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Background: The leaf epidermis plays an important role in the transmission of light and the regulation of water and gas exchange, which influences the photosynthesis of mesophyll cells. Small papillae (SP) are one of the important structural elements of the leaf epidermis. The mechanism of the effect that small papillae have on rice leaf photosynthetic performance remains unclear. Results: In this study, a small papilla deficient 25 (spd25) mutant was isolated from japonica rice Longjin1. Small papillae were absent on the adaxial and abaxial leaf surfaces of the spd25 mutant and the silicon and cuticular wax content in the spd25 mutant leaves decreased. Map-based cloning and functional analysis revealed that SPD25, encoding a guanine nucleotide exchange factor for Rop, is a novel allele of OsRopGEF10. The spd25 mutant showed an increased water loss rate and reduced relative water content. The lower stomatal conductance in the spd25 mutant prevented water loss but decreased the intercellular CO2 concentration and net assimilation rate. The fluorescence parameters showed that the inhibited CO2 assimilation reaction feedback regulated the photochemical electron-transfer reaction, but the performance of Photosystem II was stable. Further analysis indicated that the excess light energy absorbed by the spd25 mutant was dissipated in the form of non-photochemical quenching to avoid photodamage through the optical properties of small papillae. Conclusions: SPD25 regulates the development of small papillae on the surface of rice leaves, which play an important role in balancing photosynthetic gas exchange and water loss. This study deepens our understanding of the physiological mechanisms by which small papillae affect photosynthetic performance. [ABSTRACT FROM AUTHOR]

Background: The environmental stresses caused by climate change have become more severe in recent decades, affecting tree growth and physiology. Tropical forests have great potential for global carbon sequestration. However, they suffer from heavy rainfall and prolonged dry periods due to climate change. Swietenia macrophylla King and Melia azedarach L. are economically valuable trees that are widely planted in southern Taiwan. Plantations are exposed to either prolonged dry periods or heavy rainfall within the seasons of tropical monsoon areas. Photo-physiological comparisons may provide information that can improve management of S. macrophylla and M. azedarach plantations in tropical regions. Results: Both species exhibited a midday depression in leaf photosynthesis regardless of the season. The net photosynthetic rate ( P ), stomatal conductance ( g ), and transpiration rate ( E) in the dry season all significantly decreased in both tree species. In addition, M. azedarach used water more efficiently than did S. macrophylla during the dry season, but S. macrophylla had higher P compared with that in M. azedarach during the wet season. Temperature and vapor pressure deficit influenced P variation in S. macrophylla and M. azedarach, respectively. Our data suggested that the P and g of M. azedarach, but not of S. macrophylla, were linearly correlated during the dry season. The reduction of the leaf area was more sever in M. azedarach than in S. macrophylla, thus preventing water loss more efficiently. Conclusions: M. azedarach adapted to drought by reducing total leaf area and maintaining higher P , g , E, and WUE compared with those measured in S. macrophylla during the dry season. M. azedarach is more drought adaptation and more suitable for both humid and semi-humid areas than S. macrophylla, whereas the latter should be limited to more humid areas. [ABSTRACT FROM AUTHOR]

