Alternations in the element stoichiometry of the grasses drive the aboveground C:N:P ratio of an agriculturally improved pasture on karst in response to differential N and P fertilization

Imbalances in nitrogen (N) and phosphorus (P) inputs in grasslands, induced by human activities, can significantly alter the C:N:P stoichiometry of plant communities and thereby affect ecosystem processes. However, in grasslands on karst, the effects of N and P inputs on aboveground C:N:P stoichiometry, species turnover, and plant nutrition remain unresolved. We conducted a full factorial experiment with three levels of N and P fertilization levels to explore the effects of variable N and P fertilization on aboveground vegetation C:N:P stoichiometry. The C, N, and P concentrations were determined by elemental analysis and inductively coupled plasma − optical emission spectrometry. N and P fertilization significantly increased the vegetation N and P concentrations, while the C concentration remained stable or dropped. We observed reductions in the C:N, C:P, and N:P mass ratios, with the P addition impact being more pronounced than that of N. Interestingly, legumes and grasses, the dominant functional groups of plants, exhibited divergent stoichiometric reactions to nutrient additions. Grasses were more responsive, possibly because of greater C:N:P homeostatic flexibility and efficient nutrient acquisition. The alterations in community C:N:P stoichiometry were mainly driven by intragroup trait variation, especially in the dominant grass functional group, which responded most to increased soil N and P availability. Our findings imply that the community stoichiometric alterations were driven by the grasses, the dominant plant functional group in the studied agriculturally improved pasture on karst.