Intraspecific Functional Trait Responses to Experimental Warming Vary With Precipitation and Growth Form

Aims: Rising ambient air temperatures may have adverse effects on alpine plant communities. To avoid extinction and to mitigate the demographic impacts of climate warming, migration and the ability to adapt become increasingly important. Experimental studies that simulate warming help test the extent and direction of functional adaptation. We ask: (1) To what extent does experimental warming drive intraspecific trait shifts in alpine species? (2) Do these trait responses vary across a precipitation gradient? (3) Do responses vary between forbs and graminoids?. Location: Alpine grasslands along a precipitation gradient in south-western Norway. Methods: At three alpine sites spanning 1315–3601 mm of annual precipitation, we measured 10 plant functional traits across 17 species of graminoids, perennial forbs and dwarf shrubs. We compared the traits of plants in open-top warming chambers with those under ambient temperature conditions. Effect sizes were estimated using Cohen's d and analysed with respect to precipitation regimes and growth form. Results: Plant height generally increased in response to warming across all sites for both growth forms. For other traits, warming effects were context-dependent and varied among species. At the medium precipitation site, plants showed shifts toward more conservative resource-use strategies in response to warming, characterised by increased leaf area and leaf dry matter content, along with reduced species leaf area and leaf nitrogen concentration. The enrichment in heavier nitrogen and carbon isotopes with warming is consistent with the expectation that warming selects for individuals with high water-use efficiency. Forbs generally exhibited stronger but more variable responses to warming than graminoids. Conclusion: Warming induces trait shifts in alpine species, but responses depend on local conditions and growth form. Predicting alpine community responses to climate change requires trait-based approaches and research designs that allow assessing and exploring patterns in both taxonomic and environmental context dependencies.