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This paper describes the ecology of a coastal alluvial plain at Chichiriviche in northern Venezuela. The area supports a great diversity of plant communities, ranging from mangroves on the seaward edge of the plain to non-halophytic, fresh-water communities on the landward side. Small differences on topography result in a mosaic of saline and less-saline environments. Rainfall is strongly seasonal, causing superficial flooding of the alluvial plain in the rainy season and the creation of a hypersaline Substratum during the dry season. As a consequence, much of the plain is devoid or vegetation. Towards the landward side of the plain there are numerous small 'vegetation islands', fringed by halophilic succulent herbs, and made up of deciduous and semi-deciduous shrubs and trees together with non-halophytic CAM plants such as cacti and bromeliads. In subsequent papers the results of ecophysiological studies of these diverse plant species are presented.

summary Clusia rosea Jacq. is abundant in the moist parts of the Caribbean island of St John (US Virgin Islands, Lesser Antilles) but relatively rare along the dry south coast. Three types of seedlings were encountered, terrestrial seedlings, seedlings growing as humus-epiphytes on other trees, and seedlings growing inside the tanks of the bromeliad Aechmea lingulata (L.) Baker. Free-living trees grow from terrestrial seedlings or from epiphytic seedlings strangling and shading their host trees. Leaf-Na+ levels were always low (1–4 mequiv I−1 tissue water); trees close to the shore were not affected by salinity. In leaves of mature C. rosea trees, levels of Ca2+, Mg2+ and K+ were about 60–90, 40–50, 45–55 mequiv I−1 tissue water, respectively. Epiphytic seedlings tended to contain lower levels of these inorganic cations than seedlings growing terrestrially or in the tanks of Ae. lingulata. Epiphytic seedlings contained significantly less nitrogen than terrestrial seedlings. In the leaves of mature trees N-levels were independent of altitude and location on the island, but shaded leaves had significantly higher N-levels than exposed leaves. Light compensation point of photosynthesis in epiphytic seedlings performing C3-photosynthesis was 17–5 (μmol photons m−2 s−1), photosynthesis was saturated at about 300μmol photons m−2 s−1 showing a maximum rate of CO2-uptake of 2–3 μmol m−2 s−1.

Extreme environmental conditions prevail on the Antarctic continent and limit plant diversity to cryptogamic communities, dominated by bryophytes and lichens. Even small abiotic shifts, associated with climate change, are likely to have pronounced impacts on these communities that currently exist at their physiological limit of survival. Changes to moisture availability, due to precipitation shifts or alterations to permanent snow reserves, will most likely cause greatest impact. In order to establish a baseline for determining the effect of climate change on continental Antarctic terrestrial communities and to better understand bryophyte species distributions in relation to moisture in a floristically important Antarctic region, this study surveyed finescale bryophyte patterns and turf water and nutrient contents along community gradients in the Windmill Islands, East Antarctica. The survey found that the Antarctic endemic, Schistidium antarctici, dominated the wettest habitats, Bryum pseudotriquetrum di...

Polyhydroxy compounds such as cyclitols, acyclic polyols and sugars are produced by a wide variety of organisms under stressful conditions in order to protect macromolecular structure. Plants undergoing abiotic stresses like heat and dehydration accumulate enormous amounts of polyhydroxy compounds (up to 400 mM) in their cellular tissues. Not only do they serve as osmoprotectants ("compatible solutes"), they also protect membrane structure and preserve enzymatic activity. To gain further insight into the mechanism of protein protection by polyhydroxy compounds, we examined the structural and thermal stability of six model proteins (bovine serum albumin, glutamine synthetase of Escherichia coli, malate dehydrogenase of pig heart, SH2 domain of phospholipaseCgamma1, SH2_Myc and GST_MycMax fusion proteins) upon the addition of various polyhydroxy compounds by circular dichroism spectroscopy. Our results show that D-pinitol (1D-3-O-methyl-chiro-inositol), L-quebrachitol (1L-2-O-methyl-chiro-inositol), myo-inositol, D-chiro-inositol, mannitol, glucose and trehalose promoted improved structural and thermal stability for each protein, whereas conduritol (1,4/2,3-cyclohexanetetrol) and glycerol were not effective. An increase in the midpoint denaturation temperature (T(m)) of 3.3 degrees C to 4.7 degrees C was observed for each protein upon the addition of 400 mM myo-inositol. Although the apparent T(m) of each protein was shifted by the addition of polyhydroxy compounds, the influence seems to be dependent on attributes like the protein surface topology, the hydration shell and on the nature of the protective solute, as well as on its concentration. The O-methylated cyclitols D-pinitol and L-quebrachitol were more effective preservatives than the less hydrophobic non-methylated myo-inositol and D-chiro-inositol. Amongst various polyhydroxy compounds, hydrophobic cyclitols were the most effective stabilizers.

Climate change is expected to affect the high latitudes first and most severely, rendering Antarctica one of the most significant baseline environments for the study of global climate change. The indirect effects of climate warming, including changes to the availability of key environmental resources, such as water and nutrients, are likely to have a greater impact upon continental Antarctic terrestrial ecosystems than the effects of fluctuations in temperature alone. To investigate the likely impacts of a wetter climate on Antarctic terrestrial communities a multiseason, manipulative field experiment was conducted in the floristically important Windmill Islands region of East Antarctica. Four cryptogamic communities (pure bryophyte, moribund bryophyte, crustose and fructicose lichen-dominated) received increased water and/or nutrient additions over two consecutive summer seasons. The increased water approximated an 18% increase in snow melt days (0.2 degrees C increase in temperature), while the nutrient addition of 3.5g Nm(-2) yr(-1) was within the range of soil N in the vicinity. A range of physiological and biochemical measurements were conducted in order to quantify the community response. While an overall increase in productivity in response to water and nutrient additions was observed, productivity appeared to respond more strongly to nutrient additions than to water additions. Pure bryophyte communities, and lichen communities dominated by the genus Usnea, showed stronger positive responses to nutrient additions, identifying some communities that may be better able to adapt and prosper under the ameliorating conditions associated with a warmer, wetter future climate. Under such a climate, productivity is overall likely to increase but some cryptogamic communities are likely to thrive more than others. Regeneration of moribund bryophytes appears likely only if a future moisture regime creates consistently moist conditions.

The accumulation of cyclitols in plants is a widespread response that provides protection against various environmental stresses. The capacity of myo-Inositol, pinitol, quercitol, and other compatible solutes (i.e., sorbitol, proline, and glycinebetaine) to protect proteins against thermally induced denaturation and deactivation was examined. Enzymatic activity measurements of L-glutamine synthetase from Escherichia coli and Hordeum vulgare showed that the presence of cyclitols during heat treatment resulted in a significantly higher percentage of residual activity. CD spectroscopy experiments were used to study thermal stabilities of protein secondary structures upon the addition of myo-Inositol, pinitol, and glucose. 0.4 M myo-Inositol was observed to raise the melting temperature (Tm) of GS from E. coli by 3.9 degrees C and MDH from pig heart by 3.4 degrees C, respectively. Pinitol showed an increase in Tm of MDH by 3.8 degrees C, whereas glucose was not effective. Our results show a great potential of stabilizing proteins by the addition of cyclitols.

