Element Stoichiometry Across Grassland Plant Tissues and Rhizospheres: Role of Plant Traits, Soil and Land‐Use Intensity

ABSTRACT Long‐term land use management including fertilization, grazing, and mowing shapes grassland ecosystems. A gradient of nutrient availability and stoichiometry is created which affects above‐ and belowground ecosystem functioning. Understanding how plant traits, land‐use intensity (LUI), and abiotic soil properties jointly are related to nutrient contents and stoichiometric patterns in leaves, roots, and the rhizosphere is essential for a mechanistic understanding of ecosystem processes. We analyzed 12 common grassland species across 15 experimental plots in the Hainich‐Dün Biodiversity Exploratories, measuring multiple nutrient concentrations beyond carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in leaves, roots and rhizosphere soil (extractable fraction, microbial biomass), along with extracellular enzyme kinetics (C‐, N‐, P‐, and S‐cycle) in rhizosphere soil. Plant traits, including plant life strategies and fine root characteristics (specific root length, root average diameter, root tissue density), were strongly linked to nutrient contents and stoichiometry in leaves and roots but had minimal correlation with rhizosphere nutrient pools and enzyme kinetics. In contrast, LUI and abiotic soil properties, such as bulk soil C/N and C/S ratios as well as texture, predominantly shaped microbial biomass, extractable soil nutrients, and enzyme activity. In addition, soil pH and water content were important. Principle component analyses revealed distinct stoichiometric patterns among plant functional groups (forbs, grasses, legumes) in leaf and root tissues, whereas rhizosphere compartments were structured primarily by LUI and abiotic soil gradients. Enzyme kinetics (characterized by V max and K m of the Michaelis–Menten kinetic) responded more strongly to LUI and soil properties than to plant traits, indicating a decoupling between aboveground nutrient allocation and belowground microbial processes. Overall, our results demonstrate that plant traits determine plant tissue nutrient composition, while LUI and abiotic soil properties govern rhizosphere nutrient distribution and microbial activity, suggesting a mechanistic link between plant strategies, soil processes, and ecosystem functioning in grasslands.