Global negative effects of livestock grazing on arbuscular mycorrhizas: A meta-analysis

Livestock grazing activities substantially contribute to worldwide grassland degradation and potentially alter the growth of arbuscular mycorrhizal fungi. The global patterns of arbuscular mycorrhizal fungi in response to grazing, especially grazing intensity, are still unclear. In this study, we performed a meta-analysis of grazing intensity experiments to examine the grazing intensity effects on arbuscular mycorrhizal fungi across global grasslands. The results showed that heavy or moderate grazing consistently reduced arbuscular mycorrhizal fungal abundance by 34.38% and 9.14%, but light grazing had no significant effect. Arbuscular mycorrhizal fungal abundance was reduced with longer duration of grazing (-22.91%) and lower annual precipitation (-17.43%). Grazing decrease the abundance of arbuscular mycorrhizal fungal was possibly attributedto the reduction of above-ground biomass, in agreement with the carbon limitation hypothesis. It suggests the inhibition of arbuscular mycorrhizal fungal abundance by grazing at the cost of plant above-ground biomass. These findings highlight the negative effect of heavy grazing on arbuscular mycorrhizaes across worldwide grassland, and which may contribute to understand the effects of livestock grazing activities on symbiotic relationships between host plants and arbuscular mycorrhizal fungi.