The Central Asian Taklamakan desert is characterized by a hyperarid climate with less than 50 mm annual precipitation but a permanent shallow groundwater table. The perched groundwater (2-16 m) could present a reliable and constant source of nitrogen throughout the growing season and help overcome temporal nitrogen limitations that are common in arid environments. We investigated the importance of groundwater and nitrogen fixation in the nitrogen metabolism of desert plants by assessing the possible forms and availability of soil N and atmospheric N and the seasonal variation in concentration as well as isotopic composition of plant N. Water availability was experimentally modified in the desert foreland through simulated flooding to estimate the contribution of surface water and temporally increased soil moisture for nutrient uptake and plant-water relations. The natural vegetation of the Taklamakan desert is dominated by plants with high foliar nitrogen concentrations (2-3% DM) and leaf nitrate reductase activity (NRA) (0.2-1 micromol NO2- g(-1) FW h(-1)). There is little evidence that nitrogen is a limiting resource as all perennial plants exhibited fast rates of growth. The extremely dry soil conditions preclude all but minor contributions of soil N to total plant N so that groundwater is suggested as the dominant source of N with concentrations of 100 microM NO3-. Flood irrigation had little beneficial effect on nitrogen metabolism and growth, further confirming the dependence on groundwater. Nitrogen fixation was determined by the 15N natural abundance method and was a significant component of the N-requirement of the legume Alhagi, the average contribution of biologically fixed nitrogen in Alhagi was 54.8%. But nitrogen fixing plants had little ecological advantage owing to the more or less constant supply of N available from groundwater. From our data we conclude that the perennial species investigated have adapted to the environmental conditions through development of root systems that access groundwater to satisfy demands for both water and nutrients. This is an ecologically favourable strategy since only groundwater is a predictable and stable resource.

International audience; As a measure of frost hardiness, we determined an index of injury (I-30) in living bark tissue of 20-year-old pedunculate oaks (Quercus robur L.) that had been manually and almost completely defoliated in the first half of May of one or two years, and of non-defoliated control trees. I-30 was calculated as a percentage value on the basis of electrolyte leakage from samples artificially frozen at a temperature of -30 °C, and from unfrozen control samples. In parallel, the bark's concentrations of soluble sugars, of nitrogen and of quercitol, a cyclic polyol, were measured. Repeated defoliation significantly reduced the frost hardiness of the bark as well as its concentrations of raffinose, stachyose, nitrogen and quercitol. The I-30 values were correlated with the total concentration of soluble sugars and with the concentrations of the individual sugar compounds, but not with the quercitol concentration. Less tight, yet significant correlations were obtained between I-30 and nitrogen concentrations. We conclude that repeated defoliation decreases the bark's capability to acclimatize to winter frost due to a reduction in the concentrations of soluble sugars, particularly those of raffinose and stachyose.; Effets de la défoliation sur la résistance au gel et les concentrations de sucres solubles et de cyclitols dans le liber de chênes pédonculés (Quercus robur L.). Comme mesure de la résistance au gel du liber vivant de chênes pédonculés âgés de vingt ans et ayant déjà été défoliés manuellement presque entièrement dans la première moitié du mai d'une ou deux années, on a calculé un index de dommage (I-30) et on a comparé avec la valeur correspondante d'arbres témoins non défoliés. On a déterminé I-30 comme une valeur de pourcentage sur la base de perte d'électrolytes des échantillons congelés artificiellement à -30 °C, et des échantillons pas congelés. Parallèlement on a mesuré les concentrations de sucres solubles, d'azote et de quercétol, un polyalcool cyclique, du liber. La deuxième défoliation a réduit de manière significative tant la résistance au gel du liber que ses concentrations en raffinose, stachyose, azote et quercétol. Les indices de dommage (I-30) étaient en corrélation avec la concentration totale de sucres solubles et avec les concentrations de sucres individuels, mais pas avec la concentration de quercétol. Des corrélations moins étroites mais toutefois significatives ont été mises en évidence entre les valeurs I-30 et les concentrations d'azote. Ces résultats nous permettent de conclure qu'une défoliation répétée réduit la capacité d'acclimatation du liber aux gels d'hiver en raison d'une diminution des concentrations de sucres solubles, surtout de raffinose et de stachyose.

Low temperature driven carbon shortage is often assumed to explain slow growth and treeline formation at high elevations. To test this hypothesis, we analysed mobile carbon pools in Pinus cembra across the treeline ecotone in the Swiss Alps. Concentrations of non-structural carbohydrates (NSC) in needles, branches, stems and roots, as well as lipids (acylglycerols) in all woody tissues were measured throughout the growing season. Starch was the most prominent non-structural carbon compound in needles, whereas lipids represented 50–75% of the mobile carbon compounds in wood. The relative seasonal variation of the lipid fraction was very small, but due to the high absolute amount of lipids, the annual variability of carbon in lipids exceeded that of NSC in woody tissues. Mobile carbon compounds were highly abundant throughout the year and were never significantly depleted. Across a 110 m altitudinal transect from timberline to the uppermost site of tree existence, NSC and lipid concentrations generally increased. This trend became even more pronounced when the increasing structural density of tissues at higher elevations was accounted for. An estimation of the whole tree mobile carbon concentration (fraction of mobile carbon compounds within the whole tree biomass) also revealed an increasing trend of NSC and lipid pools with elevation. We therefore conclude that carbon limitation is unlikely to be responsible for reduced tree growth at the alpine treeline studied. Increased concentrations of NSC and lipids at the upper tree limit rather suggest that sink activity is limited. Hence, treeline formation is most likely the result of a direct thermal restriction of tissue formation (investment in structures) under otherwise sufficient carbon assimilation during the growing season.

