火烧对森林土壤有机碳的影响研究进展

对国内外火烧影响森林土壤有机碳动态的研究成果进行了综合述评。较多研究表明低强度火烧不会造成土壤有机碳贮量的明显变化,但火烧非常强烈而彻底,土壤有机碳明显减少。有限研究表明火烧对森林土壤呼吸的影响结果有增加、降低或无影响,因火烧强度、火后观测时间、森林类型、火烧迹地上植被恢复进程和气候条件等而异。同时,火烧对土壤有机碳组分(活性有机碳和黑碳)也具有不同程度的影响。随着全球变化研究的深入,火烧作为森林主要管理措施对大气CO2浓度影响亦愈来愈受重视,今后应着重开展以下几方面研究:(1)扩大气候和经营管理的变化对森林土壤有机碳贮量时空动态影响研究;(2)深入探讨火烧影响土壤CO2释放的过程及机理;(3)加强火烧历史和频率对黑碳影响的研究;(4)从广度和深度上加强火烧等经营措施对亚热带森林土壤碳动态影响的研究。

A review of effects of fire on soil organic carbon in forests

Soils have twice content the amount of carbon (C) present in the atmosphere and C in soils is about two to three times greater than that accumulated in living organisms in terrestrial ecosystems. Due to the large C pool in soils, small deviations in the different C forms may also have a significant effect on the global C balance and consequently on climate change. Fire is a major driver of ecosystem processes and the C cycle process in forests. The forest fires are widespread worldwide phenomenon. It is important to understand the effect of high intensity fires and prescribed fire on soils. This paper reviews the effect of forest fires on the quantity and quality of soil organic C (SOC) and C release. It is focused mainly on soil respiration and soil organic C fractions; i.e. microbial biomass C (MBC), light fraction organic carbon (LFOC), dissolved organic C (DOC) and black carbon. Generally, intense prescribed fire or wildfire can lead to complete destruction of the organic layer and SOC in the topsoil. On the other hand, the effect of moderate prescribed fire is often minor and sometimes organic C increases after fire due to increased input of partly charred material or litter from decaying trees. Low-intensity prescribed fire usually results in little change of soil C. Soil respiration, including autotrophic and heterotrophic respiration, is an integrated result of the belowground processes. It has been widely used to evaluate the effects of disturbance on soil carbon pools. Fire can change the rate of soil respiration by reducing soil moisture and organic matter, increasing surface temperature, and reducing soil microbial populations at varying degrees. Soil respiration rates have been shown to be an increase, decrease or no significant change with burning, depending primarily upon fire intensity, observation time after fire, forest type, vegetation regrowth process, and climatic condition, etc. On the other hand, fire not only perturbs the level of SOC, but also redistributes different labile fractions of organic carbon. Changes in labile SOC induced by fire have been noted to be more complex. Overall, fire significantly increases the soil DOC, but decreases soil LFOC and MBC. Relative to labile fractions of SOC, black carbon, a byproduct of wildfires and prescribed fires, is more stable and contributes to the long-term C sequestration. Despite the importance of black carbon on forest soils, there is limited information about the influence of fire on soil black carbon. Some studies note an increase, and some other studies indicate no effect or little effect of fire. Forest frequency, fire intensity and soil sampling depth are important variables for assessing the impact of fire on soil black carbon. In the future, more researches would be required (1) to determine effects of climate and forest management on dynamics of forest soil organic C, (2) to elucidate the process and mechanisms of CO₂ release following fire, (3) to assess the influence of fire history and frequency on soil black carbon, and (4) to determine forest soil carbon dynamics affected by forest management such as fire under field conditions and especially in subtropical ecosystems.