The functional role of soil biodiversity in grassland habitats: effects of land use and climate on niche properties, decomposition and greenhouse gas fluxes

我们之前在DFG生物多样性探索实验室内进行的研究表明，土壤动物生物多样性和草原功能对土地利用和气候梯度的重要且往往是非线性的响应。现在，我们需要通过询问土壤生物过程的改变是通过群落物种组成的变化(物种周转)还是通过现有群落内的变化来理解驱动这些反应模式的机制。后者包括种间转移(优势结构的改变)和种内转移(某些形态、功能、行为或生殖特征表达的变化)。土壤动物的表型可塑性提供了一个特别具有挑战性的案例，因为性状变化允许物种功能角色随着环境条件的变化而快速和可逆地改变。考虑到由于地下生物群的低迁移潜力，物种在土壤中的周转很慢，这种种内反应机制很可能比之前认为的要重要得多。我们的关键假设是，在气候变化和土地利用强度增加的条件下，个体物种的可塑性显著有助于土壤动物群落显着的功能冗余和弹性。我们进一步假设，由于优势度和物种组成的改变而导致的地下食物网的功能转移可以部分地被其余物种与特征相关的功能扩展所补偿。群落一级的组成反应和物种一级的特征反应都将通过继续、扩大和改进实地研究以及在前两个项目(SoilFoodWeb，SoilFun)中成功建立的微观世界的实验方法来量化。关于实地研究的扩展，SoilTRAIT的目标是与解决与草原土壤生物多样性有关的过程的所有项目合作。在这方面，一个特别的重点将是量化土壤动物的广泛功能特征及其对不同环境条件的反应变化。基于土壤样本的群落分析将覆盖尽可能广泛的无脊椎动物分类群，但具体的特征分析将侧重于具有代表性的土壤分解者(千足类、弹尾类、甲螨类、线虫和蚯蚓)和捕食者(革螨、蜘蛛、步甲甲虫)。将这些新的见解整合到我们在以前的项目中建立的草原土壤动物功能作用的食物网方法中，不仅将增加土壤生态过程描述性和预测性模型的可靠性，而且还将使我们能够量化面对环境变化或短期压力时土壤群落的弹性和可持续性的极限。

Our previous studies carried out within the DFG Biodiversity Exploratories revealed a significant and very often non-linear response of soil fauna biodiversity and functioning in grasslands to land-use and climatic gradients. Now we need to understand the mechanisms driving these response patterns by asking whether modifications of soil biotic processes occur through changes in species composition of the community (species turnover) or through shifts within the existing community. The latter include both interspecific shifts (alterations of the dominance structure) and intraspecific shifts (changes in the expression of certain morphological, functional, behavioral or reproductive traits). The phenotypic plasticity of soil animals provides a particular challenging case, since trait shifts allow rapid and reversible changes of the species functional roles in response to changing environmental conditions. Considering that species turnover in soil is slow due to the low migratory potential of belowground biota, such intraspecific response mechanisms most probably are much more important than previously thought. Our key hypothesis is that individual species trait plasticity significantly contributes to the striking functional redundancy and resilience of soil animal communities under conditions of climate change and increasing land-use intensity. We further hypothesize that functional shifts of belowground food webs resulting from alterations in dominance and species composition can partly be compensated by trait-related functional expansion of the remaining species. Both compositional responses at the community level and trait responses at the species level will be quantified by continuing, extending and refining field studies as well as by experimental approaches in microcosms that have been successfully established in the two preceding projects (SoilFoodWeb, SoilFun). Concerning the extension of field studies, SoilTRAIT aims at collaborating with all projects addressing processes that are related to soil biodiversity in grasslands. Within this context, a particular focus will be on quantifying a wide range of functional traits of the soil fauna and their changes in response to varying environmental conditions. Community analyses based on soil samples will cover the broadest range of invertebrate taxa possible, but specific trait analyses will focus on representative groups of soil decomposers (millipedes, collembolans, oribatid mites, enchytraeids, and earthworms) and predators (gamasid mites, spiders, carabid beetles). Integrating these new insights into our food web approach to the functional role of soil animals in grasslands established in previous projects will not only increase the reliability of descriptive and predictive models on soil ecological processes, but it will also allow us to quantify the limits of soil community resilience and sustainability in the face of environmental change or of short-term stress.