Zhou Xue, Fornara Dario, Ikenaga Makoto, Akagi Isao, Zhang Ruifu, Jia Zhongjun
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of SciencesNanjing, China; University of Chinese Academy of SciencesBeijing, China.
Agri-Food and Biosciences Institute Belfast, Ireland.
Front Microbiol. 2016 Jul 19;7:1101. doi: 10.3389/fmicb.2016.01101. eCollection 2016.
Forest soil ecosystems are associated with large pools and fluxes of carbon (C) and nitrogen (N), which could be strongly affected by variation in rainfall events under current climate change. Understanding how dry and wet cycle events might influence the metabolic state of indigenous soil microbes is crucial for predicting forest soil responses to environmental change. We used 454 pyrosequencing and quantitative PCR to address how present (DNA-based) and potentially active (RNA-based) soil bacterial communities might response to the changes in water availability across three different forest types located in two continents (Africa and Asia) under controlled drying and rewetting cycles. Sequencing of rRNA gene and transcript indicated that Proteobacteria, Actinobacteria, and Acidobacteria were the most responsive phyla to changes in water availability. We defined the ratio of rRNA transcript to rRNA gene abundance as a key indicator of potential microbial activity and we found that this ratio was increased following soil dry-down process whereas it decreased after soil rewetting. Following rewetting Crenarchaeota-like 16S rRNA gene transcript increased in some forest soils and this was linked to increases in soil nitrate levels suggesting greater nitrification rates under higher soil water availability. Changes in the relative abundance of (1) different microbial phyla and classes, and (2) 16S and amoA genes were found to be site- and taxa-specific and might have been driven by different life-strategies. Overall, we found that, after rewetting, the structure of the present and potentially active bacterial community structure as well as the abundance of bacterial (16S), archaeal (16S) and ammonia oxidizers (amoA), all returned to pre-dry-down levels. This suggests that microbial taxa have the ability to recover from desiccation, a critical response, which will contribute to maintaining microbial biodiversity in harsh ecosystems under environmental perturbations, such as significant changes in water availability.
森林土壤生态系统与大量的碳（C）和氮（N）库及通量相关联，在当前气候变化下，降雨事件的变化可能会对其产生强烈影响。了解干湿循环事件如何影响原生土壤微生物的代谢状态对于预测森林土壤对环境变化的响应至关重要。我们使用454焦磷酸测序和定量PCR技术，来研究在受控的干燥和再湿润循环条件下，位于两大洲（非洲和亚洲）的三种不同森林类型中，现存（基于DNA）和潜在活性（基于RNA）的土壤细菌群落如何对水分有效性的变化做出反应。rRNA基因和转录本的测序表明，变形菌门、放线菌门和酸杆菌门是对水分有效性变化反应最敏感的门类。我们将rRNA转录本与rRNA基因丰度的比率定义为潜在微生物活性的关键指标，发现该比率在土壤干燥过程中增加，而在土壤再湿润后降低。再湿润后，一些森林土壤中类似奇古菌门的16S rRNA基因转录本增加，这与土壤硝酸盐水平的增加有关，表明在较高的土壤水分有效性下硝化速率更高。发现（1）不同微生物门类和纲的相对丰度变化，以及（2）16S和amoA基因的变化具有位点和分类群特异性，可能是由不同的生命策略驱动的。总体而言，我们发现，再湿润后，现存和潜在活性细菌群落结构以及细菌（16S）、古菌（16S）和氨氧化菌（amoA）的丰度均恢复到干燥前水平。这表明微生物分类群有能力从干燥中恢复，这是一种关键反应，将有助于在环境扰动（如水分有效性的显著变化）下的恶劣生态系统中维持微生物多样性。