Oxygen flux between aquatic ecosystems and the water column is a measure of ecosystem metabolism. However, the oxygen flux varies during the day in a 'hysteretic' pattern: there is higher net oxygen production at a given irradiance in the morning than in the afternoon. In this study, we investigated the mechanism responsible for the hysteresis in oxygen flux by measuring the daily pattern of oxygen flux, light, and temperature in a seagrass ecosystem ( Zostera muelleri in Swansea Shoals, Australia) at three depths. We hypothesised that the oxygen flux pattern could be due to diel variations in either gross primary production or respiration in response to light history or temperature. Hysteresis in oxygen flux was clearly observed at all three depths. We compared this data to mathematical models, and found that the modification of ecosystem respiration by light history is the best explanation for the hysteresis in oxygen flux. Light history-dependent respiration might be due to diel variations in seagrass respiration or the dependence of bacterial production on dissolved organic carbon exudates. Our results indicate that the daily variation in respiration rate may be as important as the daily changes of photosynthetic characteristics in determining the metabolic status of aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Biological soil crusts (BSC) are the dominant functional vegetation unit in some of the harshest habitats in the world. We assessed BSC response to stress through changes in biotic composition, CO2 gas exchange and carbon allocation in three lichen-dominated BSC from habitats with different stress levels, two more extreme sites in Antarctica and one moderate site in Germany. Maximal net photosynthesis (NP) was identical, whereas the water content to achieve maximal NP was substantially lower in the Antarctic sites, this apparently being achieved by changes in biomass allocation. Optimal NP temperatures reflected local climate. The Antarctic BSC allocated fixed carbon (tracked using 14CO2) mostly to the alcohol soluble pool (low-molecular weight sugars, sugar alcohols), which has an important role in desiccation and freezing resistance and antioxidant protection. In contrast, BSC at the moderate site showed greater carbon allocation into the polysaccharide pool, indicating a tendency towards growth. The results indicate that the BSC of the more stressed Antarctic sites emphasise survival rather than growth. Changes in BSC are adaptive and at multiple levels and we identify benefits and risks attached to changing life traits, as well as describing the ecophysiological mechanisms that underlie them. [ABSTRACT FROM AUTHOR]

This study evaluates acclimation of photosynthesis and stomatal conductance in three evolutionary lineages of C, C-C intermediate, and C species grown in the low CO and hot conditions proposed to favo r the evolution of C photosynthesis. Closely related C, C-C, and C species in the genera Flaveria, Heliotropium, and Alternanthera were grown near 380 and 180 μmol CO mol air and day/night temperatures of 37/29°C. Growth CO had no effect on photosynthetic capacity or nitrogen allocation to Rubisco and electron transport in any of the species. There was also no effect of growth CO on photosynthetic and stomatal responses to intercellular CO concentration. These results demonstrate little ability to acclimate to low CO growth conditions in closely related C and C-C species, indicating that, during past episodes of low CO, individual C plants had little ability to adjust their photosynthetic physiology to compensate for carbon starvation. This deficiency could have favored selection for more efficient modes of carbon assimilation, such as C-C intermediacy. The C-C species had approximately 50% greater rates of net CO assimilation than the C species when measured at the growth conditions of 180 μmol mol and 37°C, demonstrating the superiority of the C-C pathway in low atmospheric CO and hot climates of recent geological time. [ABSTRACT FROM AUTHOR]

Immediate leaf functional responses to drought, such as stomatal closure and photosynthetic rate reduction, are already known from short-term studies. We tested the hypothesis that long-term acclimation of leaves to drought includes hydraulic and stomatal anatomical changes and that gas exchange and nitrogen allocation patterns are inevitably adjusted to the new structural status. 26 structural and functional traits in one sensitive cultivar (Simeto) and two drought resistant landraces (Ntopia Heraklion 184, Kontopouli 17) of field- grown wheat ( Triticum turgidum L. var. durum) were examined under four water shortage levels. Drought acclimation responses were more intense in Simeto than in the two landraces. In accordance to the working hypothesis, drought-acclimated leaves showed lower hydraulic conductance due to narrower vessels and higher stomatal and vein densities than the control leaves, resulting in a safe mode of water transfer and consumption which is essential for the survival in water limiting conditions.Irrespectively of genotype and water regime, significant correlations among structural (hydraulic characteristics, stomatal and vein patterns) and functional (gas exchange, nitrogen content) parameters were found, indicating the functional adjustment to the new structural status. The Principal Component Analysis showed that these structure-function interactions reflected the trade-off between growth and protection against water losses (Axis 1), as well as the competition between different sinks (carbon gain vs structural reinforcement and reproductive effort) in N allocation (Axis 2). Drought acclimation in wheat leaf is integrally processed by the coordination of structural and functional parameters in order to compensate for the adverse effects of water shortage. This structure-function network that regulates the transition from normal growth-mode to protection- mode, includes at least two important 'nodal points': xylem conducting efficiency (water entry) and stomatal function (water exit). This transition also includes the redirection of nitrogen resources to different sinks. [ABSTRACT FROM AUTHOR]