The drought-tolerant tree species Ziziphus mauritiana Lamk. and Z. rotundifolia Lamk. were shown to have similar high mucilage concentrations (7-10% dry weight) in their leaves, with large numbers of mucilage-containing cells in the upper epidermis and extracellular mucilage-containing cavities in the leaf veins and stem cortex. The main sugar constituents of the water-soluble mucilage extract were rhamnose, glucose and galactose. During drought-stress in two independent studies, foliar mucilage content was unaffected in both species, but glucose and starch contents declined significantly in crude mucilage extracts from droughted leaves. Enzymatic hydrolysis of the mucilage extract using alpha-amylase and amyloglucosidase released glucose, indicating that a mucilage-associated water-soluble glucan, with alpha-1,4- and alpha-1,6-linkages, may exist which was extracted together with the mucilage. From the current data, it is not possible to localize the glucan to determine whether or not it is associated with mucilage-containing cells. Data from pressure-volume analyses of drought-stressed and control leaves showed that, in line with their similar mucilage contents, the relative leaf capacitance isotherm (change in relative water content per unit change in water potential) was similar in both species. During drought-stress, reduced relative capacitance resulted from osmotic adjustment and decreased wall elasticity. Data suggest that in Ziziphus leaves, intracellular mucilages play no part in buffering leaf water status during progressive drought. In Ziziphus species, growing in environments with erratic rainfall, the primary role of foliar mucilage and glucans, rather than as hydraulic capacitors, may be as sources for the remobilization of solutes for osmotic adjustment, thus enabling more effective water uptake and assimilate redistribution into roots and stems prior to defoliation as the drought-stress intensified.

Seasonal changes in the activity of phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31), a key enzyme in the interaction of carbohydrate and nitrogen metabolism, were studied in leaves of the C3 semiparasitic mistletoe, Viscum album, growing on different host trees. Maximum extractable PEPCase activities were higher in leaves of mistletoes growing on Betula pendula and Alnus glutinosa hosts compared with those on the conifers, Abies alba and Larix decidua. Independent of host, maximum extractable PEPCase activities were high in spring and autumn while low in summer. Samples with higher PEPCase activities showed higher amounts of PEPCase protein and higher PEPCase mRNA levels. A curvilinear correlation between leaf total nitrogen content and the maximum extractable PEPCase activity as well as PEPCase mRNA level suggested that nitrogen might affect the activity of PEPCase of mistletoe by up-regulating gene expression. In addition to extractable activity, seasonal changes of the PEPCase activation state, the ratio of activities resulting from limited:non-limited assays, were found, which was correlated to the variation of malate content in leaves of mistletoe. ATP-dependent activation of PEPCase was characterized by an increase in I0.5(L-malate), indicating that PEPCase of leaves of mistletoes is probably regulated via phosphorylation.

Summary As part of an ongoing project to understand the effects of elevated atmospheric CO 2 on plants in complex, tropical communities, we studied biomass accumulation in a simplified model seedling community consisting of two species of tropical trees ( Ficus insipida , a fast growing pioneer species, and Virola surinamensis , a slow-growing, shade-tolerant late successional species). The plants were grown at ambient and elevated (about two times ambient) CO 2 concentrations using open-top chambers at a field site in Panama. Communities grew in heavily fertilized soil. Compared to a previous experiment with model communities of F. insipia and V. surinamensis grown on unfertilized soil (Winter et al., Flora [2000] 195, 289) application of soil fertilizer markedly accelerated community growth rates at ambient CO 2 , and biomass accumulation was enhanced by an additional 52% at elevated CO 2 . In contrast, elevated CO 2 had no significant effect on biomass accumulation in unfertilized communities. Communities growing on fertilized soil showed greater biomass allocation into leaves, i.e. higher leaf weight ratios (LWRs) than did communities on unfertilized soil. Higher LWRs were related to lower root: shoot ratios and together with greater specific leaf areas (area per unit leaf mass), largely a consequence of lower leaf starch contents, resulted in higher leaf area ratios (LARs). While elevated CO 2 caused the relatively low LARs in unfertilized communities to decrease further, by strongly increasing leaf starch levels and decreasing specific leaf areas, these leaf characteristics changed only slightly in fertilized communities exposed to elevated CO 2 . Thus, by maintaining relatively high LARs at elevated CO 2 , fertilized plants were able to effectively use enhanced CO 2 concentrations for increased carbon gain and growth. Leaves of plants on fertilized soil were characterized by relatively low C: N ratios which were largely unaffected by CO 2 concentration. In contrast, C: N ratios in leaves of unfertilized plants were higher than those of fertilized plants and increased in response to elevated CO 2 .

Summary Biomass accumulation of model seedling communities of two tropical tree species was studied at ambient and elevated CO 2 levels (four replicates per CO 2 concentration), using open-top chambers situated in a cleared area at the edge of a tropical forest near Panama City, Republic of Panama. Each chamber (diameter about 2 m) contained a mixture of 18 plants of Ficus insipida , a fast-growing pioneer species, and 18 plants of Virola surinamensis , a slow-growing late-successional species. Plants grew in well-drained, well-watered, loose, unfertilized soil. During the 30 week experimental period, biomass accumulation by F. insipida , which increased in height from about 20 to 180 cm, predominated, whereas V. surinamensis grew only slowly in the strongly shaded understorey. Neither community biomass accumulation (above- plus belowground) nor the biomass ratio ( F. insipida: V. surinamensis ) of the two species was significantly affected by elevated CO 2 , although community biomass accumulation was on average slightly higher at elevated than at ambient CO 2 , and the biomass of F. insipida increased on average relative to V. surinamensis at elevated CO 2 . Plants grown at elevated CO 2 contained greater levels of starch and lower levels of nitrogen per unit leaf dry mass, and, therefore, showed higher ratios of C: N than plants at ambient CO 2 . Specific leaf area, the area per unit leaf dry mass; and the leaf area ratio (LAR), the total leaf area per total plant dry mass, decreased in response to elevated CO 2 . This decrease in LAR counteracted the potential effect on biomass gain of increases in both net assimilation rate (the rate of dry mass accumulation per unit leaf area) and rates of photosynthetic leaf net CO 2 uptake at elevated as compared to ambient CO 2 , particularly in Ficus insipida .

Thylakoid membranes isolated from either spinach or chickpea leaves were used as a model system for evaluating the capacity of cyclitols to act as cryoprotectants. The effect of freezing for 3 h at -18 degrees C on cyclic photophosphorylation and electron transport was measured. The cyclitols, ononitol, O-methyl-muco-inositol, pinitol, quebrachitol and quercitol at 50-150 mol m(-3) decreased membrane damage by freezing and thawing to a similar degree as the well known cryoprotectants sucrose and trehalose. On addition of the cryotoxic solute NaCl (100 mol m(-3)) to the test system these methylated cyclohexanhexols again provided a protection comparable to that of the two disaccharides. Quercitol (cyclohexanpentol) was not effective when added in lower concentrations (50-100 mol m(-3)) and in case of this cyclitol a ratio of membrane toxic to membrane compatible solute of 0.66 was apparently needed to prevent a loss of cyclic photophosphorylation. Little difference was observed in the results from spinach or chickpea thylakoids although these plants naturally accumulate different cyto-solutes (spinach: glycinebetaine; chickpea: pinitol).

