The ecological role of silicon in tropical forests: consequences of inter- and intraspecific variation of silicon accumulation for woody seedling regeneration in the forest understory

• Applicant: Professorin Dr. Bettina M.J. Engelbrecht
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423584219

Silicon (Si) can contribute more than 10% of the dry mass of plants, and is considered a non-essential but beneficial element. It is well-recognized that Si can alleviate stress due to drought, low nutrients and herbivory. These stressors play an important role for seedling regeneration, species distribution, forest dynamics and ecosystem function in tropical forests. At the same time, leaf Si contents exhibit tremendous inter- and intraspecific variation in tropical tree species, and soil Si availability varies vastly across sites. Yet, the ecological role of Si in tropical forests, which harbor an enormous diversity and provide globally important ecosystem services, has hardly been addressed. The first phase of this project focused on evaluating effects of Si under controlled experimental conditions, and showed for the first time that stress alleviating effects of Si that have mainly been documented in agricultural plants and grasses, also occur in seedlings of tropical tree species. However, the effects vary tremendously across species, both in direction and magnitude. These results suggest, that Si may change species performance rank hierarchies across sites with different soil Si availability, and may indeed play an important, yet unrecognized role, in tropical forests. Nevertheless, in the natural habitat, many abiotic and biotic factors simultaneously influence seedling growth and survival, and may mask effects of Si. The second project phase will therefore focus on evaluating the effects of variation of plant and soil Si on seedling performance and stress responses in the natural habitat, the forest understory, and whether they are relevant for seedling regeneration. We will examine if and how inter- and intraspecific variation of leaf Si contents and spatial variation of soil Si availability affect seedling vital rates, i.e. growth and survival, in the understory - and how such effects change across environmental gradients. The study will integrate observational, experimental and trait-based approaches. We will link interspecific variation of leaf Si contents with long-term seedling dynamics in plots across environmental gradients at the Isthmus of Panama, and with leaf functional traits. We will further examine effects of soil Si availability on intraspecific variation of seedling performance and stress responses, and implications for species performance rank hierarchies in a common garden transplant experiment. The study will provide novel and important insights into the ecological role of silicon in tropical forests. At the same time, it will address a main pending question in Si biology, if leaf Si accumulation in plants confers an inter- and intraspecific ecological advantage.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partner: Dr. Liza S. Comita