藏东南林芝地区典型农业土地利用方式对土壤微生物群落特征的影响

为研究藏东南林芝地区土壤微生物群落对农业土地利用方式的响应特征及其关键影响因素,可深入认识农业土地利用对该区域生态系统稳定性的影响,并为该地区农业土地资源合理利用提供科学依据。采集藏东南林芝地区2种典型农业土地利用方式(农田及放牧草地)土壤样品,以自然森林土壤样品为对照,利用磷脂脂肪酸法(PLFA)和MiSeq高通量测序分析不同土地利用方式下土壤微生物数量、多样性和群落组成的差异性,并结合土壤理化指标探讨影响土壤微生物群落组成和结构的关键因素。结果表明:与自然森林相比,农田和放牧草地土壤中微生物PLFA总量降低了38.7%~51.8%,其中革兰氏阳性细菌、革兰氏阴性细菌、放线菌和真菌的生物量分别降低了26.1%~47.6%、40.0%~61.1%、44.1%~60.6%和5.2%~31.3%。农田种植显著降低土壤真菌的多样性,其丰富度、香农多样性相比于森林土壤分别降低了53.0%和71.4%,而细菌群落的丰富度、香农多样性则显著降低了15.7%和5.1%。农田种植显著增加土壤细菌中放线菌门(A ctinobacteria)的相对丰度,但是显著降低了浮霉菌门(Planctomycetes)、绿弯菌门(Chloroflexi)和厚壁菌门(Firmicutes)的相对丰度,放牧草地则显著促进拟杆菌门(Bacteroidetes)和蓝藻门(Cyanobacteria)的生长。农业土地利用显著提高土壤真菌群落中担子菌门伞菌纲(A garicomycetes)的优势度,其在农田和放牧草地土壤中的相对丰度分别是自然森林土壤的23倍和19倍,而子囊菌门(A scomycota)和接合菌门(Zygomycota)的相对丰度则分别降低了67.7%~89.6%和58.7%~67.4%。基于距离矩阵的冗余分析表明,土壤细菌和真菌的群落结构在3种土地利用方式下有显著差异。土壤微生物的数量、多样性和群落组成受到土壤pH值、土壤有机碳、土壤C/N等理化性质的显著影响,并且土壤真菌对环境因子改变的响应比细菌敏感。研究表明,典型农业土地利用方式导致藏东南林芝地区土壤微生物群落的数量和多样性相比于自然植被显著降低,并改变细菌和真菌的群落组成和结构,而且真菌对农业土地利用方式的响应比细菌敏感。

Impact of typical agricultural land use on the characteristics of soil microbial communities in the Nyingchi region of southeastern Tibet

Changes in the soil microbial community can have a significant impact on ecosystem functionality and stability. The Nyingchi region, which is located in the southeastern part of the Tibetan Plateau, has a long history of agricultural cultivation and land use. However, the impact of agricultural land use on soil microbial communities remains unclear. Therefore, it is necessary to investigate the effect of agricultural land use on soil microbial communities and the factors that control the variations in microbial communities. This will help to understand the influence of agricultural land use on the stability of ecosystems in southeastern Tibet and provide a scientific basis for the sustainable management of agricultural soils in this region. In the present study, soil samples were collected from two typical agricultural land use types(cropland and pasture)and native forest in the Nyingchi region of southeastern Tibet. Phospholipid fatty acids(PLFA)analysis and MiSeq pyrosequencing, in combination with analyses of soil properties, were conducted to analyze the differences in the biomass, diversity, and composition of microbial communities in soils under agricultural land use types compared with those of native forest soil and to determine the controlling factors of the variation in microbial communities. The total PLFA concentration indicated that the microbial biomass in cropland and pasture soils decreased by 38.7%~51.8% compared with that of native forest soils. The decreases in the PLFA concentrations of Gram-positive bacteria, Gram-negative bacteria, actinomycetes, and fungi under agricultural land use were 26.1%~47.6%, 40.0%~61.1%, 44.1%~60.6%, and 5.2%~31.3%, respectively. The diversity of the soil fungal community was markedly decreased in cropland soil with 53.0% and 71.4% lower richness index(Chao)and Shannon diversity index values, respectively, compared with those of native forest soil, while the decrease in the richness and Shannon diversity of the bacterial community was 15.7% and 5.1%, respectively. The relative abundance of Actinobacteria(bacterial phylum)was significantly increased in cropland soil, whereas those of Planctomycetes, Chloroflexi, and Firmicutes were reduced compared with those of pasture and forest soil. The relative abundances of Bacteroidetes and Cyanobacteria were promoted in pasture soil compared with those of the other land use types. The relative abundance of Agaricomycetes(fungal class)in cropland and pasture soils was 23 and 19 times greater than that in native forest soil, thereby suggesting the significant dominance of Agaricomycetes in the fungal community under agricultural land use. Meanwhile, the relative abundances of Ascomycota and Zygomycota(fungal phyla)in cropland and pasture soils were 67.7%~89.6% and 58.7%~67.4% lower than those of native forest soil, respectively. The distance-based redundancy analysis showed that there were significant differences in the structure of the bacterial and fungal communities among the three land use types. Changes in the microbial biomass, diversity indexes, and community composition were strongly influenced by soil properties such as pH, soil organic carbon, and the C/N ratio. In addition, the response of the soil fungal community to these changes in soil variables due to agricultural land use was more sensitive than that of the bacterial community. The results of the present study showed that typical agricultural land use in the Nyingchi region exerts a significant impact on the soil microbial community by decreasing the microbial biomass and diversity and altering the composition and structure of the soil bacterial and fungal communities. Furthermore, the soil fungal community was more sensitive to agricultural land use than the soil bacterial community. Therefore, there is a great need to emphasize the physiological and ecological understanding of soil bacterial and fungal taxa that could be sensitive to agricultural land use and the potential influence of these taxa on the functionality of the ecosystem in southeastern Tibet.