Summary Intact plants and cells (photoautotrophic, photomixotrophic, heterotrophic) in suspension culture of Cicer arietinum L. were compared for their ability to synthesize and accumulate O -methyl-inositols. In intact plants (leaves, shoot axis, roots), pinitol (1D-3- O -methyl- chiro -inositol) was the major cyclitol of the polyol fraction and it was accumulated in response to drought stress. Withholding water from the plants for 14 days caused an increase in pinitol from 5 to 195 mmol kg -1 dry matter in the leaves, from 9 to 67 mmol kg -1 dry matter in the shoot axis and from 5 to 22 mmol kg -1 dry matter in the roots, which was far beyond the levels in controls of the same age. In contrast to the intact plants pinitol was not detectable in most of the suspension cultured cells. It was only present in small amounts ( -1 dry matter) in photoautotrophic cells when cells were stressed with either 100 mol m -3 NaCl or 200 mol m -3 sorbitol. The precursor of pinitol, ononitol (1D-4- O -methyl- myo -inositol), appeared in traces under control conditions in photomixotrophic cells, but was accumulated up to 27 mmol kg -1 dry matter under salinity conditions (100 mol m -3 NaCl). No methylated cyclitol was detectable in heterotrophic cells. However, when photoautotrophic cells were reverted to heterotrophic conditions they maintained the ability to synthesize ononitol for more than 6 months. The presented data provide evidence that O-methyl-inositol synthesis can be induced on the cellular level. Photosynthetic activity of the cells is not a necessary prerequisite for accumulation of methylated polyols.

The foliar content of nitrogen and the relative abundances of 13C and 15N were analysed in vascular epiphytes collected from six sites along an altitudinal gradient from tropical dry forests to humid montane forests in eastern Mexico. The proportion of epiphyte species showing crassulacean acid metabolism (CAM) (atmospheric bromeliads, thick-leaved orchids, Cactaceae, and Crassulaceae) decreased with increasing elevation and precipitation from 58 to 6%. Atmospheric bromeliads, almost all of which had δ13C values indicating CAM, were more depleted in 15N (x=−10·9‰± 2·11) than the C3 bromeliads which form water-storing tanks (−6·05‰± 2·26). As there was no difference in δ15N values between C3 and CAM orchids, the difference in bromeliads was not related to photosynthetic pathways but to different nitrogen sources. While epiphytes with strong 15N depletion appear to obtain their nitrogen mainly from direct atmospheric deposition, others have access to nitrogen in intercepted water and from organic matter decomposing on branches and in their phytotelmata. Bromeliads and succulent orchids had a lower foliar nitrogen content than thin-leaved orchids, ferns and Piperaceae. Ground-rooted hemi-epiphytes exhibited the highest nitrogen contents and δ15N values.

Mature trees have already experienced substantial increases in CO2 concentrations during their lifetimes, and will experience continuing increases in the future. Small open-top chambers were used to enclose branchlets that were at a height of between 20 and 25 m in the canopy of the tree species Luehea seemannii Tr. & Planch. in a tropical forest in Panama. Elevated concentrations of CO2 increased the rate of photosynthetic carbon fixation and decreased stomatal conductance of leaves, but did not influence the growth of leaf area per chamber, the production of flower buds and fruit nor the concentration of nonstructural carbohydrates within leaves. The production of flower buds was highly correlated with the leaf area produced in the second flush of leaves, indicating that the branchlets of mature trees of Luehea seemannii are autonomous to a considerable extent. Elevated levels of CO2 did increase the concentration of nonstructural carbohydrates in woody stem tissue. Elevated CO2 concentration also they increased the ratio of leaf area to total biomass of branchlets, and tended to reduce individual fruit weight. These data suggest that the biomass allocation patterns of mature trees may change under future elevated levels of CO2. Although there were no effects on growth during the experiment, the possibility of increased growth in the season following CO2 enrichment due to increased carbohydrate concentrations in woody tissue cannot be excluded.

Communities of ten species of tropical forest tree seedlings from three successional classes were grown at ambient and elevated CO2 in large open-top chambers on the edge of a forest in Panama. Communities grew from 20 cm to approximately 2 m in height in 6 months. No enhancements in plant biomass accumulation occurred under elevated CO2 either in the whole communities or in growth of individual species. Reductions in leaf area index under elevated CO2 were observed, as were decreases in leaf nitrogen concentrations and increases in the C:N ratio of leaf tissue. Species tended to respond individualistically to elevated CO2, but some generalizations of how successional groupings responded could be made. Early and mid-successional species generally showed greater responses to elevated CO2 than late-successional species, particularly with respect to increases in photosynthetic rates and leaf starch concentrations, and reductions in leaf area ratio. Late-successional species showed greater increases in C:N ratios in response to elevated CO2 than did other species. Our results indicate that there may not be an increase in the growth of regenerating tropical forest under elevated CO2, but that there could be changes in soil nutrient availability because of reductions in leaf tissue quality, particularly in late-successional species.

bulk tissue elastic modulus (wall rigidity) which resulted in turgor loss at the same h in both stressed Ber (Ziziphus mauritiana Lamk.) is a major fruit tree and unstressed leaves. The possible ecological signicrop of the north-west Indian arid zone. In a study of ficance of maintenance of turgor potential and cell the physiological basis of drought tolerance in this volume at low water potentials for drought tolerance species, two glasshouse experiments were conducted in Ziziphus is discussed. in which trees were droughted during single stresscycles. In the first experiment, during a 13 d drying Key words: Ziziphus mauritiana, drought, solute accumulacycle, pre-dawn leaf water (Y leaf ) and osmotic (Y p ) tion, osmotic adjustment, proline. potentials in droughted trees declined from ’0.5 and ’1.4 MPa to ’1.7 and ’2.2 MPa, respectively, for a decrease in relative water content (h) of 14%. During Introduction drought stress, changes in sugar metabolism were associated with significant increases in concentra- Drought is probably the most important factor limiting tions of hexose sugars (3.8-fold), cyclitol (scyllo- crop productivity world-wide (Jones and Corlett, 1992). inositol; 1.5-fold), and proline (35-fold; expressed per In semi-arid regions, where the amounts and patterns of unit dry weight), suggesting that altered solute parti- seasonal rainfall are often erratic and unpredictable, deeptioning may be an important factor in drought toler- rooting perennial species may exploit deep soil water ance of Ziziphus. On rewatering, pre-dawn Y leaf and h reserves. This facilitates production of yields in situations recovered fully, but Y p remained depressed by 0.4 MPa of high light coupled with drought, where shallow-rooted relative to control values, indicating that solute con- annual crops would normally fail. The use of perennials centration per unit water content had changed during may help buVer farmers’ production against year-to-year the drought cycle. fluctuations in yields from annual crop species. Under Evidence for osmotic adjustment was provided from such conditions, an ability to maintain cell water status a second study during which a gradual drought (e.g. through osmotic adjustment and/or leaf area adjustwas imposed. Pressure‐volume analysis revealed a ment) and cell integrity (by protecting cells against photo0.7 MPa reduction in osmotic potential at full turgor, and chemical oxidation) may be an advantage. There are with Y leaf at turgor loss depressed by ~1 MPa in many cases where plants growing in hostile environments drought-stressed leaves. Coupled with osmotic adjust- exhibit increased oxy-stress enzyme activities to combat lipid peroxidation by free radicals, hydrogen peroxide

Kalanchoe pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved crassulacean-acid-metabolism plant, was grown in open-top chambers at ambient and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffected by CO2 treatments. However, under elevated CO2, dry matter accumulation increased by 42–51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime in the light. Malic acid was the major organic acid accumulated overnight. Nocturnal malate accumulation exceeded nocturnal citrate accumulation by six-to eightfold at both CO2 concentrations. Basal (predawn) starch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both ambient and elevated CO2. In both treatments, nocturnal starch degradation accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to exhibit marked day-night fluctuations.

