Effects of grassland management on plant C:N:P stoichiometry: implications for soil element cycling and storage

Abstract The functioning of human‐managed grassland ecosystems strongly depends on how common management practices (e.g., animal grazing and the chronic addition of fertilizing materials to soils) interact to influence plant and soil element stoichiometry. Here we use data from a 22‐yr‐long grassland experiment to address whether and how plant element stoichiometry (i.e., carbon [C], nitrogen [N], phosphorus [P] ratios) might respond to (1) animal grazing, (2) agricultural liming (i.e., Ca CO 3 ) applications, and (3) nutrient fertilization. We also ask whether plant C:N:P stoichiometry could predict changes in soil N and P availability and in soil C, N, and P stocks. We found that grassland management significantly affected plant C:N:P ratios as predicted by ecological stoichiometry theory. For example, plant aboveground and belowground C:N and C:P ratios decreased under chronic N and P fertilization, respectively. Plant C:N and C:P ratios were significantly greater in unfertilized (control) soils. Also plant C:N ratios were highest under P‐only additions, whereas plant C:P ratios were highest under N‐only additions. However, unpredictable changes in C:N:P ratios also occurred, suggesting that plant tissue chemistry may not be a simple reflection of soil nutrient availability. Changes in plant C:nutrient ratios well predicted variation in soil nutrient availability, but not in soil C, N, and P stocks. Contrary to expectations, soil C stocks significantly increased with decreasing plant C:N ratios in the nutrient‐fertilized grasslands and not with increasing plant C:N ratios in the unfertilized grasslands. We suggest that a better mechanistic understanding of the negative relationship between plant C:N stoichiometry and soil C accrual will greatly help in improving the sustainability of human‐managed grasslands.