| Quercus aquifoliodes, belonging to a type of sub-alpine sclerophyllous oak forest, is a very special vegetation type in China, and transiting from the forest to shrub continuously with the increasing of the elevation from south to north. Quercus aquifoliodes is widely distributed in the hengduan mountains region, where is a typical ecological fragile zone and the global climate sensitive area, also national important area of soil and water conservation. It forms a large climax community in the sunny slope of the alpine gorges usually. Because of its well-developed root system and high sprouting ability and wide adaptability, Quercus aquifoliodes has great water and soil conservation ability in the southwestern mountains.In this paper, soil samples collected from Guafu mountain Q. aquifolioides forest (GF) at2551m, Zhaizipo mountain Q. aquifolioides forest (ZP) at3091m, Zhaizipo mountain Q. aquifolioides secondary forest (ZPS) at3091m and in Huayan mountain Q. aquifolioides forest (HY) at3549m in Balangshan, Wolong Natural Reserve, Sichuan. The soil physico-chemical properties, soil enzymatic activities and bacterial diversity were determined. The result showed that:1. The physico-chemical properties were different in soil samples collected from different Q. aquifolioides forests, such as pH, soil total organic carbon and total nitrogen, etc. The soil pH value was weakly acidic and increased gradually along with the elevation rise. The pH value in0-15cm/16-30cm soil layer in GF, ZP, ZPS and HY soil sample was5.32/5.59,5.44/5.67,5.67/5.43and6.41/6.65, respectively.The soil organic matter content in0-15cm layer was higher than that in16-30cm layer, and it was lower in ZPS soil than in ZP soil. Among all samples, the organic matter content in0-15cm layer in ZP sample was126.27g·kg-1, which was the highest one, and that in GF, ZPS and HY soil was107.27g-kg"1,110.02g-kg"1and115.04g·kg-1, respectively. In16-30cm soil layer, the organic matter content was71.22g·kg-1,95.62g·kg-1,97.37g·kg-1and103.28g·kg-1in GF, ZP, ZPS and HY soil, which increased with the elevation rising.The total nitrogen content (TN) in0-15cm layer was higher than that in16-30cm layer soil, and increased with the elevation rising; And TN in ZPS soil was lower than that in ZP soil. In0-15cm layer, the total nitrogen content of GF, ZP, ZPS and HY were3.13g·kg-1,4.16g·kg-1,3.30g·kg-1and4.53g·kg-1; in16-30cm layer were2.08g·kg-1,2.89g·kg-1,2.42g·kg-1and3.09g·kg-1respectively.(2) The soil enzymatic activity showed significantly seasonal variation. Urease and acid phosphatase activity was lower in summer than that in winter. However, the cellulase activity was higher in April than that in other seasons. The Urease activity in GF, ZP, ZPS and HY soil was1.15±0.39U,1.84±0.15U,1.55±0.17U and0.74±0.10U in0-15cm layer in August; and6.58±0.16U,5.99±0.35U,5.03±0.64U and5.44±0.28U in December, respectively.The enzymatic activities were higher in0-15cm layer soil than those in16-30cm layer soi. For example, the cellulase activity of GF, ZP, ZPS and HY was0.37±0.05U,0.39±0.10U,0.24±0.03U and0.13±0.07U in0-15cm layer soil; and was0.12±0.01U,0.13±0.02U,0.09±0.04U and0.09±.01U in16-30cm layer in April, respectively.The enzymatic activity in0-15cm layer of ZPS soil was lower than that of ZP soil, but there was little difference between ZPS and ZP in16-30cm layer. For example, in April, acid phosphatase activity of ZPS and ZP was4.66±0.28U and5.77±0.33U in0-15cm layer; however, which was3.31±0.71U and3.57±0.53U in16-30cm layer.(3) A total of forty-four bacteria were isolted from all soil samples, and the genetic diversity was determined by16S rDNA PCR-RFLP analysis. The results showed that there werer12groups formed at the similarity of95%.16S rDNA sequencing analysis of the representative isolates showed that these strains belonged to genus Bacillus, Pseudomonas, Arthrobacter and Janthinobacterium.Bacillus was the dominant genus, isolated from all Q. aquifoliodes forest soils; Arthrobacter was isolated from the soils except ZPS; Janthinobacterium was isolated from HY soil; Rhodooccus and Pseudomonas was isolates from HY and ZPS soil.(4) PCR-DGGE clustering and diversity index analysis showed that, bacterial diversity in the soil was very similar; bacterial diversity in HY and GF was higher than that in ZP in the same season; but the bacterial diversity in ZPS was lower than that in ZP sample. Sequencing results of cloned DGGE bands showed that most of the bacteria belonged to the uncultured, only very few bacterial strains were culturable, and these strains distributed in genus Acinetobacter, Pseudomonas and Singulisphaera. |
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