Changes in chlorophyll a fluorescence during the day and diurnal-changes of net CO2-exchange and organic acid contents were determined in two species of the genus Clusia during the dry season in Venezuela. The investigations included plants of the C3/CAM intermediate species Clusia minor and the C3 species C. multiflora growing at exposed and shaded sites. Both species showed a C3 pattern of net CO2-exchange at the exposed site. In the shade under extreme drought stress C. minor showed a weak expression of CAM without CO2-uptake during the afternoon (phase IV of CAM). C. multiflora growing in the shade exhibited a C3-pattern of net CO2-exchange and a small but significant nocturnal accumulation of citrate. Shaded plants of C. minor were able to double their light utilisation for electron transport and to reduce non-photochemical quenching during phase III compared to phase II of CAM. Furthermore, increase of electron transport rate through photosystem II in phase III of CAM is correlated to decarboxylation of malate. At the exposed site C. multiflora was less negatively affected by high PPFD than C. minor. This was shown by a lower reduction of potential electron quantum yield (Fv/Fm) and higher light utilisation of electron transport of C. multiflora compared to C. minor. At the exposed site C. minor did not make use of the CAM option to increase light utilisation of electron transport and to reduce non-photochemical quenching as did the plants growing in the shade.

Four different Clusia species showing C 3 photosynthesis (C. multiflora) or crassulacean acid metabolism (CAM) (C. rosea, an unidentified Clusia sp. and C. alata) co-occur in the same habitat in the northwest of Venezuela. The aim of this field study was to correlate the adaptive changes in chlorophyll a fluorescence with gas exchange patterns and deacidification of nocturnally accumulated organic acids. The results indicate that in C. rosea and Clusia sp. a lowering of the potential quantum yield, measured as F v /F m after 10 min of dark adaptation, is restricted to the early morning hours. With the onset of deacidification there was no further decline in F v /F m , although the irradiance upon the leaves remained high. For the C 3 -plant, C. multiflora, changes in F v /F m were correlated with changes in irradiance incident on the leaves before predarkening for 10 min for F v /F m measurements. The fast relaxation of F v /F m under low light indicates that C. multiflora was not suffering photoinhibitory damage. Effective quantum yield as determined by ΔF/F' m , was low under high irradiances for C. rosea and Clusia sp. and did not change significantly for C. rosea during phase III of CAM. During the time of low incident irradiance C. alata and C. multiflora reached an effective quantum yield that was close to the optimal quantum yield of electron transport. It is noteworthy that apparent electron transport rates through photosystem II (PS II) ((ΔF/F' m ) x PPFD) were highest for C. rosea, Clusia sp. and C. alata during phase III of CAM. Electron transport rates in C. multiflora were lower under high irradiance and did not differ from those found in phases II and IV of CAM. The possible role of CO 2 evolution from acid decarboxylation with respect to photosynthetic efficiency is discussed.

In search of a reliable drying method, which might be used even under field conditions, microwave drying was compared to freeze-drying of plant material. Leaves of Ananas comosus and Avicennia germinans as well as buds and phloem of Acer pseudoplatanus were used and checked for one or more of the following substances: sugars, sugar alcohols, organic and amino acids, total nitrogen, and glycinebetaine. With most samples good agreement was achieved between the two drying methods. Only in the case of the Ananas comosus leaves, which exhibited low pH and high water content, did appreciable differences occur in organic and amino acids. Besides that, sucrose was the compound most susceptible to alterations, which was especially evident when leaves of Sambucus nigra were dried in the two different compartments (condenser compartment, drying bell jar) of the freeze-dryer in use. For Ananas comosus leaf samples it was shown that microwaving can also be used prior to extraction of tissue sap.

