Phosphorus amendment mitigates nitrogen addition-induced phosphorus limitation in two plant species in a desert steppe, China

The increasing deposition of atmospheric nitrogen (N) due to anthropogenic activities has significantly enhanced N inputs to ecosystems, resulting in an imbalance in the N: phosphorus (P) ratios in plants and soils. This study aimed to determine whether, and to what extent, P addition alleviates N-induced P limitation in a desert steppe ecosystem. We conducted a multi-level N:P supply experiment (i.e., constant N with varied P-addition levels) for a grass species, Pennisetum centrasiaticum, and a N-fixing species, Glycyrrhiza uralensis. With increasing amounts of P addition (thereby decreasing the N:P ratio), green-leaf P concentrations of the two species studied tended to increase, while P-resorption proficiency and efficiency tended to decrease. There were no consistent trends in green-leaf N concentrations in response to P addition. However, both species exhibited high N-resorption proficiency, especially in G. uralensis, with high P addition. Generally, the carbon (C):P and N:P ratios both in soils and in green leaves had positive relationships with green-leaf N concentration and P-resorption proficiency of P. centrasiaticum as well as P-resorption traits of G. uralensis, but negative relationships with green-leaf P concentrations in both species. Our study indicates that P addition can alter P-conservation strategy and thereby releasing plant species from the N-induced imbalance of N:P ratios. However, large amounts of P addition could overcompensate and pose a risk of N limitation in desert steppe ecosystems.