川西亚高山云杉天然林转换为人工林对土壤细菌群落及功能的影响

Effects of the conversion of subalpine spruce natural forest to plantation on soil bacterial communities and function in western Sichuan,China

川西亚高山地区天然林向人工林的转换造成了土壤生态功能的退化,而细菌群落对土壤生态功能维持和提升有重要的调节作用;然而,关于天然林向人工林转换对土壤细菌群落及功能群影响的研究目前还比较缺乏.以川西亚高山云杉天然林和人工林为研究对象,采用高通量测序和Faprotax功能预测相结合的研究方法测定土壤细菌群落组成、多样性和功能群,分析森林转换对它们的影响,阐明驱动变化的关键因子.结果表明:云杉天然林土壤细菌群落的Shannon指数显著高于云杉人工林土壤,而Simpson指数显著低于人工林.主坐标分析(PCoA)显示天然林和人工林土壤细菌群落组成存在明显差异.两个林分共同拥有81.61%的OTUs数量,属水平上相对丰度大于1%的土壤细菌群落组成基本一致,共有23个属.其中慢生根瘤菌属(Bradyrhizobium)、Vicinamibacterales和KD4-96是两个森林类型中具有显著差异的优势属.通过功能预测分析发现,云杉人工林中化能异养作用、有氧化能异养作用和固氮作用优势细菌功能群的相对丰度显著高于天然林.冗余分析(RDA)结果表明土壤pH、含水率、全氮、铵态氮、微生物生物量氮是影响土壤细菌群落组成和功能群的主要因子.综上,川西亚高山云杉天然林向人工林转换显著影响土壤细菌群落多样性和组成,并提高了与碳氮循环相关的细菌功能群的相对丰度;上述研究结果可为深入理解森林转换对土壤生态功能的影响提供科学依据.

The conversion of natural forests to plantations in the subalpine region of western Sichuan in China has resulted in the degradation of soil ecological function.Bacterial communities play an important role in regulating the maintenance and improvement of soil ecological functions.However,studies on the effects of conversion from natural forests to plantations on soil bacterial communities and functional groups are still lacking.Therefore,this study used a combination of high-throughput sequencing and Faprotax function prediction to determine the structure,diversity,and functional groups of soil bacterial communities in natural and planted subalpine spruces in western Sichuan.The effects of forest conversion were analyzed and the key factors driving these changes were clarified.The Shannon index of the bacterial community in spruce natural forest soil was significantly higher than that in spruce plantation soil whereas the Simpson’s index was significantly lower than that of the spruce plantation soil.The principal co-ordinates analysis(PCoA)showed significant differences in the soil bacterial community composition between natural forests and plantations.The two forests shared 81.61%of the operational taxonomic units(OTUs),and the composition of bacterial communities with a relative abundance greater than 1%at the genus level was consistent,with a total of 23 genera.Bradyrhizobium,Vicinamibacteria,and KD4-96 were the dominant genera with significant differences between the two forest types.Functional prediction analysis revealed that the relative abundances of the dominant bacterial functional groups involved in chemoheterotrophy,aerobic chemoheterotrophy,and nitrogen fixation in the plantations were significantly higher than those in the natural forest.Redundancy analysis showed that soil pH,water content,total nitrogen,ammonium nitrogen,and microbial biomass nitrogen led to changes in soil bacterial community composition and functional groups.In conclusion,the conversion of subalpine spruce from natural to plantation forests in western Sichuan significantly affected the diversity and composition of soil bacterial communities and promoted an increase in the relative abundance of bacterial functional groups related to the carbon and nitrogen cycles.Our results provide a scientific basis for further understanding the effects of forest conversion on the ecological functions of soil.