Gas exchange patterns and water relations of two mistletoes, Tapinanthus oleifolius and Viscum rotundifolium on the same deciduous host tree, Acacia nebrownii, have been studied intensively in the dry and wet seasons in semi-arid south-eastern Namibia, where rain falls only in the summer. Comparative measurements of Tapinanthus oleifolius on the stem-succulent CAM plant, Euphorbia virosa, and on Ziziphus mucronata in the same area were also made. All measurements of CO2 exchange and transpiration were performed in fully acclimatized cuvettes of a gas exchange system which allowed continuous measurements of the host and the parasite simultaneously. The water potential results confirm previous observations that mistletoes have a lower water potential throughout the day than their hosts. In the dry season, pre-dawn and minimum water potential was about 1 MPa lower than in the wet season, for both the leafless and fully foliated host and the evergreen mistletoes. There was an effective stomatal control in all mistletoe plants investigated. The results obtained for transpiration, leaf conductance, internal CO2 concentration and water-use efficiency (WUE) contradicted commonly accepted generalizations. Transpiration and leaf conductance were found to be higher for the host than for any of its common mistletoes as long as the leaf-to-air water vapour pressure difference (Δw) did not exceed 30 mPa Pa− 1, At higher values of Δw, Tapinanthus oleifolius, but not Viscum rotundifolium, transpired at higher rates than the host. CO2 balance over 24 hours and photosynthetic CO2 uptake were significantly higher for the host than for any of its parasites. Although the WUE over 24 h was slightly better for Acacia nebrownii compared with Tapinanthus oleifolius, apparent WUE during photosynthetic CO2 uptake was always better for both mistletoes. Measurements of CO2 and water balance over 24 h, photosynthetic CO2 uptake, night respiration, internal CO2 concentration, leaf conductance and WUE indicate that Tapinanthus oleifolius and Viscum rotundifolium behaved in opposite ways in the dry and wet seasons, indicating that different phenological cycles of both species might be involved in determining mistletoe performance on the same host. The results presented contribute to a better understanding of the host/parasite relationship and indicate that commonly accepted generalizations may not always be applicable. Gaswisselingspatrone en waterverhoudings van twee voelente Tapinanthus oleifolius en Viscum rotundifolium op dieselfde bladwisselende gasheerplant Acacia nebrownii is bestudeer in die droe en nat seisoene in Suid-Oos-Namibie. Vergelykende studies van Tapinanthus oleifolius op Ziziphus mucronata en die stamsukkulente CAM plant Euphorbia virosa is ook uitgevoer. Alle bepalings is in ten voile ge-akklimatiseerde kuvette uitgevoer wat deurlopende bepalings op die gasheer en parasiet moontlik gemaak het. Die resultaat van die waterpotensiaalbepalings bevestig vorige waarnemings dat voelente’n laer waterpotensiaal gedurende die dag het as hulle gashere. Die minimum waterpotensiaal voor dagbreek in die droe seisoen was ongeveer 1 MPa laer as in die nat seisoen vir beide die blaarlose en blaarbevattende gasheerplant en die immergroen voelente wat ondersoek is. In al die voelente was daar effektiewe stomatere beheer teenwoordig. Die resultate wat behaal is vir transpirasie, blaargeleiding, interne koolsuurgaskonsentrasle en waterbenuttingsdoeltreffendheid het nie ooreengestem met aanvaarde veralgemenings nie. Transpirasie en blaargeleiding was hoer vir die gasheer as vir enige van die voelente solank as die blaar-tot-lug waterdampdruk verskil nie 30 mPa Pa− 1 oorskry het nie. By hoer waardes het Tapinanthus oleifolius, maar nie Viscum rotundifolium nie, teen’n hoer tempo as die gasheerplant getranspireer. Die koolsuurgasbalans oor 24 uur en die fotosintetiese koolsuurgasopname was betekenisvol hoer vir die gasheer as vir enige van die parasiete. Alhoewel die waterbenuttingsdoeltreffendheid oor 24 uur effens beter vir Acacia nebrownii as vir Tapinanthus oleifolius was, was die skynbare waterbenuttingsdoeltreffendheid gedurende fotosintetiese koolsuurgasopname altyd beter. Bepaling van die koolsuurgas en waterbalans oor 24 uur, fotosintetiese koolsuurgasopname, nagrespirasie, interne koolsuurgaskonsentrasie, blaargeleiding en waterbenuttingsdoeltreffendheid het aangedui dat die twee parasiete teenoorgesteld gereageer het in die nat en droe seisoene. Dit mag beteken dat verskillende fenologiese siklusse van albei spesies betrokke mag wees in die bepaling van voelentprestasie op dieselfde gasheer. Die resultate lei tot’n beter begrip van gasheer/parasietverwantskappe en dui daarop dat die aanvaarde veralgemenings nie altyd korrek is nie.

The inorganic ion and organic solute composition of Tapinanthus oleifolius (Loranthaceae) and Viscum rotundifolium (Viscaceae) growing on various host trees in Namibia were investigated. Organic osmolytes accounted for 22.8–45.1% of the total solutes determined in leaves of the mistletoes parasitizing Acacia nebrownii, Catophractes alexandri, Grewia flava and Ziziphus mucronata. On other hosts (Acacia karroo, Euphorbia virosa, Salvadora persica and Tamarix usneoides) T. oleifolius showed distinct succulence with increasing leaf age, with leaves more than 3 mm thick on E. virosa. In the more succulent leaves (> 1.1 kg H2O m−2 leaf area) organic solutes were only of minor importance. Water content per leaf area was significantly correlated with chloride content per leaf area, suggesting that succulence served as a means to keep ion concentration at a physiological tolerable level. At whole plant levels 93.7% of the total sodium of the mistletoe bush was located in leaves thicker than 1 mm for T. oleifolius parasitizing Tamarix usneoides. This pronounced sequestration of sodium in older leaves as well as the high variability of the K/Na ratio in various parts of the parasite-host system point to highly selective ion distribution processes in this association.

Cyclitols are low molecular weight substances which accumulate in plant cells in response to various environmental stress situations, for example drought (Ford 1984), salinity (Gorham et al. 1984), low temperature (Richter et al. 1990).Apart from their more general role in osmotic adjustment, only in the case of salt stress is their mode of function well understood. Cyclitols (e.g. pinitol) accumulate when plants are exposed to increasing salt concentration (Paul & Cockburn 1989) and act as compatible solutes (Sommer et al. 1990) as defined by Brown & Simpson (1972).The significance of cyclitol accumulation in stress adaptation of plants to drought and cold still remains uncertain. However, it is generally accepted that drought and cold as well as several other stress situations lead to an enhanced generation of oxygen free radicals (Elstner 1990; Smirnoff & Colombe 1988), including the hydroxyl radical as the most harmful one. The report by Smirnoff & Cumbes (1989) that myo-inositol is an effective hydroxyl radical scavenger prompted us to test other naturally-occuring cyclitols like pinitol, quebrachitol, 1-D-1-O-methyl-muco-inositol, ononitol and quercitol for their ability to scavenge hydroxyl radicals.

SUMMARY Investigations of Viscum album on 16 different host species revealed an endogenous cyclitol pattern with pinitol, 1-O-methyl-muco-inositol, quebrachitol, chiro-inositol, an unidentified O-methyl-inositol and traces of ononitol. Host-specific cyclitols including bornesitol, quercitol, viburnitol, scyllo-inositol and the hexitol, sorbitol, were also stored in the mistletoe. The endogenous cyclitols were accumulated to such high concentrations that they made a large contribution to the osmotic potential. It was estimated that 22.6–43 % of mistletoe carbon is derived from the host.

Clusia rosea Jacq. is abundant in the moist parts of the Caribbean island of St John (US Virgin Islands, Lesser Antilles) but relatively rare along the dry south coast. Three types of seedlings were encountered, terrestrial seedlings, seedlings growing as humus-epiphytes on other trees, and seedlings growing inside the tanks of the bromeliad Aechmea lingulata (L.) Baker. Free-living trees grow from terrestrial seedlings or from epiphytic seedlings strangling and shading their host trees. Leaf-Na+ levels were always low (1-4 mequiv I-1 tissue water); trees close to the shore were not affected by salinity. In leaves of mature C. rosea trees, levels of Ca2+ , Mg2+ and K+ were about 60-90, 40-50, 45-55 mequiv I-1 tissue water, respectively. Epiphytic seedlings tended to contain lower levels of these inorganic cations than seedlings growing terrestrially or in the tanks of Ae. lingulata. Epiphytic seedlings contained significantly less nitrogen than terrestrial seedlings. In the leaves of mature trees N-levels were independent of altitude and location on the island, but shaded leaves had significantly higher N-levels than exposed leaves. Light compensation point of photosynthesis in epiphytic seedlings performing C3 -photosynthesis was 17-5 (μmol photons m-2 s-1 ), photosynthesis was saturated at about 300μmol photons m-2 s-1 showing a maximum rate of CO2 -uptake of 2-3 μmol m-2 s-1 .

