Long-term biomass removal in grasslands reduces plant and soil phosphorus, increases carbon:phosphorus stoichiometry, but does not lead to microbial phosphorus limitation

Grassland management practices can disrupt the stoichiometric balance between available soil nutrients and microbial communities, thereby impacting ecosystem functioning. Using a long-term field trial, we investigated the effects of four contrasting mowing treatments with/without nitrogen (N) addition on the elemental concentrations and stoichiometries of soil, plant, and microbial biomass. Retaining biomass after mowing resulted in lower C:N and C:P in plant shoots (C:N = 18.8, C:P = 283.9) compared with never mowing (C:N = 24.5, C:P = 493.4). Similarly, the mean soil available C:N when retaining biomass after mowing (C:N = 2.68) was lower than the ratio in the never mown grassland (C:N = 3.44). Removing biomass after mowing strongly depleted soil available phosphorus (P) concentration, leading to significantly higher C:P (C:P = 16.10) than that in the never mown grassland (C:P = 3.85). There were no significant differences in soil available carbon (C) concentration among the treatments, indicating that shifts in the C:N and C:P ratios of available resources were largely due to differences in nutrient rather than C availability. Despite differences in the stoichiometry of available resources, microbial biomass C:N and C:P was similar among treatments and consistently higher than those for the available substrates. This indicates that soil microbes were unresponsive to varying nutrient availability across treatments, suggesting they may be C- rather than nutrient-limited. In this long-term trial, microbial stoichiometry was resilient to soil P depletion and insensitive to N addition. The components of agroecosystems (plants, soil, and soil microorganisms) can contrast in their stoichiometries. Managing one component’s nutrient limitation may have little influence with that of the other components. • Nitrogen addition was not related to variation in plant and soil C:N and C:P ratios. • Retaining biomass was associated with lower plant and soil C:N and C:P ratios. • Removing biomass strongly depleted soil available P. • Soil microbial community was C-limited in all management combinations. • Plant and soil nutrient stoichiometry can contrast soil microbial stoichiometry.