Department of Microbiology, University of Massachusetts Amherst, MA, USA.
Department of Natural Resources and the Environment, University of New Hampshire Durham, NH, USA.
Front Microbiol. 2015 Feb 13;6:104. doi: 10.3389/fmicb.2015.00104. eCollection 2015.
Soil microbes are major drivers of soil carbon cycling, yet we lack an understanding of how climate warming will affect microbial communities. Three ongoing field studies at the Harvard Forest Long-term Ecological Research (LTER) site (Petersham, MA) have warmed soils 5°C above ambient temperatures for 5, 8, and 20 years. We used this chronosequence to test the hypothesis that soil microbial communities have changed in response to chronic warming. Bacterial community composition was studied using Illumina sequencing of the 16S ribosomal RNA gene, and bacterial and fungal abundance were assessed using quantitative PCR. Only the 20-year warmed site exhibited significant change in bacterial community structure in the organic soil horizon, with no significant changes in the mineral soil. The dominant taxa, abundant at 0.1% or greater, represented 0.3% of the richness but nearly 50% of the observations (sequences). Individual members of the Actinobacteria, Alphaproteobacteria and Acidobacteria showed strong warming responses, with one Actinomycete decreasing from 4.5 to 1% relative abundance with warming. Ribosomal RNA copy number can obfuscate community profiles, but is also correlated with maximum growth rate or trophic strategy among bacteria. Ribosomal RNA copy number correction did not affect community profiles, but rRNA copy number was significantly decreased in warming plots compared to controls. Increased bacterial evenness, shifting beta diversity, decreased fungal abundance and increased abundance of bacteria with low rRNA operon copy number, including Alphaproteobacteria and Acidobacteria, together suggest that more or alternative niche space is being created over the course of long-term warming.
土壤微生物是土壤碳循环的主要驱动因素，但我们对气候变暖将如何影响微生物群落缺乏了解。哈佛森林长期生态研究（LTER）站点（马萨诸塞州彼得汉姆）正在进行的三项野外研究将土壤温度升高了 5°C，比环境温度高出 5°C、8°C 和 20 年。我们利用这个时间序列来检验这样一个假设，即土壤微生物群落已经发生了变化，以应对长期变暖。使用 Illumina 对 16S 核糖体 RNA 基因进行测序来研究细菌群落组成，使用定量 PCR 评估细菌和真菌的丰度。只有经过 20 年加热的站点在有机土壤层中表现出细菌群落结构的显著变化，而在矿物质土壤中没有显著变化。优势类群，在 0.1%或更高的丰度上丰富，代表了丰富度的 0.3%，但几乎占了 50%的观察值（序列）。放线菌门、α变形菌门和酸杆菌门的个别成员表现出强烈的变暖响应，其中一种放线菌从相对丰度的 4.5%下降到 1%随着变暖。核糖体 RNA 拷贝数可能会混淆群落谱，但也与细菌的最大生长速率或营养策略相关。核糖体 RNA 拷贝数校正并不影响群落谱，但与对照相比，加热区的 rRNA 拷贝数显著降低。细菌均匀度增加，β多样性转移，真菌丰度降低，rRNA 操纵子拷贝数低的细菌丰度增加，包括α变形菌门和酸杆菌门，这些共同表明，在长期变暖的过程中，正在创造更多或替代的生态位空间。
