Flexibility of Crassulacean Acid Metabolism in Kalanchoe pinnata (Lam.) Pers. I. Response to Irradiance and Supply of Nitrogen and Water

Abstract

Summary Plants of Kalanchoe pinnata (Lam.) Pers. were grown in the glass chamber of a phytotron in high-light (16-23 mol photons m -2 day -1 ) and in the shade (0.8-2.1 mol photons m -2 day -1 ) respectively, without or with nitrogen nutrition (12 mol m -3 NO 3 - in irrigation solution) and well watered or droughted for 18-22 days (high-light) and 26 to 32 days (shade) respectively, prior to measurements and analyses. Part of the high-light plants were transferred to the shade and part of the shade plants to high-light before measurements. Gas-exchange (H 2 O-vapour, CO 2 ) was measured and contents of total leaf nitrogen, chlorophyll a and b and carotenoids were analysed. Both high-light and low-light grown plants showed typical CAM gas exchange. When high-light plants were transferred to the shade under all conditions diurnal net CO 2 -balance was negative. Shade plants transferred to high-light greatly increased their daily net CO 2 -uptake, particularly by extended CO 2 -fixation at high rates in the light period, if supplied with H 2 O and N. Thus, shade plants were very successful in high-light provided N and H 2 O were not limiting. Shade adaptation of shade-plants as compared to high-light plants was indicated by higher absolute chlorophyll and carotenoid contents and lower chlorophyll a/b as well as lower CO 2 -uptake to chlorophyll (a + b) ratios. The results show, that the factors irradiance, nitrogen-nutrition and water-availability interact in eliciting flexible responses of the photosynthetic mechanism in the constitutive CAM-plant K. pinnata . Highlight plants were not shade tolerant; low-light plants were shade tolerant but not shade demanding.