| Along with the progress of global climate warming, forest fires frequently happened in the global, which led to the forest ecosystem destruction and resources loss, it caused huge ecological and economic loss. Meanwhile, lots of Greenhouse gases (GHGs) were emissed in the forest fire, which feedback to the progress of global climate warming and increase the forest fire danger, the ecological positive feedback cycle pathway is formed from climate warming to forest fire.Daxingan Mountain is the only high latitude forest and permafrost region in cold temperate zone of China, and also the "Northeast Asia" environmental sensitive areas. As an important forest carbon-sink in China, lots of GHGs sealed in permafrost. However, as one of the important interference factors, forest fires led to the thawing of frozen soil and GHGs emission. In this study, Larix gmelinii forest burned areas were experienced in different fire years (2003,2008and2012) and different fire intensities (lightly burned and severely burned). The soil GHGs efluxes, vegetation, hydrothermic factors, edaphon and soil organic carbon were observed and researched in two consecutive years from2011to2012. The objectives were to demonstrate the trends of soil GHGs effluxes in permafrost region after forest fire, and explore the responses of soil GHGs effluxes to vegetation, hydrothermic factors, edaphon and soil organic carbon, which provide important value to further study on carbon and nitrogen cycle after forest fire in Daxingan Mountain. The fingings were summarized as follows:1. Soil CO2efflux in different burned areas showed unimodal curve pattern, which increased with fire ages and intensities. Soil CH4efflux (uptake efflux in growing season, emission efflux in freezing and thawing period) showed polymodal curve pattern and had a significant difference between burned and unburned areas. Soil N2O efflux (uptake efflux in growing season, uncertain in freezing and thawing period) also showed polymodal curve pattern, but there is no significant difference in different burned areas.2. Lightly fire trends to increase the Shannon-Wiener and Margalef index in different burned areas, but decrease the above-ground biomass. The severely burned areas had an opposite results with lightly burned areas. The Pielou index in different burned areas increase, as a ranking of lightly burned>severely burned. Howere, the Pielou index significantly was not difference in different fire years. A significant positive linear relationship showed between soil CO2efflux and above-ground biomass. Either soil CH4efflux or above-ground biomass showed a significant negative index relationship. However, there were no significant correlation between soil N2O efflux and above-ground biomass.3. Atmospheric temperatures, humidities and soil temperatures in different burned areas showed a unimodal curve pattern, but soil water contents trended an index decline pattern. A significant index regression relationship was found between soil CO2efflux and atmospheric temperatures, soil temperatures, respectively, and a positive linear relationship was obtained between soil CO2efflux and soil temperatures, but there was no significant relationship with soil water content. A positive and a negative linear relationship were showed between soil CH4efflux and soil water content, soil temperature, respectively. A quadratic function and a linear relationship were fitted between soil N2O efflux and soil temperature, soil water content, respectively.4. Soil microbial quantities in2003and2008burned areas were lower than unburned areas, but soil microbial quantities in2012burned areas were higher than unburned areas. The forest fire significantly affected the soil microbial quantity. Soil microbial biomass carbon decreased in lightly burned areas, and increased in severely burned areas. The soil microbial biomass nitrogen was significantly influenced on forest fire, and which decreased the ratio of soil microbial biomass carbon and nitrogen. A significant positive linear relationship was showed both soil CO2efflux and CH4efflux with soil microbial biomass carbon, and a significant positive relationship was fitted between soil microbial biomass nitrogen and soil N2O efflux.5. A negative relationship of soil bulk density and soil layer depth was showed,but the positive relationship between soil organic carbon content, soil organic carbon density and soil layer. Compared with unburned areas, soil organic carbon accumulated at the depth of10cm-20cm by forest fire, but soil organic carbon decreased at the depth of0-10cm,20cm-40cm by forest fire. Soil organic carbon content and density showed a ranking of unburned>2003burned areas>2008burned areas>2012burned areas. The same significant linear relationship was showed between soil CO2efflux, CH4efflux and soil organic carbon, but there was no significant relationship between soil N2O efflux and soil organic carbon.6. In the period of thawing and growing season, a positive relationship were showed between CO2equivalent of GHGs and at different forest fire years and intensities, the Global Warming Potential (GWP) increased with the intentsity of fire. In freezing period, about15%GWP decreased in lightly burned areas, but GWP increased in severely burned areas. The fire years and intensities significantly affected GWP increment. |
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