Growth responses of Polytrichum commune and Hylocomium splendens to simulated environmental change in the sub‐arctic

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Abstract
Summary: Total moss cover and the growth responses of the two dominant bryophytes within a sub‐arctic heath ecosystem,Polytrichum communeHedw, andHylocomium splendens(Hedw.) Br. Eur., were investigated in response to simulated environmental change. Temperature, water supply and nutrients (NPK fertilizer) were increased in a factorial field study in Swedish Lapland. After 3 yr of treatment, total moss caver on fertilized plots was found to be less than 50% of that on unfertilized plots.H. splendensmade a smaller contribution to total cover, and also had fewer shoots on the fertilizer treated plots. The relative contribution ofP. communeto the bryophyte community was greater on the fertilized plots, although total shoot numbers ofP. communewere not greater. There was, however, a larger number of dead shoots ofP. communeon the fertilized plots. Total moss cover, relative contribution to moss cover by P.communeandH. splendens, and the numbers of shoots of these two species, were unresponsive to both the temperature and water treatments. The growth of the current year's segment ofH. splendenswas retarded by both the fertilizer and temperature treatments. Furthermore, the dry weight of the physiologically active shoot was found to be significantly altered by all three treatments. The current year's growth ofP. communeshowed increases in d. wt and morphological parameters in response to the fertilizer treatment. There were also interactive effects of both the fertilizer and temperature treatments with the water treatment on the current year's stem length increment.