Nelson Michaeline B, Martiny Adam C, Martiny Jennifer B H
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697;
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697; Department of Earth System Science, University of California, Irvine, CA 92697.
Proc Natl Acad Sci U S A. 2016 Jul 19;113(29):8033-40. doi: 10.1073/pnas.1601070113.
Microorganisms drive much of the Earth's nitrogen (N) cycle, but we still lack a global overview of the abundance and composition of the microorganisms carrying out soil N processes. To address this gap, we characterized the biogeography of microbial N traits, defined as eight N-cycling pathways, using publically available soil metagenomes. The relative frequency of N pathways varied consistently across soils, such that the frequencies of the individual N pathways were positively correlated across the soil samples. Habitat type, soil carbon, and soil N largely explained the total N pathway frequency in a sample. In contrast, we could not identify major drivers of the taxonomic composition of the N functional groups. Further, the dominant genera encoding a pathway were generally similar among habitat types. The soil samples also revealed an unexpectedly high frequency of bacteria carrying the pathways required for dissimilatory nitrate reduction to ammonium, a little-studied N process in soil. Finally, phylogenetic analysis showed that some microbial groups seem to be N-cycling specialists or generalists. For instance, taxa within the Deltaproteobacteria encoded all eight N pathways, whereas those within the Cyanobacteria primarily encoded three pathways. Overall, this trait-based approach provides a baseline for investigating the relationship between microbial diversity and N cycling across global soils.
微生物驱动着地球上大部分的氮循环,但我们仍缺乏对参与土壤氮转化过程的微生物的丰度和组成的全球概述。为了填补这一空白,我们利用公开可用的土壤宏基因组,对微生物氮特性的生物地理学进行了表征,将其定义为八种氮循环途径。氮途径的相对频率在不同土壤中表现出一致的变化,以至于各个氮途径的频率在土壤样本中呈正相关。生境类型、土壤碳和土壤氮在很大程度上解释了样本中的总氮途径频率。相比之下,我们无法确定氮功能类群分类组成的主要驱动因素。此外,编码某一途径的优势属在不同生境类型中通常相似。土壤样本还显示,携带异化硝酸盐还原为铵所需途径的细菌频率出乎意料地高,这是一个在土壤中研究较少的氮过程。最后,系统发育分析表明,一些微生物类群似乎是氮循环专家或通才。例如,δ-变形菌门中的分类单元编码了所有八种氮途径,而蓝细菌中的分类单元主要编码三种途径。总体而言,这种基于特性的方法为研究全球土壤中微生物多样性与氮循环之间的关系提供了一个基线。