Different variations in soil CO2, CH4, and N2O fluxes and their responses to edaphic factors along a boreal secondary forest successional trajectory

Forest succession is an important process regulating the carbon and nitrogen budgets in forest ecosystems. However, little is known about how and extent by which vegetation succession predictably affects soil CO2, CH4, and N2O fluxes, especially in boreal forest. Here, a field study was conducted along a secondary forest succession trajectory from Beuda platyphylla forest (early stage), then Benda platyphylla-Larix grnelinii forest (intermediate stage), to Lcuix gmelinii forest (late stage) to explore the effects of forest succession on soil greenhouse gas fluxes and related soil environmental factors in Northeast China. The results showed significant differences in soil greenhouse gas fluxes during the forest succession. During the study period, the average soil CO2 flux was greatest at mid-successional stage (444.72 mg m(-2) h(-1)), followed by the late (341.81 mg m(-2) h(-1)) and the early-successional (347.12 mg m(-2) h(-1)) stages. The average soil CH4 flux increased significantly during succession, ranging from - 0.062 to -0.036 mg m(-2) h(-1).The average soil N2O flux was measured as 17.95 mu g m(-2) h(-1) at intermediate successional stage, significantly lower than that at late (20.71 mu g m(-2) h(-1)) and early-successional (20.85 mu g m(-2) h(-1)) stages. During forest succession, soil greenhouse gas fluxes showed significant correlations with soil and environmental factors at both seasonal and successional time scales. The seasonal variations of soil GHG fluxes were mainly influenced by soil temperature and water content. Meanwhile, soil MBN and soil NO3--N content were also important factors for soil N2O fluxes. Structural equation modelling showed that forest succession affected soil CO2 fluxes by changing soil temperature and microbial biomass carbon, affected soil CH4 fluxes mainly by changing soil water content and soil pH value, and affected soil N2O fluxes mainly by changing soil temperature, microbial biomass nitrogen, and soil NO3--N content. Our study suggests that forest succession mainly alters soil nutrient and soil environment/chemical properties affecting soil CO2 and N2O fluxes and soil CH4 fluxes, respectively, in the secondary forest succession process.