Dynamic photo-inhibition and carbon gain in a C4 and a C3 grass native to high latitudes

C-4 plants are rare in the cool climates characteristic of high latitudes and altitudes, perhaps because of an enhanced susceptibility to photo-inhibition at low temperatures relative to C-3 species. In the present study we tested the hypothesis that low-temperature photo-inhibition is more detrimental to carbon gain in the C-4 grass Muhlenbergia glomerata than the C-3 species Calamogrostis Canadensis. These grasses occur together in boreal fens in northern Canada. Plants were grown under cool (14/10 degreesC day/night) and warm (26/22 degreesC) temperatures before measurement of the light responses of photosynthesis and chlorophyll fluorescence at different temperatures. Cool growth temperatures led to reduced rates of photosynthesis in M. glomerata at all measurement temperatures, but had a smaller effect on the C-3 species. In both species the amount of xanthophyll cycle pigments increased when plants were grown at 14/10 degreesC, and in M. glomerata the xanthophyll epoxidation state was greatly reduced. The detrimental effect of low growth temperature on photosynthesis in M. glomerata was almost completely reversed by a 24-h exposure to the warm-temperature regime. These data indicate that reversible dynamic photo-inhibition is a strategy by which C-4 species may tolerate cool climates and overcome the Rubisco limitation that is prevalent at low temperatures in C-4 plants.