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The vegetative desiccation tolerance of Tripogon spicatus (Nees) Ekman was confirmed by its ability to recover the physiological functionality of intact plants previously subjected to extreme dehydration. Photosynthesis became undetectable when leaf relative water content (RWCleaf) achieved ~60%, whereas photochemical variables showed a partial decrease. Until the minimum RWCleaf of 6.41%, total chl decreased by 9%, and total carotenoids increased by 29%. Superoxide dismutase (SOD) activity decreased by 57%, on average, during dehydration, but catalase (CAT) and peroxidase (APX) activities showed no significant differences throughout the experiment. Malondialdehyde (MDA) content increased by 151%, total leaf and root amino acids decreased by 62% and 77%, respectively, whereas leaf and root proline decreased by 40% and 61%, respectively, until complete desiccation. After rehydration, leaves completely recovered turgidity and total chl contents. Carotenoids and MDA remained high, whereas SOD was 60% lower than the measured average measured before dehydration. With the exception of root amino acid contents, total amino acids and proline concentrations recovered completely. Gas exchange and photochemical variables remained substantially higher 4 days after rehydration, compared with the control. Besides increasing MDA, the overall physiological results showed that membrane functionality was preserved, leading to the vegetative desiccation tolerance of T. spicatus during the dehydration-rehydration cycle. [ABSTRACT FROM AUTHOR]

Low soil water content can limit photosynthesis by reducing stomatal conductance. Here, we explore relationships among traits pertaining to carbon uptake and pre-dawn leaf water potential (as an index of soil water availability) across eight species found in semiarid central Australia. We found that as pre-dawn leaf water potential declined, stomatal limitations to photosynthesis increased, as did foliar nitrogen, which enhanced photosynthesis. Nitrogen-fixing Acacia species had higher foliar nitrogen concentrations compared with non-nitrogen fixing species, although there was considerable variability of traits within the Acacia genus. From principal component analysis we found that the most dissimilar species was Acacia aptaneura Maslin & J.E.Reid compared with both Eucalyptus camaldulensis Dehnh. and Corymbia opaca. (D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson, having both the largest foliar N content, equal largest leaf mass per area and experiencing the lowest pre-dawn water potential of all species. A. aptaneura has shallow roots and grows above a hardpan that excludes access to groundwater, in contrast to E. camaldulensis and C. opaca, which are known to access groundwater. We conclude that ecohydrological niche separation is an important factor driving the variability of within-biome traits related to carbon gain. These observations have important implications for global vegetation models, which are parameterised with many of the traits measured here, but are often limited by data availability. [ABSTRACT FROM AUTHOR]

The drought-tolerant plant Caragana korshinskii Kom· was used to investigate the relative contribution of photorespiration and antioxidative mechanisms to water-stress adaptations across the Loess Plateau. The samples were collected from Shenmu, Yulin and Dongsheng along with the reduction of rainfall. The results showed the lower leaf water potential and the lower content of O2 - and malondialdehyde (MDA) were found in the plants in drier zone· H2O2 didn't show a significant difference among these sampling sites. Both photorespiratory rate (PR) and net photosynthetic rate (PN) increased with the decrease of rainfall. Low rainfall upregulated the gene expression and activities of photorespiratory enzymes. In addition, ascorbate peroxidase (APX), glutathione peroxidase (GPX) and superoxide dismutase (SOD) activity and reduced glutathione (GSH), ascorbic acid (AsA) contents increased with the decrease of rainfall, whereas catalase (CAT) activity decreased. These results indicate photorespiration could play a protective role for the photosynthetic apparatus from photoinhibition and photodamage under low rainfall levels, which could also act together with the antioxidation system to improve the tolerance to drought in C. korshinskii. [ABSTRACT FROM AUTHOR]

