Studies On Effects Of Different Models Of Conversion Of Cropland To Forest On Soil Microbes And Enzyme Activities

Conversion of cropland to forest is a social ecosystem engineering of forestry sustainable development, which is regarded the ecological benefit as principle, looking after the economic and social benefit, in order to prevent from the soil erosion and the cropland sands. In recent years, the people studied conversion of cropland to forest engineering widely .But so far, we didn't still see a report on the effects of different models of conversion of cropland to forest on soil microecology (soil microbes and enzyme activities) . Performing the research of this aspect has very important theoretical and practical meaning to carry into conversion of cropland to forest engineering and improve environment. In key demonstrating area of two kinds of main models of conversion of cropland to forest, seasonal variation and vertical distribution of soil biological characteristics, rhizosphere effect of forests and so on were studied systemically and embedly in Hongya county , Sichuan province. The main research results were as follows:1. In Betula luminifera forest, Pleioblastus amarus forest and cropland, the quantity of bacteria was predominant, actinomyces was the next, and fungi was the least among compositions of soil microbes. And the quantity of bacteria, actinomyces and total microbes were all cropland > Pleioblastus amarus forest > Betula luminifera forest, but the quantity of fungi was Betula luminifera forest > Pleioblastus amarus forest > cropland.2. Seasonal variation of quantity of total microbes and the three types of soil microbes and was similar in two forestland, but it was very different between two forestland and the cropland. In two forestland, the quantity of fungi and actinomyces was the highest in winter, but the quantity of bacteria was the highest in autumn , and the least in winter; while the quantity of fungi and actinomyces was higher in summer and winter than in spring and autumn, but bacteria was the highest in winter in cropland.3. Six kinds of microbial preponderant species were isolated and identified in this study, and they were Micrococcus, Bacillus, Streptomyces, Actinoplanes, yeast(The genus wasn't confirmed) and Trichoderma respectively . Among them, the quantity ofMicrococcus and yeast was higher in summer and winter than spring and autumn; and the quantity of Bacillus was the highest in autumn, and the least in summer; and in Pleioblastus amarus forest and cropland, the quantity of Streptomyces was the highest in summer, and the least in winter; while it was higher in spring than other seasons in Betula luminifera. Seasonal variation of quantity of Actinoplanes and Trichoderma was less than other microbial preponderant species.4. In Betula luminifera forest and Pleioblastus amarus forest, the R/S values of the three types of soil microbes were 1.37 and 1.24 respectively. And among microbial preponderant species, the quantity of Streptomyces and Trichoderma was higher in rhizosphere soil than those in non- rhizosphere soil. But yeast was less in rhizosphere soil than that in non- rhizosphere soil. In Betula luminifera forest, Micrococcus and Actinoplanes were higher quantity in rhizosphere soil than those in non- rhizosphere soil, but in Pleioblastus amarus forest, they were opposite. The average R/S values of activity of four soil enzyme were higher in rhizosphere soil than those in non- rhizosphere soil.5. The quantity of Micrococcus and Bacillus, Streptomyces and Actinoplanes, yeast and Trichoderma, Streptomyces and Bacillus, Actinoplanes and yeast was significant or very significant negative correlation; and this showed they may have effects of competition and antibiosis among them respectively. But the quantity of Micrococcus and Streptomyces, Trichoderma and Actinoplanes was very significant positive correlation respectively, and this showed they may have effects of promoting the growth and the reproduction.6. General trend of vertical distribution of the three types of soil microbes was soil surface layer (0~15cm) >subsurface layer(15~30cm) >deep layer (30~45cm), especially this trend of actinomyces and fungi was very distinct in different soil layers, but bacteria wasn't very distinct. And among microbial preponderant species, proportion of Micrococcus, Actinoplanes and Trichoderma was decreased with increasing of soil depths; but Bacillus and Streptomyces ware increased with increasing of soil depths; while variation of yeast wasn't distinct in soil layers7. Among four soil enzyme, the activity of invertase was significant positive correlation to urease and catalase; and the activity of urease was significant positive correlation to cellulosase and catalase. Activity of nvertase, urease and catalase was highest in summer, and cellulosase was highest in winter. Activity of four soil enzyme was weakened with increasing of soil depths, which was consistent with distribution of soil microbes, especially that of actinomyces and fungi in soil layers.8. This research indicated: There were significant or very significant positive correlation between the quantity of actinomyces and fungi and four soil enzyme. And there were also significant positive correlation between some microbial preponderant speciesand four soil enzyme, such as Micrococcus and invertase, Bacillus and cellulosase, yeast and urease, Trichoderma. Actinoplanes and catalase.9. System of evaluating indexes of the effects of different models of conversion of cropland to forest on soil biological characteristics was based by applying factor analysis showed: The diversity of actinomyces, fungi and their microbial preponderant species was very important to evaluate soil biological fertility; and activity of four soil enzyme was an important index of evaluating soil biological fertility. But the bacteria and yeast were less contribution to evaluate soil biological fertility than other biological indexes. The sequence of soil biological fertility evaluated by IFI from high to low was surface layer of Pleioblastus amarus forest > surface layer of Betula luminifera forest > surface layer of cropland > subsurface layer of cropland > deep layer of cropland > subsurface layer of Betula luminifera forest and Pleioblastus amarus forest > deep layer of Betula luminifera forest > deep layer of Pleioblastus amarus forest.