Variation in the soil ‘silicon landscape’ explains plant silica accumulation across environmental gradients in Serengeti

Abstract

Beneficial aspects of plant silicon (Si) have been identified, but little is known about how multiple abiotic conditions interact in a natural environment to influence plant Si-accumulation. Consequently, we identified abiotic correlates of soil and plant Si pools in a pristine African savanna and quantified relationships among precipitation, soil properties, and grass silicon concentration along environmental gradients. Soil properties were measured at 63 sites spanning soil and precipitation gradients in the Serengeti ecosystem of northern Tanzania. Bulk and species-specific grass samples were collected at 18 of those sites and combined with soil and climate data into a structural equation model to describe landscape drivers of foliar silicon concentration. Soil amorphous silicon (ASi) was negatively related to precipitation but was unrelated to soil dissolved silicon (DSi). The final structural equation model included three predictor variables, each negatively associated with soil DSi: precipitation, soil percent sand, and soil pH, which, together, explained ~74 % of variation in soil DSi. Finally, soil DSi was positively related to grass Si concentration, explaining ~60 % of variation. While evidence exists for biotic induction of silicon accumulation (e.g. herbivory), our results indicate that natural abiotic variation, which has largely been ignored, is equally important and may determine the extent to which inducibility is possible. Environmental heterogeneity, by constraining or promoting Si dissolution and availability, plays a significant role in silicon accumulation by grasses.