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The interrelationships between the induction of CAM and the turnover of malate and citrate in the dicotyledenous tree Clusia monor were compared with seasonal changes in rainfall, leaf water status, PFD and photoinhibitory responses during the transition from wet to dry season in Trinidad. Over a period of 8 weeks, as rainfall declined from a maximum observed around week 3, leaf xylem tensions measured at dusk and dawn reflected the concurrent reduction in day-time carbon gain and an increase in the diel turnover of malate (exposed leaves) and citrate (shaded leaves). Clear seasonal trends were observed in the turnover of malate and citrate during the transition from wet to dry season. In contrast to the declining background concentrations of citrate during the Wet-dry season transition, malate accumulation was markedly enhanced and the ration of malate:citrate accumulated overnight increased as the dry season advanced. Photoinhibitory responses, assessed by chlorophyll fluorescence, indicated that photochemistry was largely determined by the diurnal course of PFD incident on leaves, regardless of the magnitude of internal CO2 release from malate and citrate decarboxylation. In the long term, photochemical efficiency in both shaded and exposed leaves appeared to decline as the dry season progressed. Although there was a clear linear relationship between integrated PFD and overnight accumulation of malate, so such correlation was found for citrate. However, citrate breakdown during the day showed a much closer correlation with PFD as compared to malate, with levels of citrate measured at dusk declining in response to higher daily light intensities. Moreover, enhanced citrate decarboxylation during the day was strongly correlated with increased CAM and overnight accumulation of both malate and citrate. [ABSTRACT FROM AUTHOR]

Analyzes the effect of elevated carbon dioxide concentration on photosynthesis in European forest species using meta-analysis techniques. Relationship between the down-regulation of photosynthesis and poor nutrient status or accumulation of starch; Induction of nutrient limitation by carbon availability.