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. [ABSTRACT FROM AUTHOR]