbial abundance and function in grassland ecosystems. At one time point, three sites at low (unfertilized pastures), at intermediate (fertilized mown pastures) and at high (fertilized mown meadows) LUIs were selected in southern Germany. Within each of these nine grassland sites, 54 soil samples (0–10cm) were taken in a 10m×10m area in spring. Plot-scale spatial dependence and autocorrelation of soil biogeochemical properties, microbial biomass and enzymes involved in C-, N- and P-cycling were analyzed. Applying geostatistics (exponential or spherical model) revealed that most chemical and microbiological properties showed at least a moderate spatial autocorrelation. Chemical soil properties (e.g. Corg, Nt, pH) were characterized by practical ranges (pRange) of between 1 and 14m, whereas soil microbiological properties showed a greater variation of pRanges, providing evidence of spatial heterogeneity at multiple scales. The expected decrease in small-scale spatial heterogeneity in high LUI could not be confirmed for microbiological soil properties, because sampling in early spring might have reduced the influence of growing plants and fertilization. However, microbial biomass carbon was significantly greater in high LUIs, indicating that the benefit to soil microbial populations from the long-term increase in substrate and nutrient availability in fertilized grasslands is independent from factors affecting spatial structures in the short-term. [Copyright &y& Elsevier]

In heterogeneous environments such as soil it is imperative to understand the spatial relationships between microbial communities, microbial functioning and microbial habitats in order to predict microbial services in managed grasslands. Grassland land-use intensity has been shown to affect the spatial distribution of soil microorganisms, but so far it is unknown whether this is transferable from one geographic region to another. This study evaluated the spatial distribution of soil microbial biomass and enzyme activities involved in C-, N- and P-cycling, together with physico-chemical soil properties in 18 grassland sites differing in their land-use intensity in two geographic regions: the Hainich National Park in the middle of Germany and the Swabian Alb in south-west Germany. Enzyme activities associated with the C- and N-cycles, namely β-glucosidase, xylosidase and chitinase, organic carbon (Corg), total nitrogen (Nt), extractable organic carbon, and mineral nitrogen (Nmin) were higher in the Swabian Alb (Leptosols) than in the Hainich National Park (primarily Stagnosols). There was a negative relationship between bulk density and soil properties such as microbial biomass (Cmic, Nmic), urease, Corg, and Nt. The drivers (local abiotic soil properties, spatial separation) of the enzyme profiles (β-glucosidase, chitinase, xylosidase, phosphatase, and urease) were determined through a spatial analysis of the within site variation of enzyme profiles and abiotic properties, using the Procrustes rotation test. The test revealed that physical and chemical properties showed more spatial pattern than the enzyme profiles. β-glucosidase, chitinase, xylosidase, phosphatase, and urease activities were related to local abiotic soil properties, but showed little spatial correlation. Semivariogram modeling revealed that the ranges of spatial autocorrelation of all measured variables were site specific and not related to region or to land-use intensity. Nevertheless, land-use intensity changed the occurrence of spatial patterns measurable at the plot scale: increasing land-use intensity led to an increase in detectable spatial patterns for abiotic soil properties on Leptosols. The conclusion of this study is that microbial biomass and functions in grassland soils do not follow general spatial distribution patterns, but that the spatial distribution is site-specific and mainly related to the abiotic properties of the soils. [ABSTRACT FROM AUTHOR]