Effects of plant-available soil silicon on seedling growth and foliar nutrient status across tropical tree species

Plant-available silicon (Si) concentrations vary considerably across tropical soils, yet the ecological importance of that variation remains largely unresolved. Increased Si availability can enhance growth and modulate foliar nutrient status in many crop species suggesting similar effects might occur in natural systems. However, how growth, foliar Si and macronutrient concentrations as well as their stoichiometry respond to plant-available Si and how these responses differ across tropical tree species is unknown. We experimentally exposed seedlings of 12 tropical tree species to a gradient of plant-available Si concentrations, representing 85 % of the variation found across central Panama, and assessed responses in aboveground growth and foliar nutrient status. Furthermore, we assessed whether higher plant-available Si increases P availability. Increasing plant-available Si led to increased foliar Si concentrations (by up to 140%). It also led to higher aboveground growth (by up to 220%), and it affected foliar C and N concentrations, and nutrient stoichiometry across species. However, at the species-level only a small subset of two to four species showed significant growth and foliar nutrient responses. At the soil-level, plant-available P remained unchanged along the experimental soil Si gradient. Our results showed that Si can improve growth and/or modulate foliar nutrient status in a number of tropical tree species. Furthermore, species' growth and foliar nutrient concentrations might vary differently across tropical forest sites varying in plant-available Si. Additionally, Si-induced responses in foliar nutrient stoichiometry have the potential to affect herbivory and litter decomposition. Taken together, natural variation in plant-available Si might influence plant performance unequally across tropical tree species, and change trophic interactions, with potential implications for ecosystem processes.