Abstract
The carbon balance and changes in leaf structure in Clusia minor L. were investigated in controlled conditions with regard to nitrogen supply and responses to low and high photosynthetically active radiation (PAR). Nitrogen deficiency and high PAR led to the production of smaller leaves with higher specific leaf dry weight (SLD W) and higher leaf water content, but with lower chlorophyll content. Nitrogen and PAR levels at growth also affected C02 exchange and leaf area. In — N conditions, total daily net C02 uptake and leaf area accumulation were slightly less for high-PTP-grown plants. In contrast, high-P/f P-grown plants supplied with nitrogen showed about a 4-fold higher total daily C02 uptake and about twice the total leaf area of low-PAR grown plants. Although total daily net C02 uptake of +N plants was only slightly higher than — N plants under the low PAR level, +N plants produced almost three times more leaf area but with lower SLDW. Under well-watered conditions, low-P/l P-grown plants showed only C02 evolution during the night and malic acid levels decreased. However, there was considerable night-time accumulation of titratable protons due to day/night changes in citric acid levels. High-PTP-grown plants showed net C02 uptake, malate and citrate accumulation during the dark period. However, most of the C02 fixed at night probably came from respiratory C02. Positive night-time C02 exchange was readily observed for low PA P-grown plants when they were transferred to high PAR conditions or when they were submitted to water stress. In plants grown in high and low PAR, CAM leads to a substantial increase in daily water use efficiency for water-stressed plants, although total net C02 uptake decreased.
Published Version
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