Effects Of Forest Fire On Carbon Stability In Deep Soil Of Boreal Forests

Soil carbon pool is the world's largest carbon pool,about 73% of the global soil carbon pool is stored in forest ecosystem soil pool.Soil carbon balance in forest ecosystems is the main component of global carbon cycle,and the accumulation and decomposition of soil carbon directly affect the global carbon cycle.Deep soil carbon(below 40cm)of boreal forest accounted for 46%-63% of total soil carbon,forest fire is the most important natural disturbance to the carbon cycle of boreal forest,and the influence of forest fire on deep soil carbon is also an important part in the process of studying the global carbon cycle.At the same time,the study of deep soil carbon can improve the prediction accuracy of soil organic carbon reserves and provide scientific basis for soil management of forest ecosystem.Great Xing'an Mountains is the representative forest area of the northern forest in China,where the forest fire rate is very high.In this paper,the deep soil carbon of burned area in 2010 and control area in Great Xing'an Mountains forest area were analyzed using field investigation and laboratory cultivation to study the influence of forest fire on the carbon stability of deep soil.The results of the study were as follows:The physical and chemical properties of deep soil were changed by the occurrence of forest fire,soil temperature and pH were significantly higher than that in control sites,but soil moisture in burned sites was significantly lower than the control,and the deep soil carbon content and soluble carbon content were significantly reduced.Forest fire reduced the organic carbon content and soil carbon density of deep soil,and the trees which were the source of soil organic carbon took place by the inverted wood and the withered stand wood.Forest fire significantly changed the chemical composition of deep soil organic carbon,significantly increased microbial biomass carbon and oxidized organic carbon in deep soil,which increased its active ingredient.And forest fire also significantly reduced the carbon and nitrogen ratio of deep soil,increased the availability of organic carbon in deep soil and reduced the stability of deep soil.Forest fire significantly increased the mineralization rate of soil organic carbon and accelerated the turnover of organic carbon indeep soil.The occurrence of forest fire increased the biomass of microorganism in deep soil,changed the composition of microbial community structure,reduced the proportion of fungi,anaerobic bacteria and actinomycetes in the microbial community of deep soil,increased the percentage of Gram-negative bacteria and decreases the proportion of Gram-positive bacteria in the 60-120 cm layer.Thus,the carbon source availability of deep soil was increased,and the stability of deep soil carbon was reduced.The path analysis of the structural equation model affecting soil stability by driving factors showed that the changes of soil organic carbon chemical composition were caused by the change of the composition of plant community,which changed the microbial community composition,and finally changed the decomposition rate of soil organic carbon,resulting in the change of soil stability.The key process in this study was the occurrence of forest fires leaded to a large number of aboveground vegetation deaths,withered and inverted wood became the main source of soil carbon and the active composition of deep soil organic carbon increased.And the forest fire also leaded to the change of the physical and chemical properties of deep soil,so that microbial communities in deep soil were changed,and microbial activity was improved,which led the decomposition of soil organic carbon accelerated and the stability of organic carbon in deep soil reduced.