SP05: Soil nutrient dynamics

随着气候的持续变化，极端事件的频率正在增加。洪水或干旱等极端事件影响水的可用性，因此不可避免地影响土壤中的养分循环。大多数草地研究报告了干旱后土壤再湿润时的养分冲刷，最终导致干旱后养分淋失损害水质。养分流失与植物和土壤微生物的养分动态有关，并由干旱期间（=抗性）和随后的再湿润（=恢复）的相反过程决定。在此背景下，我们的子项目（SP05）的目标是(i)分别评估干旱期间和之后土壤微生物养分动态的抗性和恢复，（ii）测试植物多样性对土壤微生物养分动态抗性和恢复的影响，并将其与其他生物（植物，土壤动物）联系起来，以及（iii）测试极端事件下植物多样性对土壤养分动态的长期影响。我们假设土壤微生物群落减少养分吸收，在干旱期间容易释放养分，但在干旱后迅速吸收养分。换句话说，干旱后土壤微生物养分库恢复迅速，并且在植物多样性高的情况下比低的情况下恢复得更快。特别是在植物多样性高的情况下，土壤微生物和其他生物的营养动态是互补的，即在时间上是不同步的。因此，从长远来看，尽管极端事件频繁发生，植物多样性仍能稳定养分动态。为了验证这些假设，我们的研究将基于常见的研究平台（ResCUE Experiment; Main Experiment）。此外，我们将依靠不同时间分辨率的数据来评估与抗性、恢复和稳定性相关的养分动态。我们将使用最先进的方法（土壤微生物养分浓度）、稳定同位素标记和稳定同位素的自然丰度水平。我们的SP将受益于与研究小组其他SP合作所产生的协同效应。总体而言，SP05将提供多功能稳定性的各个方面，以验证由于各种形式的生态互补性，在高多样性样地中多功能稳定性最高的中心假设。最终，通过生态互补的植物多样性的稳定效应预计将最大限度地减少干旱引起的养分流失，从而维持紧密的养分循环。鉴于当代气候变化，植物多样性可以减轻伴随极端事件对水体产生有害影响的风险。

With ongoing climate change, the frequency of extreme events is increasing. Extreme events such as floods or droughts affect the availability of water and, thus, inevitably impact nutrient cycling in soils. The majority of grassland studies reported a nutrient flush in soil upon rewetting after drought which is eventually followed by nutrient leaching losses compromising water quality after droughts. The nutrient flush is linked to nutrient dynamics of plants and soil microorganisms and is determined by opposing processes during the drought (= resistance) and after the subsequent rewetting (= recovery).In this context, the objectives of our subproject (SP05) are (i) to assess the resistance and recovery of soil microbial nutrient dynamics during and after a drought, respectively, (ii) to test the effect of plant diversity on the resistance and recovery of microbial nutrient dynamics in soil and link this to other organisms (plants, soil fauna), and (iii) to test the long-term effect of plant diversity on soil nutrient dynamics under extreme events. We hypothesize that the soil microbial community reduces nutrient uptake and is prone to nutrient release during drought but rapidly takes up nutrients after a drought. In other words, microbial nutrient pools in soil quickly recover after drought and furthermore, faster at high as compared to low plant diversity. Particularly at high plant diversity, the nutrient dynamics of soil microorganisms and other organisms are complementary, i.e. temporally asynchronous. Consequently, plant diversity stabilizes nutrient dynamics in spite of frequent extreme events in the long run.To test these hypotheses, our research will be based on the common research platforms (ResCUE Experiment; Main Experiment). Furthermore, we will rely on data of different temporal resolutions to assess nutrient dynamics related to resistance, recovery and stability. We will use state-of-the-art methods (soil microbial nutrient concentrations), stable isotope labeling and natural abundance levels of stable isotopes. Our SP will benefit from synergies arising from cooperation with the other SPs involved in the Research Unit. Overall, SP05 will contribute facets of multifunctional stability to test the central hypothesis that multifunctional stability is highest in high-diversity plots due to a variety of forms of ecological complementarity. Ultimately, stabilizing effects of plant diversity by ecological complementarity are expected to minimize drought-induced nutrient flushes and thus, to maintain tight nutrient cycles. In view of contemporary climate change, plant diversity could mitigate the risk of detrimental effects on water bodies that accompany extreme events.