Drought stress is known to limit plant performance in Mediterranean-type ecosystems. We have investigated the dynamics of the hydraulics, gas exchange and morphology of six co-existing Mediterranean woody species growing under natural field conditions during a drought that continued during the entire summer. Based on the observed minimum leaf water potentials, our results suggest that the six co-existing species cover a range of plant hydraulic strategies, from isohydric to anisohydric. These differences are remarkable since the selected individuals grow within several meters of each other, sharing the same environment. Surprisingly, whatever the leaf water potentials were at the end of the dry period, stomatal conductance, photosynthesis and transpiration rates were relatively similar and low across species. This result contradicts the classic view that anisohydric species are able to maintain gas exchange for longer periods of time during drought stress. None of the plants showed the expected structural acclimation response to the increasing drought (reduction of leaf-to-sapwood area ratio), thereby rejecting the functional equilibrium hypothesis for our study system. Instead, three of the six species increased photosynthetic area at the branch level. The observed dissimilar patterns of gas exchange, hydraulics and morphology across species seem to be equally successful given that photosynthesis at the leaf level was maintained at similar rates over the whole dry period. [ABSTRACT FROM AUTHOR]

mesoscale meteorological model (FOOT3DK) is coupled with a gas exchange model to simulate surface fluxes of CO and HO under field conditions. The gas exchange model consists of a C3 single leaf photosynthesis sub-model and an extended big leaf (sun/shade) sub-model that divides the canopy into sunlit and shaded fractions. Simulated CO fluxes of the stand-alone version of the gas exchange model correspond well to eddy-covariance measurements at a test site in a rural area in the west of Germany. The coupled FOOT3DK/gas exchange model is validated for the diurnal cycle at singular grid points, and delivers realistic fluxes with respect to their order of magnitude and to the general daily course. Compared to the Jarvis-based big leaf scheme, simulations of latent heat fluxes with a photosynthesis-based scheme for stomatal conductance are more realistic. As expected, flux averages are strongly influenced by the underlying land cover. While the simulated net ecosystem exchange is highly correlated with leaf area index, this correlation is much weaker for the latent heat flux. Photosynthetic CO uptake is associated with transpirational water loss via the stomata, and the resulting opposing surface fluxes of CO and HO are reproduced with the model approach. Over vegetated surfaces it is shown that the coupling of a photosynthesis-based gas exchange model with the land-surface scheme of a mesoscale model results in more realistic simulated latent heat fluxes. [ABSTRACT FROM AUTHOR]

Grafting is an easier and faster approach than plant breeding to take advantage of both existing resistant plants, especially wild cultivars, and high-bred cultivars. The aim of this study was to investigate the changes in leaf photosynthetic capacity of a hybrid eggplant Solanum melongena L., cv. Rima (R), widely used in Greece] when grafted on tomato rootstocks known for their resistance to nematodes and diseases. For this purpose, a hybrid egg-plant has been used as a control and has been self-grafted (grafting of a scion on its own roots used as rootstock) RR and also as a scion on two hybrid tomatoes rootstocks, as follows: Primavera (RP) and Heman (RH). Leaf photosynthetic capacity was estimated by measuring the leaf gas exchanges under several light levels at ambient CO2 concentration to approximate the leaf light response curve. The measurements performed control plant Rand self-grafted eggplants RR show that the leaf respiration per unit leaf area is not altered by the scion/rootstock combination. These elements point out a scion controlled respiration, independent of the rootstock. The leaf photosynthetic capacities of the R and RR treatments were not different, while one of the scion/rootstock combinations (RH) showed a significant change with respect to the control treatments. The rootstock therefore seems to be able to modify the scion leaf photosynthetic capacity, but this may not be true for some scion/rootstock combinations (RP in our case). Leaf stomatal conductance and transpiration were not modified by the grafting, so that the water use efficiency was only altered by the modifications of the net assimilation. [ABSTRACT FROM AUTHOR]

