Climate change, snow cover and microbial diversity in mountain soils: critical processes during snowmelt

在高山地区，土壤微生物多样性和活性强烈依赖于积雪形成的年度模式。它位于冬季隔热积雪的下面，是微生物生物量最高的地方。在融雪处，有一种巨大的、仍未被很好理解的快速更替：冬季的细菌和真菌群落完全消失，取而代之的是春季的群落。全球变暖正在影响山脉，因为它增加了年平均气温，减少了冬季积雪，提前了融雪时间，增加了冻结和融化周期的频率。了解土壤微生物群如何受到气候变暖的影响，进而影响它，例如通过释放更多的温室气体，对于建立可预测的情景至关重要。我们计划调查融雪前、融雪中和融雪后土壤微生物生物多样性(首次包括原生生物)及其功能，融雪期间微生物周转的方式，以及变暖如何影响土壤微生物多样性。我们的研究将在阿尔卑斯山(瑞士达沃斯)的三座山上进行，分三个不同的海拔和三个季节进行，收集了200多个土壤样本。将记录植被、相关土壤和气候参数。此外，我们将通过实验性地修改积雪覆盖来模拟气候变暖的影响--压缩和移除积雪以模拟六个地点的早期融化。我们将使用高通量的RNA测序来同时获得关于土壤群落的组成和功能的信息。因为我们正在寻找短期的时间转移，所以我们将提取RNA以仅针对活细胞。简而言之，核糖体RNA将被用来确定细菌、真菌和原生生物群落及其相互作用；信使RNA将表征细菌和真菌的功能图谱和解冻前、解冻期间和解冻后的活跃代谢途径，以及实验性处理如何影响这些动态。我们的研究将有助于从根本上了解山区春季土壤微生物动态，这些微生物在融化时土壤有机质矿化以及气候变暖导致温室气体排放的生物地球化学循环中起重要作用。我们的德国-瑞士合作项目汇集了多种资质(申请者：原生生物学、环境聚合酶链式反应、生物信息学；T.URICH：变态翻译学、土壤中的细菌功能；C.Rixen：雪盖对土壤和植被的影响、采样地点的知识；M.Bonkowski：生态学、植物-微生物相互作用、土壤食物网)，将确保项目的顺利完成。因此，我们的项目将对了解高山和亚高山生态系统的功能做出重大贡献。

In alpine zones, soil microbial diversity and activity are strongly dependent on the annual patterns of snowpack formation. It is under the insulating winter snowpack where the highest microbial biomass is found. At snowmelt, there is a drastic and still not well understood rapid turnover: the winter bacterial and fungal communities entirely disappear and are replaced by spring communities. Global warming is affecting the mountain ranges by increasing the annual mean temperatures, reducing the winter snow cover, advancing the time of snowmelt and increasing the frequency of freeze-and-thaw cycles. Understanding how the soil microbiome is affected by warming and in turn affects it, e.g. by releasing more greenhouse gas, is essential for establishing predictive scenarios. We plan to investigate the soil microbial biodiversity (including, for the first time, protists) and its functions before, during and after snowmelt, the modalities of the microbial turnover during snowmelt and how it is affected by warming. Our study will be carried out on three mountains in the Alps (Davos, Switzerland), at three different altitudes and in three seasons, with a collection of more than 200 soil samples. Vegetation, relevant soil and climate parameters will be recorded. In addition, we will mimic the effects of climate warming by experimentally modifying the snow cover - compacting and removing to simulate earlier melt at six sites. We will use high-throughput sequencing of RNAs to simultaneously obtain information on both composition and function of the soil communities. Because we are looking for short-term temporal shifts, we will extract RNA to target only living cells. Briefly, the ribosomal RNAs will be used to identify the bacterial, fungal and protistan communities and their interactions; messenger RNAs will characterize bacterial and fungal functional profiles and metabolic pathways active before, during and after thaw and how the experimental treatments affect these dynamics. Our study will contribute to the fundamental understanding of spring soil microbial dynamics in the mountains responsible of soil organic matter mineralization at thaw and the biogeochemical cycles contributing to greenhouse gas emissions as a result of climate warming. The multiple qualifications assembled in our German-Swiss collaborative project (applicant: protistology, environmental PCR, bioinformatics; T. Urich: metatranscriptomics, bacterial functions in soils; C. Rixen: effects of snow cover on soil and vegetation, knowledge of the sampling sites; M. Bonkowski: ecology, plant-microbe interactions, soil food webs) will ensure a successful completion of the project. Our project will thus make a significant contribution to understanding the functioning of alpine and subalpine ecosystems.