The ecological role of silicon in tropical forests: effects on plant nutrient stochiometry, drought resistance and herbivory

硅（Si）是地壳中仅次于氧的第二丰富的元素。它被广泛认为在植物中具有多种功能，包括减轻生物和非生物胁迫，改变营养关系和促进生物质生产。植物可以积累Si或避免积累，因此植物物种在其叶片中表现出宽范围的Si浓度。硅的生态学和生理学在禾本科植物中得到了最好的研究，禾本科植物包括许多硅。然而，在一些非单子叶被子植物家族中也记录了显著的叶片硅积累，并且即使对于非单子叶植物，叶片硅的变化也可以在植物和生态系统水平上产生实质性的生态影响。热带森林是地球上物种最丰富的系统之一，提供重要的生态系统服务。由于它们具有任何生物群落中最高的硅吸收率，因此它们被建议作为研究硅的生态作用的模型系统。与此同时，硅是已知的影响几个关键过程，是重要的植物性能，物种分布和群落组成的热带森林，包括营养和水的关系，以及草食动物。尽管如此，我们的知识硅跨植物物种的变化及其生态作用仍然是初步的热带森林。我们最近发现，Si浓度在热带树种内部和之间变化很大，这应该具有普遍的，尚未认识到的生态后果，与理解生物多样性的维持机制和全球变化下的热带森林管理有关。和草食动物的防御实际上发生在热带森林。为了实现这一目标，我们将把观测数据与实验方法结合起来，在屏幕上，实验室和现场。我们将（1）在巴拿马中部的一个多样化的当地树木群落内进行广泛的叶硅浓度调查，并分析与植物发生和生态的关系。对于12个物种的一个子集，我们将（2）评估不同的土壤硅有效性的叶片硅含量和C：N：P化学计量学在硅肥试验的后果。在此基础上，我们将进一步（3）在森林林下植物园干旱灌溉试验中评估硅对植物抗旱性的作用，（4）评估硅对自然栖息地草食动物的影响，并在喂养试验中与模式草食动物。因此，拟议的研究将大大有助于缩小对热带森林中这种丰富元素的生态作用的巨大知识差距，并提高他们在当前和未来条件下的理解。

Silicon (Si) is the second most abundant element in the Earth´s crust after oxygen. It is widely recognised to have a variety of functions in plants, including the alleviation of biotic and abiotic stress, changing nutrient relations and promoting biomass production. Plants can accumulate Si or avoid accumulation, and plant species thus exhibit a wide range of Si concentrations in their leaves. The ecology and physiology of Si has been best studied in grasses, which include many Si accumulators. Nevertheless, significant foliar Si accumulation has also been documented in a number of non-monocot angiosperm families, and even for non-accumulators variation of foliar Si can have substantial ecological impacts both at the plant and ecosystem level. Tropical forests are among the most species rich systems on earth and provide important ecosystem services. Because they have the highest Si uptake rates of any biome, they have been suggested as a model system to study the ecological role of Si. At the same time, Si is known to influence several key processes that are important for plant performance, species distribution and community composition in tropical forests, including nutrient and water relations, as well as herbivory. Nevertheless, our knowledge about variation of Si across plant species and its ecological role remains rudimentary for tropical forests. We recently showed that Si concentrations vary tremendously within and across tropical tree species, which should have pervasive, as yet unrecognized, ecological consequences, relevant for understanding mechanisms of maintenance of biodiversity and for managing tropical forests under global change.Building upon this initial study, we will take the next step and evaluate, whether the potential effects of Si on nutrient and water relations, and on herbivore defenses actually occur in tropical forests. Towards this aim, we will integrate observational data with experimental approaches in the screenhouse, the laboratory and the field. We will (1) conduct an extensive survey of leaf Si concentrations within a diverse local tree community in Central Panama, and analyse relations to phylogeny and ecology. For a subset of 12 species we will (2) assess the consequences of different soil Si availability for leaf Si contents and C:N:P stochiometry in a Si fertilization experiment. Based on experimental manipulations of leaf Si concentrations we will further (3) evaluate the role Si for plant drought resistance in a common garden drought-irrigation experiment in the forest understory, and (4) assess the effect of Si on herbivory in the natural habitat, and in feeding trials with a model herbivore. The proposed study will thus substantially contribute to closing the vast knowledge gap on the ecological role of this abundant element in tropical forests, and improve their understanding under current and future conditions.