Showing papers by "Bernhard Schmid published in 2021"

Diversity and asynchrony in soil microbial communities stabilizes ecosystem functioning

Abstract: Theoretical and empirical advances have revealed the importance of biodiversity for stabilizing ecosystem functions through time. Despite the global degradation of soils, whether the loss of soil microbial diversity can destabilize ecosystem functioning is poorly understood. Here, we experimentally quantified the contribution of soil fungal and bacterial communities to the temporal stability of four key ecosystem functions related to biogeochemical cycling. Microbial diversity enhanced the temporal stability of all ecosystem functions and this pattern was particularly strong in plant-soil mesocosms with reduced microbial richness where over 50% of microbial taxa were lost. The stabilizing effect of soil biodiversity was linked to asynchrony among microbial taxa whereby different soil fungi and bacteria promoted different ecosystem functions at different times. Our results emphasize the need to conserve soil biodiversity for the provisioning of multiple ecosystem functions that soils provide to the society.

Functional diversity effects on productivity increase with age in a forest biodiversity experiment.

Abstract: Forest restoration increases global forest area and ecosystem services such as primary productivity and carbon storage. How tree species functional composition impacts the provisioning of these services as forests develop is sparsely studied. We used 10-year data from 478 plots with 191,200 trees in a forest biodiversity experiment in subtropical China to assess the relationship between community productivity and community-weighted mean (CWM) or functional diversity (FD) values of 38 functional traits. We found that effects of FD values on productivity became larger than effects of CWM values after 7 years of forest development and that the FD values also became more reliable predictors of productivity than the CWM values. In contrast to CWM, FD values consistently increased productivity across ten different species-pool subsets. Our results imply that to promote productivity in the long term it is imperative for forest restoration projects to plant multispecies communities with large functional diversity.

Co‐occurrence history increases ecosystem stability and resilience in experimental plant communities

Abstract: Understanding factors that maintain ecosystem stability is critical in the face of environmental change. Experiments simulating species loss from grassland have shown that losing biodiversity decreases ecosystem stability. However, as the originally sown experimental communities with reduced biodiversity develop, plant evolutionary processes or the assembly of interacting soil organisms may allow ecosystems to increase stability over time. We explored such effects in a long‐term grassland biodiversity experiment with plant communities with either a history of co‐occurrence (selected communities) or no such history (naive communities) over a 4‐yr period in which a major flood disturbance occurred. Comparing communities of identical species composition, we found that selected communities had temporally more stable biomass than naive communities, especially at low species richness. Furthermore, selected communities showed greater biomass recovery after flooding, resulting in more stable post‐flood productivity. In contrast to a previous study, the positive diversity–stability relationship was maintained after the flooding. Our results were consistent across three soil treatments simulating the presence or absence of co‐selected microbial communities. We suggest that prolonged exposure of plant populations to a particular community context and abiotic site conditions can increase ecosystem temporal stability and resilience due to short‐term evolution. A history of co‐occurrence can in part compensate for species loss, as can high plant diversity in part compensate for the missing opportunity of such adaptive adjustments.

Effects of plant community history, soil legacy and plant diversity on soil microbial communities

Abstract: Plant and soil microbial diversities are linked through a range of interactions, including the exchange of carbon and nutrients but also herbivory and pathogenic effects. Over time, associations between plant communities and their soil microbiota may strengthen and become more specific, resulting in stronger associations between plant and soil microbial diversity. We tested this hypothesis at the end of a 4-year field experiment in 48 plots with different plant species compositions established 13 years earlier in a biodiversity experiment in Jena, Germany. We factorially crossed plant community history (old vs. new plant communities) and soil legacy (old vs. new soil) with plant diversity (species richness levels 1, 2, 4 and 8, each with 12 different species compositions). We use the term ‘plant community history’ to refer to the co-occurrence history of plants in different species compositions in the Jena Experiment. We determined soil bacterial and fungal community composition in terms of operational taxonomic units (OTUs) using 16S rRNA gene and ITS DNA sequencing. Plant community history (old plants) did not affect overall soil community composition but differentially affected bacterial richness and abundances of specific bacterial taxa in association with specific plant species compositions. Soil legacy (old soil) markedly increased soil bacterial richness and evenness and decreased fungal evenness. Soil fungal richness increased with plant species richness, regardless of plant community history or soil legacy, with the strongest difference between plant monocultures and mixtures. Specific plant species compositions and functional groups were associated with specific bacterial and fungal community compositions. Grasses increased fungal richness and evenness and legumes decreased fungal evenness, but bacterial diversity was not affected. Synthesis. Our findings indicate that as experimental ecosystems varying in plant diversity develop over time (2002–2010), plant species associate with specific soil microbial taxa. This can have long-lasting effects on below-ground community composition in re-assembled plant communities, as reflected in strong soil legacy signals still visible after 4 years (2011–2015). Effects of plant community history on soil communities are subtle and may take longer to fully develop.

