Crown Thinning Effects On Soil Microbes And Enzymes In Masson Pine And Cinnamon Artificial Multi-Layer Forests

When compared with single-layer forest, multi-layer forests have a more complicate structure which may permit they display strong stress tolerance when suffered from disturbance. They may also be good at forest multifunction and effectively solve the prominent contradictions that was caused by directional cultivation of artificiall forests. Cultivating multi-layer forest has been an effective model for forest sustainable management and are gradually becoming the hot topic of forestry research. Four different thinning models were carried out in masson pine (Pinus massoniana Lamb) forest which was just in its20years. After thinning, the canopy density was0.4,0.5,0.6and0.7, respectively. In the same year, a economic species cinnamon (Cinnamomum cassia Presl) was planted under each model, forming a8-years double-layer artifical forest. In this comtribution, soil microorganism population, soil microbial community functional diversity, soil microbial biomass, soil enzyme activity and the correlation among them were analyzed by three different methods, that is, variance analysis, principal component analysis and correlation analysis. The soil microorganism quantity was determined by dilution plate method, the soil microbial community functional diversity was tested by Biolog-ECO microplate method, and the soil microbial biomass was examined by fumigation-extraction, the soil enzyme activity was checked by colorimetric method. The main results were listed as follows:(1) Bacteria population of woodland soil account for majority in each thinning model. However, the population of bacteria, fungi, actinobacteria and microorganism were ranged from multi-layer forests to pure stand of masson pine to pure forest of cinnamon. There was a significant level (p<0.05) between multi-layer forest and single-layer forest. The number of each index was gradually reduced with the increase of soil depth on vertical direction. There was a positive correlation between microorganism population and soil nutrient.(2) In utilization of carbon sources, average well color development (AWCD) value of each treatment in soil microbial communities was gradually increased as incubation time went by, and tended to stability in the end. There was little difference in AWCD value of4kinds of multi-layer forests, but AWCD value of pure forest of cinnamon was minimum.(3) The Simpson index, Shannon-Wiener diversity index and McIntosh index of soil microorganism ranked from high to low was multi-layer forests, pure forest of masson pine and cinnamon. The Simpson index and Shannon-Wiener diversity index of the six types of models was similar, however, the McIntosh index of each multi-layer forest was much more than that of single-layer forest. On the vertical layer, the Simpson index and Shannon-Wiener diversity index of A layer of model1,2,3were more than that of B layer. On the contrary, the residual stand showed a completely different law. Exception for layer B> layer A in pure forest of cinnamon, the McIntosh index of soil microorganism showed a law that layer A was bigger than layer B.(4) The utilization of carbon sources differed from each other in each thinning model. And there was significant difference for utilization of amino acids, esters, amines, and carboxylic acids (p<0.05), the same to the utilization sugar, alcohol and carboxylic acids in different soil layers (p<0.05). On the whole, utilization of carbon sources among multi-layer forests were higher than that in single-layer forest. And the soil microbial communities of the six types of thinning model can be divided into three classes according to the principal component score. That is multi-layer forests, pure forest of masson pine and cinnamon.(5) The soil microbial biomass of multi-layer forests were higher than that of pure forest among six types of researching forests. Soil microbial biomass carbon and nitrogen had the highest value in the third multi-layer forest, the highest value of soil microbial biomass phosphorus was appeared at the first multi-layer forest. Nevertheless, soil microbial biomass in the pure forest of cinnamon had the lowest content. The value of all tested indexs were gradually reduced with the increase of soil depth on vertical direction. There was a positive correlation between soil microbial biomass and microorganism population and soil nutrient.(6) Soil enzyme activity of multi-layer forests was higher than that of single-layer forest among six kinds of researching stands. The highest value of enzyme activity of catalase and urease was appeared in the secomd multi-layer forest and the maximum of proteinase was the first multi-layer forest, and sucrase and phosphatase in the third multi-layer forest had the highest value. The pure cinnamon forest had lowest activity among the measured enzymes which were gradually reduced, accompanied by an increase in the depth of soil on vertical direction. There was a positive correlation among the5kinds of soil enzymes and microorganism population and soil nutrient.The tested results may supply scientific basics for evaluating the quality of forest land and for managing artificial multi-layer forest in which the site quality could be further improved. It may be helpful to the utilization of woodland and to faster the development of forestry in China too.