Consequences of an excess Al and a deficiency in Ca and Mg for stomatal functioning and net carbon assimilation of beech leaves

Abstract

Stomatal function and photosynthesis were investigated in beech seedlings submitted to excess Al, or/and to a deficiency in Ca and Mg. Excess Al in the nutrient solution promoted a decrease of Ca and Mg leaf contents, while K was increased. Stomata l responses to darkness, ABA and ambient CO 2 remained normal. In contrast, steady-state stomatal conductance in light was signifi- cantly smaller and correlated to a lower accumulation of K in the guard cells. Similar stomatal responses were observed for Ca- Mg deficient plants. In response to combined Al stress and low Ca and Mg nutrition, stomata remained almost insensitive to the dif ferent stimuli. The constancy in K guard cell concentration revealed a disturbance in K fluxes. Lower CO 2 assimilation rates and chloro- phyll contents, on a leaf area basis, were recorded in response to all treatments. In conclusion, excess Al associated to low C a and Mg nutrition lead to a strong stomatal dysfonction and reduced photosynthesis of beech seedlings.