urately representing complex land-surface processes balancing complexity and realism remains one challenge that the weather modelling community is facing nowadays. In this study, a photosynthesis-based Gas-exchange Evapotranspiration Model (GEM) is integrated into the Noah land-surface model replacing the traditional Jarvis scheme for estimating the canopy resistance and transpiration. Using 18-month simulations from the High Resolution Land Data Assimilation System (HRLDAS), the impact of the photosynthesis-based approach on the simulated canopy resistance, surface heat fluxes, soil moisture, and soil temperature over different vegetation types is evaluated using data from the Atmospheric Radiation Measurement (ARM) site, Oklahoma Mesonet, 2002 International HO Project (IHOP_2002), and three Ameriflux sites. Incorporation of GEM into Noah improves the surface energy fluxes as well as the associated diurnal cycle of soil moisture and soil temperature during both wet and dry periods. An analysis of midday, average canopy resistance shows similar day-to-day trends in the model fields as seen in observed patterns. Bias and standard deviation analyses for soil temperature and surface fluxes show that GEM responds somewhat better than the Jarvis scheme, mainly because the Jarvis approach relies on a parametrised minimum canopy resistance and meteorological variables such as air temperature and incident radiation. The analyses suggest that adding a photosynthesis-based transpiration scheme such as GEM improves the ability of the land-data assimilation system to simulate evaporation and transpiration under a range of soil and vegetation conditions. [ABSTRACT FROM AUTHOR]

Sky conditions play an important role in the Earth's climate system and CO uptake by plants. We used eddy covariance and meteorological data, including global and diffuse photosynthetic photon flux density (PPFD), recorded over the 2008 and 2009 growing season at two Sitka spruce [ Picea sitchensis ( Bong.) Carr.] forest sites in northern Britain, in order to establish relationships between physiological properties under diverse sky conditions, i.e. (1) sunny, (2) cloudy, and (3) overcast, and several canopy activity-related properties. These properties are: (1) response to PPFD, (2) photosynthetic light use efficiency, and (3) canopy stomatal conductance. We found that Sitka spruce forests utilise PPFD in a more efficient way when solar radiation is dominated by diffuse radiation. Furthermore, our results show that diffuse radiation enhances canopy stomatal conductance, an effect which may be the result of both blue light enrichment within the canopy and the reduction in vapour pressure deficit during cloudy and overcast weather. Diffuse radiation does not only influence short-term (hourly, daily, monthly) canopy activity but also long-term forest growth. [ABSTRACT FROM AUTHOR]

Meconopsis horridula var. racemesa Prain. is a famous alpine flower and medicinal plant native to high elevations in the Himalayas, but cultivating it at lower altitudes presents great challenges. The photosynthetic gas exchange and chlorophyll fluorescence of M. horridula were investigated at three temperatures to evaluate its photosynthetic performance and the relative importance of biochemical limitation, stomatal limitation, and mesophyll limitation to photosynthesis under different temperature regimes. Meconopsis horridula grown at 20°C could obtain the highest photosynthetic rate and photochemical efficiency among the three temperatures, and photosynthetic performance at low temperature was better than at high temperature. Non-photochemical quenching was an important mechanism protecting the photosynthetic apparatus of M. horridula under temperature stress conditions. Although mesophyll conductance was the dominant factor for limiting photosynthesis of M. horridula both at low temperature and high temperature, the photosynthesis at high temperature was also limited by stomatal conductance and biochemical efficiency. The poor photosynthetic performance at high temperature may be what limits M. horridula cultivation at low altitude. [ABSTRACT FROM AUTHOR]

