Nitrogen availability mediates the effects of roots and mycorrhizal fungi on soil organic carbon decomposition:A meta-analysis

Plant roots and their associated mycorrhizal fungi critically mediate the decomposition of soil organic carbon(C),but the general patterns of their impacts over a broad geographical range and the primary mediating factors remain unclear.Based on a synthesis of 596 paired observations from both field and greenhouse experiments,we found that living roots and/or mycorrhizal fungi increased organic C decomposition by 30.9%,but low soil nitrogen(N)availability(i.e.,high soil C:N ratio)critically mitigated this promotion effect.In addition,the positive effects of living roots and/or mycorrhizal fungi on organic C decomposition were higher under herbaceous and leguminous plants than under woody and non-leguminous plants,respectively.Surprisingly,there was no significant difference between arbuscular mycorrhizal fungi and ectomycorrhizal fungi in their effects on organic C decomposition.Furthermore,roots and/or mycorrhizal fungi significantly enhanced the decomposition of leaf litter but not root litter.These findings advance our understanding of how roots and their symbiotic fungi modulate soil C dynamics in the rhizosphere or mycorrhizosphere and may help improve predictions of soil global C balance under a changing climate.

Climate warming suppresses abundant soil fungal taxa and reduces soil carbon efflux in a semi-arid grassland

Soil microorganisms critically affect the ecosystem carbon(C)balance and C-climate feedback by directly controlling organic C decomposition and indirectly regulating nutrient availability for plant C fixation.However,the effects of climate change drivers such as warming,precipitation change on soil microbial communities,and C dynamics remain poorly understood.Using a long-term field warming and precipitation manipulation in a semi-arid grassland on the Loess Plateau and a complementary incubation experiment,here we show that warming and rainfall reduction differentially affect the abundance and composition of bacteria and fungi,and soil C efflux.Warming significantly reduced the abundance of fungi but not bacteria,increasing the relative dominance of bacteria in the soil microbial community.In particular,warming shifted the community composition of abundant fungi in favor of oligotrophic Capnodiales and Hypocreales over potential saprotroph Archaeorhizomycetales.Also,precipitation reduction increased soil total microbial biomass but did not significantly affect the abundance or diversity of bacteria.Furthermore,the community composition of abundant,but not rare,soil fungi was significantly correlated with soil CO_(2) efflux.Our findings suggest that alterations in the fungal community composition,in response to changes in soil C and moisture,dominate the microbial responses to climate change and thus control soil C dynamics in semi-arid grasslands.