Mechanisms Of Mycorrhizal Fungi And Soil Nitrogen And Phosphorus Affecting Community Productivity Changes In The Stipa Steppe

Arbuscular mycorrhizal fungi (AMF) are important components of terrestrial ecosystems, and can form mycorrhizal symbioses with about80%of all terrestrial plant species. AMF provide soil resources such as nitrogen (N) and phosphorus (P) for plants and receive photosynthates in return. Soil available N and phosphorus P and their balance (ecological stoichiometry, N:P) mediate AMF-plant symbiosis along the mutualism-antagonism spectrum and affect the mycorrhizal contribution to plant growth. Numerous studies show that AMF impact plant community productivity through mediating plant nutrients acquisition, plant-plant interactions and vegetation regeneration. However, relatively little is known about how AMF interact with soil N and P availability and their balance to influence the productivity changes of plant communities.In this study, we combined field and pot experiments to address the following three contents:(1) the effects of fungicide (benomyl) application and P addition on diversity, productivity and temporal stability of the Stipa krylovii Steppe community in a field experiment;(2) the interaction effects of AMF and soil N and P availability and their balance on plant community diversity and productivity;(3) the effects of AMF and the adult plant species establishing the mycorrhizal networks on seedling recruitment. The main results are as follows:(1) In the three-year field experiment, AMF did not influence the species diversity of the plant communities, but AMF are essential for maintaining species richness of legumes. At the zero-P addition rate, AMF did not affect plant community productivity, but increased productivity under P addition treatments. At low P addition rates, AMF did not affect the temporal stability, but increased the temporal stability of plant community productivity and the compensatory effects between plants of high abundance under high P addition rates.(2) In the pot experiment, the interaction between N addition and AMF inoculation did not significantly affect Shannon diversity of plant community, while there was a significant interaction between AMF inoculation and N addition found for community productivity at the highest P level. At high P and low N levels, AMF inoculation decreased plant community productivity, but did not affect the productivity at the highest P and N level. At low P levels, AMF inoculation increased plant community productivity independent of N addition. The interaction between P addition and AMF inoculation significantly affect Shannon diversity of plant community. AMF inoculation suppressed plant community diversity at low P levels, and P addition reduced the negative effect of AMF on the diversity. AMF inoculation decreased the community productivity at low N:P ratios, but increased it at high N:P ratios. Shannon diversity was reduced by AMF inoculation at the intermediate N:P ratios, while did not show significant response to AMF at low and high N:P ratios. AMF inoculation increased the stoichiometric homoeostasis of the plant community and the stability of plant community productivity at different N:P ratios, but reduced the complementary effects between plants.(3) The mycorrhizal networks established by the adult plants of S. krylovii or Leymus chinensis provide more P benefit for the seedlings of the same species with the adult plants than the other species. However, the mycorrhizal networks established by the adult plants of Artemisia frigida provide more P benefit for S. krylovii and Agropyron cristatum seedlings. The mycorrhizal networks established by the adult plants of A. frigida showed more positive effects on the seedling growth of A. frigida than other species. The mycorrhizal networks established by the adult plants of S. krylovii or L. chinensis suppressed the seedling growth of A. cristatum, while the mycorrhizal networks established by the adult plants of A. cristatum or A. frigida suppressed the seedling growth of L. chinensis. The P benefit from AMF did not confirm the mycorrhizal growth response of both the seedlings plants.In conclusion, AMF interact with soil N and P availablility and their balance to influence plant community productivity, diversity and ecosystem stability in the Stipa krylovii Steppe. AMF increased the stoichiometric homoeostasis of the plant community and compensatory effects between plants, and reduced the complementary effects between plants, which may contribute to the increase in stability of the Stipa Steppe ecosystem. Mycorrhizal networks established by various adult plant species differently affected the recruitment of surrounding seedling.