The role of nutrients for the variability of drought effects on community composition and productivity across land use gradients in grasslands: a trait-based approach (BETol 2)

土地利用和降水是影响草地群落多样性和生态系统功能的重要驱动因素，是全球变化的两个主要驱动因素。生态系统将暴露于土壤养分变化（例如通过施肥）和更频繁、更强烈的干旱事件的组合之下。结合起来，这两个因素可以加起作用，或相互作用，导致加速或抑制效果。因此，草地群落和生态系统对干旱的反应因营养状况而异。然而，我们缺乏对养分和干旱相互作用机制的理解，因此目前无法预测在哪种土地利用制度下草原对干旱更有弹性或更敏感。该项目的主要目的是通过在性状和全株性能水平上评估养分和干旱的联合效应，并将其与干旱对草地群落组成和生产力的影响结合起来，提高我们预测全球变化对草地影响的能力。在一项温室试验中，我们将比较评估16种草地物种对养分响应的可塑性，包括与植物抗旱性相关的20多种生理、形态和全株性状。在一个普通的园林试验中，我们将量化营养和干旱（及其相互作用）对这些物种的整个植物干旱性能的综合影响。我们还将评估实验干旱和自然干旱对各试验区养分可利用性和土地利用（特别是施肥）梯度的影响。将性状、全株、群落和生态系统水平的数据直接联系起来，将增加我们对当前和未来条件下草地营养和干旱联合效应的机理认识。研究结果将具有重要的应用和科学意义。

Land use and precipitation are important drivers for shaping community diversity, and ecosystem function in grasslands worldwide, and are two of the main global change drivers. Ecosystems will be exposed to a combination of changes of soil nutrients (e.g. through fertilization) and more frequent and intense drought events. In combination, both factors can act additively, or interact and result in accelerating or dampening effects. Consequently, grassland community and ecosystem responses to drought vary depending on nutrient regimes. However, we lack an understanding of the mechanisms underlying interactions of nutrients and drought, and are therefore currently unable to project under which land-use regimes grasslands are more resilient or sensitive to drought. The main aim of this project is to improve our capability of predicting consequences of global change for grasslands through assessing the combined effects of nutrients and drought at the trait and whole plant performance level, and integrating them with drought effects on community composition and productivity across land use gradients in grasslands.In a greenhouse experiment we will for 16 grassland species comparatively assess the plasticity in response to nutrients of a comprehensive suite of more than 20 physiological, morphological and whole plant traits that are relevant for plant drought resistance. In a common garden experiment, we will quantify the combined effects of nutrients and drought (and their interactions) for whole plant drought performance of these species. We will also assess the effects of experimental and natural drought across gradients of nutrient availability and land use (especially fertilization) in the Exploratories. Directly linking the data at the trait, whole plant, community and ecosystem level will increase our mechanistic understanding of combined nutrient and drought effects on grasslands under current and future conditions. The results will have important applied and scientific implications.