Relationship Of Spatial Distribution Between Soil Bacteria And Environmental Factors In Two Forests In The Three Gorges Reservoir Area

Soil microbes play an important role in soil ecosystem system. However, the research of interrelationship between soil microbes and the environment has been one of the tough issues in microbial ecology field, due to the microscopic size of the individual, mass quantities, soil microbial diversity, the variability of space-time distribution, and the complexity of the influence factors. The correlation between above-ground and under-ground parts in ecological system is a hotspot in the current field of ecology research. Therefore, it's important and meaningful to reveal the laws of soil geographic distribution and interrrelationship with environmental factors, in order to give an accurate assessment of the soil microbes'role in maintaining the functions of the ecosystem.In this paper, two typical vegetation types (the Chinese-fir and Masson-pine mixed forests and the Masson-pine pure forests) in three gorges reservoir area were chosen to carry out this research work. In the scale of standing forest, using dilution-plate method combining 16SrDNA sequence analysis and Biolog identification technology, the number and diversity of the bacterium which soil can nurture were compared and analised; On this basis, using simple correlation analysis, the linear regression analysis, and canonical correspondence analysis (CCA) method, the relationship between the major groups of soil bacteria and bacterial diversity with the environmental factors were studied; Finally, geostatistics was used for analyzing the space-time heterogeneous distribution of the soil bacteria and the correlation with the spatial structure of the environmental impact factors. Conclusions are as follows:1.The quantity of culturable soil microbes:Under two vegetation types mentioned above and different seasons conditions, the quantity of the three major soil microbes groups sorted by size always are:bacteria> actinomycetes> fungi, in which the quantity of bacteria is 2.475×106cfu/g～3.675×106cfu/g, actinomycetes1.031×106cfu/g 1.635×106cfu/g, fungi 4.836×104cfu/g～11.88×104cfu/g; Quantities of the three types are all higher in pine forests than in mixed fir-pine forests in different seasons, in addition, exclude of bacteria and fungi in autumn there are significant differences. Fir-pine forests has less soil bacteria and fungi but slightly more actinomycetes in spring than in fall, and there are not significant differences. In pure pine forests, the quantities of bacteria and actinomycetes in spring are higher than in fall, spring fungi below autumn, also no significant difference. Vegetation type is the main reason lead to quantity variance of the soil microbes and that there are no significant differences between spring and fall seasons.2.The community composition of culturable soil bacteria:The main bacteria groups and their proportions in spring fir-pine mixed forests are:Pseudomonas 69.86%, Burkholderia 1.97%, Bacillus 14.39%; In autumn fir-pine mixed forests are: Pseudomonas 50.56%, Burkholderia 16.29%, Bacillus 14.82%, Lysobacter 1.95%, Acinetobacter 0.52%, Chryseobacterium 2.81%. The main bacteria groups and their proportions in spring pure pine forests are:Pseudomonas,66.02%, Burkholderia,13.45%, Flavobacterium 0.04%, Bacillus,10.10%; In autumn pure pine forests are:Pseudomonas, 49.22%, Burkholderia,8.42%, Klebsiella 4.73%, Chryseobacterium 1.86%, Micrococcus 0.11%, Bacillus subtilis,16.48%. The community composition of soil bacteria is varied between different vegetation types. There are more bacterial species in autumn than spring, and those new types are with relatively low quantities, for the same vegetation type there are not much difference in the major soil bacteria species despite different seasons.3.The diversity of culturable soil bacteria:There is no significant difference between the 4 diversity indexs of the soil bacteria under two kinds of forests in spring, but indexs except Pielou are significantly higher in pine forests than that of fir-pine mixed forests in the fall. The indexmovement varied under different seasons for both vegetation types. Exclude Margalef index, other diversity indexs are all higher for fir-pine mixed forests in autumn than spring. In pine forests, all 4 diversity indexs are higher in the fall. The diversity of culturable soil bacteria is effected by both season and vegetation type. Compared with the diversity of above ground Arbor-Bush-Grass layers vary from vegetation types, the change of diversity of soil bacteria proves the contrary.4.The correlation between soil bacteria and soil properties:The content of soil organic matter, total nitrogen, carbon nitrogen ratio, moisture content and PH value are all significantly higher in fir-pine mixed forests than pure pine forests. The overwhelming majority of the correlations between soil bacteria and soil properties are not significant. Canonical Correlation Analysis(CCA) ordination well demonstrated the relationship between soil bacteria and the 5 soil properties selected for this research, the first two axises explained as high as 90.4% and 81.7% separately for two vegetation types.5.The regression analysis between soil bacteria and forest structure factors:Among those factors Average DBH (diameter at breast height) has the strongest linear correlation with soil bacteria in fir-pine mixed forests, moreover, soil bacteria is commonest relevant with Average DBH within 4.00m, Average DBH (4) together with quantities of Pseudomonas, Burkholderia, Dissolving bacteria, Bacillus cereus and total bacteria and the diversity index of Shanon-Wiener constitute a significant linear regression equation. In pure pine forests, Average DBH and Max DBH were entered in the equation of linear regression,separately with Average DBH (6), Average DBH (5), and Max DBH (8), Max DBH (7), Max DBH (4), Max DBH (3), among all this the Average DBH(6) had most significant linear correlation with soil bacteria, it together with quantities of Pseudomonas, Bacillus, Bacillus cereus, other unidentified bacteria and total bacteria, and the diversity index of Shanon-Wiener constitute a significant linear regression equation. Canonical Correlation Analysis(CCA) ordination well demonstrated the relationship between soil bacteria and the environmental factors added with forest structure factors, the correctly explained volume of the first two axises slightly dropped, accounted for 87.4% and 77.1% separately for two vegetation types.6.The analyse of spatial heterogeneity based on geostatistics method:On the forest stand scale, the results of semivariance analysis and kriging interpolation showed significant spacestructure and space-time heterogeneity for soil bacteria under two vegetation types. The range of spatial autocorrelation is 51.00m. Spatial heterogeneity obviously differs from directions and scales for soil bacteria under two vegetation types, thus spatial variation of soil bacteria shows remarkable anisotropy. The variation trend of the soil bacteria anisotropy ratio between the two directions of X-axis 45°and 135°is nearly the same in spring and autumn season under the two kinds forests. The space-time heterogeneity of soil bacteria is independent of the seasonal variation in quantity and diversity. 7.The relationship of spatial variation between soil bacteria and environmental factors:Results of geostatistical analysis showed that the spatial structure of soil bacteria is very similar to that of environmental factors including their closely interrelated soil properties and forest structure factors. There is very significant correlation between their average semivariograms. Not only the quantity and diversity of soil bacteria closely related to environment factors but also the spacial structure formed by spatial heterogeneity of environmental factors.