Pinitol (1d-3-O-methyl-chiro-inositol) and 1d-1-O-methyl-muco-inositol, two cyclitols wide-spread in the plant kingdom, were isolated from plant sources in order to test their compatibility with malate dehydrogenase activity. Both compounds had no inhibitory effect on malate dehydrogenase from Rhizophora mangle in a range of 100 to 1000 mol . m−3. Their influence on malate dehydrogenase activity from different plant sources (Rh. mangle L., Mesembryanthemum crystallinum L., Cicer arietinum L. and Spinacia oleracea L.) was also small and similar to that observed for a number of well established compatible solutes (e.g. proline, glycine betaine). A possible role of cyclitols as cryoprotectants or radical scavengers is discussed.

Populations of Acrostichum aureum growing under contrasting conditions of soil salinity and sunlight exposure were studied in two sites in the north coast of Puerto Rico. Plant size and density of clumps under full sun exposure are larger in sites with lower soil salinity. In shady habitats with relatively high soil salinity (understory of Laguncularia forests), plants grow larger but occur at lower densities as compared with nonshaded sites. Apparently salt stress in shady habitats is reduced due to lower evaporative demands. Osmotic concentration of leaf cell sap increases markedly with soil salinity (except in shade plants), a process accompanied by corresponding increases in leaf water content per unit leaf area, and reductions in leaflet size and specific leaf area. The major solutes responsible for increases in cell sap osmotic pressure are Na+, Mg2+, and sucrose. However, the largest relative response to salinity is shown by the cyclitol D-1-0-methyl-muco-inositol, a cytoplasmic compatible solute. ...

Antarctic bryophyte communities presently tolerate physiological extremes in water availability, surviving both desiccation and submergence events. We investigated the relative ability of three Antarctic moss species to tolerate physiological extremes in water availability and identified physiological, morphological, and biochemical characteristics that assist species performance under such conditions. Tolerance of desiccation and submergence was investigated using chlorophyll fluorescence during a series of field- and laboratory-based water stress events. Turf water retention and degree of natural habitat submergence were determined from gametophyte shoot size and density, and δ13C signatures, respectively. Finally, compounds likely to assist membrane structure and function during desiccation events (fatty acids and soluble carbohydrates) were determined. The results of this study show significant differences in the performance of the three study species under contrasting water stress events. The results indicate that the three study species occupy distinctly different ecological niches with respect to water relations, and provide a physiological explanation for present species distributions. The poor tolerance of submergence seen in Ceratodon purpureus helps explain its restriction to drier sites and conversely, the low tolerance of desiccation and high tolerance of submergence displayed by the endemic Grimmia antarctici is consistent with its restriction to wet habitats. Finally the flexible response observed for Bryum pseudotriquetrum is consistent with its co-occurrence with the other two species across the bryophyte habitat spectrum. The likely effects of future climate change induced shifts in water availability are discussed with respect to future community dynamics.

Adaptation to aridity is considered a major factor in the evolution of the genus Eucalyptus. For the first time, targeted metabolite profiling has uncovered a quantitative yet discrete phytochemical link with eucalypt taxonomy. The distribution of cyclitols among Eucalyptus species, and a range of other Australian tree genera, support their proposed functions in plant tissues and provide putative links with the acclimation of trees to arid environments.

The ecological situation of oases at the southern border of the Taklamakan desert is shortly described, and the importance of a vegetation from indigenous species at the transition from the oases to the desert is emphasized. This vegetation serves as a shelter against sand drift and as a source of livestock feed as well as of fuel and construction material. Its destruction through overexploitation and other interventions during the last decades has considerably promoted sand drift and the deterioration of arable land. Therefore, a management of this protective vegetation is to be developped that leads to a sufficient regeneration and that ensures both its preservation and its use. A research project that is carried through jointly by Chinese and European scientists shall yield an ecological basis for this sustainable management.

The progressive desertification in many semiarid regions of the world increases the need for plants that can cope with arid environments and meet peoples’ requirements for food, fodder and fuel. Species of fruit trees in the genus Ziziphus represent examples of such multipurpose plants with great potential for selection and use in drought-prone regions.

Stachyose is the major soluble carbohydrate in seeds of a number of important crop species. It is synthesized from raffinose and galactinol by the action of stachyose synthase (EC 2.4.1.67). We report here on the identification of a cDNA encoding stachyose synthase from seeds of adzuki bean (Vigna angularis Ohwi et Ohashi). Based on internal amino acid sequences of the enzyme purified from adzuki bean, oligonucleotides were designed and used to amplify corresponding sequences from adzuki bean cDNA by RT-PCR, followed by rapid amplification of cDNA ends (RACE-PCR). The complete cDNA sequence comprised 3046 nucleotides and included an open reading frame which encoded a polypeptide of 857 amino acid residues. The entire coding region was amplified by PCR, engineered into the baculovirus expression vector pVL1393 and introduced into Spodoptera frugiperda (Sf21) insect cells for heterologous expression. The recombinant protein was immunologically reactive with polyclonal antibodies raised against stachyose synthase purified from adzuki bean and was shown to be a functional stachyose synthase with the same catalytic properties as its native counterpart. High levels of stachyose synthase mRNA were transiently accumulated midway through seed development, and the enzyme was also present in mature seeds and during germination.

The term “mistletoe” has a double meaning: sensu stricto it applies to Viscum album L. (European mistletoe), but it is more generally used to describe perennial (usually woody) flowering plants which are attached to the shoot of trees or shrubs (Barlow 1987). The majority of the approximately 1300 mistletoe species fall into the two closely related families Loranthaceae and Viscaceae within the order Santalales (Calder 1983).

The unusual gas-exchange stoichiometries of succulent plants which engage in crassulacean acid metabolism (CAM) have been recognized since de Saussure (1804), whose observations are best accessible today via Thomas (1949). In beautifully crafted sentences, sometimes exceeding 100 words, Thomas reviewed the history of gas-exchange experimentation in CAM plants. He left his indelible mark on the dark reactions of CAM with the words “The positive contribution made by the Leipzig workers was to draw attention to the possible cardinal importance (cf. Gustafson’s qualified statement) of carbon dioxide rather than oxygen in controlling diurnal fluctuations in the acidity of the green cells of plants showing crassulacean acid metabolism. The present writer felt that this possibility became a probability when he had considered the experimental results obtained at Leipzig and elsewhere in the light of Wood and Werkman’s discovery”. There is no clearer, and more generous, expression of the origins of the hypothesis that led us to an understanding of the mechanisms of dark CO2 fixation and malic-acid synthesis in CAM plants. Appreciation of photosynthetic CO2 fixation in CAM plants is less clear, historically. Bennet-Clark (1933) attributed the recognition of malate decarboxylation as an internal CO2 source for photosynthesis to A. Mayer (1878, 1899) and to H.A. Spoehr (1913) (cited in Bennet-Clark 1933).

