Paper Title
Responses of Plant Traits to 23 Years of Experimental Warming in Alpine Plant Communities

To improve our understanding of how global warming may affect competitive interactions among plants, information on the responses of plant functional traits across species to long-term warming is needed. Plant functional traits are directly linked to plant performance, and are also responsible for community assembly and community dynamics. Moreover, competitive interactions are an important component of community assembly and such interactions are mediated through functional traits. Here we report the effect of 23 years of experimental warming on plant traits across four different alpine subarctic plant communities: tussock tundra, Dryas heath, dry heath and wet meadow. Open-top chambers (OTCs) were used to passively warm the vegetation by 1.5-3 0 C. Changes in leaf width, leaf length and plant height of 22 vascular plant species were measured. Long-term warming significantly affected all plant traits. Overall, plant species were taller, with longer and wider leaves when compared with control plots, indicating an increase of biomass in warmed plots. 13 species having significant increases in at least one trait and three species having only negative responses. The response varied among species and plant community, in which species was sampled, indicating community-warming interactions. Thus, plant trait responses are both species- and community-specific. Importantly, here we show that there is likely to be great variation between plant species in their ability to maintain positive growth responses over the longer term, which might cause shifts in their relative competitive ability. Plant height and leaf traits are the most important and consistent drivers of ecosystem functioning. Particularly, these functional traits are linked to plant resource economy, biomass production and soil water retention. Hence changes in the leaf traits and plant height that we see in our study after 23 years of experimental warming are directly going to impact ecosystem services and in particularly biomass production. These findings, which are largely consistent with results in previous studies, imply that trait-based studies should be linked to community studies and ecosystem services, in order to better understand how long-term warming can change the structure of plant communities and ecosystem functioning.