Effects of tree species mixture on soil organic carbon stocks and greenhouse gas fluxes in subtropical plantations in China. (Special Issue: Shaping forest management to climate change.)

摘要

Indigenous broadleaf plantations are increasingly being developed as a prospective silvicultural approach for substituting coniferous plantations in subtropical China. Three plantations of monoculture and mixed Pinus massoniana and Castanopsis hystrix were selected to examine soil organic carbon (SOC) stocks and temporal and spatial patterns of the main greenhouse gases fluxes for understanding the effects of mixed forests on soil carbon and nitrogen (N) cycling processes. We found that SOC stock in 0-20 cm layer in the mixed plantation was 14.3% higher than that in the P. massoniana, and 8.1% higher than that in the C. hystrix plantations. Differences in SOC stock among the plantations were attributed to soil N stock and leaf litterfall input. Soil CO₂ and N₂O fluxes in the mixed plantation displayed the seasonal trends, while soil CH₄ flux did not show the seasonal trend. The seasonal variations in soil CO₂ and N₂O emissions were positively related to soil temperature and moisture. Mean soil CO₂ and N₂O emissions (53.2 mg C m-2 h-1 and 5.21 micro g N m-2 h-1, respectively) were significantly higher in the mixed plantation than in the P. massoniana plantation, while they were lower than in the C. hystrix plantation. Mean soil CH₄ uptake (38.4 micro g C m-2 h-1) was significantly higher in the mixed plantation than in the C. hystrix plantation, while it is similar to that in the P. massoniana plantation. Variations in soil CO₂ flux among the plantations were influenced by fine root biomass, leaf litterfall mass, soil N stock and soil C:N ratio. Differences in soil N₂O flux among the plantations could be attributed to the differences in soil N stock, soil NO₃--N content and soil C:N ratio. Soil respiration rate and soil NO₃--N content could account for variations in soil CH₄ flux among the plantations. This study confirms that the mixed plantation has a higher SOC stock than the monoculture plantations, and there is an increase in amount of GHG absorbed by the soil of mixed plantations compared to C. hystrix plantations. Therefore, a mixture of C. hystrix versus P. massoniana, could be a better silvicultural approach for SOC sequestration than monoculture C. hystrix plantation for substituting P. massoniana plantations in subtropical China.