Plasticity of photosynthetic performance of the Indian tree Butea monosperma TAUB at three sites with different microclimates.

The Fabaceae tree Butea monosperma (TAUB.; syn. Erythrina monosperma (LAM.)) is widely distributed in Central and West-India. We studied it at three sites, i.e. at two locations with contrasting exposure (NE and SW, respectively) in a small mountain range with poor soil on highly drained rocky slopes and at a third location in a plane with deeper soils and better water supply. The two mountain range sites differed in the light climate where the NE-slope obtained more day-integrated irradiance. Chlorophyll fluorescence was measured with a portable fluorometer and leaf samples for stable isotope analyses (δ(13)C, δ(15)N, δ(18)O) were collected. No differences were seen in carbon and nitrogen contents of leaves at the three sites. N and O isotope signatures of the leaves were similar at the two rocky hill slope sites. More positive values for both signatures were obtained in the leaves in the plane. For all sites saturation of ETR was only achieved well above a PPFD of 1,000 µmol m(-2) s(-1) indicating that the leaves were sun-type leaves. The photosynthetic performance of Butea at the plane was very similar to that at the SW-slope of the mountain range and higher ETRs were obtained at the NE-slope. Ecophysiological flexibility allows Butea to perform well in a variety of habitats and yet gives it particular fitness at specific sites. The best performance was observed in the highly insolated steep rocky hill site (NE-slope) underlining the suitability of the tree for reforestation.

Light stress is not effective to enhanced crassulacean acid metabolism.

Clusia minor L., a C3-CAM intermediate, and Clusia multiflora H. B. K., a C3 obligate, present two physiotypes of a similar morphotype occurring sympatrically in the field. Both species, exposed 2 days to high light, show similar responses to this kind of stress: (i) the level of xanthophyll pigments in tested plants during the daycourse adapts to stress, (ii) the levels of antheraxanthin and zeaxanthin clearly increase during the afternoon showing increased de-epoxidation, (iii) the changes in the xanthophyll cycle are similar. Exposure to high light increases the malate levels in C. minor during the afternoon while decreases the day/night changes of the malate levels, and hence the Crassulacean Acid Metabolism (CAM) expression. It can be concluded that strong light applied as a single stress factor to well-watered plants is not effective in strengthing the CAM metabolism in a C3-CAM intermediate plant but rather suppresses the CAM activity despite exposure to high light energy. It is suggested that, when water supply is not limiting and other stresses do not prevail, C3 allows to use up the citrate pool, especially in the afternoon and enables a superior daily photon utilization.

The Golden Section and beauty in nature: The perfection of symmetry and the charm of asymmetry.

It is not unanimous among scientists if there is beauty in science. Some deny it. Mental clarity of conclusions when captured in simple looking equations is mathematical beauty. This we also find in the Euclidian geometry when performing the Golden Section and by deriving the Golden or Devine Number in golden rectangles, spirals and the Golden Angle. The Golden Section is considered as most beautiful and used in architecture and art. It is found everywhere in nature, e.g. in the pentagram of flowers, in the spirals of the shells of snails and Nautilus and even in galaxies of space. The Golden Angle in plants is realized in the phyllotaxis of spirals of leaf rosettes, in fruit stands and in the cones of conifers and cycads. It optimizes packing of modules such as seeds and fruits as well as the capture of light by leaves for photosynthesis and the fitness of productivity. Although we can mathematically deduce it and scientifically explain its role in organization and formation of patterns of structure and function, we cannot explain why we find it beautiful. In a methodological dualism esthetics and beauty are transcendental categories besides science. Or are the pleasant sensations of the Golden Section elicited by different stimuli to which our brain is adapted? Perhaps the Golden Section found everywhere in the entire universe is a link between natural science and the transcendental dimension, while a flower of a rose remains both a complex scientific system and an object of overwhelming beauty.

Clusia: Holy Grail and enigma.

