Abstract: Grazing is a major anthropogenic activity threating grassland biodiversity. Understanding plant responses to grazing and identifying measures to effectively alleviate grazing-induced negative effects are critical for sustainable grassland management. Nutrient addition may support compensatory growth by offsetting nutrient loss from tissue removal, while clonal integration may enhance this effect by effectively sharing nutrients among connected ramets. However, little is known about the complex interactions of grazing, nutrient addition and clonal integration on plant performance. Here, we examined how the addition of N and P, and clonal integration jointly affect the growth of a rhizomatous grass Leymus chinensis, an important forage in Inner Mongolian grasslands, under three levels of simulated grazing (i.e., no grazing, moderate grazing, and heavy grazing). The growth of L. chinensis decreased significantly under moderate and heavy grazing. The addition of P, instead of the commonly proposed addition of N, significantly improved plant growth across all grazing intensities. However, clonal integration did not significantly improve the growth of L. chinensis under heavy grazing with N or P addition. Overall, we experimentally demonstrate that suitable nutrient addition may help avoid detrimental effects of heavy grazing on grasslands irrespective of the presence or absence of clonal integration. Our findings highlight the importance of P addition on sustainable management of grasslands under grazing. Since, our findings are based on a short-term defoliation experiment involving a single species, future long-term field studies with multiple species are encouraged to further inform grassland management strategies.

Key words: Clonal integration, Grasslands, Grazing, Leymus chinensis, Nutrient addition