One of the now widely used definitions of halophytes is that of Jennings (1976), describing them as “the native flora of saline habitats”. This is very close to the description by Warming (1909 English Edition, 1895 Plantesamfund Danish Edition), who coined this and a larger number of still commonly used terms like hydro-, meso-, and xerophytes. According to Warming (1909), “a certain amount of soluble salts must be present before halophytic vegetation is called into existence; but the nature of the salts seems to be a matter of indifference”. Following Munns et al. (1983), such a habitat is one “containing saline water with an osmotic pressure (π) of more than 3.3 bar” (equivalent to 70 mM monovalent salts).

The various components of salt resistance were tested for their importance for salt adaptation in mangroves. Evidently avoidance of salt uptake by special mechanisms in the mangrove roots is of paramount importance. Retention of NaCl in roots and lower parts of the stem was negligible in young, glasshouse-grown mangroves. Salt excretion by specialized glands contributed essentially to the maintenance of a certain NaCl level in mangrove leaves. However, only a few mangrove species are salt-excreting. For non-excreting species retranslocation of NaCl via the phloem and increasing succulence seemed to contribute decisively to the maintenance of a stable NaCl level in the leaves. Although there is not a lot of direct evidence, it might be assumed that NaCl is mainly stored in the vacuole. In 29 out of 30 mangrove species organic solutes, which are thought to serve for the intracellular osmotic adjustment, were present in appreciable amounts. In a number of cases it was shown that concentrations of these organic solutes corresponded to the salinity stress applied.

Nitrogen availability is one of the most decisive factors for plant performance in agricultural systems as well as in natural habitats. Not solely the amount of nitrogen, but also the presence of its different forms — nitrate or ammonium — has been considered important for plant distribution (cf. Lee et al. 1983; Runge 1983). A number of reviews and proceedings have dealt with these ecological aspects of nitrogen assimilation (Smirnoff and Stewart 1985; Lambers et al. 1986; Sprent 1987). However, in view of some recent developments, it seems justified to dedicate a further review to this subject.

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001. The C3-crassulacean acid metabolism tropical hemiepiphytic tree, Clusia minor L., is highly flexible in terms of ecological sites occupied, life forms, and photosynthetic and metabolic pathways. We studied nitrogen uptake patterns in two glasshouse 15N-labelling experiments using hydroponically-grown plants and excised roots of pot-grown C. minor, and investigated leaf and root nitrate reductase activity (NRA) in a field study in Venezuela. The results of both 15N-uptake experiments indicate that C. minor utilized all offered nitrogen sources, but clearly preferred to take up NH4+ over glycine (GLY) and NO3-. The uptake pattern of NH4+ and NO3- was identical in intact plants and excised roots, and NH4+ was taken up to a much larger extent in both experiments. Gas chromatography-mass spectrometry (GC-MS) analysis of amino acids in excised roots revealed that glutamine (45 atom-%), glutamate (23 atom-%) and alanine (34 atom-%) accounted for most of the labelled soluble amino acids after 2-h labelling with 15NH4+. High amounts of 15N in GLY and serine confirmed that GLY was taken up as an intact molecule and metabolized in the excised roots. With 15NO3- labelling, only a small amount of 15N was found in the amino acid fraction, indicating a low NO3- assimilation rate by nitrate reductase. This was confirmed by low NRA of leaves and roots in C. minor plants in Venezuela. It appears, therefore, that a high degree of plasticity is not reflected in nitrogen uptake and metabolism. Although C. minor exhibits clear preferences for NH4+ uptake, it can utilize other sources of nitrogen, and the nitrogen uptake pattern represents an adaptation to the natural environments in which C. minor can grow.

Tolerance of desiccation was examined in three species of moss, Grimmia antarctici Card., Ceratodon purpureus (Hedw.) Brid. and Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb. collected from two sites of contrasting water availability in the Windmill Islands, continental Antarctica. Physiological tolerance to desiccation was measured using chlorophyll fluorescence in plugs of moss during natural drying in the laboratory. Differences in relative water content, rate of drying and the response of photosynthesis to desiccation were observed among the three species and between sites. Of the three species studied, G. antarctici showed the lowest capacity to sustain photosynthetic processes during desiccation, B. pseudotriquetrum had an intermediate response and showed the greatest plasticity and C. purpureus showed the greatest capacity to sustain photosynthesis during desiccation. These results fit well with the known distribution of the three species with G. antarctici being limited to relatively wet sites, C. purpureus being common in the driest sites and B. pseudotriquetrum showing a wide distribution between these two extremes. Levels of soluble carbohydrates were also measured in these samples following desiccation and these indicate the presence of stachyose, an oligosaccharide known to be important in desiccation tolerance in seeds, in B. pseudotriquetrum. Both gross morphology and carbohydrate content are likely to contribute to differences in desiccation tolerance of the moss species. These results indicate that if the Casey region continues to dry out, as a result of local geological uplifting or global climate change, we would expect to see not only reductions in the moss community but also changes in community composition. G. antarctici is likely to become more limited in distribution as C. purpureus and B. pseudotriquetrum expand into drying areas.

1d-1-O-Methyl-muco-inositol was isolated from Viscum album as well as from Rhizophora mucronata and identified by GC retention times, GC-MS, 13C NMR and by specific rotation. In V. album and in various members of the Rhizophoraceae the compound was stored in large amounts up to 8.4% of dry wt. Increase of concentrations under salinity stress (Ceriops tagal) and during the cold season (V. album) suggested a role of 1d-1-O-methyl-muco-inositol as a stress metabolite and cryoprotectant respectively.

To investigate the importance of phosphorus and carbohydrate concentrations in influencing photosynthetic capacity of tropical forest tree seedlings under elevated CO2, we grew seedlings of Beilschmiedia pendula (Sw.) Hemsl. (Lauraceae) under elevated CO2 concentrations either with or without vesicular-arbuscular (VA) mycorrhizae. VA-mycorrhizae increased phosphorus concentrations in all plant organs (leaves, stems and roots). Maximum rates of photosynthesis (Amax) measured under saturating levels of CO2 and light were correlated with leaf phosphorus concentrations. VA-mycorrhizae also increased leaf carbohydrate concentrations, particularly under elevated CO2, but levels were low and within the range observed in naturally occurring forest species. Root carbohydrate concentrations were reduced in VA-mycorrhizal plants relative to non-mycorrhizal plants. These results indicate an important role for VA-mycorrhizae in controlling photosynthetic rates and sink strength in tropical trees, and thus in determining their response to future increases in atmospheric CO2 concentrations.