In situ effects of elevated CO 2 on chlorophyll fluorescences and chloroplast pigments of alpine plant

Abstract

Alpine vegetation responds to elevated CO 2 with downward adjustment of photosynthesis. The experiments should show if doubling of ambient CO 2 reduces the maximum quantum yield and the chlorophylls thus altering the pigment composition of the thylakoid membranes in typical species of an alpine grassland ( Caricetum curvulae). The studies were part of a CO 2 enrichment experiment with open-top chambers in the Swiss Central Alps in 2 470 m altitude over a period of four years. The leaves of Carex curvula and Trifolium alpinum were analysed in situ under ambient (355 μl/l) or elevated (680 μl/l) CO 2 and at two different nutrient levels. In each vegetation period both species showed a tendency to lower ratios of variable to maximum fluorescence (F v/F m) in plants with elevated CO 2 treatment compared to the ambient variants. These reductions in F v/F m were statistically different only for Carex curvula in 1993 and 1995. CO 2 enrichment caused reductions of leaf pigment concentrations of 10–30% especially for Trifolium alpinum whereas Carex curvula was less affected. The lower pigment contents per leaf were probably due to reductions of thylakoid membranes. In most cases, the influences of elevated CO 2 or of nutrient treatments on pigment composition and primary photochemistry were very small. This indicates that the downward regulation begins at early stages in the photosynthetic process. Some changes of the photosynthetic apparatus are species-specific and possibly reflect different strategies of protective acclimation processes of alpine vegetation.