Effects of extreme rainfall on biotic interactions in grassland ecosystems: The importance of waterlogging timing and frequency

在包括中欧在内的世界许多地区，极端降雨事件和随后的内涝将在气候变化下增加频率和持续时间。这不仅将直接影响单个物种或个体，还将导致生物相互作用的变化，从而反馈植物的生产力和适合性。然而，关于气候变化对生物相互作用的影响，特别是内涝对生物相互作用的影响的知识，在很大程度上是缺乏的。此外，极端天气事件对社区和相互作用的后遗症，以及事件时间对社区反应的作用被忽视。作为即时反应的变化可能会随着时间的推移而改变，因为极端天气事件也会改变生物相互作用的先决条件。对一种特定相互作用的直接影响，例如菌根的丧失，可能会在一段时间后影响其他生物相互作用，例如草食或授粉。因此，与单一干扰的影响相比，更频繁、更反复的内涝或压力事件可能会导致完全不同的反应，因为它们作用于已经转移的生物相互作用。内涝事件的时间也将对生态系统的反应起到很大的作用，但仍未得到研究。在一个包含中等草地多样性梯度(1，6，9个物种)和在时间上(春季和秋季)和在频率/重复(单一和重复内涝)上操纵内涝事件的受控中围隔实验中，我的目标是：i)研究内涝对植物和植物群落的影响以及对生物相互作用(植物-分解者，植物-传粉者，植物-菌根，植物-食草动物，植物-病原体和植物-植物相互作用)的影响；ii)从植物叶片质量变化的影响中解开内涝对单个行为者的直接影响分解和群落组成与多样性)研究了受涝时间对系统响应的作用，并比较了对单一受涝事件和多次受涝事件的响应。在拟议的项目中，将同时评估许多生物相互作用，并在几个生长季节内，比较春季受涝和秋季受涝的影响，以及比较单一受涝和重复受涝的效果。选择中欧草原作为研究系统，是因为它在中欧具有重要的农业意义，而且未来可能会出现更严重的内涝，但目前还不适应极端内涝。总体目标是确定生态系统对生物相互作用中的胁迫反应的驱动因素(例如，哪些相互作用具有弹性，哪些相互作用没有弹性，或者相互作用的变化在较长的时间段内放大或缓冲影响)，并调查相互作用水平和时间上的级联影响。

Extreme rainfall events and subsequent waterlogging are going to increase in frequency and duration under climate change in many parts of the world, including Central Europe. This will not only directly affect single species or individuals, but will also lead to shifts in biotic interactions and will thus feedback on plant productivity and fitness. However, knowledge about the effects of climate change on biotic interactions and specifically of waterlogging on biotic interactions is largely missing. Further, after-effects of extreme weather events on communities and interactions, as well as the role of timing of events for community response are neglected. Changes found as an immediate response can change over time, as preconditions for biotic interactions are also altered by extreme weather events. Direct effects on one particular interaction, e.g. loss of mycorrhiza may subsequently affect other biotic interactions after a time lag, e.g. herbivory or pollination. More frequent, repeated waterlogging or stress events may thus lead to totally different responses when compared to effects of a single disturbance, as they act upon already shifted biotic interactions. The timing of waterlogging events will also play a large, yet still unstudied role for ecosystem response. In a controlled mesocosm experiment incorporating a mesic grassland diversity gradient (1, 6, 9 species) and manipulating waterlogging events both in timing (spring vs. autumn) and in frequency/repetition (single vs. repeated waterlogging) I aim to i) investigate the effects of waterlogging on plants and plant communities and on biotic interactions (plant-decomposer, plant-pollinator, plant-mycorrhiza, plant-herbivore, plant-pathogen and plant-plant interactions)ii) disentangle direct effects of waterlogging on single actor from effects mediated by shifts in plant leaf qualityiii) assess the longevity of shifts in biotic interactions and possible feedback on primary production, herbivory, decomposition and community composition and diversityiv) study the role of timing of waterlogging for system response and compare the response towards single vs. repeated waterlogging eventsIn the proposed project, numerous biotic interactions will be assessed simultaneously and over several growing seasons, comparing effects of spring vs. autumn waterlogging and comparing effects of single vs. repeated waterlogging. Mesic grassland is chosen as study system, because of its great agricultural importance in Central Europe and because it might be prone to more intense waterlogging in the future, but is currently not adapted to extreme waterlogging. The overall aim is to identify drivers of ecosystem response towards stress in biotic interactions (e.g. which interactions are resilient and which not, or which changes in interactions amplify or buffer effects over a longer time-period) and to investigate cascading of effects over interaction levels and over time.