Grazing intensity mediates effects of plant arbuscular mycorrhizal symbiosis on nitrogen and phosphorus resorption in semiarid grasslands

Background and Aims Plant-arbuscular mycorrhizal fungi (AMF) symbiosis and nutrient resorption are key to resource use and conservation strategies for wild plants. However, it remains unclear how grazing and plant-AMF symbiosis affects nutrient resorption by perennial plants in grasslands. Methods Using combined field grazing and AMF suppression with benomyl experiments, we examined the impact of grazing intensity and plant-AMF symbiosis on nitrogen (N) and phosphorus (P) resorption by dominant species, and quantified the relative contributions of leaves and culms to the total amount of nutrient resorption. Results AMF suppression increased N rather than P concentrations in green and senesced leaves of dominant species, resulting in greater N:P ratios within these organs. AMF suppression increased P resorption efficiency under no-light and moderate grazing and negatively affected P resorption efficiency under heavy grazing. Additionally, the younger leaves had higher N and P concentrations and greater resorption efficiencies than the older leaves regardless of AMF suppression. Although less than leaves, culms (photosynthetic stems) contributed to a large proportion of the resorbed and remaining N and P in shoots. Conclusion The effects of AMF on nutrient resorption by dominant perennial species are mediated by grazing intensity, which modifies the costs and benefits of plant-AMF symbiosis. Different aged leaves differ in their N and P resorption efficiencies, and nutrient resorption of culms also plays an important role in whole-plant nutrient budgets. This study provides new insight into the whole-plant economic spectrum and has important implications for optimizing grazing management and improving biogeochemical models.