Clusia is the only genus with bona fide dicotyledonous trees performing Crassulacean acid metabolism (CAM). Clusia minor L. is extraordinarily flexible, being C(3)/CAM intermediate and expressing the photosynthetic modes C(3), CAM, CAM-cycling, and CAM-idling. C(3) photosynthesis and CAM can be observed simultaneously in two opposite leaves on a node and possibly even within the same leaf in the interveinal lamina and the major vein tissue, respectively. The relative activity of photosystem II (PhiPSII) indicating photosynthetic energy use, is larger under photorespiratory than under non-photorespiratory conditions due to the particular energy demand of photorespiration. The heterogeneity of PhiPSII over the leaves as visualized by chlorophyll fluorescence imaging in the C(3) mode is larger under non-photorespiratory conditions than under photorespiratory conditions. These observations indicate that photorespiration, presumably by its particular energy demand, synchronizes photosynthetic activity over the leaves. In the CAM mode, the heterogeneity of PhiPSII is more dependent on the transitions between CAM phases. Free-running circadian oscillations of photosynthesis are strongly dampened in both the C(3) and the CAM mode. Photorespiration is under circadian clock control in both the C(3) and the CAM mode. PhiPSII and the heterogeneity of PhiPSII oscillate in phase with CO(2) uptake and photorespiration only under non-photorespiratory conditions. Under photorespiratory conditions, PhiPSII does not oscillate and there is no heterogeneity, again indicating the stabilizing function of photorespiration. Plants acclimatized to perform CAM switch to C(3) photosynthesis during free-running oscillations while subjected to constant illumination.

Strong quenching of chlorophyll fluorescence in the desiccated state in three poikilohydric and homoiochlorophyllous moss species indicates photo-oxidative protection on highly light-exposed rocks of a tropical inselberg.

The three poikilohydric and homoiochlorophyllous moss species Campylopus savannarum (C. Muell.) Mitt., Racocarpus fontinaloides (C. Muell.) Par. and Ptychomitrium vaginatum Besch. grow on sun-exposed rocks of a tropical inselberg in Brazil subject to regular drying and wetting cycles. Effective photo-oxidative protection in the light-adapted desiccated state in all three species is achieved by a reduction of ground chlorophyll fluorescence, F', to almost zero. Upon rewatering, the kinetics of the recovery of F' in air dry cushions to higher values is very fast in the first 5 min, but more than 80 min are needed until an equilibrium is reached gradually. The kinetics were not different between the three species. The three moss species, have a distinct niche occupation and form a characteristic zonation around soil vegetation islands on the rock outcrops, where C. savannarum and R. fontinaloides form an inner and outer belt, respectively, around vegetation islands and P. vaginatum occurs as small isolated cushions on bare rock. However, they were not distinguished by the reduction of F' in the dry state and the rewetting recovery kinetics and only slightly different in their photosynthetic capacity. Stable isotope ratios (delta(13)C, delta(15)N) indicate that liquid films of water limiting diffusion of CO(2) are important in determining carbon acquisition and suggest that limitation of CO(2) fixation by water films must be more pronounced over time in P. vaginatum than in the latter species. This is determined by both the micro site occupied and the form of the moss cushions.

Carbon dioxide signalling in plant leaves.

The role of carbon dioxide (CO(2)) as a signal in biochemical regulation networks of plants is fathomed. Transport mechanisms of CO(2) and HCO3- are surveyed, which are the prerequisite for signalling. A CO(2) sensor is not known to date, but any reaction where CO(2)/HCO3- is a substrate can be a candidate. Carbon concentrating mechanisms, e.g., in higher plants C(4)-photosynthesis and crassulacean acid metabolism (CAM), generate high internal CO(2) concentrations, important for photosynthesis, but also as a basis for signalling via diffusion of CO(2). Spatiotemporal dynamics of desynchronization/synchronization of photosynthetic activity over leaves can be followed by chlorophyll fluorescence imaging. One example of desynchronization is based on patchiness of stomatal opening/closing in heterobaric leaves due to anatomic constraints of lateral CO(2) diffusion. During CAM, largely different internal CO(2) concentrations prevail in the leaves, offering opportunities to study the effect of lateral diffusion of CO(2) in synchronizing photosynthetic activity over the entire leaves.

Responses of chlorophyll fluorescence parameters of the facultative halophyte and C3-CAM intermediate species Mesembryanthemum crystallinum to salinity and high irradiance stress.