In order to reveal the mechanism of succession in subtropical forest along a light gradient, we investigated photosynthetic physiological responses to three light environments in five tree species including a pioneer species Pinus massoniana Lamb., two mid-successional species Schima superba Gardn. et Champ. and Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils., and two late-successional species Cryptocarya concinna Hance. and Acmena acuminatissima (BI.) Merr et Perry) that were selected from Dinghu Mountain subtropical forest, South China. Results showed that,amongthe three kinds of species in all light conditions (100%,30%and 12% of full sunlight), the pioneer species had the highest photosynthetic capacity (Amax), light saturation point (LSP), carboxylation efficiency (CE) and maximum utilisation rate of triose phosphate (TPU) that characterised a strong photosynthetic capacity and high carbon dioxide uptake efficiency. However, a higher light compensation point (LCP) and dark respiration (Rd) as well as lower apparent quantum yield (AQY) indicated that the pioneer specie cannot adapt to low light conditions. Mid-successional species had photosynthetic characteristics in between pioneer and late-successional species, but had the greatest effective quantum yield of PSII (ΦPSII) and light use efficiency (LUE, expressed in terms of photosynthesis). In contrast to pioneer and mid-successional species, late-successional species had lower photosynthetic capacity and carbon uptake efficiency, but higher shade tolerance and high-light heat dissipation capacity, as characterised by higher levels of total xanthophylls cycle pigments (VAZ) and de-epoxidation state of xanthophyll cycle (DEPs). These results indicate that photosynthetic capacity decreases along the successional axis and that late-successional species have more responsive heat dissipation capability to compensate for their inferior photosynthetic capacity. [ABSTRACT FROM AUTHOR]

The south-central Rocky Mountains, USA, are characterised by a dry, continental mesoclimate with typical convective cloud formation during the afternoon. Little is known about the specific influence of such predictable cloud patterns on the microclimate and ecophysiology of associated species. During the summer of 2012, days with afternoon clouds were most common (50% of all days) compared with completely clear (24%) or cloudy days (6.5%). In two representative alpine species, Caltha leptosepala DC. and Arnica parryi A. Gray, fully overcast days reduced mean daily photosynthesis (A) by nearly 50% relative to fully clear days. Mean afternoon A was significantly lower on fully cloudy days relative to days with afternoon clouds only or no clouds in both species. Notably, A did not differ during afternoon cloud days relative to clear afternoons. Afternoon clouds significantly reduced transpiration (E) in C. leptosepala relative to clear days, and both species showed mean reductions in plant water stress (i.e. higher Ψ), though this difference was not significant. Water use efficiency (WUE) (A/E) decreased from morning to afternoon, especially on cloudy days, and the presence of clouds had a positive effect on the light reactions of photosynthesis based on fluorescence measurements (Fv'/Fm'), in both species. Cloudy days were characterised by higher F[sub v]/F[sub m] than afternoon clouds and clear days during both the morning and the afternoon (especially for A. parryi) and recovery to near pre-dawn values for cloudy and afternoon cloud day types, but not clear days. Overall, similar ecophysiological advantages of this typical afternoon cloud pattern was apparent in both species, although their spatial microsite differences related to winter snow accumulation may also play an important role. Natural cloud regimes across the globe are expected to change with continued global warming. Yet, little is known about the impacts on plants, except for a few studies showing potentially strong effects on photosynthetic carbon gain and transpirational water loss. We found that these changes to the natural cloud regime had substantial impacts on photosynthesis, transpiration and water use efficiency. [ABSTRACT FROM AUTHOR]

A leaf gross photosynthesis (A) model for three Mediterranean species from different functional groups (the evergreen sclerophyll Arbutus unedoL., the deciduous tree Quercus frainettoTen. and the semi-deciduous shrub Phlomis fruticosaL.) has been developed through a 3-year seasonal study of gas exchange and plant ecophysiological parameters. The model estimates photosynthesis through four easily measured ecophysiological parameters (chlorophyll content, leaf mass per area (LMA), pre-dawn water potential, leaf temperature) and two meteorological parameters (PAR and average temperature of the 33-day period before measurement (T33)), with a coefficient of determination r2=0.88 (P<0.001). The enhanced accuracy of the presented model may be ascribed to the incorporation of (i) water potential effects on Aand (ii) temperature effects on Anot only in the short term, but also in the long term (acclimation). Water potential and temperature effects may be considered especially important for species of Mediterranean ecosystems, where strong seasonal variation of these parameters often have a major role in plant growth and survival. [ABSTRACT FROM AUTHOR]