Plant diversity enhances production and downward transport of biodegradable dissolved organic matter

Abstract: 1. Plant diversity is an important driver of belowground ecosystem functions, such as root growth, soil organic matter (SOM) storage, and microbial metabolism, mainly by influencing the interactions between plant roots and soil. Dissolved organic matter (DOM), as the most mobile form of SOM, plays a crucial role for a multitude of soil processes that are central for ecosystem functioning. Thus, DOM is likely to be an important mediator of plant diversity effects on soil processes. However, the relationships between plant diversity and DOM have not been studied so far. 2. We investigated the mechanisms underlying plant diversity effects on concentrations of DOM using continuous soil water sampling across 6 years and 62 plant communities in a long‐term grassland biodiversity experiment in Jena, Germany. Furthermore, we investigated plant diversity effects on the molecular properties of DOM in a subset of the samples. 3. Although DOM concentrations were highly variable over the course of the year with highest concentrations in summer and autumn, we found that DOM concentrations consistently increased with plant diversity across seasons. The positive plant diversity effect on DOM concentrations was mainly mediated by increased microbial activity and newly sequestered carbon in topsoil. However, the effect of soil microbial activity on DOM concentrations differed between seasons, indicating DOM consumption in winter and spring, and DOM production in summer and autumn. Furthermore, we found increased contents of small and easily decomposable DOM molecules reaching deeper soil layers with high plant diversity. 4. Synthesis. Our findings suggest that plant diversity enhances the continuous downward transport of DOM in multiple ways. On the one hand, higher plant diversity results in higher DOM concentrations, on the other hand, this DOM is less degraded. The present study indicates, for the first time, that higher plant diversity enhances the downward transport of dissolved molecules that likely stimulate soil development in deeper layers and therefore increase soil fertility.

Tree phylogenetic diversity structures multitrophic communities

Abstract: 1. Plant diversity begets diversity at other trophic levels. While species richness is the most commonly used measure for plant diversity, the number of evolutionary lineages (i.e. phylogenetic diversity) could theoretically have a stronger influence on the community structure of co-occurring organisms. However, this prediction has only rarely been tested in complex real-world ecosystems. 2. Using a comprehensive multitrophic dataset of arthropods and fungi from a species-rich subtropical forest, we tested whether tree species richness or tree phylogenetic diversity relates to the diversity and composition of organisms. 3. We show that tree phylogenetic diversity but not tree species richness determines arthropod and fungi community composition across trophic levels and increases the diversity of predatory arthropods but decreases herbivorous arthropod diver- sity. The effect of tree phylogenetic diversity was not mediated by changed abun- dances of associated organisms, indicating that evolutionarily more diverse plant communities increase niche opportunities (resource diversity) but not necessarily niche amplitudes (resource amount). 4. Our findings suggest that plant evolutionary relatedness structures multitrophic communities in the studied species-rich forests and possibly other ecosystems at large. As global change non-randomly threatens phylogenetically distinct plant species, far-reaching consequences on associated communities are expected.

An experimental approach to assessing the impact of ecosystem engineers on biodiversity and ecosystem functions.

Abstract: Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant-insect interaction analysis and variance partitioning of biodiversity effects. We present a case-study experiment in which facilitation by a cushion-plant species and a dwarf-shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity-ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects.