Mesembryanthemum crystallinum L. (Aizoaceae) is a facultative annual halophyte and a C(3)-photosynthesis/crassulacean acid metabolism intermediate species currently used as a model plant in stress physiology. Both salinity and high light irradiance stress are known to induce CAM in this species. The present study was performed to provide a diagnosis of alterations at the photosystem II level during salinity and irradiance stress. Plants were subjected for up to 13 days to either 0.4M NaCl salinity or high irradiance of 1000 micromol m(-2)s(-1), as well as to both stress factors combined (LLSA=low light plus salt; HLCO=high light of 1000 micromol m(-2)s(-1), no salt; HLSA=high light plus salt). A control of LLCO=low light of 200 micromol m(-2)s(-1), no salt was used. Parameters of chlorophyll a fluorescence of photosystem II (PSII) were measured with a pulse amplitude modulated fluorometer. HLCO and LLSA conditions induced a weak degree of CAM with day/night changes of malate levels (Deltamalate) of approximately 12mM in the course of the experiment, while HLSA induced stronger CAM of Deltamalate approximately 20 mM. Effective quantum yield of PSII, DeltaF/F'(m), was only slightly affected by LLSA, somewhat reduced during the course of the experiment by HLCO and clearly reduced by HLSA. Potential quantum efficiency of PSII, F(v)/F(m), at predawn times was not affected by any of the conditions, always remaining at 0.8, showing that there was no acute photoinhibition. During the course of the days HL alone (HLCO) also did not elicit photoinhibition; salt alone (LLSA) caused acute photoinhibition which was amplified by the combination of the two stresses (HLSA). Non-photochemical, NPQ, quenching remained low (<0.5) under LLCO, LLSA and HLCO and increased during the course of the experiment under HLSA to 1-2. Maximum apparent photosynthetic electron transport rates, ETR(max), declined during the daily courses and were reduced by LLSA and to a similar extent by HLSA. It is concluded that M. crystallinum expresses effective stress tolerance mechanisms but photosynthetic capacity is reduced by the synergistic effects of salinity and light irradiance stress combined.

Phenotypic subunit composition of the tobacco (Nicotiana tabacum L.) vacuolar-type H(+)-translocating ATPase.

The model plant tobacco (Nicotiana tabacum L.) was chosen for a survey of the subunit composition of the V-ATPase at the protein level. V-ATPase was purified from tobacco leaf cell tonoplasts by solubilization with the nonionic detergent Triton X-100 and immunoprecipitation. In the purified fraction 12 proteins were present. By matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) and amino acid sequencing 11 of these polypeptides could be identified as subunits A, B, C, D, F, G, c, d and three different isoforms of subunit E. The polypeptide which could not be identified by MALDI analysis might represent subunit H. The data presented here, for the first time, enable an unequivocal identification of V-ATPase subunits after gel electrophoresis and open the possibility to assign changes in polypeptide composition to variations in respective V-ATPase subunits occurring as a response to environmental conditions or during plant development.

The role of crassulacean acid metabolism (CAM) in the adaptation of plants to salinity.

Two case studies are presented illustrating how the behaviour of plants using crassulacean acid metabolism (CAM) provides adaptation to salinity. Perennial cacti having constitutive CAM show adaptation at the whole-plant level, engaging regulation of stomata, internal CO2 -recycling and root physiology with salt exclusion. They are stress avoiders. Annual plants such as Mesembryanthemum crystallinum, with inducible CAM, are salt includers. They are stress-tolerant and show reactions at an array of levels: (i) regulation of turgor and gas exchange at the whole-plant level; (ii) metabolic adjustments at the cellular level; (iii) adapptive transport proteins at the membrane level and also (iv) at the macromolecular level; and (v) inductive changes at the gene expression level of the enzyme complement for metabolism (in particular involving glycolysis and malic-acid synthesis with phosphoenolpyruvate carboxylase (PEPC) as the key enzyme, and gluconeogenesis (with pyruvate-phosphate dikinase (PPDK) as a key enzyme) and membrane transport (in particular involving the tonoplast ATPase).

Metabolite gradients and carbohydrate translocation in rosette leaves of CAM and C3 bromeliads.

