重度火烧迹地微地形对土壤微生物特性的影响——以坡度和坡向为例

通过对大兴安岭重度火烧迹地不同坡度和坡向的土壤微生物群落进行调查研究,旨在揭示重度火烧迹地过火6a后森林恢复过程土壤微生物群落的变化规律与影响因素.研究结果表明:平地土壤微生物生物量碳含量(MBC)和土壤微生物生物量碳氮比(MBC/MBN)均高于坡地,其中MBC/MBN达到差异极显著水平.平地土壤微生物的代谢活性AWCD值、对31种4类碳源(糖类、脂类、氨基酸、代谢物)的利用能力和Shannon-Winner多样性指数(H')均极显著低于坡地.西坡土壤微生物AWCD值和H'高于南坡,但AWCD和H'与土壤养分、pH值、EC无显著相关关系,说明坡向可能与土壤微生物代谢活性和多样性的关系并不密切,反映了两坡向土壤微生物群落结构的相似性.坡度由于影响了土壤养分和水分条件,进而影响了土壤微生物的生物量、群落结构、物种多样性和碳源利用能力.火烧迹地恢复初期平地土壤微生物量碳高于坡地,西坡高于南坡；恢复6a后,土壤微生物量碳的差异己不显著,但土壤微生物群落结构、物种多样性以及代谢特性仍具有显著差异,这可能与地形坡度仍然显著影响土壤水分含量的因素有关.

The study of characteristics of soil microbial communities at high severity burned forest sites for the Great Xingan Mountains: an example of slope and aspect

It is well known that the Great Xingan Mountain forest region is one of the most important parts of the northeast forest region. Not only does it serve as an important resource for lumber, it also is an important ecological regulator that keeps balance in this area. Fires are common disturbances in this area. Severe fires can cause enormous losses, and can significantly change the structure of the forest ecosystem and disturb its succession process. In order to help the forest recover from such disturbances, it is necessary to study the restoration of soil quality, which can directly affect the forest restoration process. Soil microorganisms, which are common residents in soil, can interact with soil environment during the process of soil quality restoration. They are very sensitive to the changes in soil quality, thus serving as very useful indicators of soil quality. Among many environmental factors, topographic factors, such as slope and aspect, are very important to the restoration of forest soil quality. They affect the distribution of other environmental factors (such as light, heat, water, soil, etc.), and further affect ecological processes in various degrees. In this study we focused on the response of microbial populations to changes in the soil environment of different topographic factors (such as slope and aspect) in recently severe burned areas in the Great Xingan Mountain, where the restoration was at the early regeneration stage. The purpose of this study was to examine the effects of slope and aspect on soil microbial biomass distribution, soil microbial community structure, and soil microbial functional diversity in these areas. Soil samples were collected from severly burned forest sites (2003 fires) with different slopes and aspects. Standard experimental methods were used to measure typical physical and chemical indicators, such as total nitrogen (TN), total carbon (TC), soil organic carbon (SOC), soil moisture (SM), soil available nitrogen (AN), and electrical conductance (EC). Fumigation, extraction, and Biolog methods were used to detect soil microbial biomass, soil microbial community structure, and soil microbial functional diversity, respectively. Our results showed that soil microorganism biomass carbon (MBC) on flat land is higher than that on sloped lands. The ratio between soil microorganism biomass carbon and microorganism biomass nitrogen (MBN) has the same pattern, with the flat land having a significantly higher value (9.49) than that of the sloped land (6.76). Soil microorganism metabolic activities and carbon use capacities of microorganism community, which are assessed by average well-color development (AWCD), however, showed different patterns. That is, the value of AWCD on flat land was significantly lower than that on the sloped land, with values of 0.39 and 1.21 on the flat land and sloped land, respectively. Four types of carbon source use capacities and the Shannon-Weiner index of diversity (H') of microorganism community exhibited a pattern similar to AWCD. AWCD and H' values were higher on west (facing) slopes than those on south slopes, but data analysis showed that AWCD and H' have no significant correlations with soil nutrition, pH or electricity conductance (EC), which suggests that aspect might not be closely related with soil microorganism metabolic activities and diversity of microorganism community. Soil microorganism community structures on these two aspects showed similarity. Slope influenced the soil nutrition and water supply condition of different areas, which can affect soil microorganism biomass, soil microbial community structure, and soil microbial functional diversity in these areas. In the early restoration stages of severely burned areas, MBC values on the flat land were higher than those on slope land, and those on west slopes were higher than those on south slopes. Differences in MBC are not significant among these areas after rehabilitation for 6 years. However, soil microbial community structure and soil microbial functional diversity are still significantly different which might due to different soil water content caused by different slope.