Tackling trade-offs? Understanding how trait coordination for drought- and shade-tolerance regulates seedling dynamics in fragmented wet tropical forests

热带森林拥有地球三分之一以上的生物多样性，在全球碳汇方面发挥着关键作用，但受到气候变化和人类土地利用造成的碎片化的威胁。因此，当务之急是理清在未来易发生干旱的气候中，碎片化改变热带森林动态的机制。植物对多种胁迫的耐受性协调是生态学中的一个基本问题，对物种分布、群落组成和生态系统功能具有普遍的影响。两个长期相互矛盾的假说提出，耐旱和耐荫--植物表现的两个关键维度--正相关(协同假说)或权衡(权衡假说)。第三种可能性是遮荫和干旱反应是独立的(独立性假说)。关于耐旱性和耐荫性的协调研究结果仍然相互矛盾。在这项拟议的研究中，我们的首要目标是提供基本的见解，了解在全球变化的影响下，耐旱性和耐荫性的协调如何影响潮湿热带森林的苗木动态。具体地说，我们的目标是了解(1)破碎森林中光和水可获得性的边缘效应，(2)光和水可获得性的梯度如何与苗木分布和群落组成相关，(3)苗木表现(存活和生长)对光和水可利用性的响应的种间差异，(4)苗木对水和光可用性反应的基于特征的机制，以及(5)物种耐旱性和耐荫性之间的协调及其对气候变化中碎片化森林更新动态的影响。我们的完全一体化的印度-德国工作方案将在印度西部高止山脉中部的一个人工改良的森林综合体中进行。我们将结合观察和实验方法，在苗木小区网络中整合微立地条件的详细特征和苗木表现和群落组成的评估，并对25-30个树种的苗木进行18个相关的生理、解剖和形态功能性状的比较评估。这一史无前例的数据集将使人们能够对物种耐旱性和耐荫性的协调及其对森林更新的影响进行前沿评估。总体而言，我们的研究将解决基于特征的生态学的基本知识差距，增进我们对森林对全球变化的反应的理解，并为旨在支持脆弱物种或选择能够减轻全球变化对生物多样性热带森林的影响的物种的恢复努力提供以科学为基础的投入。

Tropical forests house over a third of Earth’s biodiversity and play a critical role as global carbon sinks, but stand threatened by climate change and fragmentation due to human land-use. It is therefore an urgent concern to disentangle the mechanisms by which fragmentation alters tropical forest dynamics in a drought-prone future climate. The coordination of plant tolerance to multiple stresses is a fundamental question in ecology with pervasive consequences for species distributions, community composition and ecosystem function. Two long-standing conflicting hypotheses propose that tolerance to drought and shade - two key dimensions of plant performance - correlate positively (synergy hypothesis) or trade-off (trade-off hypothesis). A third possibility is that shade and drought responses are independent (independence hypothesis). Results concerning the coordination of drought- and shade-tolerance remain conflicting.In this proposed research, our overarching goal is to provide fundamental insights into how the coordination of drought- and shade-tolerance influences seedling dynamics in wet tropical forests subject to global change. Specifically, we aim to understand (1) edge effects on light and water availability in fragmented forests, (2) how gradients of light and water availability correlate with seedling distributions and community composition, (3) interspecific variation in seedling performance (survival and growth) responses to light and water availability, (4) the trait-based mechanisms underlying seedling responses to water and light availability, and (5) the coordination between drought- and shade-tolerance of species and its consequences for regeneration dynamics of fragmented forests in a changing climate.Our fully integrated Indo-German work programme will be conducted in a human-modified forest complex in the central Western Ghats (India). We will combine observational and experimental approaches to integrate detailed characterizations of microsite conditions and assessment of seedling performance and community composition in a network of seedling plots, with comparative assessments of 18 relevant physiological, anatomical and morphological functional traits for seedlings of 25-30 tree species. This unprecedented data set will allow for a cutting-edge evaluation of the coordination of species drought- and shade-tolerance and its consequences for forest regeneration. Overall, our study will address fundamental knowledge gaps in trait-based ecology, advance our understanding of forest response to global change, and generate science-based inputs for restoration efforts geared towards supporting vulnerable species or selecting species that can mitigate the impacts of global change on biodiverse tropical forests.