title: Direct and interaction-mediated effects of environmental changes on peatland bryophytes.
abstract: Ecosystem processes of northern peatlands are largely governed by the vitality and species composition in the bryophyte layer, and may be affected by global warming and eutrophication. In a factorial experiment in northeast China, we tested the effects of raised levels of nitrogen (0, 1 and 2 g m(-2) year(-1)), phosphorus (0, 0.1 and 0.2 g m(-2) year(-1)) and temperature (ambient and +3°C) on Polytrichum strictum, Sphagnum magellanicum and S. palustre, to see if the effects could be altered by inter-specific interactions. In all species, growth declined with nitrogen addition and increased with phosphorus addition, but only P. strictum responded to raised temperature with increased production of side-shoots (branching). In Sphagnum, growth and branching changed in the same direction, but in Polytrichum, the two responses were uncoupled: with nitrogen addition there was a decrease in growth (smaller than in Sphagnum) but an increase in branching; with phosphorus addition growth increased but branching was unaffected. There were no two-way interactions among the P, N and T treatments. With increasing temperature, our results indicate that S. palustre should decrease relative to P. strictum (Polytrichum increased its branching and had a negative neighbor effect on S. palustre). With a slight increase in phosphorus availability, the increase in length growth and production of side-shoots in P. strictum and S. magellanicum may give them a competitive superiority over S. palustre. The negative response in Sphagnum to nitrogen could favor the expansion of vascular plants, but P. strictum may endure thanks to its increased branching.
authors.affiliation: State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation Restoration, Institute for Peat and Mire Research, Northeast Normal University, Renmin, Changchun, China.
authors.forename: Zhao-Jun
authors.initials: ZJ
authors.lastname: Bu
authors.forename: Håkan
authors.initials: H
authors.lastname: Rydin
authors.forename: Xu
authors.initials: X
authors.lastname: Chen
mesh_terms: D044002:Bryophyta / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D017753:Ecosystem; D009584:Nitrogen / Q000032:analysis* / Q000378:metabolism; D010758:Phosphorus / Q000032:analysis* / Q000378:metabolism; D011157:Population Dynamics; D013045:Species Specificity; D013696:Temperature
chemical_list: D010758:Phosphorus; D009584:Nitrogen