We quantified the potential influence of arbuscular mycorrhizal fungi (AMF) on primary productivity and community stability and tested whether the effects of AMF depend on soil phosphorus (P) availability and grazing intensity in a semiarid grassland. We manipulated the abundance of AMF and soil P availability (P addition and no P addition) under four levels of grazing intensity. The aboveground biomass of plant species, functional groups and community, as well as community temporal stability were examined under these conditions. Under no to moderate grazing, benomyl decreased the aboveground biomass in C4 grasses and forbs, but increased the aboveground biomass in C3 grasses under low P conditions; thus no obvious changes in community primary productivity were observed. These results indicated that the mycorrhizal dependency of C4 grasses and forbs is higher than that of C3 grasses under low P conditions. However, community primary productivity was greatly enhanced by benomyl due to the increased biomasses of C3 grasses and forbs under high P conditions. Under heavy grazing conditions, benomyl increased community primary productivity under both low and high P conditions. AMF presence increased the community temporal stability by promoting the compensatory effects between plant species under no to moderate grazing conditions; whereas AMF decreased the community stability by forming a parasitic symbiosis with their plant hosts under heavy grazing conditions. Our findings demonstrate that the effects of benomyl application to suppress AMF on primary productivity and community stability are strongly mediated by soil P availability and grazing intensity, which improves our understanding for the roles of AMF-plant symbiosis on ecosystem functioning in grazed systems.

中文翻译：

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重度放牧破坏了丛枝菌根共生对低磷和高磷条件下群落生产力和稳定性的积极影响

我们量化了丛枝菌根真菌 (AMF) 对初级生产力和群落稳定性的潜在影响，并测试了 AMF 的影响是否取决于半干旱草地的土壤磷 (P) 可用性和放牧强度。我们在四个放牧强度水平下操纵了 AMF 的丰度和土壤磷的有效性（加磷和不加磷）。在这些条件下检查了植物物种、功能群和群落的地上生物量，以及群落的时间稳定性。在不放牧到中度放牧下，苯菌灵降低了C4草和杂草的地上生物量，但在低磷条件下增加了C3草的地上生物量；因此没有观察到社区初级生产力的明显变化。这些结果表明，在低磷条件下，C4 草和杂草的菌根依赖性高于 C3 草。然而，由于在高磷条件下 C3 草和杂草的生物量增加，苯菌灵大大提高了群落初级生产力。在重度放牧条件下，苯菌灵提高了低磷和高磷条件下的群落初级生产力。AMF 的存在通过促进无到中等放牧条件下植物物种之间的补偿效应，增加了群落时间稳定性；而 AMF 通过在重度放牧条件下与植物宿主形成寄生共生来降低群落稳定性。