Roles of biotic and abiotic variables in determining spatial variation of soil respiration in secondary oak and planted pine forests

Monoculture pine plantation (PP) was widely established after clear-cutting of natural forests last century in China. However, its effects on soil CO₂ efflux (R_S) temporally and spatially are still poorly understood. Biotic and abiotic factors that control spatio-temporal variation of R_S were assessed in a naturally regenerated oak forest (OF) and a nearby PP in a warm temperate area of China. We hypothesized that spatial variation of R_S in PP is lower than that in OF and is less influenced by biotic factors due to its homogeneous stand structure compared to the regenerated OF. R_S measurement campaigns were conducted in two 40 m × 60 m plots in OF and PP from Oct. 2008 to Oct. 2009. Soil temperature at 5 cm depth (T₅) exerted considerable influence on the temporal variation in R_S. However, the spatial variation of R_S was not affected by T₅ in either PP or OF. The observed spatial pattern of R_S remained comparatively consistent throughout the measurement campaigns for both forests. Soil chemical and physical parameters such as soil organic carbon (SOC), light fraction organic carbon (LFOC), total nitrogen (TN), bulk density (BD), total porosity (TP), water-filled pore space (WFPS), and water-holding capacity (WHC) had significant impact on the spatial variation of R_S for both OF and PP. We found that biotic factors such as fine root biomass (FR) and stand structure parameters including basal area (BA), maximum diameter at breast height (max. DBH), and mean DBH within 4–5 m of the measurement points had significant influence on the spatial variation of R_S in OF, while no similar significant correlation was found in PP. A stepwise multi-linear regression showed that water-holding capacity (WHC), max. DBH within 4 m of the measurement points (max. DBH₄), and total porosity (TP) contributed 68.7% to the spatial variation of R_S in OF, while light fraction organic carbon (LFOC) and bulk density (BD) accounted for 46.9% of the spatial variation of R_S in PP. These differentiated the importance of biotic and abiotic factors in controlling the spatial variation of R_S between the naturally regenerated OF and the artificially regenerated monoculture PP. Therefore, compared to OF, relatively lower coefficients of spatial variation for R_S were observed in PP across the year, which was partly attributed to its simple stand structure of PP. Our findings are valuable for accurately estimating regional carbon fluxes by considering the spatio-temporal variation of R_S in artificially and naturally regenerated forests.