N2-fixation by methanotrophs sustains carbon and nitrogen accumulation in pristine peatlands

作者：Melanie A. Vile, R. Kelman Wieder, Tatjana Živković, Kimberli D. Scott, Dale H. Vitt, Jeremy A. Hartsock, Christine L. Iosue, James C. Quinn, Meaghan Petix, Hope Fillingim, Jacqueline M.A. Popma, Katherine A. Dynarski, Todd R. Jackman, Cara M. Albright, Dennis D. Wykoff · 发表于：Biogeochemistry · 年份：2014 · DOI：10.1007/s10533-014-0019-6 · 被引用次数：162 · 研究领域：Peatlands and Wetlands Ecology、Coastal wetland ecosystem dynamics、Methane Hydrates and Related Phenomena

Symbiotic relationships between N 2 -fixing prokaryotes and their autotrophic hosts are essential in nitrogen (N)-limited ecosystems, yet the importance of this association in pristine boreal peatlands, which store 25 % of the world’s soil (C), has been overlooked. External inputs of N to bogs are predominantly atmospheric, and given that regions of boreal Canada anchor some of the lowest rates found globally (~1 kg N ha −1 year −1 ), biomass production is thought to be limited primarily by N. Despite historically low N deposition, we show that boreal bogs have accumulated approximately 12–25 times more N than can be explained by atmospheric inputs. Here we demonstrate high rates of biological N 2 -fixation in prokaryotes associated with Sphagnum mosses that can fully account for the missing input of N needed to sustain high rates of C sequestration. Additionally, N amendment experiments in the field did not increase Sphagnum production, indicating that mosses are not limited by N. Lastly, by examining the composition and abundance of N 2 -fixing prokaryotes by quantifying gene expression of 16S rRNA and nitrogenase-encoding nifH , we show that rates of N 2 -fixation are driven by the substantial contribution from methanotrophs, and not from cyanobacteria. We conclude biological N 2 -fixation drives high sequestration of C in pristine peatlands, and may play an important role in moderating fluxes of methane, one of the most important greenhouse gases produced in peatlands. Un...