Effects Of Tree Species Diversity On Soil Enzyme Activity And Microorganism Diversity

The changes of tree species diversity in aboveground can influence the soil ecological processes and adjust soil enzymes and soil microorganisms,which influece underground processes directly or indirectly.As important roles in material transformation and energy flow in soil ecosystems,soil enzymes and soil microorganisms are of great research significance.To study soil enzyme activity and soil microbial diversity under different tree species diversity will help to explore relationship between aboveground plant diversity and he process of underground ecosystem.Furthermore,it lays a theoretical foundation for the sustainable management of forest ecosystem and provides a theoretical basis for the maintenance of forest ecosystem services.In this research,we setted tree cluster experiment in greadient of tree species diversity,from 1 to 4 tree species,to investigate the effects of tree species diversity on the soil enzymes and soil microorganisms,and to assess the correlation between them.The soil enzymes(acid phosphatase,invertase,urease and catalase)activity in the different soil layers(humus layer,0-15 cm,15-30 cm,30-45 cm,45-60 cm)were determined by colorimetric method.The soil bacterial,fungal diversity and community structure in 0-15 cm soil layer were determined by high-throughput sequencing method.By conbining soil enzyme activity and soil microbial diversity two aspects to study the influence of tree species diversity on soil ecosystem and provides theoretical basis for forestry management and land use.The main research results are as follows:(1)In general,with the increasing of tree species diversity,soil acid phosphatase,sucrase and urease activities first increased and then decreased,and the soil enzyme activities reached the maximum when the diversity was 3.Soil catalase activity decreased with the increase of tree species diversity.However,in different soil layers,the effects of tree species diversity on soil acid phosphatase and sucrase activities were different.In the soil layer of 0-15cm and 15-30cm,acid phosphatase increased with species diversity.In the soil layer of 30-45cm and 45-60cm,soil acid phosphatase activities first increased and then decreased,and the soil enzyme activities reached the maximum when the diversity of tree species was 3,but there was no obvious regularity in the humus layer.In humus layer and soil layer of 15-30cm,soil sucrase activity decreased with the increase of tree species diversity,but there was no obvious regularity in other soil layers.The change of soil comprehensive enzyme index(SEI)with species diversity was as follows:diversity of species 2>diversity of species 3>diversity of species 4>diversity of species 1.Four kinds of soil enzyme activities decreased with the increasing of soil depth in the vertical distribution of different tree species diversity.The enzyme activities of the four types of soil decreased significantly between humus layer and soil depth of 30cm,and decreased gently between soil depth of 30cm and soil depth of 60cm.(2)There were no significant differences in soil bacterial diversity and community structure under different tree species diversity gradients.The increasing of species richness had no significant effect on the number and diversity index of soil bacterial OTU.Acidobacteria(37.81-42.18%)and Proteobacteria(27.95-32.67%)were the dominant bacteria in the gradient soil of different species diversity.With the increasing of species diversity,the relative abundance of acidobacteria decreased,while the relative abundance of proteobacteria and actinomycetes increased.The diversity and community structure of soil fungi under different tree species diversity gradient were significantly different.The diversity of tree species had a significant impact on the relative abundance and diversity of the fungal community.With the increasing of tree species diversity,the number of OTU fungi and the diversity index first increased and then decreased.Basidiomycota(49.80-72.13%)and Ascomycota(19.58-34.48%)were the dominant flora of soil with different tree species diversity gradient.At the phylum level,with the increasing of species diversity,the relative abundance of basidiomycetes showed no significant change,and the relative abundance of ascomycetes showed an increasing trend.(3)There was a significant positive correlation between soil urease activity and fungal aroma index and bacterial OTU number,and a significant positive correlation between soil sucrase activity and bacterial OTU number.The richness and diversity of soil bacteria and fungi were closely related to specific soil enzyme activities.(4)There was a significant negative correlation between soil pH and four soil enzyme activities,and the order of correlation coefficients was:acid phosphatase>sucrase>urease>catalase.Soil organic carbon was positively correlated with four soil enzymes activities,and the sequence of correlation coefficients from large to small was:invertase>acid phosphatase>urease>catalase.The physicochemical properties of soil had significant effect on the community structure of soil bacteria and fungi.Soil bacterial community structure was mainly affected by soil pH and organic carbon,while soil fungal community structure was mainly affected by soil moisture content.