长期人为干扰对桂西北喀斯特草地土壤微生物多样性及群落结构的影响

人为干扰是喀斯特草地正向演替的主要障碍因素, 从土壤微生物角度探讨草地对干扰的响应可为喀斯特生态恢复与科学利用提供依据。该研究依托中国科学院环江喀斯特生态系统观测站长期干扰监测样地, 通过高通量测序测定3个干扰模式(火烧、刈割、刈割除根)和1个对照(封育)处理的土壤细菌、真菌α多样性和群落结构, 并分析它们与环境因子(坡位、土壤理化性质)的关系, 揭示人为干扰对桂西北喀斯特草地土壤微生物的影响及机制。结果显示: 1)对于α多样性, 在中坡和下坡, 火烧均显著降低了真菌Chao1指数, 刈割均显著降低了细菌的香农指数和谱系多样性指数; 刈割除根在中、下坡分别显著降低了真菌Chao1指数和细菌香农指数。2)对于群落结构, 火烧、刈割和刈割除根在中、下坡均显著降低了酸杆菌门细菌相对丰度, 火烧在下坡使子囊菌门真菌相对丰度从74.49%显著降低至34.72%。3)冗余分析显示, 微生物生物量碳含量解释细菌和真菌α多样性变化的29.8%和26.8%以及细菌群落结构变化的31.7%; 细根生物量解释细菌α多样性和真菌群落结构变化的13.9%和10.3%。可见, 长期人为干扰对土壤微生物α多样性产生负面影响, 并显著改变微生物群落结构, 影响程度因干扰方式、微生物种类不同而异, 且受坡位调控。土壤微生物生物量碳含量和细根生物量的减少是人为干扰影响土壤微生物多样性和群落结构的重要因素。α多样性及子囊菌的减少将不利于土壤生态系统稳定性的维持, 酸杆菌的减少将不利于土壤有机质降解和铁循环。因此, 长期火烧、刈割等人为干扰将导致喀斯特草地生态系统功能发生退化。

Effects of long-term human disturbances on soil microbial diversity and community structure in a karst grassland ecosystem of northwestern Guangxi,China

Aims Human disturbance is one of the main obstacles to the forward succession of karst grassland, exploring the response of grassland to disturbance in terms of soil microorganism can provide the basis for the restoration and rational utilization of karst land. Our objective was to study the effects of different human disturbances on soil microorganisms and the underlying mechanisms in a karst grassland ecosystem of northwestern Guangxi, China.Methods Three patterns of disturbances (burning, mowing, and mowing plus root removal) and one control treatment (enclosure) were conducted at the long-term monitoring plots in the Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences. We analyzed the changes of soil microbial diversity and community structure by high-throughput sequencing, and determined their relationships with environmental factors (slope position, soil physicochemical properties).Important findings 1) For α diversity, at both middle and lower slope positions, the burning treatment significantly reduced the fungal Chao1 index, while the mowing treatment significantly reduced the bacterial Shannon index and Pedigree diversity index. However, the mowing plus root removal treatment significantly reduced the fungal Chao1 index and the bacterial Shannon index, respectively, at middle and lower slope positions. 2) For microbial community structure, burning, mowing and mowing plus root removal treatments significantly reduced the relative abundance of Acidobacteria at both middle and lower slope positions, while the fire treatment significantly reduced the relative abundance of Ascomycota from 74.49% to 34.72% at the lower slope position. 3) Redundancy analysis showed that soil microbial biomass carbon explained 29.8% and 26.8% of the changes of bacterial and fungal α diversity, respectively, and 31.7% of the changes of bacterial community structure. Root biomass explained 13.9% and 10.3% of the changes of bacterial α diversity and fungal community structure, respectively. In conclusion, the three studied human disturbances have significantly negative influence on soil microbial α diversity as well as having a significant change in and changed community structure, and the degree of influence varied among the pattern of disturbances and the type of microorganisms. Moreover, the effects were also regulated by slope position. Long-term human disturbances mainly affected the diversity and structure of soil microbial communities by changing soil microbial biomass carbon and root biomass. The decreases of α diversity and Ascomycota will not be conducive to the maintenance of soil ecosystem stability, and the decrease of Acidobacteria will not facilitate to soil organic matter degradation and iron cycling. Therefore, the long-term human disturbances such as burning and mowing will induce the functional degradation of grassland ecosystem.