Nitrogen nutrition and the level of Crassulacean acid metabolism in Kalanchoë lateritia Engl.
Abstract. The influence of different nitrogen levels was studied in the CAM facultative Kalanchoe lateritia by watering some plants with Hoagland's solution (which contains, besides other ions, NO3−= 14.47mol m−3and NH4+= 1.04mol m−3; N group), and others with the same solution but with combined nitrogen concentration reduced to either one fifth (NO3−= 2.894mol m−3 and NH4+= 0.208mol m−3; N/5 group) or one tenth (NO3−= 1.447mol m−3and NH4+= 0.104mol m-3;N/10 group). The influence of the three nitrogen levels on CAM expression was assessed through activities of PEP-Case, PPD and RuBisCo, diurnal fluctuation of titratable acidity, mesophyll succulence, soluble protein, chlorophyll, nitrate, starch contents, pattern of nocturnal CO2 exchange and electron microscopy. CAM photosynthesis was more intense in N/5 plants which also had the highest Sm value. The activity of RuBisCo showed no significant differences in the three situations (expressed on chlorophyll basis) whereas both PEP-Case and PPD had higher values in N/5” plants. Chlorophyll and soluble protein were more abundant in the N plants followed by N/5 and N/10 plants. Nitrate was higher in N plants and starch content in N/5 plants. IRGA determination of CO2 nocturnal uptake showed that N/5 plants began CO2 capture earlier and at a more intense rate and for a longer period than plants from other groups also having a daily variation of titratable acidity (97.71 ± 10.8 μeq. G−1 f.w.) indicative of performing strong CAM. Electron microscope morphometric analysis revealed larger chloroplasts in N plants and smaller in N/10 plants, with starch fractional volume higher in N/5 plants, correlating with more intense CAM activity of these plants.