Abstract:

【Objective】Forests play an important role in the global carbon (C) cycle. Fire disturbance in forests is a key driving factor of the global biogeochemical cycle, as it affects vegetation structure and the direction of forest succession, which play important roles in soil organic C density and C turnover in forest ecosystems, thus affecting the forest C cycle and C balance. A quantitative study of the effects of forest fire disturbance on soil organic C density and active organic C in forest ecosystems was conducted. It also contributed to clarification of the mechanism of forest fire disturbance on soil organic C in forest ecosystems, and provided information about the recovery of burned land and forest C emission reduction effects.【Method】In a subtropical P. massoniana forest in Guangdong Province, adjacent plot comparison and chemical analysis methods were used to quantitatively determine the soil organic C density, soil active organic C content and fine root biomass at different levels of fire disturbance (low, moderate and high) in the forest ecosystem. The impact of forest fire disturbance on soil organic C density, and the mechanism of forest fire disturbance on soil organic C density and active organic C were investigated and an in-depth analysis of the C cycle and partitioning of soil organic C in the forest ecosystem process was undertaken.【Result】The results showed that forest fire disturbance had an effect on soil organic C density, soil labile organic C content and fine root biomass in P. massoniana forest, and the trend for soil organic C density and soil labile organic C content was: control > low forest fire disturbance > moderate forest fire disturbance > high forest fire disturbance. There was no significant difference in the effect of low forest fire disturbance on soil organic C density (P > 0.05), whereas moderate and high forest fire disturbances significantly reduced soil organic C density (P < 0.05). The soil fine root biomass in P. massoniana forest was lower than that in the control plots, and the trend was: high forest fire disturbance > moderate forest fire disturbance > low forest fire disturbance. Low forest fire disturbance only significantly reduced the soil surface fine root biomass (P < 0.05), whereas moderate and high forest fire disturbances significantly reduced the soil surface and shallow fine root biomass (P < 0.05). 【Conclusion】The results show that forest fire disturbance reduces soil organic C density, and the decrease gradually declines as the soil profile depth increases. The low forest fire disturbance significantly reduced the soil organic C density only at the soil surface, whereas the moderate and high forest fire disturbances significantly reduced the soil organic C density at the soil surface and in shallow soil, which led to significant changes in soil organic C density. Forest fire disturbance had an effect on the soil active organic C content. The contents of soil active organic C in the four species of P. massoniana forest decreased after forest fire disturbance but only moderate and high forest fire disturbances were significantly different. The components of active organic C content showed some difference along the decreasing profile of the soil profile with an increase in forest fire disturbance intensity, and the decreasing trend after high forest fire disturbance was the greatest. Forest fire disturbance had an effect on the fine root biomass of P. massoniana forest.

Key words: forest fire disturbance, Pinus massoniana forest, soil organic carbon, labile organic carbon, fine root biomass