• The Bromeliaceae encompass predominantly rosette, terrestrial or epiphytic species, including C3 and crassulacean acid metabolism (CAM) photosynthetic types within its three subfamilies. Here, leaf diurnal changes and longitudinal gradients of soluble sugars, organic acids and starch, were quantified to estimate the rates of carbohydrate translocation from mature leaves of C3 and CAM species. • Leaves of Ananas comosus, Aechmea fendleri, Bromelia humilis, Guzmania mucronata, Tillandsia fendleri, Tillandsia flexuosa and Tillandsia utriculata, were sampled at the base, middle, and upper sections during the day. We measured osmolality in sap from frozen subsamples, sugars and organic acids in hot-water extracts from microwave-dried subsamples, and starch hydrolysed with α-amylase or 1.1% HCl. • CAM activity was expressed by malate accumulation, citrate was present, but fluctuations were not significant. Nocturnal reductions in sucrose in bromelioid CAM species accounted for most of the acidification requirements. Tillandsioid CAM species used starch for acid synthesis. Both CAM and C3 bromeliads exported significant amounts of hexose during the night, particularly from the leaf base. • Leaf bases of CAM species showed lowest acid accumulation but similar or more positive δ13 C-values to the active CAM sections. Exported carbohydrates probably derive from carbon fixed during the night period.

Effects of high irradiances on photosynthesis, growth and crassulacean acid metabolism in the epiphyteKalanchoö uniflora.

Kalanchoë uniflora was grown in the glasshouse with and without shading. Chlorophyll content, area/FW ratio and specific leaf area were higher in leaves of shaded as compared to unshaded plants. Light saturation curves and continuous gas exchange measurements showed that the apparent quantum yield and the light-saturated photosynthetic rate were higher in shaded plants. Shaded plants had lower "mesophyll resistances" than unshaded plants, indicating that the different photosynthetic capacities reflected different contents of ribulose biphosphate carboxylase-oxygenase. Highlight treatment of plants grown in the shade resulted in a decreased photosynthetic efficiency, showing that these plants were sensitive to photoinhibition. However, dry matter production was higher in unshaded than in shaded plants. Obviously the difference in irradiance between the two growth regimes did more than offset the differences in photosynthetic efficiency. Applying additional nutrients did not alter the effects of high PFDs. The results are discussed in respect to photosynthetic performence and plant distribution in the epiphytic habitat.

Water relation parameters of the CAM plant Kalanchoë daigremontiana in relation to diurnal malate oscillations.

In the CAM plant Kalanchoë daigremontiana, kept in an environmental rhythm of 12 h L: 12 h D in a growth chamber at 60% relative humidity and well watered in the root medium, decreasing water potentials and osmotic potentials of the leaves are correlated with malate accumulation in the dark. In the light increasing water and osmotic potentials (ψ W and ψ S ) are associated with decreasing malate levels. Transpiratory H2O loss is high in dark and low in light.In continuous light, the CAM rhythm rapidly disappears in the form of a highly damped endogenous oscillation. Malate levels, and water and osmotic potentials of the leaves remain correlated as described above. However, transpiration is very high as malate levels decrease and water and osmotic potentials increase.It can concluded, that water relation parameters like total water potential (ψ W ) and osmotic potential (ψ S ) change in close correlation with changes of malic acid levels. As an important osmotically active solute in CAM plants, malic acid appears to affect water relations independently of and in addition to transpiration. The question remains open, whether turgor (ψ P ) is involved in CAM regulation in intact plants in a similar way as it determines malate fluxes in leaf slices.

Changes of water-relation characteristics and levels of organic cytoplasmic solutes during salinity induced transition of Mesembryanthemum crystallinum from C3-photosynthesis to crassulacean acid metabolism.

