TY - JOUR

T1 - Extreme freeze-thaw cycles do not affect moss-associated nitrogen fixation across a temperature gradient, but affect nutrient loss from mosses

AU - Rousk, Kathrin

AU - Pedersen, Pia

AU - Priemé, Anders

AU - Michelsen, Anders

N1 - CENPERMOA[2021] Funding Information: We thank Maja H. Wahlgren for assistance with the ethylene analyses, and Karina E. Clemmensen for assistance with collection of mosses at Fiby Urskog. We thank Karina E. Clemmensen, Klaus S. Larsen and Teis N. Mikkelsen for providing climate data. Funding was provided by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 947719 to KR), by the Independent Research Fund Denmark (IRFD) Sapere Aude Grant (Grant id: 7027-00011B to KR) and the Danish National Research Foundation (Center for Permafrost, CENPERM DNRF100). Publisher Copyright: © 2021 The Authors

PY - 2021/11

Y1 - 2021/11

N2 - Moss-associated nitrogen (N2) fixation performed by epiphytic, N2-fixing bacteria (diazotrophs) contributes significantly to ecosystem N input in pristine habitats. While we have some understanding of the effects of climate warming on moss-associated N2 fixation, we lack data on effects of freeze-thaw cycles (FTCs) on diazotroph activity, although increased frequency of FTCs is predicted. We collected the widespread moss Pleurozium schreberi along a climate gradient (temperate, boreal, arctic) and exposed moss and associated diazotrophs to severe (20 °C difference, cycling between +10 and −10 °C) and mild (6 °C difference, ±3 °C) diurnal FTCs. We measured N2 fixation in mosses over 8 weeks and assessed their nutrient loss (fixed N2, total dissolved N, ammonium, phosphate) during the FTCs. We expected lower nitrogenase activity in mosses exposed to more severe FTCs and different sensitivities of N2 fixation towards FTCs along the climate gradient. However, no differences were found in N2 fixation between mild and severe FTCs, but N2 fixation in mosses from the temperate heath was less susceptible to FTCs than those from colder sites, suggesting adapted temperate diazotroph communities. Mosses lost little N, most at constant, positive temperatures, while more phosphate was lost from mosses exposed to FTCs, depending on the positioning along the climate gradient, mirroring nutrient demand and limitation. Our results show that moss-associated N2 fixation is less susceptible towards FTCs than expected but nutrient loss from moss carpets can increase following FTCs, with consequences for nutrient pools and fluxes.

AB - Moss-associated nitrogen (N2) fixation performed by epiphytic, N2-fixing bacteria (diazotrophs) contributes significantly to ecosystem N input in pristine habitats. While we have some understanding of the effects of climate warming on moss-associated N2 fixation, we lack data on effects of freeze-thaw cycles (FTCs) on diazotroph activity, although increased frequency of FTCs is predicted. We collected the widespread moss Pleurozium schreberi along a climate gradient (temperate, boreal, arctic) and exposed moss and associated diazotrophs to severe (20 °C difference, cycling between +10 and −10 °C) and mild (6 °C difference, ±3 °C) diurnal FTCs. We measured N2 fixation in mosses over 8 weeks and assessed their nutrient loss (fixed N2, total dissolved N, ammonium, phosphate) during the FTCs. We expected lower nitrogenase activity in mosses exposed to more severe FTCs and different sensitivities of N2 fixation towards FTCs along the climate gradient. However, no differences were found in N2 fixation between mild and severe FTCs, but N2 fixation in mosses from the temperate heath was less susceptible to FTCs than those from colder sites, suggesting adapted temperate diazotroph communities. Mosses lost little N, most at constant, positive temperatures, while more phosphate was lost from mosses exposed to FTCs, depending on the positioning along the climate gradient, mirroring nutrient demand and limitation. Our results show that moss-associated N2 fixation is less susceptible towards FTCs than expected but nutrient loss from moss carpets can increase following FTCs, with consequences for nutrient pools and fluxes.

KW - Acetylene reduction

KW - Climate change

KW - Cyanobacteria

KW - Diazotrophs

KW - Nutrient limitation

KW - Phosphorus

U2 - 10.1016/j.actao.2021.103796

DO - 10.1016/j.actao.2021.103796

M3 - Journal article

AN - SCOPUS:85117758327

VL - 113

JO - Acta Oecologica

JF - Acta Oecologica

SN - 1146-609X

M1 - 103796

ER -