| The forest litter is the basic carrier of soil nutrients and the tie which connect forest plants and soil, the soil microbial especially.The leaf litter occupies a great proportion in the litter and it is the main source of the fertilizer regeneration on the soil. Soil microbes are the most active part in the soil and play a key role in the circulation of forest ecosystems material and energy. The change of quality and quantity about forest leaf litter has a significant impact on the soil microbial community during the decomposition. The study which on the soil microbial community structure characteristics effected by natural secondary forest litter leaf in the Loess Plateau is helpful to further understand the relationship between forest plant communities and soil microbial community, the mechanism of Loess Plateau secondary forest succession and the result is an useful reference for vegetation construction and management of the Loess Plateau.The study area is in the Malan forest district of Xunyi county town in Shaanxi Province. The leaf litter and soil were collected from this area. There are two treatments in the laboratory:1)The abandoned land soils were dealt with different leaf litter extracts;2) The abandoned land soils were dealt with different leaf litter covering. The microbial culture method (MPN method) and the Denaturing Gradient Gel Electrophoresis (DGGE) technology were taken to measured in the microbial main groups, the main physiological groups and genetic composition. By using the mathematical statistics and multivariate analysis, the effect of leaf litter on soil microbial community features was studied, the main results are as follows:1. The main microbial groups:1) The S4and S7showed negative effect, the rest of the treatment showed positive effect of changes. The number of bacteria and fungi of S5was the highest, the most obvious effect of changes.2) In the single leaf litter treatment, the number of bacteria and fungi of S1was the highest, the most obvious effect of changes.2. The microbial physiological groups:1) The number of Ammonifying bacteria, Azotobacter and Nitrobacteria showed a positive effects of changes in the7kinds of treatments, and Cellulose-decomposing bacteria showed negative effects of changes.The S3was the highest for the number of Azotobacter and Nitrobacteria; The S4was the highest for the number of Ammonifying bacteria.2) In the a single leaf litter treatment, S3was the highest for the number of Azotobacter and Nitrobacteria, the treatment effect was more obvious, while the difference between S1and S2ware not obvious.3) PCA results further confirmed the different of leaf litter had obvious effects on soil microbial physiological groups. Compared with the control,7kinds of treatments were changed significantly.3. The soil bacterial communities characteristics:1) diversity trends:S4>S1> S6=S8>S3>S5>S2>S7.The S1, S4and S6showed a positive effect; The S3, S5, S2and S7showed a negative effect.2) The cluster results based DGGE profiles showed that extracts of leaf litter had an obvious effect on soil bacteria, and S7was significantly different from the rest6kinds of treatments.4. The character of soil bacterial communities on the temporal and spatial variation:1) After five months, the soil bacterial diversity of8treatments showed a increased trend;7samples changed in volatile in the five-month:in the a single leaf litter treatment, the sequence of diversity from large to small:S1>S2>S3, the trend of S1and S2were similar; In the mixed leaf litter treatment, the sequences of diversity from large to small:S7>S5>S6>S4, and the trend of first three were similar.2) The cluster results based on the DGGE profiles of each month showed the dissimilarity of single leaf litter treatments (S1, S2, and S3) and the control (S8). The S1, S2and S3had an obvious effect on the soil bacterial community structure; Until the fifth month, S1, S2and S3were clustered as a class, and the trend of S1and S2are more similar; In the composition of the bacterial community, single leaf litter treatments (S1, S2, and S3), the control (S8) and mixed leaf litter treatment (S4, S5, S6and S7) are significant different.3) The PCA results based DGGE profiles showed, each treatment was different on the temporal variation; The bacterial community structure of S3, S4and S5changed obviously in the1to2months, and consistently in the3to5months. The bacterial community structure of S6and S7changed obviously in the in the1to3months and consistently in the4to5months. The bacterial community structure of S1and S2changed obviously in time-varying volatility.This study has shown that:the quantity and composition of soil microbial which were effected by the different types of leaf litter extracts changed significantly, and it exhibited some certain rules, this might relate to the type of trees and different successional stages of vegetation; The soil microbial diversity changed with the different of leaf litter composition.The component of leaf litter were more closer, the soil bacterial community were more similar, which might be affected by the interactions of different leaf litter; The leaf litter coverage experiments indicated:each treatment showed that bacterial communities had different temporal and spatial structure, the main reason was the variety of composition and proportion of organic matter in the leaf litter, and this affected the difference of bacterial community structure. |
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