Effects of Warming, Nitrogen and Grazing on Plant Functional Traits Differ Between Alpine and Sub-Alpine Grasslands

Abstract

Questions: Alpine grasslands are affected by a range of global change drivers, including land-use change, climate warming and pollution. How these drivers interact and affect plant functional communities is poorly understood. We used plant functional traits to test the single and interactive effects of warming, nitrogen addition and grazing on alpine grassland communities and assessed the importance of intraspecific trait variation.

Location: Alpine and sub-alpine grasslands in western Norway.

Methods: For three years, we applied global change treatments to test the effects of warming with nitrogen addition, and warming with grazing at an alpine and sub-alpine plant community. We measured six plant functional traits related to plant size and leaf economics, including intraspecific trait variation.

Results: Our results show that warming and nitrogen addition shifted size-related traits in plant communities towards taller plants with larger leaves, and more strongly in the alpine than in the sub-alpine plant community. Warming also affected leaf economic traits, promoting faster traits in the alpine and slower traits in the sub-alpine plant community. Grazing shifted communities to faster leaves (grazing tolerant) in the sub-alpine community and slower leaves (grazing avoidance) in the alpine community. There were no interactive effects between the global change drivers. The relative contributions of species turnover and intraspecific trait variation to overall trait variation differed between origins of the two plant communities.

Conclusions: We show that these global change drivers shift alpine and sub-alpine plant communities in different directions, likely due to differences in resource availability. Our results support the need for site-specific management strategies in these systems.