Arbuscular mycorrhizal fungi alter plant N and P resorption of dominant species in a degraded grassland of northern China

Abstract

Plant nutrient resorption is an important regulator of biogeochemical cycling and decomposition. Arbuscular mycorrhizal fungi (AMF) may influence this process by helping plants absorb nutrients, although the mechanism by which this occurs remains unclear. We examined variations in nutrient resorption over a period of 3 years in three dominant species, namely, Artemisia frigida, Potentilla acaulis, and Stipa krylovii, treated with or without fungicide in a degraded grassland in Inner Mongolia in 2017. Our results showed that AMF increased the nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) in A. frigida but decreased NRE and PRE in S. krylovii and PRE in P. acaulis. The inconsistent nutrient resorption responses of A. frigida and S. krylovii to AMF were primarily attributed to the changes in biomass in the presence of AMF, thereby changing the nutrient requirements. For P. acaulis, the reduction in PRE with AMF was because AMF-induced its N limitation, which is consistent with the relative nutrient resorption hypothesis. AMF increased internal nutrient cycling in A. frigida, which may promote its dominance in degraded grassland in Inner Mongolia, China. Moreover, AMF reduced senesced leaf N concentrations, thereby reducing the carbon (C):N ratio in senesced leaves, which may affect nutrient return to the soil. Our findings indicate that AMF substantially affect the biomass and nutrient requirements of dominant plant species, potentially leading to changes in nutrient resorption during grassland degradation, which may provide a deep insight into plant nutrient retranslocation in degraded grasslands.