外源氮素调控C/N比对杉木林凋落叶细菌群落结构的影响

为探究不同C/N比对杉木凋落叶分解特性的影响，通过添加外源氮，采用分解袋法，分析林下植被保留和林下植被去除2种林分中不同C/N比值的杉木凋落叶分解300 d时细菌群落结构差异。研究显示：一定范围内，初始C/N比降低有利于杉木凋落叶分解和细菌群落多样性提升，过低的C/N比则具有抑制作用；相比于林下植被去除，林下植被保留管理措施更有利于杉木凋落叶的分解，且细菌群落多样性更高，但当初始C/N比值为20.3时，杉木凋落叶分解所受的抑制作用更为明显；在门水平上，变形菌门、放线菌门和浮霉菌门为杉木凋落叶中主要优势种群；在属水平上，慢生根瘤菌属、嗜酸栖热菌属和Singulisphaera属在杉木凋落叶中相对丰度较高；不同处理间的杉木凋落叶细菌群落结构具有显著差异，变形菌门、放线菌门和酸杆菌门等细菌门中的多类细菌相对丰度差异显著；在门分类水平上，杉木凋落叶C/N比值与主要细菌种群相对丰度的相关性最高，C/P比值与杉木凋落叶细菌群落结构变异的相关性最高；在属水平上，杉木凋落叶全碳含量、C/N比值和全钾含量与主要细菌种群相对丰度的相关性最高，全钾含量与杉木凋落叶细菌群落结构变异的相关性最高。结果表明初始C/N比的降低改变了杉木凋落叶细菌群落结构，进而作用于杉木凋落叶的分解。

Effects of C/N ratio under the control of exogenous nitrogen on the bacterial community structure in litters of Cunninghamia lanceolata plantation under different undergrowth vegetation management measures

To study the effects of different C/N ratios on the decomposition characteristic of Chinese fir (Cunninghamia lanceolata, CL) litters, in this study, the CL litters with different C/N ratios by adding exogenous nitrogen were placed in the CL plantation with two management measures including undergrowth vegetation preservation and undergrowth vegetation removal by decomposition bag method, and its bacterial community structure was determined at 300 days. The results are as follows: within a certain range, the reduction of initial C/N ratio was beneficial to the decomposition and the improvement of bacterial community diversity of CL litters, while the excessively low initial C/N ratio had an inhibitory effect. Compared with undergrowth vegetation removal, the undergrowth vegetation preservation was more beneficial to the decomposition and the improvement of bacterial community diversity of CL litters, but the inhibition effect of the initial C/N ratio of 20.3 on the decomposition of CL litters was more obvious in the undergrowth vegetation preservation plantation. At the level of phylum, Proteobacteria, Actinomycetes and Planctomycetes were the main dominant species in CL litters; On the genus level, the relative abundance of Bradyrhizobium, Acidothermus and Singulisphaera were high in the CL litters. The bacterial community structure among CL litters with different treatments, as well as the relative abundance of various bacteria belonging to Proteobacteria, Actinomycetes and Acidobacteria and so on, were significantly different. At the level of phylum classification, the correlation between the C/N ratio of CL litters and the relative abundance of major bacterial populations was the highest, and the correlation between the C/P ratio and the structural variation of bacterial communities was the highest; At the level of genus classification, the correlation between total carbon content, C/N ratio and total potassium content of CL litters and relative abundance of major bacterial populations was the highest, and the correlation between total potassium content and the structural variation of bacterial communities was the highest. The reduction of the initial C/N ratio changed the bacterial community structure of CL litters, thus affecting the decomposition of CL litters.