NaCl was added to the nutrient solution of 4-6-week old Mesembryanthemum crystallinum plants so that the concentration rose by 50 mM per day. Ten to fifteen days after a concentration of 400 mM was reached, pronounced diurnal oscillations of malate levels indicated that plants had changed from C3-photosynthesis to crassulacean acid metabolism (CAM). Due to the NaCl-treatment the solute potential (Ψs) decreased from about -6 bar to -25 bar, and the water potential (Ψ) changed from about -5 bar to -23 bar on average. Ψ showed small diurnal oscillations both in controls and NaCl-treated plants, with an amplitude of 1 to 3 bar, the value at the end of the dark phase being less negative than that at the end of the light phase. Changes of ion levels due to the NaCl-treatment were average increases in Na+ and Cl- from 10-20 to 370-470 mmol kg-1 FW and from below 10 to 280-325 mmol kg-1 FW, respectively, and a decrease in K+ from 70-80 to 25 mmol kg-1 FW. These changes of ion levels corresponded very closely to an increase of dry weight in per cent of fresh weight observed during the NaCl-treatment (e.g. a change of 2% in one experiment), and osmotically they matched the measured change in Ψs (e.g. about 18-20 bar in one experiment).Most of the organic solutes analysed did not show any significant changes as a result of the NaCl-treatment. The following compounds were identified within the respective ranges of concentrations: mannitol (0.2 to 0.5 mmol kg-1 FW), sum of quaternary ammonium compounds (60 to 140 mg kg-1 FW), choline (0.1 to 0.4 mmol kg-1 FW), betaine (0.3 to 0.7 mmol kg-1 FW), hexoses (2-9 mmol kg-1 FW), pentoses (1-5 mmol kg-1 FW) and sucrose (2-4 mmol kg-1 FW). The levels of proline and of total amino acids minus proline rose during the NaCl-treatment from 0.1-1 mmol kg-1 FW to 2.5-5 mmol kg-1 FW and from 2.5-4 mmol kg-1 FW to 6-8 mmol kg-1 FW, respectively.The changes of Ψs and Ψ, and of Na+- and Cl--levels were complete, and new steady levels were attained by the time 400 mM NaCl was reached in the nutrient solution, i.e. many days before pronounced diurnal malate oscillations indicated that the change from C3-photosynthesis to CAM had occurred. The attainment of new steady levels of proline and K+, however, was much slower and coincided with the onset of CAM.

Seasonal shift from C3 photosynthesis to Crassulacean Acid Metabolism in Mesembryanthemum crystallinum growing in its natural environment.

Changes in δ13C value, diurnal malate content, water content and Na+, K+ and Cl- content of the annual Mesembryanthemum crystallinum (Aizoaceae) were followed in a natural population on a coastal cliff at the Mediterranean Sea shore close to Caesarea (Israel). Plants germinated in the middle of the rainy season in December 1976/January 1977. Diurnal malate fluctuations in the leaves were not detected until the end of March. Later on, at the start of the dry season, pronounced diurnal changes in malate developed. This was correlated with a progressive change in δ 13C value from about -26‰ to about -16‰ which is consistent with a change from normal C3 photosynthetic CO2 fixation to a predominantly nocturnal CO2 assimilation pattern involving Crassulacean Acid Metabolism.

Mineral Ion composition and occurrence of CAM-like diurnal malate fluctuations in plants of coastal and desert habitats of israel and the Sinai.

