Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Environ Microbiol. 2011 Oct;13(10):2778-93. doi: 10.1111/j.1462-2920.2011.02548.x. Epub 2011 Sep 1.
Elevated atmospheric CO(2) generally increases plant productivity and subsequently increases the availability of cellulose in soil to microbial decomposers. As key cellulose degraders, soil fungi are likely to be one of the most impacted and responsive microbial groups to elevated atmospheric CO(2). To investigate the impacts of ecosystem type and elevated atmospheric CO(2) on cellulolytic fungal communities, we sequenced 10,677 cbhI gene fragments encoding the catalytic subunit of cellobiohydrolase I, across five distinct terrestrial ecosystem experiments after a decade of exposure to elevated CO(2). The cbhI composition of each ecosystem was distinct, as supported by weighted Unifrac analyses (all P-values; < 0.001), with few operational taxonomic units (OTUs) being shared across ecosystems. Using a 114-member cbhI sequence database compiled from known fungi, less than 1% of the environmental sequences could be classified at the family level indicating that cellulolytic fungi in situ are likely dominated by novel fungi or known fungi that are not yet recognized as cellulose degraders. Shifts in fungal cbhI composition and richness that were correlated with elevated CO(2) exposure varied across the ecosystems. In aspen plantation and desert creosote bush soils, cbhI gene richness was significantly higher after exposure to elevated CO(2) (550 µmol mol(-1)) than under ambient CO(2) (360 µmol mol(-1) CO(2)). In contrast, while the richness was not altered, the relative abundance of dominant OTUs in desert soil crusts was significantly shifted. This suggests that responses are complex, vary across different ecosystems and, in at least one case, are OTU-specific. Collectively, our results document the complexity of cellulolytic fungal communities in multiple terrestrial ecosystems and the variability of their responses to long-term exposure to elevated atmospheric CO(2).
大气中 CO2 浓度升高通常会提高植物生产力，进而增加土壤中纤维素对微生物分解者的可利用性。作为关键的纤维素降解菌，土壤真菌可能是受大气 CO2 升高影响最大和响应最迅速的微生物类群之一。为了研究生态系统类型和大气 CO2 升高对纤维素分解真菌群落的影响，我们对五个不同陆地生态系统实验在经历了长达十年的 CO2 升高处理后，共测序了 10677 个 cbhI 基因片段，这些基因片段编码的是细胞外纤维素酶 I 的催化亚基。加权 Unifrac 分析（所有 P 值均<0.001）支持 cbhI 组成在各个生态系统中均存在差异，具有很少的操作分类单元（OTU）在生态系统之间共享。利用从已知真菌中编译的 114 个 cbhI 序列数据库，不到 1%的环境序列可以在科水平上进行分类，这表明原位纤维素分解真菌可能主要由新型真菌或尚未被认为是纤维素降解菌的已知真菌所主导。与 CO2 升高暴露相关的真菌 cbhI 组成和丰富度的变化在各个生态系统中均有所不同。在山杨林和荒漠地衣灌丛土壤中，暴露于升高的 CO2（550 µmol mol(-1)）下的 cbhI 基因丰富度明显高于在大气 CO2 下（360 µmol mol(-1) CO2）。相比之下，尽管丰富度没有改变，但荒漠土壤结皮中主要 OTU 的相对丰度发生了显著变化。这表明，响应是复杂的，在不同的生态系统中存在差异，并且在至少一种情况下是特定于 OTU 的。总的来说，我们的研究结果记录了多个陆地生态系统中纤维素分解真菌群落的复杂性及其对长期暴露于大气 CO2 升高的响应的可变性。
