Biological Nitrogen Fixation and Nitrogen Accumulation in Peatlands

Abstract

Peatlands cover about 3% of the Earth’s surface and are regarded as a vital carbon (C) pool and sink. The formation of peatland is supported by continuously supplied nitrogen (N) but the sources of this N remain unclear. Here, we first review N stocks and the rate they accumulate in peatlands, then we present the sources of N, especially through biological nitrogen fixation (BNF). We found that global peatlands store 5.9–25.9 Gt N. In the past millennia, northern peatlands have a lower N accumulated rate than tropical undisturbed peatlands. BNF rate is approximately 1.9 ± 2.7 g m−2 yr−1 in northern peatlands, higher than the rate of N deposition, 0.5 ± 0.4 g m−2 yr−1. For tropical peatlands, BNF observation has hardly been reported yet and needs further investigation. This review provides a broad picture of peatland N cycling and suggests that there are large uncertainties, due to limited observations of BNF and N fluxes by inflow and outflow runoff. Therefore, we call for more efforts contributing to field observations and modelling of the N budget in peatlands.Systematic Review Registration: (website), identifier (registration number).

Impact of changing climate on bryophyte contributions to terrestrial water, carbon, and nitrogen cycles

“…Unfortunately, there currently are few reports of BNF rates in tropical biomes but higher BNF rates have been associated with dense epiphyllic bryophyte cover and biomass (Bentley, 1987). In particular, Yin et al (2022) identify tropical peatlands as an important knowledge gap, since their high N accumulation rates suggest that their associated BNF could be even higher than in their northern counterparts. In terms of relative contribution to N requirements for primary productivity in various ecosystems, bryophyte-associated BNF typically contributes 2-10% of annual requirements in Alaskan coniferous forests (Jean et al, 2018), but only c. 0.1-2.5% in temperate grasslands (Calabria et al, 2020).…”

Discovery of Eremiobacterota withnifHhomologs in tundra soil

“…The conversion of atmospheric N2 to ammonia by microbial diazotrophs represents the largest external source of nitrogen in tundra soils [1][2][3]. Tundra N2 fixation rates are generally low but are predicted to increase with the rise in atmospheric temperatures and precipitation levels associated with anthropogenic climate change [2,4].…”

Climate‐driven spatial and temporal patterns in peatland pool biogeochemistry

“…A large number of small water bodies (often <0.001 km 2 ) consist of pools developing in peatlands, especially in the mid‐ and high latitudes. Peatlands are globally important ecosystems, covering nearly 5 million km 2 (UNEP, 2022) and storing >600 Pg C (Yu et al, 2010) and 5–25 Pg N (Yin et al, 2022). However, while they are historically relatively stable ecosystems (Morris et al, 2015), they face challenges related to climate and land‐use changes that could modify their current structural and functional state (Juutinen et al, 2018) and that of their components, such as streams and pools.…”

“…A large number of small water bodies (often <0.001 km 2 ) consist of pools developing in peatlands, especially in the mid-and high latitudes. Peatlands are globally important ecosystems, covering nearly 5 million km 2 (UNEP, 2022) and storing >600 Pg C (Yu et al, 2010) and 5-25 Pg N (Yin et al, 2022).…”