Effects of nitrogen and phosphorus addition on leaf N ꞉ P stoichiometry and resorption efficiency of Hordeum vulgare and Elymus nutans in northern Tibet

Nitrogen (N) and phosphorus (P) are key elements that affect plant growth, development, and reproduction. To investigate the response of leaf N ꞉ P stoichiometry characteristics to soil N ꞉ P nutrient addition ratios and gradients in artificial grasses in northern Tibet, two typical forage (Hordeum vulgare and Elymus nutans) were studied using nutrient addition experiments (N ꞉ P input levels: 0.5, 1.5, 4.5, 13.5, 40.5, and 121.5; nutrient gradients: high, medium, and low), greenhouse incubation, and indoor analysis. Our objectives were to quantify the N concentration, P concentration, N ꞉ P ratio, and resorption efficiency in the leaves of the two forage species with multiple nutrient additions. The results showed that green leaf N concentrations of the two species increased significantly with increasing N ꞉ P input level (P < 0.001), and nutrient gradient and its interaction with N ꞉ P input level had significant effects on green leaf P concentrations and N ꞉ P (P < 0.01). Results also indicated that the N concentration in senesced leaves of Hordeum vulgare showed an overall increasing trend with increasing N ꞉ P input level, while the change in N concentration of Elymus nutans was not significant (P > 0.05). The P concentration in senesced leaves of the two species decreased and then increased with increasing N ꞉ P input level. The interaction between the nutrient gradient and N ꞉ ificant effects on the N ꞉ P stoichiometry of senesced leaves of both species (P < 0.05). With the increase in N ꞉ P input level, the N resorption efficiency of Hordeum vulgare showed a decreasing trend, but the N resorption efficiency of Elymus nutans showed an increasing trend. The mean values of P resorption efficiency ꞉ N resorption efficiency ratios of Hordeum vulgare and Elymus nutans were 1.93 and 0.61, respectively. The results indicated that Hordeum vulgare had a more conservative P utilization strategy, while Elymus nutans showed a more conservative N utilization strategy. This differential response may be determined by species attributes, reflecting the diverse nutrient utilization and allocation strategies of plants. In this study, the response patterns of plant nutrient utilization to multiple nutrient gradients could provide a scientific basis for clarifying the utilization strategies of typical forage species in alpine nutrient-poor environments.