Conversion of primary mixed forest into secondary broadleaved forest and coniferous plantations: Effects on temporal dynamics of soil CO2 efflux

Soil CO2 efflux varies significantly in time and space in terrestrial ecosystems, obtaining a detailed understanding of what controls the dynamics of soil respiration (SR) can improve the estimation accuracy of forest carbon budgets. We examined the effects of forest conversion (from primary forest to both secondary forest and coniferous plantations) on the temporal dynamics of SR and its components (heterotrophic = RH, and autotrophic = RA), at both seasonal and inter-annual time scales within four adjacent forest stands in north-eastern China. Trenching method was used to partition RH and RA. The results showed that RH was the primary contributor to the overall magnitude and variability of SR, which showed similar seasonal and inter-annual variation, while RA displayed higher temporal variation compared to SR and RH. Generally, the between-year seasonal variation of SR and RH varied significantly in both secondary forest and plantations. The secondary forest exhibited a relatively higher seasonal change in RA compared to that in primary forest and coniferous plantations, while there was no significant disparity in the seasonal and inter-annual variation of SR and RH among forest stands. Soil temperature was the primary factor driving the temporal dynamics of RH and accounted for 63-91% and 22-64% of seasonal and inter-annual variations, respectively. However, RA was less controlled by soil temperature. This study implies that forest conversion magnifies the responses of RH to the minor variations in the between-year seasonal patterns of soil temperature and increases the seasonal variability of RA.