光皮桦细根与扁穗牛鞭草草根分解的土壤微生物数量及优势类群

Varieties of soil microorganisms decomposing Betula luminifera fine roots and Hemarthria compressa roots

通过室内模拟试验研究向土壤添加单一光皮桦直径为0～1mm细根（处理1）、1～2mm细根（处理2）、扁穗牛鞭草草根（处理3）、0～2mm细根与扁穗牛鞭草草根混合物（处理4）分解过程中土壤微生物数量以及微生物优势类群的变化。结果表明，120d后，与未加植物根系的对照相比各处理都显著的增加了土壤微生物的数量，其中细根、草根混合处理的微生物总数大于添加单一细根和草根的处理（P〈0．05）。真菌在分解过程中占主要地位，其次是放线菌，最后是细菌。对土壤微生物进行分离、纯化、鉴定出参与细根、草根分解初期的主要优势类群是假单胞菌属（Pseudomonas）、木霉菌属（Trichoderma）、游动放线菌属（Actinoplanes），在培养后期（120d后）起主要作用的优势类群是芽孢杆菌属（Bacillus）、曲霉属（Aspergillus）、青霉属（Penicillium）、链霉菌属（Streptomyces）、诺卡氏菌属（Nocardia）。8种土壤微生物优势类群数量在分解过程中未表现出明显的变化规律，但分解120d后，各处理优势类群的数量显著大于对照（P〈0．05）。由此可见，细根、草根的不同处理对其分解过程中土壤微生物数量及种类有较大影响，不同的分解阶段发育着不同的土壤微生物。

Fine root decomposition often plays an important role in maintaining soil fertility and mass nutrient cycling in soil ecosystems. As irreplaceable decomposers of fine roots, soil microorganisms are closely linked to bioelement components. Birch （Betula luminifera）-grass （Hemarthria compressa） is a successful forest and grass compound model for converting farmland to forest and is beneficial to the development of the environment and economy. There is a lack of information on quantities of soil microbes in relation to fine root decomposition and few published reports on soil microorganisms in birch-grass plantations. Therefore, soil microbial amount and dominant microbial groups during decomposition of fine roots and grass roots were investigated in order to obtain an understanding of the mechanisms of fine root decomposition. Birch fine roots and grass roots from a birch-grass compound model in converting farmland to forest in Hongya, Sichuan, were used in a 120-d laboratory incubation experiment. The roots were mixed with the same soil in the following five treatments. 1） 0-1 mm birch fine roots, 2） 1-2 mm birch fine roots, 3） grass roots, 4） 0-2 mm birch fine roots＋grass roots, and 5） no roots （CK）. Treatments of addition of fine roots （and grass roots） significantly increased soil microbial content. The ranked orders of total microbial content were： Treatment 4〉treatment 3 = treatment 1 treatment 2 （P〈0.05）. Fungi played a more important role in fine root decomposition than bacteria and actinomycetes. Eight dominant microbial groups were isolated and identified. Pseudomonas, Trichoderma, and Actinoplanes played the most important role at the initial phase of fine and grass root decomposition, while Bacillus, Aspergillus, Penicillium, Streptomyces, and Nocardia dominated the later phase of decomposition. Regular fluctuations were not observed during the first 120 d of the decomposition processes but after 120 d eight dominant microbial groups increased significantly （P〈0.05）. The different treatments with birch fine roots and grass roots greatly influenced soil microbial amount and the dominant microbial groups in root decomposition.