探究平地与坡地森林土壤微生物对不同火烈度的响应,以及土壤微生物群落组成及其影响因素,对于火烧迹地生态恢复具有重要意义。以内蒙古毕拉河林业局内经历低烈度、中烈度及高烈度火干扰后恢复1年的落叶松林火烧迹地为研究对象,采用磷脂脂肪酸(PLFA)分析法测定0~5 cm土层深度的土壤微生物量及群落组成,分析不同火烈度干扰下平地与坡地土壤微生物量、群落组成及多样性的差异。通过冗余分析(RDA)和结构方程模型(SEM),进一步探讨火烈度、坡度和土壤养分指标对土壤微生物量的综合影响。结果表明:1)在对照样地和不同火烈度干扰后的样地中,平地与坡地土壤中革兰氏阴性菌生物量最高,其次为细菌和革兰氏阳性菌,真菌和放线菌的生物量较低,丛枝菌根真菌的生物量最小。2)火干扰对丛枝菌根真菌生物量的影响有限。除丛枝菌根真菌外,火干扰后平地土壤微生物类群的生物量及群落多样性指数略有增加但不显著,而坡地土壤微生物类群的生物量显著增加(P<0.05)。在低烈度火干扰后,坡地土壤微生物类群的生物量和群落多样性指数达到最高。革兰氏阳性菌生物量的变化是坡地土壤微生物群落对火烈度响应的主要驱动力。3)火烈度、坡度和土壤养分指标均显著影响(P<0.01)微生物类群的生物量,其直接影响程度由大到小依次为土壤养分指标、火烈度、坡度。在土壤养分指标中,水溶性有机碳含量与真菌生物量呈强正相关,铵态氮含量与革兰氏阳性菌的生物量呈正相关。因此,火烈度和坡度不仅直接影响土壤微生物量及群落组成,还通过调节土壤养分指标间接影响土壤微生物类群的生物量。

Understanding the response of soil microbial communities to fire severity in flat and sloping forests,as well as the factors influencing microbial composition in fire slash,is crucial for guiding ecological restoration efforts.The fire slash of Larix gmelinii forest after restoration for 1 year from low,medium and high severity fires in the Bilahe Forestry Bureau of Inner Mongolia were selected as research subjects.Using phospholipid fatty acid(PLFA)analysis,soil microbial biomass and community composition were assessed at soil depth from 0 to 5 cm.Differences in soil microbial biomass,community composition and diversity in flat and sloping lands of different fire severities were analyzed.The combined effects of fire severity,slope,and soil nutrient indicators on soil microbial biomass were further explored by redundancy analysis(RDA)and structural equation modeling(SEM).1)Among microbial groups in both control plots and burnt areas,Gram-negative bacteria had the highest biomass,followed by Bacteria and Grampositive bacteria,then Fungi and Actinomycetes,and the smallest was Arbuscularmycorrhizal fungi.2)The biomass of Arbuscularmycorrhizal fungi was hardly affected by fire.Except for the Arbuscularmycorrhizal fungi,the biomass of microbial groups and community diversity indices of flat soil increased but were insignificant after fire,while in sloping soils,microbial biomass increased significantly(P<0.05).Biomass and community diversity indices of soil microbial groupsinsloping soil were largest after low severity fires.The change of Grampositive bacterial biomass was the main driving force of the response of soil microbial community to fire severities in sloping land.3)Fire severity,slope,and soil nutrient indicators all significantly(P<0.01)affected the biomass of microbial groups,with the direct effect in the order of soil nutrient indicators,fire severity,and slope.Soil nutrient indicators of water-soluble organic carbon content were strongly and positively correlated with the biomass of fungi,and ammonium nitrogen content was positively correlated with the biomass of Gram-positive bacteria.Consequently,fire severity and slope not only have a direct effect on soil microbial biomass and community composition,but also have an indirect effect on the biomass of soil microbial groups by regulating soil nutrient indicators.