Ambient and experimental warming effects on an alpine bryophyte community

Abstract

Alpine and arctic bryophytes have been found to respond negatively to climate change, but since they are often analysed as one functional group, there is limited knowledge on species-specific responses. In this study, we examine how nearly two decades of experimental warming by open top chambers (OTC) and ambient warming have affected the bryophyte community structure in an alpine Dryas octopetala heath in Finse, southwest Norway. In contrast to what we expected, we found that bryophyte abundance, species richness and evenness increased over time in the control plots, indicating a positive response to ambient warming. However, the increase in bryophyte abundance and cover was suppressed in experimentally warmed plots compared to control plots. Bryophyte community composition changed in a similar direction in response to both ambient and experimental warming. Acrocarpous mosses were not affected stronger by warming than pleurocarpous mosses, but individual species and taxa showed contrasting responses. Our study highlights the importance of studying bryophyte responses to environmental change, as well as combining long-term observations with experimental warming.

Bryophyte species differ widely in their growth and N2-fixation responses to temperature

“…Feather mosses dry out relatively easily (Elumeeva et al 2011), yet their positive responses to temperature suggest that they can be active even at low moisture content, as implied by decreased δ 13 C at high temperatures. Positive temperature response agrees with field observations of increasing growth and cover of feather mosses with warming (Callaghan et al 1997;Lang et al 2012;Zuijlen et al 2021). Interestingly, H. splendens grew well even at 3 • C, which is in line with its Arctic-boreal provenance compared to boreotemperate Pleurozium schreberi (Busby et al 1978;Lang et al 2012).…”

“…We found large differences and nonlinearity of temperature responses in growth and N dynamics across the 10 bryophyte species, which correspond with large species differences in warming responses in field studies (Lang et al 2012;Alatalo et al 2020;Zuijlen et al 2021). Warming particularly increased the growth of Sphagnum species, but their higher demand for N was likely not fully met by the increased N 2 -fixation.…”

“…Elevated temperatures enhance microbial decomposition and increase nutrient availability in usually nutrient-poor soils (Voigt et al 2017). Increased temperatures and nutrient availability generally decrease bryophyte diversity and abundance, as bryophytes are outcompeted by vascular plants, but responses are mixed (Wijk et al 2004;Elmendorf et al 2012;Alatalo et al 2020;Zuijlen et al 2021). Bryophytes play im-portant roles in tundra ecosystems for primary production (Turetsky et al 2012) and nutrient cycling (Longton 1997).…”

“…Similarly, at a specific location, species with a more southern provenance might respond positively to temperature increases while those typical to higher latitudes might not benefit from higher temperatures (Vandvik et al 2020). For these reasons, responses of organisms, including bryophytes, to climate change often seem complex and context dependent (Zuijlen et al 2021). Understanding how tundra bryophytes respond across a spectrum of temperatures, and how these responses vary between species, could help unravel the fate of bryophytes in a rapidly warming Arctic.…”

Three decades of environmental change studies at alpine Finse, Norway: climate trends and responses across ecological scales

“…In addition, total species cover and richness did not respond to 16 years of experimental warming, although lichen richness was lower and forb richness higher in experimentally warmed compared to control plots (Hasvik, 2018). Bryophytes responded more strongly to experimental warming than vascular plants and lichens (Van Zuijlen et al, 2022a, Van Zuijlen et al, 2022b. Specifically, bryophyte species abundance increased over time under ambient warming, but not in experimentally warmed plots.…”