We examined the relationship between variation in phyllode nerve density and the spatio-temporal response of the photosynthetic apparatus to water-stress in two Acacias.str. species with contrasting nerve patterns: Acacia floribunda(Vent.) Willd and Acacia pycnanthaBenth. A. floribundahad greater primary nerve density than A. pycnanthaand also showed greater spatial homogeneity in photosynthetic function with drought than phyllodes of A. pycnantha. A. pycnanthahad lower maximum quantum efficiency of PSII in phyllode tissue further from primary nerves consistent with its lower primary nerve density. Further, A. floribundaphyllodes maintained function of the photosynthetic apparatus with drought for longer and recovered more swiftly from drought than A. pycnantha. These findings suggest that greater primary nerve density may enhance drought tolerance and are consistent with the observed predominance of acacias with high primary nerve density in areas with lower precipitation. [ABSTRACT FROM AUTHOR]

Understanding the impacts of combined resource supplies on seedlings is critical to enable prediction of establishment growth, and forest dynamics. We investigated the effects of irradiance and water treatments on absolute growth, and relative growth rate (RGR) and its components, for seedlings of four Quercusspecies differing in leaf habit and with a wide variation in seed mass. Plants were grown for 6.5 months at three levels of irradiance (100, 27, and 3% daylight), and treated during the last 2.5 months with two watering treatments (frequent watering v.suspended watering). Both shade and drought reduced seedling growth rates, with a significant interaction: under full irradiance the drought treatment had a stronger impact on RGR and final biomass than under deep shade. For three species, seed mass was positively related to absolute growth, with stronger correlations at lower irradiance. The evergreen species grew faster than the deciduous species, though leaf habit accounted for a minor part of the interspecific variation in absolute growth. Seedling biomass was determined positively either by RGR or seed mass; RGR was positively linked with net assimilation rate (NAR) and leaf mass fraction (LMF), and seed mass was negatively linked with RGR and LMF, but positively linked with NAR. Seedling RGR was not correlated with light-saturated net photosynthetic rate, but was strongly correlated with the net carbon balance estimated, from photosynthetic light-response curves, considering daily variation in irradiance. These findings suggest an approach to applying short-term physiological measurements to predict the RGR and absolute growth rate of seedlings in a wide range of combinations of irradiance and water supplies. [ABSTRACT FROM AUTHOR]

Plant species with longer leaf longevity tend to maintain lower photosynthetic rates. Among other factors, differences in stomatal limitation have been proposed to explain the negative effects of leaf longevity on photosynthesis, although it is not yet clear why stomatal limitations should be stronger in species with longer leaf longevity. We measured carbon isotopic composition (δ13C) in the fresh leaf litter of several Mediterranean woody species to estimate the mean stomatal limitations during the photosynthetically active part of the leaf life. Interspecific differences in δ13C were best explained by a multiple regression including, as independent variables, the maximum leaf longevity and the annual water deficit. For a similar level of water availability, stomatal limitations were higher in species with longer leaf longevity. We hypothesise that stronger stomatal control of transpiration in longer-living leaves arose as a mechanism to reduce the risk of leaf desiccation and to avoid the high costs for the future C assimilation of anticipated leaf mortality in species with a long leaf life expectancy. This stronger sensitivity to drought should be added to the suite of traits accompanying long leaf longevity and contributes decisively to the overall limitations to C assimilation in long-lived leaves. [ABSTRACT FROM AUTHOR]

