Changes in soil greenhouse gas fluxes by land use change from primary forest.

Primary forest conversion is a worldwide serious problem associated with human disturbance and climate change. Land use change from primary forest to plantation, grassland or agricultural land may lead to profound alteration in the emission of soil greenhouse gases (GHG). Here, we conducted a global meta-analysis concerning the effects of primary forest conversion on soil GHG emissions and explored the potential mechanisms from 101 studies. Our results showed that conversion of primary forest significantly decreased soil CO2 efflux and increased soil CH4 efflux, but had no effect on soil N2 O efflux. However, the effect of primary forest conversion on soil GHG emissions was not consistent across different types of land use change. For example, soil CO2 efflux did not respond to the conversion from primary forest to grassland. Soil N2 O efflux showed a prominent increase within the initial stage after conversion of primary forest and then decreased over time, while the responses of soil CO2 and CH4 effluxes were consistently negative or positive across different elapsed time-intervals. Moreover, either within or across all types of primary forest conversion, the response of soil CO2 efflux was mainly moderated by changes in soil microbial biomass carbon and root biomass, while the responses of soil N2 O and CH4 effluxes were related to the changes in soil nitrate and soil aeration-related factors (soil water content and bulk density) respectively. Collectively, our findings highlight the significant effects of primary forest conversion on soil GHG emissions, enhance our knowledge on the potential mechanisms driving these effects, and improve future models of soil GHG emissions after land use change from primary forest.