1. The mineral ion composition and the occurrence of CAM-like diurnal malate fluctuations in species from 6 field locations in Israel and the Sinai were studied during the spring of 1974. The sites were a) a salt swamp near Acre on the Mediterranean Sea shore in the northern part of Israel, b) the high coast near Tel Aviv, c) the southern Dead Sea area near Sedom, d) the Negev highlands surrounding the ancient town of Avdat, e) the Wadi Paran in the southern Negev desert, and f) the Red Sea shore near the southeastern tip of the Sinai peninsula close to the Bedouin village of Nabek. The carbon assimilatory organs of the plants were analysed for Na+, K+, Cl- and SO42- as well as for malate at dawn and dusk. 2. Most species analysed are characterized by high levels of mineral ions (mainly Na+/and Cl-) often exceeding 300-400 µeq per g fresh weight, and by high Na+/K+ ratios in their tissues mainly ranging from 10 to 20. These typical halophytic attributes are particularly found in species of the Acre salt swamp, of the Dead Sea area and the Red Sea shore and in many species of the Negev highlands. 3. In plants occupying the Tel Aviv high coast habitats Na+ and Cl- are lower averaging 100 to 200 µeq per g fresh weight. The Na+/K+ ratio is about 5. 4. Numerous species mainly inhabiting the less saline loessial plains and wadis of the Negev desert contain only up to 100 µeq Na+ and Cl- per g fresh weight and are characterized by Na+/K+ ratios of about 1 and below. 5. The salt-accumulating species of the coastal habitats contain Na+ and Cl- in more or less equivalent amounts, i.e. halophytes of the "chloride type" in the terminology of Walter dominate these sites. In contrast, many inland halophytes chiefly belonging to the Chenopodiaceae accumulate much more Na+ than Cl- and/or SO42-. 6. The special feature of Na+ contents which far exceed the sum of Cl- and SO42- distinguishes the inland Chenopodiaceae as a "physiotype" from members of other taxa. The Zygophyllaceae included in this study form a further "physiotype" which is characterized by higher Cl- than Na+ concentrations. 7. Five species of the Aizoaceae family investigated showed no special pattern of mineral ion content. 8. Certain species, especially some belonging to the Brassicaceae, showed a slight malate accumulation during the day. 9. CAM-like diurnal malate fluctuations were only observed in four species: the halophytic Aizoaceae Mesembryanthemum crystallinum, M. forsskalii and M. nodiflorum and the non-halophytic Asclepiadaceae Caralluma It is suggested that, among halophytes, the capability to perform CAM is generally restricted to members of the Aizoaceae.

Specific regulation of SOD isoforms by NaCl and osmotic stress in leaves of the C3 halophyte Suaeda salsa L.

The halophyte Suaeda salsa L., exposed to different NaCl concentrations (100 and 400 mmol/L) and polyethylene glycol (isoosomotic to 100 mmol/L NaCl) containing nutrient solutions under normal or K+-deficient conditions for 7 days, was used to study effects of NaCl salinity and osmotic stress on chlorophyll content, chlorophyll fluorescence characteristics, malonedialdehyde (MDA) content, and superoxide dismutase (SOD) isoform activities. Photosynthetic capacity was not decreased by NaCl treatment, indicating that S. salsa possesses an effective antioxidative response system for avoiding oxidative damage. Seven SOD activity bands were detected in S. salsa leaf extracts, including an Mn-SOD and several isoforms of Fe-SOD and CuZn-SOD. It turned out that NaCl salinity and osmotic stress lead to a differential regulation of distinct SOD isoenzymes. This differential regulation is suggested to play a major role in stress tolerance of S. salsa.

Malate and malate-channel antibodies inhibit electrogenic and ATP-dependent citrate transport across the tonoplast of citrus juice cells.

Citrus juice cells accumulate high levels of citric acid in their vacuoles when compared to other organic ions including malate. Uptake of citrate into tonoplast vesicles from Citrus juice cells was investigated in the presence of malate, and after incubation with antibodies raised against the vacuolar malate-specific channel of Kalanchoë diagremontiana leaves. Antibodies against the vacuolar malate channel immunoreacted with a protein of similar size in tonoplast extracts from three Citrus varieties differing in citric acid content. Malate channel antibodies inhibited both delta MicroH(+)-dependent and delta MicroH(+)-independent ATP-dependent citrate transport, indicating common domains in both transport systems and to the malate-specific channel of Kalanchoë diagremontiana leaves. Malate strongly inhibited electrogenic citrate transport, whereas ATP-dependent citrate uptake was less affected. Kinetic analysis of citrate transport in the presence of malate confirmed the existence of two citrate transport mechanisms and indicated that both citrate and malate share a common transport channel across the tonoplast of Citrus juice cells.

Independent fluctuations of malate and citrate in the CAM species Clusia hilariana Schltdl. under low light and high light in relation to photoprotection.

