Simulated global change: contrasting short and medium term growth and reproductive responses of a common alpine/Arctic cushion plant to experimental warming and nutrient enhancement

Abstract

Cushion plants are important components of alpine and Arctic plant communities around the world. They fulfill important roles as facilitators, nurse plants and foundation species across trophic levels for vascular plants, arthropods and soil microorganisms, the importance of these functions increasing with the relative severity of the environment. Here we report results from one of the few experimental studies simulating global change impacts on cushion plants; a factorial experiment with warming and nutrient enhancement that was applied to an alpine population of the common nurse plant, Silene acaulis, in sub-arctic Sweden. Experimental perturbations had significant short-term impacts on both stem elongation and leaf length. S. acaulis responded quickly by increasing stem elongation and (to a lesser extent) leaf length in the warming, nutrient, and the combined warming and nutrient enhancements. Cover and biomass also initially increased in response to the perturbations. However, after the initial positive short-term responses, S. acaulis cover declined in the manipulations, with the nutrient and combined warming and nutrient treatments having largest negative impact. No clear patterns were found for fruit production. Our results show that S. acaulis living in harsh environments has potential to react quickly when experiencing years with favorable conditions, and is more responsive to nutrient enhancement than to warming in terms of vegetative growth. While these conditions have an initial positive impact, populations experiencing longer-term increased nutrient levels will likely be negatively affected.

Keywords: Alpine; Biomass; Climate change; Cover; Fruit production; Meadow; Silene acaulis; Tundra.

Figure 1

S. acaulis stem elongation after three years of simulated global change. Response of S. acaulis plants by treatment (control, temperature enhancement, nutrient enhancement and combined temperature and nutrient enhancement) after three years of simulated global change. Error bars represent one standard error and letters denote groupings from posthoc testing, with different letters indicating significant differences (p < 0.05).

Figure 2

Response to simulated global change in S. acaulis leaf size. Leaf width (A) and length (B) of S. acaulis plants by treatment and year. Letters represent groupings of treatments from post-hoc testing within each year only, with different letters indicating significant differences (p < 0.05). Numbers within the bars for control measurements represent groupings of years from post-hoc testing of this treatment type.

Figure 3

S. acaulis biomass and cover response to simulated global change. (A) Dry biomass of S. acaulis in simulated global change treatments from 1996 through 2001. (B) Changes in S. acaulis cover relative to 1995, the first year of the study; for all years except 2001, there were no significant differences between treatments. (C) Proportion of original cover extent at the end of the study in 2001, with different letters indicating significant differences between treatments in posthoc testing (p < 0.05).

Figure 4

Response of S. acaulis fruit production to simulated global change. (A) Yearly fruit production by S. acaulis across treatments; in 1995, 1998, and 2000, there were no posthoc differences between fruit production by treatment. (B) Differences in mean fruit production by S. acaulis plants in different treatments in the three years where temperature or nutrient manipulation had significant effects on flowering. Different letters indicate significant differences between treatments (p < 0.05). In both panels, error bars represent one standard error.