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The Wawushan Mountain National Forest Park in Sichuan Province, where there is relatively intact Castanopsis platyacantha-Schima sinensis formations, is a typical representative of the mid-subtropical moist evergreen broad-leaved forest in West China. Using the soil core method, this study investigated the fine root distribution and characteristics of carbon and nitrogen of sample C. platyacantha which is the main constructive species in this formation. The results were as follows: (1) The total fine root biomass of C. platyacantha was 173.62 g·m−2 and the total biomass of live fine roots was 135.29 g·m−2. (2) The fine root biomass, root length density, root surface area and specific root length decreased with the increase of soil depth, and their proportions in 0－30 cm layers were 67.23%, 69.53%, 69.48% and 57.20%, respectively; root length density, root surface area and specific root length decreased significantly with increasing root diameter, and 58.84%, 52.59% and 51.36% of them were in the roots that diameter was less than 1 mm, respectively. (3) Root extinction coefficient in biomass, length and surface area of C. platyacantha fine root increased with the rise of the root diameter. (4) In the first soil layer, the roots C content increased significantly with the rising root diameter, but there was no significant difference in other soil layers; the C content of the roots whose diameter was less than 2 mm in the first soil layer was significantly lower than other soil layers, while the differences of roots C content of greater than 2 mm among soil layers was insignificant. (5) The roots N content decreased with the increase of soil depth and root diameter while the C/N ratio value was opposite. These results reflected the vertical distribution of the secondary forest underground fine root system and nutrient characteristics, which would provided some basic data for revealing the subsurface ecological processes and the effects of environmental change on ecological processes in the underground in the ecosystem. [ABSTRACT FROM AUTHOR]

: [Objective] The present paper aimed to study the effects of soil reconstruction and improvement on soil bacterial community structure of debris flow waste-shoal land, providing a scientific basis for the utilization of debris flow waste-shoal land. [ Method] The soil of debris flow waste-shoal land was improved by replacing with out-soil and silting with flood, and then planted com on it. Based on 16S sequencing of soil bacteria, we analyzed the bacterial community diversity. To study the structural characteristics of soil bacterial community, we used the random forest model to predict the key OTU s. [ Result] ( i) The soil bacteria in the debris flow waste-shoal land were mainly involved by Proteobacteria, Actinobacteria, Bacteroidetes and Acitobacterium. The total relative abundance of the four bacterial species was 75%, a mong which Proteobacteria was the most abundant and the relative abundance was more than 40%. (ii) Com planting after silting with flood ( SY) and com planting after replacing with out-soil and silting with flood ( TY) had significant impact on the soil bacterial community structure of debris flow waste-shoal land. The bacteria of soil OTU abundance decreased by the order of magnitude, and the number of unique OTU s was lower than that of unmodified soil ( SS). ( iii) Compared with SS, SY increased the number of soil bacterial species, and changed the abundance of key species of soil bacteria, and reduced species diversity and uniformity. TY could significantly reduce the number of soil bacterial species, and reconfigured the soil community structure. ( iv) SY had the largest proportion of independent explanations for the total variance ( 34. 38 % ), and the direct effect of silting with flood on soil bacterial community structure was significant. ( v) The structure of soil bacterial community was closely related to 2. 68% of the OTUs. According to the importance, the top 6 OTUs belonged to Proteobacteria ( two different families), Ateobacteria, Verrucomicrobia, Planctomycetes and Candidatus_Saccharibacteria [ Conclusion] The direct effect of silting with flood on soil bacterial community structure in debris flow waste-shoal land is significant. After replacing with out-soil, silting with flood and the planting com is conducive to reconfiguring soil bacterial community structure and maintaining the stability of soil community structure. [ABSTRACT FROM AUTHOR]