title: The interactive effects of temperature and light on biological nitrogen fixation in boreal forests.
abstract: Plant productivity is predicted to increase in northern latitudes as a result of climate warming; however, this may depend on whether biological nitrogen (N)-fixation also increases. We evaluated how the variation in temperature and light affects N-fixation by two boreal feather mosses, Pleurozium schreberi and Hylocomium splendens, which are the primary source of N-fixation in most boreal environments. We measured N-fixation rates 2 and 4 wk after exposure to a factorial combination of environments of normal, intermediate and high temperature (16.3, 22.0 and 30.3°C) and light (148.0, 295.7 and 517.3 μmol m(-2) s(-1)). Our results showed that P. schreberi achieved higher N-fixation rates relative to H. splendens in response to warming treatments, but that the highest warming treatment eventually caused N-fixation to decline for both species. Light strongly interacted with warming treatments, having positive effects at low or intermediate temperatures and damaging effects at high temperatures. These results suggest that climate warming may increase N-fixation in boreal forests, but that increased shading by the forest canopy or the occurrence of extreme temperature events could limit increases. They also suggest that P. schreberi may become a larger source of N in boreal forests relative to H. splendens as climate warming progresses.
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE901-83 Umeå, Sweden.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gundale
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE901-83 Umeå, Sweden.
authors.forename: Madeleine
authors.initials: M
authors.lastname: Nilsson
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE901-83 Umeå, Sweden.
authors.forename: Sheel
authors.initials: S
authors.lastname: Bansal
authors.affiliation: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, SE901-83 Umeå, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Jäderlund
mesh_terms: D000704:Analysis of Variance; D044002:Bryophyta / Q000502:physiology* / Q000528:radiation effects*; D008027:Light; D009586:Nitrogen Fixation / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013045:Species Specificity; D013696:Temperature; D014197:Trees / Q000502:physiology* / Q000528:radiation effects*
chemical_list: D045332:Photosystem II Protein Complex