Excess irradiance can reduce the quantum yield of photosynthesis via photoprotective energy dissipation, inactivation or downregulation of PSII. We examined variation in photoprotection as part of a study of adaptive radiation in photosynthetic light responses by Hawaiian lobeliads. We measured the maximum efficiency of PSII (Fv/Fm) and recovery of Fv/Fm after high light stress in field populations of 11 lobeliad species and in four species growing under common-garden greenhouse conditions. Species showed no difference in Fv/Fm (0.82 ± 0.02 (mean ± s.e.)) or in their ability to recover from light stress under field conditions. Average recovery was 74 ± 1.4% within 1 h of removal of the stress suggesting that all species maintain the ability to recover from high light stress, at least in the short-term. In contrast, the results from the common-garden indicate that long-term exposure to high irradiance and associated higher temperatures can cause a sustained reduction in PSII function. Species showed decreased Fv/Fm and percentage recovery as treatment irradiance increased. Fv/Fm and percentage recovery were positively related to native habitat PFD across species, suggesting that there has been a diversification in high light tolerance, with species from sunnier environments better able to avoid sustained declines in PSII function. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an important determinant of plant productivity, particularly in the tropical grasslands of Australia, which contain both C3 and C4 species. Few studies have compared the responses of such species to P deficiency. Previous work led us to hypothesise that C3 photosynthesis and the three subtypes of C4 photosynthesis have different sensitivities to P deficiency. To examine their dynamic response to P deficiency in more detail, four taxonomically related tropical grasses (Panicum laxum (C3) and Panicum coloratum, Cenchrus ciliaris and Panicum maximum belonging to the C4 subtypes NAD-ME, NADP-ME and PCK, respectively) were grown under contrasting P supplies, including P withdrawal from the growing medium. Changes in photosynthesis and growth were compared with leaf carbohydrate contents and metabolic fingerprints obtained using high-resolution proton nuclear magnetic resonance (1H-NMR). The response of CO2 assimilation rates to leaf contents of inorganic phosphate ([Pi]) was linear in the C3 grass, but asymptotic for the three C4 grasses. Relative growth rate was affected most by low P in the C3 species and was correlated with the leaf content of glucose 6-phosphate more than with carbohydrates. Principal component analysis of the 1H-NMR spectra revealed distinctive profiles of carbohydrates and amino acids for the four species. Overall, the data showed that photosynthesis of the three C4 subtypes behaved similarly. Compared with the C3 counterpart, photosynthesis of the three C4 grasses had a higher P use efficiency and lower Pi requirement, and responded to a narrower range of [Pi]. Although each of the four grass species showed distinctive 1H-NMR fingerprints, there were no differences in response that could be attributed to the C4 subtypes. [ABSTRACT FROM AUTHOR]

Leaves of many evergreen species turn red when exposed to high sunlight during winter due to production of photoprotective anthocyanin pigments, while leaves of other species, lacking anthocyanin, remain green. Why some evergreen species synthesise anthocyanin pigments while others do not is currently unknown. Furthermore, the relative photosynthetic performance of anthocyanic (red) and acyanic (green) evergreens has yet to be described. Here we present seasonal ecophysiological data for five red and green broadleaf evergreen species. We hypothesise that species which synthesise anthocyanins in winter leaves correspond to those with the most drastic seasonal photosynthetic declines, as reduced energy sinks increase vulnerability to photoinhibition and need for photoprotection. Our results did not support this hypothesis, as gas exchange measurements showed no difference in mean seasonal photosynthetic capacity between red- and green-leafed species. Consistent with anthocyanin's shading effect, red-leafed species had significantly higher chlorophyll content, lower chlorophyll a/b ratios, and higher maximum light capture efficiency of PSII (Fv/Fm) than green-leafed species during the winter, but not during the summer (when all leaves were green). We conclude that anthocyanin production during winter is likely not associated with diminished photosynthetic capacity, and may simply represent an alternative photoprotective strategy utilised by some species during winter. [ABSTRACT FROM AUTHOR]