Barnacle fouling has shown to impede gas exchange ability of mangroves. Fouled mangrove plants may therefore obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production, but such hypothesis remains untested. The objective of the present study compared the stomata density (essential for obtaining carbon dioxide and water molecules) and leaf chlorophyll concentration (essential for photosynthesis) of fouled and non-fouled (control) of seedlings, juveniles and adults of the mangroves Kandelia obovata, in Hong Kong and Taiwan. The seedlings and juveniles of the dominant mangrove plant species, Kandelia obovata, in Hong Kong and Taiwan had a higher density of stomata but a lower chlorophyll concentration in the leaves, when the trunks and twigs were fouled by the barnacle Fistulobalanus albicostatus. Fouled K. obovata appears to develop more stomata in the leaves to compensate the blocking effect of the lenticel from barnacle fouling. As fouling impacts the gaseous exchange ability of mangroves, fouled plants could obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production. Fouled adult plants, however, had variable responses in leaf chlorophyll concentrations among the study sites, suggesting adults were more tolerant of barnacle fouling. The present study reveals seedling and juvenile mangrove plants are very susceptible to barnacle fouling, which impedes the gaseous exchange mechanism and food production, which can subsequently result in reduced growth, fitness and survival. [ABSTRACT FROM AUTHOR]

A range of traits, including metabolic costs, biomass allocation and seed reserves, may contribute to interspecific variation in the shade tolerance of tree seedlings. In addition, shade tolerance may be affected by differential responses of species to soil resource availability at low light. We used a custom-built whole-plant gas-exchange chamber to quantify instantaneous whole-plant light compensation point (WPLCP) and to parameterize whole-plant daily C gain models for seedlings of eight temperate deciduous tree species. We examined the relationship of WPLCP to growth, biomass allocation and gas-exchange under high and low light and nutrient availabilities and compared it to WPCLP of naturally recruited saplings. For species showing a response, both increased light and nutrient availability resulted in increased WPLCP. However, species’ responses to resource availability did not correspond closely with shade tolerance as has generally been predicted. Variation in WPLCP within species was best predicted by whole-plant dark respiration rates, leaf-level light compensation point and leaf mass per area. Among species, seed size was a strong negative correlate of WPLCP, explaining 66% of the variation. Species with the lowest WPLCP maintained lower growth rates across treatments but greater biomass in the low-light treatment compared with more light-demanding species. These data suggest that a number of traits, in particular metabolic costs and seed size, contribute to WPLCP. However, gas-exchange-based WPLCP was 1.5–3.5 times lower than corresponding growth-based field estimates of WPLCP, suggesting that other factors such as biotic interactions or ontogenetic shifts in whole-plant light requirements may substantially increase species’ WPLCP under natural conditions. [ABSTRACT FROM AUTHOR]

There have been no studies of the effect of take-all on leaf gas-exchange rates, despite the fact that take-all severely restricts plant water and nutrient uptake, which results in significant biomass and grain yield reduction. Here we describe the effect of inoculation with Gaeumannomyces graminis (Sacc.) var. tritici (Ggt) on carbon assimilation rate (A) and biomass production of wheat plants grown under two water regimes. We show that the impact of Ggt inoculation on plant growth and leaf A may be through reduced photosynthetic capacity of the leaves and not water stress per se. The nature of this reduced photosynthetic capacity remains uncertain but may involve nutrient deficiency and different enzymes produced by the fungus. In each of the 3 years the experiment was conducted, Ggt significantly reduced A, i.e. at anthesis by 18% in 2000, 15% in 2001, and 12% in 2002. In agreement with other field studies, Ggt reduced tiller number and production of all plant components, mostly root dry mass and grain mass per plant. Highly significant negative correlations were found between disease rating and A in all years, showing that at disease ratings equal or higher than 3 (on a scale from 1 to 4) A could practically be zero. While A decreased, intercellular CO2 concentration increased or did not change, and stomatal conductance was relatively high. In addition, A was more reduced under high than under low soil moisture content. These results support the idea that water stress per se did not contribute to the observed reduction of A. The mechanism of photosynthetic capacity reduction due to the Ggt root-rotting fungus is of interest as it may lead to the molecular mechanisms of plant resistance and ultimately to the development of take-all resistant plants. [ABSTRACT FROM AUTHOR]

