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

Abstract

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 Betula platyphylla forest (early stage), then Betula platyphylla-Larix gmelinii forest (intermediate stage), to Larix 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 μg m^-2 h^-1 at intermediate successional stage, significantly lower than that at late (20.71 μg m^-2 h^-1) and early-successional (20.85 μg 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.

Keywords: Boreal forest; Environmental factors; Greenhouse gas fluxes; Secondary forest succession; Soil properties.