University of Bayreuth, Department of Soil Ecology, Dr.-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany.
University of Bayreuth, Ecological Microbiology, Dr.-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany.
Sci Rep. 2016 Dec 15;6:39072. doi: 10.1038/srep39072.
Biological N fixation (BNF) in the rhizosphere of Podocarpaceae is currently attributed to unspecific diazotrophs with negligible impact on N acquisition. Here, we report specific and high associative BNF in dead cells of root nodules of Lepidothamnus fonkii distributed in ombrotrophic peatlands of Patagonia. BNF of nodulated roots, intact plants of L. fonkii and rhizospheric peat was assessed by N and acetylene reduction. Diazotrophs were identified by electron microscopy, analysis of nitrogenase encoding genes (nifH) and transcripts, and 16S rRNA. Nitrogenase encoding nifH transcripts from root nodules point to Beijerinckiaceae (Rhizobiales), known as free-living diazotrophs. Electron microscopy and 16S rRNA analysis likewise identified active Beijerinckiaceae in outer dead cells of root nodules. NifH transcripts from the rhizopshere peat revealed diverse active diazotrophs including Beijerinckiaceae. Both methods revealed high activity of nitrogenase rates in cut roots of L. fonkii (2.5 μmol N g d.w. d based on N assay; 2.4 μmol CH g d.w. d based on acetylene reduction assay). The data suggest that (i) nodules recruit diazotrophic Beijerinckiaceae from peat, (ii) dead nodule cells provide an exclusive habitat for Beijerinckiaceae, and (iii) BNF in L. fonkii is one potent pathway to overcome N deficiency in ombrotrophic peatlands of Patagonia.
目前，认为在罗汉松科的根际中进行生物固氮（BNF）的是无特定性的固氮生物，它们对氮的获取几乎没有影响。在这里，我们报告了在巴塔哥尼亚的寡营养泥炭地中分布的鳞皮冷杉根瘤死细胞中具有特异性和高关联性的 BNF。通过氮和乙炔还原来评估根瘤固氮、鳞皮冷杉完整植株和根际泥炭的 BNF。通过电子显微镜、氮酶编码基因（nifH）和转录物分析以及 16S rRNA 鉴定固氮生物。根瘤中氮酶编码 nifH 转录物指向贝日阿克氏菌科（根瘤菌目），它们被认为是自由生活的固氮生物。电子显微镜和 16S rRNA 分析同样在根瘤的外死细胞中鉴定出了活跃的贝日阿克氏菌科。根际泥炭中的 nifH 转录物揭示了包括贝日阿克氏菌科在内的多种活跃的固氮生物。这两种方法都揭示了鳞皮冷杉切割根中氮酶的高活性（基于氮测定的 2.5μmol N g d.w. d；基于乙炔还原测定的 2.4μmol CH g d.w. d）。这些数据表明：（i）根瘤从泥炭中招募了固氮贝日阿克氏菌科；（ii）死的根瘤细胞为贝日阿克氏菌科提供了一个独特的栖息地；（iii）鳞皮冷杉中的 BNF 是克服巴塔哥尼亚寡营养泥炭地中氮缺乏的一个有效途径。
