Interaction of drought and elevated CO2 concentration on photosynthetic down-regulation and susceptibility to photoinhibition in Japanese white birch seedlings grown with limited N availability

Abstract

The interaction of drought and elevated carbon dioxide concentration ([CO2]) on carboxylation capacity of Rubisco (Vcmax) and susceptibility to photoinhibition may be an important determinant of plant responses to seasonal fluctuations in precipitation in an anticipated elevated [CO2] environment. Japanese white birch (Betula platyphylla var. japonica) leaves that developed wholly during a period of drought showed an increase in leaf nitrogen and a decrease in leaf carbohydrates that could ameliorate photosynthetic down-regulation, defined as a decrease in V cmax in response to elevated [CO2]. Photochemical quenching (qP) was decreased by elevated [CO2] but increased by drought when compared at a given intercellular [CO2] (Ci), indicating that elevated [CO2] could increase the risk of photoinhibition, whereas long-term drought could alleviate the risk of photoinhibition. However, only a small variation in qP was measured among seedlings in the various water availability x [CO2] treatment combinations, consistent with the small treatment differences in chronic photoinhibition among the seedlings, as indicated by the ratio of variable to maximum chlorophyll fluorescence after overnight dark-adaptation. Our results suggest that the offsetting responses - reduced Vcmax plus increased Ci at elevated [CO2] and increased Vcmax plus reduced Ci under drought conditions - resulted in a narrow range of susceptibility to photoinhibition at the growth [CO2] in Japanese white birch seedlings grown in various water availability x [CO2] treatment combinations. © 2007 Heron Publishing.