Is relative Si/Ca availability crucial to the performance of grassland ecosystems?

Species composition of grasslands and pastures is an important control on biomass production and ecological functioning, with a significant role of grasses and legumes. A change in composition of legumes/grasses abundance and biomass ratio results in altered nutrient cycling and composition of higher trophic-level communities (e.g., grazers). However, in addition to pasturing and fire effects, other parameters may also potentially affect grassland composition. Grasses are known as silicon (Si) accumulators and legumes as calcium (Ca) accumulators. We propose a new testable hypothesis, and a conceptual model, on the role of Si/Ca availability in controlling legume/grass dominance/competition in grassland systems. Based on available literature, we argue that Si/Ca availability is an important trigger for shifts in abundance of both plant families. The differential uptake of Si and Ca by legumes and grasses affects grassland biogeochemistry and microbial (fungal) biomass. In addition, altered litter stoichiometry, through impact of Ca and Si uptake on N, C, and P turnover, affects the decomposition processes.