Grazing reduces plant sexual reproduction but increases asexual reproduction: A global meta-analysis.

Grazing affects grasslands worldwide. However, the global patterns and general mechanisms of how grazing affects plant reproductive traits are poorly understood, especially in the context of different climates and grazing duration. We conducted a meta-analysis of 114 independent grazing studies worldwide that measured plant reproductive traits in grasslands. The results showed that the number of tillers of plant increased under grazing. Grazing did not affect the number of reproductive branches of forbs, but significantly reduced the number of reproductive branches of grasses. Grazing increased the number of vegetative branches of all plants and reduced the proportion of reproductive branches. Grazing significantly reduced the number of flowers in forbs. Seed yield in the two plant functional groups was reduced compared with no-grazing. Under grazing, the sexual reproduction of grasses decreased much more substantially than that of forbs. This may be due to biomass allocation pattern of grasses under grazing (i.e., belowground versus aboveground). Under grazing, plants tended to adopt rapid, low-input asexual reproduction rather than long-term, high-risk sexual reproduction. This study represents the first large-scale evaluation of plant reproductive trait responses under grazing and demonstrates that grazing inhibits sexual reproduction and promotes asexual reproduction. The effect of grazing on plant sexual reproduction was influenced by grazing intensity, mean annual precipitation, and grazing duration. These results will assist in the development of sustainable grazing management strategies to improve the balance between human welfare and grassland ecosystem health.

Plant roots send metabolic signals to microbes in response to long-term overgrazing.

Overgrazing directly and indirectly affects soil microorganisms, which can have feedback effects on plant growth. Little is known about the root metabolites plants produce and whether they recruit beneficial microbes in response to overgrazing. Here, we used the dominant grassland species Leymus chinensis to explore correlations between root metabolites and the rhizosphere microbiome shaped by long-term overgrazing, which was determined by using LC-MS technology and high-throughput sequencing. In total, 839 metabolites were detected, with 41 significantly higher and 3 significantly lower in overgrazing versus grazing exclusion plots. The rhizosphere bacterial community was changed, but the fungal community was not altered. Moreover, 11 bacterial orders were found only in the overgrazed samples, and these showed close relationships to root metabolites and certain soil properties. Of these, Latescibacterales, B10-SB3A, and Nitrosococcales are known to be involved in growth promotion, C and N metabolism, respectively. In addition, root metabolites play an important role in mediating root-fungi interactions. The beneficial fungal orders Agaricales and Sordariales have a tread to be higher maybe due to root metabolites, mainly facilitate nutrient absorption and protect organic carbon in the soil, respectively. Our results indicate that grassland plants send metabolic signals to recruit key beneficial bacteria and stabilize fungal communities to alleviate grazing-induced stress in typical grassland ecosystems.