Leaf silicon and calcium differ between grassland plant functional groups while only calcium responds to soil background

Abstract Background and Aims Grasslands are biodiversity-rich ecosystems in which plant functional diversity strongly influences ecosystem functioning. Silicon (Si) and calcium (Ca) are often overlooked in trait-based frameworks despite their roles in plant physiology, stress tolerance and nutrient dynamics. This study investigates how leaf Si and Ca vary among plant functional groups, how they relate to soil Si and Ca availability, and whether they are associated with specific leaf area (SLA). Methods Leaf Si and Ca concentrations, soil Si and Ca availability, and SLA were quantified for 12 herbaceous species representing grasses, forbs, and legumes across 45 grassland plots in the Biodiversity Exploratories (Germany). Linear mixed-effects models were used to test relationships among Si and Ca concentrations, functional groups, soil properties, and SLA. Results Plant functional groups differed in their Si and Ca concentrations: grasses accumulated high Si and low Ca, while legumes showed opposite, and forbs showed species-specific patterns. A strong negative correlation between leaf Si and Ca across species was largely driven by functional group differences. Leaf Ca increased with soil Ca availability, whereas leaf Si was unrelated to soil Si. Functional group identity mediated a tentative Ca-SLA relationship, while leaf Si was unrelated to SLA at any level examined. Conclusion Variation in Si and Ca does not follow leaf economic concepts. Instead, Si and Ca are tightly linked to functional group identity, and Ca varies along soil environmental gradients. Both elements hold unique information and should be integrated in trait-based ecology particularly in field studies.