温带荒漠土壤细菌物种的分布格局及休眠细菌对群落的影响

Bacteria are a large group of important microbial resources. Its rich biodiversity is essential for the maintenance of ecosystem functions in temperate desert, like plants and animals, microbe communities can take a bet-hedging strategy to respond environmental perturbations, and formed "seed bank". To illustrate the role of bacterial dormancy, which is essential to reveal the ecological role of bacterial communities, and uncover the response basis of bacteria flora to climate changes, we will make comprehensive use of community phylogeny, genetic structure of typical population and ecological analysis. The project will unravel the community diversity of soil bacteria through comparative analyses based on 16S rRNA (active bacteria) and 16S rRNA gene (all bacterial flora also containing dormant bacteria). We will characterize the bacterial dormancy and their lineages; as well as the ecological distribution of bacterial community in different seasons in the Gurbantunggut Desert of north-western China. Additionally, to explore lineages' niche breadth, we will apply population genetics for representative species after their isolation and purification from the soil samples at suitable conditions. Finally, based on the collected data of community compositions, environmental factors and the genetic diversity annotations of representative species, we will unravel the distribution pattern of bacterial species in temperate desert and their ecological characteristics. The results will provide a comprehensive view of bacteria diversity in the area, and will facilitate the exploitation of desert bacteria resourcesand their biological feedback on climate changes.

细菌是一大类重要的微生物资源，其生物多样性丰富，对维持荒漠生态系统的功能不可或缺；同高等生物，微生物存在“两面下注”(bet-hedging)的繁殖策略，采取休眠应对环境的多种变化，形成微生物群落的“种子库”。阐明休眠细菌对温带荒漠土壤细菌群落谱系的影响，对明确细菌群落响应气候的变化十分关键。本项目将综合运用群体谱系、种群遗传结构和生态学方法，解析温带荒漠土壤细菌的群落结构。通过对比分析基于16S rRNA（活跃细菌）与16S rRNA基因（包含休眠细菌的全部细菌菌群）的群落多样性，认识休眠细菌对群落分布的影响；并阐明荒漠土壤细菌沿季节演替的物种分布格局；开展分离培养，对细菌群落组成的代表物种/种群进行种群遗传多样性分析，进一步判断群体物种组成的生态适应与生态位宽度，揭示荒漠土壤细菌物种的组成和生态分布格局；为温带荒漠微生物资源开发及响应气候变化提供科学依据。

温带荒漠是全球气候变化最为敏感的区域系统。生物土壤结皮（生物结皮）是中亚荒漠区最重要的地表覆盖类型之一，生物结皮微生物群落多样性对维持荒漠结皮生态系统的生态功能不可或缺，如调控荒漠土壤呼吸、碳/氮循环、水文以及生物过程等，发育良好的生物结皮也是荒漠植被形成的先决条件。气候改变进一步加剧陆地生态系统的水分及养分等限制，生态系统脆弱、营养贫乏的荒漠系统尤其相关，阐明生物结皮微生物群落多样性响应气候变化及干扰特征对明确生物结皮稳定和生态功能十分关键。本项目中，我们分析生物结皮细菌群落响应积雪变化、干扰对结皮氨氧化菌群差异分布以及长期施氮对结皮微生物群落的影响。基于DNA水平的高通量测序分析发现，雪盖初期古尔班通古特沙漠细菌群落分布符合随积雪增加-细菌群落多样性增加的特征；伴随冻融循环强烈的水热变化，融雪期构成荒漠土壤细菌群落结构显著变化的分界点；冬季与春季结皮土壤及下层土壤细菌群落网络区别响应积雪变化，进一步表明生物结皮细菌群落可用于表征荒漠气候变化的积雪生态效应。荒漠氮循环与全球气候变化间的关系密切而又复杂。氨氧化菌群丰度分析表明，氨氧化古菌（ammonia-oxidizing archaea, AOA）是古尔班通古特沙漠土壤优势氨氧化菌，生物结皮覆盖显著增加荒漠土壤硝化作用潜力，并通过耦合环境因子促使AOA和氨氧化细菌（ammonia-oxidizing bacteria, AOB）按照氨底物利用效率差异分布，为我们进一步认识生物结皮氮素转化作用提供研究依据。干旱区氮素限制及脉冲输入氮的特征使得氮沉降对生物结皮的生态学效应比其他生态系统更复杂，我们分析8年长期施氮对生物结皮细菌、真菌及固氮菌群的影响发现，长期施加氮素促使生物结皮微生物群落于N1.5添加阈值发生显著变化并同时一定程度上保持生物结皮结构和功能上的再平衡。随着干旱区的进一步扩大，更深入地了解气候变化对生物结皮微生物群落的影响，为后续有效评估荒漠生物结皮的生态分布格局提供科学依据。