Clusia hilariana Schltdl. is described in literature as an obligate Crassulacean acid metabolism (CAM) species. In the present study we assessed the effect of irradiance with low light (LL, 200µmolm(-2)s(-1)) and high light (HL, 650-740µmolm(-2)s(-1)), on the interdependency of citrate and malate diurnal fluctuations. In plants grown at HL CAM-type oscillations of concentration of citrate and malate were obvious. However, at LL daily courses of both acids do not seem to indicate efficient utilization of these compounds as CO2 and NADPH sources. One week after transferring plants from LL to HL decarboxylation of malate was accelerated. Thus, in the CAM plant C. hilariana two independent rhythms of accumulation and decarboxylation of malate and citrate take place, which appear to be related to photosynthesis and respiration, respectively. Non photochemical quenching (NPQ) of photosystem II, especially well expressed during the evening hours was enhanced. Exposure to HL for 7 d activated oxidative stress protection mechanisms such as the interconversion of violaxanthin (V), antheraxanthin (A) and zeaxanthin (Z) (epoxydation/de-epoxydation) measured as epoxydation state (EPS). This was accompanied by a slight increase in the total amount of these pigments. However, all these changes were not observed in plants exposed to HL for only 2 d. Besides violaxanthin cycle components also lutein, which shows a small, but not significant increase, may be involved in dissipating excess light energy in C. hilariana.

Functional Diversity of Photosynthetic Light Use of 16 Vascular Epiphyte Species Under Fluctuating Irradiance in the Canopy of a Giant Virola michelii (Myristicaceae) Tree in the Tropical Lowland Forest of French Guyana.

Here we present the first study, in which a large number of different vascular epiphyte species were measured for their photosynthetic performance in the natural environment of their phorophyte in the lowland rainforest of French Guyana. More than 70 epiphyte species covered the host tree in a dense cover. Of these, the photosynthesis of 16 abundant species was analyzed intensely over several months. Moreover, the light environment was characterized with newly developed light sensors that recorded continuously and with high temporal resolution light intensity next to the epiphytes. Light intensity was highly fluctuating and showed great site specific spatio-temporal variations of photosynthetic photon flux. Using a novel computer routine we quantified the integrated light intensity the epiphytes were exposed to in a 3 h window and we related this light intensity to measurements of the actual photosynthetic status. It could be shown that the photosynthetic apparatus of the epiphytes was well adapted to the quickly changing light conditions. Some of the epiphytes were chronically photoinhibited at predawn and significant acute photoinhibition, expressed by a reduction of potential quantum efficiency (F(v)/F(m))(30'), was observed during the day. By correlating (F(v)/F(m))(30') to the integrated and weighted light intensity perceived during the previous 3 h, it became clear that acute photoinhibition was related to light environment prior to the measurements. Additionally photosynthetic performance was not determined by rain events, with the exception of an Aechmea species. This holds true for all the other 15 species of this study and we thus conclude that actual photosynthesis of these tropical epiphytes was determined by the specific and fluctuating light conditions of their microhabitat and cannot be simply attributed to light-adapted ancestors.

Ability of crassulacean acid metabolism plants to overcome interacting stresses in tropical environments.

BACKGROUND AND AIMS: Single stressors such as scarcity of water and extreme temperatures dominate the struggle for life in severely dry desert ecosystems or cold polar regions and at high elevations. In contrast, stress in the tropics typically arises from a dynamic network of interacting stressors, such as availability of water, CO(2), light and nutrients, temperature and salinity. This requires more plastic spatio-temporal responsiveness and versatility in the acquisition and defence of ecological niches. CRASSULACEAN ACID METABOLISM: The mode of photosynthesis of crassulacean acid metabolism (CAM) is described and its flexible expression endows plants with powerful strategies for both acclimation and adaptation. Thus, CAM plants are able to inhabit many diverse habitats in the tropics and are not, as commonly thought, successful predominantly in dry, high-insolation habitats. TROPICAL CAM HABITATS: Typical tropical CAM habitats or ecosystems include exposed lava fields, rock outcrops of inselbergs, salinas, savannas, restingas, high-altitude páramos, dry forests and moist forests. MORPHOTYPICAL AND PHYSIOTYPICAL PLASTICITY OF CAM: Morphotypical and physiotypical plasticity of CAM phenotypes allow a wide ecophysiological amplitude of niche occupation in the tropics. Physiological and biochemical plasticity appear more responsive by having more readily reversible variations in performance than do morphological adaptations. This makes CAM plants particularly fit for the multi-factor stressor networks of tropical forests. Thus, while the physiognomy of semi-deserts outside the tropics is often determined by tall succulent CAM plants, tropical forests house many more CAM plants in terms of quantity (biomass) and quality (species diversity).