Identification of dominant features in spatial data

Abstract: Dominant features of spatial data are connected structures or patterns that emerge from location-based variation and manifest at specific scales or resolutions. To identify dominant features, we propose a sequential application of multiresolution decomposition and variogram function estimation. Multiresolution decomposition separates data into additive components, and in this way enables the recognition of their dominant features. A dedicated multiresolution decomposition method is developed for arbitrary gridded spatial data, where the underlying model includes a precision and spatial-weight matrix to capture spatial correlation. The data are separated into their components by smoothing on different scales, such that larger scales have longer spatial correlation ranges. Moreover, our model can handle missing values, which is often useful in applications. Variogram function estimation can be used to describe properties in spatial data. Such functions are therefore estimated for each component to determine its effective range, which assesses the width-extent of the dominant feature. Finally, Bayesian analysis enables the inference of identified dominant features and to judge whether these are credibly different. The efficient implementation of the method relies mainly on a sparse-matrix data structure and algorithms. By applying the method to simulated data we demonstrate its applicability and theoretical soundness. In disciplines that use spatial data, this method can lead to new insights, as we exemplify by identifying the dominant features in a forest dataset. In that application, the width-extents of the dominant features have an ecological interpretation, namely the species interaction range, and their estimates support the derivation of ecosystem properties such as biodiversity indices.

Effects of plant community history, soil legacy and plant diversity on soil microbial communities

Abstract: Plant and soil microbial diversity are linked through a range of interactions, including the exchange of carbon and nutrients but also herbivory and pathogenic effects. Over time, associations between plant communities and their soil microbiota may strengthen and become more specific, resulting in stronger associations between plant and soil microbial diversity. We tested this hypothesis in a 4-year long field experiment in which we factorially combined plant community history and soil legacy with plant diversity (1, 2, 4, 8, 60 species). Plant community history and soil legacy refer to the presence (“old”) or absence (“new”) of a common history of plants and soils in 52 different plant species compositions during 8 years in a long-term biodiversity experiment in Jena, Germany. After 4 years of growth, we took soil samples in the new field experiment and determined soil bacterial and fungal composition in terms of operational taxonomic units (OTUs) using 16S rRNA gene and ITS DNA sequencing. Plant community history did not affect overall soil community composition but differentially affected bacterial richness and abundances of specific bacteria taxa in association with particular plant species compositions. Soil legacy markedly increased soil bacterial richness and evenness and decreased fungal evenness. Soil fungal richness increased with plant species richness, regardless of plant community history or soil legacy, with the strongest difference between plant monocultures and mixtures. Particular plant species compositions and functional groups were associated with particular bacterial and fungal community compositions. Grasses increased and legumes decreased fungal richness and evenness. Our findings indicate that as experimental ecosystems varying in plant diversity develop over 8 years, plant species associate with specific soil microbial taxa. This can have long-lasting effects on belowground community composition in re-assembled plant communities, as reflected in strong soil legacy signals still visible after 4 years of growing new plant communities. Effects of plant community history on soil communities are subtle and may take longer to fully develop.

Dominant species determine ecosystem stability across scales in Inner Mongolian grassland

Abstract: There is an urgent need to extend knowledge on ecosystem temporal stability to larger spatial scales because presently available local-scale studies generally do not provide effective guide for management and conservation decisions at the level of an entire region with diverse plant communities. We investigated temporal stability of plant biomass production across spatial scales and hierarchical levels of community organization and analyzed impacts of dominant species, species diversity and climatic factors using a multi-site survey of Inner Mongolian grassland. We found that temporal stability at a large spatial scale, i.e. a large area aggregating multiple local communities, was related to temporal stability of and asynchrony among spatially separated local communities and large-scale population dynamics of dominant species, yet not to species richness. Additionally, a lower mean and higher variation of yearly precipitation destabilized communities at local and large scales by destabilizing dominant species population dynamics. We argue that, for semi-arid temperate grassland, dynamics and precipitation responses of dominant species and asynchrony among local communities stabilize ecosystems at large spatial scales. Our results indicate that reduced amounts and increased variation of precipitation may present key threats to the sustainable provision of biological products and services to human well-being in this region.