available online at httpj//www.idealibrary.com on I BE bl 0 @ Four sites with contrasting environmental stress in southeastern Brazil: relations of species, life form diversity, and geographic distribution to ecophysiological parameters Some ecophysiological parameters related to plant performance and fitness (carbon and nitrogen isotope composition and total C and N concentrations; in situ chlorophyll fluorescence measurements) were determined for over 30 species in four habitats bordering the montane Atlantic rain forest of Brazil, along a gradient of altitude and rainfall: a dry coastal forest, two areas of sandy coastal plain vegetation (restingas), and a high altitude campo. There was a considerable diversity of ecophysiological behaviour within and between the functional groups we created based on plant life-forms. For instance, both crassulacean acid metabolism (CAM) and C3 species were found in most life-forms sampled and throughout all habitats. Despite the variation in rainfall regimes, average overall water-use efficiency was similar between sites, particularly for C., species, while no clear pattern regarding nitrogen-use emerged in this respect. Acute and chronic photoinhibition were found in many species across this gradient, even in CAM plants. However, on average, chronic photoinhibition and lower energy dissipation capacity were more characteristic of plants from the restinga habitats. This suggests that, although plants colonizing these habitats have evolved features to deal with water shortage, adaptation to high light levels has not been fully achieved yet. The ecophysiological performance of some individual species in distinct habitats and in distinct microhabitats within habitats is also discussed. ! C 2001 The Linnean Society of London ADDITIONAL KEY WORDS: Atlantic forest -carbon isotopes -chlorophyll a fluorescence -dry forest -high altitude vegetation -nitrogen isotopes -sandy coastal vegetation.

The carbon isotope compositions of samples of Kalanchoë species collected at the natural stands in Madagascar were determined. The results suggest that all species of the genus Kalanchoë are capable of crassulacean acid metabolism. The observed δC values cover the whole range from -10 to -30‰. This high diversity of the δC values was found among the species of the genus as well as, in certain cases, within a single species. This suggest that the CAM patterns in Kalanchoë are generally very flexible. The δC values show a clear correlation with the climate of the habitats from where the samples derived. Values indicative of CO fixation taking place exclusively during the night were found in the dry regions of Madagascar, whereas δC values indicative of mixed CO fixation during night and day or of CO fixation entirely during the day are distributed in the humid zones.

No abstract

Photoperiodism or water stress can shift young leaves of Kalanchoe blossfeldiana from C,-type photosynthesis to Crassulacean acid metabolism (CAM). CAM induction implies synthesis of phosphoenolpyruvate carboxylase (EC 4.1.1.31, PEPC). Present results show that, in plants as well as in isolated leaves, an increase in endogenous levels of abscisic acid (ABA) preceded PEPC increase, independently of the nature of the CAM inductive parameter. I Exogenously applied ABA was taken up ~ and accumulated by isolated leaves to a level similar to the internal ABA concentration in the leaf tissues. Both in entire plants and in isolated leaves, exogenous ABA mimicked the effects of water stress or short days in triggering PEPC capacity. Using a heterologous cDNA probe (derived from Sorghum leaf PEPC gene) it could be shown that an early step of the leaf response to drought or ABA treatment consisted in an increase in the amount of PEPC transcripts. Depending on the duration of ABA application, C3 photosynthesis, typical CAM or CAMidling could be triggered in isolated leaves. In each case, similar increases in PEPC capacity (maximum extractable activity) were obtained, suggesting that the type of photosynthesis performed by the leaves is not controlled by the level of the PEPC capacity. The results suggest that the photosynthetic behaviour of the leaves is primarily governed by the progressive drop in availability of external carbon caused by the ABA-controlled closure of the stomata. Effects of ABA on PEPC synthesis proceed independently of CAM performance.