C4 photosynthesis has evolved many times in 18 different families of land plants with great variation in leaf anatomy, ranging from various forms of Kranz anatomy to C4 photosynthesis occurring within a single type of photosynthetic cell. There has been little research on photosynthetic typing in the family Cleomaceae, in which only one C4 species has been identified, Cleome gynandra L. There is recent interest in selecting and developing a C4 species from the family Cleomaceae as a model C4 system, since it is the most closely related to Arabidopsis, a C3 model system (Brown et al. 2005). From screening more than 230 samples of Cleomaceae species, based on a measure of the carbon isotope composition (?13C) in leaves, we have identified two additional C4 species, C. angustifolia Forssk. (Africa) and C. oxalidea F.Muell. (Australia). Several other species have ?13C values around ?17? to ?19?, suggesting they are C4-like or intermediate species. Eight species of Cleome were selected for physiological, anatomical and biochemical analyses. These included C. gynandra, a NAD?malic enzyme (NAD?ME) type C4 species, C. paradoxa R.Br., a C3?C4 intermediate species, and 6 others which were characterised as C3 species. Cleome gynandra has C4 features based on low CO2 compensation point (?), C4 type ?13C values, Kranz-type leaf anatomy and bundle sheath (BS) ultrastructure, presence of C4 pathway enzymes, and selective immunolocalisation of Rubisco and phosphoenolpyruvate carboxylase. Cleome paradoxa was identified as a C3?C4 intermediate based on its intermediate ? (27.5?molmol?1), ultrastructural features and selective localisation of glycine decarboxylase of the photorespiratory pathway in mitochondria of BS cells. The other six species are C3 plants based on ?, ?13C values, non-Kranz leaf anatomy, and levels of C4 pathway enzymes (very low or absent) typical of C3 plants. The results indicate that this is an interesting family for studying the genetic basis for C4 photosynthesis and its evolution from C3 species. [ABSTRACT FROM AUTHOR]

Leaves and cotyledons of the terrestrial C4 plants, Bienertia cycloptera Bunge ex Boiss. and Suaeda aralocaspica (Bunge) Freitag & Schtze (Chenopodiaceae), accomplish C4 photosynthesis within individual chlorenchyma cells: each species having a unique means of intracellular spatial partitioning of biochemistry and organelles. In this study the chlorenchyma tissue in flowers and stems of these species was investigated. Flowers have an outer whorl of green tepals with a layer of chlorenchyma cells, which are located on the abaxial side, exposed to the atmosphere. Anatomical, immunocytochemical, western blots and starch analyses show that the chlorenchyma cells in tepals are specialised for performance of single-cell C4 photosynthesis like that in leaves. In the tepals of B. cycloptera, chlorenchyma cells have a distinctive central cytoplasmic compartment, with chloroplasts which contain Rubisco, separated by cytoplasmic channels from a peripheral chloroplast-containing compartment, with phosphoenolpyruvate carboxylase (PEPC) distributed throughout the cytoplasm. In the tepals of S. aralocaspica, chlorenchyma cells have chloroplasts polarised towards opposite ends of the cells. Rubisco is found in chloroplasts towards the proximal end of the cell and PEPC is found throughout the cytoplasm. Also, green stems of B. cycloptera have a single layer of the specialised C4 type chlorenchyma cells beneath the epidermis, and in stems of S. aralocaspica, chlorenchyma cells are scattered throughout the cortical tissue with chloroplasts around their periphery, typical of C3 type chlorenchyma. During reproductive development, green flowers become very conspicuous, and their photosynthesis is suggested to be important in completion of the life cycle of these single-cell C4 functioning species. [ABSTRACT FROM AUTHOR]

Incomplete stomatal closure at night can result in substantial water loss at times when photosynthetic carbon gain is not occurring in C3 and C4 plant species. To investigate the magnitude of nighttime water loss for a crop species in the field, measurements of nighttime water loss by tomato (Lycopersicon esculentum Mill. cv. Heinz 8892) were made by three methods: a field-scale lysimeter and two leaf-level instruments, an automated viscous flow porometer and a portable photosynthesis system. The portable photosynthesis system indicated nighttime transpiration of 10% of maximal daytime transpiration and the viscous flow porometer demonstrated partially open stomata. Integrated crop water loss during the dark, non-photosynthetic hours measured on the lysimeter was 3?10.8% of total daily water loss. In the glasshouse, a survey of closely related wild and cultivated tomato species showed that under ambient conditions nighttime transpiration varied within and among species and was 8?33% of maximal daytime transpiration. Implications of such a substantial fraction of total daily crop water use occurring during the night are significant in agronomic, environmental, and economic terms. Further, variation within and among species in nighttime water loss has implications for breeding to improve crop water use efficiency. [ABSTRACT FROM AUTHOR]