Neotropical savannas are exposed to recurrent dry periods of varied duration, and forage grasses must be able to cope with such temporal stresses to maintain productive pastures. This study compared leaf water relations and net photosynthesis under drought of five perennial Brachiaria species: the tufted B. brizantha (CIAT 6780), the semi-stoloniferous B. decumbens (CIAT 606) and B. mutica, and the stoloniferous B. humidicola (CIAT 679) and B. dictyoneura (CIAT 6133). Plants of the five grasses were grown in large pots and subjected to drought by suspending watering until first wilting symptoms (14 days for B. brizantha, B. decumbens and B. mutica, and 29 days for B. humidicola and B. dictyoneura). Afterwards, they were re-watered and a second soil dry cycle was imposed. Time trends in leaf water potential (Ψl), relative water content (RWC), osmotic potential at full turgor (Ψ0100), stomatal conductance (Gs) and net photosynthesis (A) of stressed (DT) plants were compared to those of well-irrigated (CT) plants. Predawn Ψl in DT plants decreased to a minimum of -1.5 and -2.0 MPa in B. brizantha and B. mutica, compared to -2.5 to -3.0 MPa in B. decumbens, B. humidicola and B. dictyoneura. RWC decreased up to 50% in B. brizantha, compared to 75% in the other species. In B. humidicola, B. dictyoneura and in a lesser extent, B. decumbens, leaves of DT plants adjusted osmotically, by an apparent accumulation of nutrient solutes, at a rather constant ratio of turgid to dry weight of the tissue. Calculated osmotic adjustment ranged between 0.38 (B. decumbens) to 0.87 MPa (B. humidicola). This adjustment in Ψ0100 was in some cases maintained 7 days after re-watering. In B. brizantha and B. mutica, Gs and A were significantly affected by drought, with maximum reduction percentages at the second drought period of 65 and 80%, respectively. The corresponding reduction in B. decumbens was 53 and 55%, respectively; whereas in B. humidicola and B. dictyoneura Gs and A were reduced less than 20%. In all species, re-watering allowed for the water relations (except Ψ0100) and photosynthetic activity of leaves of DT plants to reach values comparable to those of CT plants. Results are discussed in term of root morphology and soil water extraction pattern, as well as leaf traits that may contribute to withstand drought under moderate soil water stress. [ABSTRACT FROM AUTHOR]

Salt-alkali stress causes serious abiotic damage during the growth stage of rice. Photosynthetic characteristics and their related physiological traits affect the growth and development of rice under stressed conditions. In this study, using a recombinant inbred line (RIL) population derived from a cross between Dongnong 425 and Changbai 10 (CB10), quantitative trait loci (QTLs) for seven photosynthetic-related traits, including net photosynthetic rate (Pn), transpiration rate, stomatal conductance, intercellular CO2 concentration, chlorophyll content (Cc), canopy temperature and leaf area (La), were identified in control, salt and alkali stress conditions at the grain filling stage of rice over two years. In total, 23 QTLs were detected by using the CIM module of Windows QTL Cartographer 2.5 software, and 19 out of the 23 QTLs were salt-alkali stress-related. qPn3-2, qTr8, qCc3, qCc12 and qLa12 were specifically expressed in salt or alkali stress conditions. qTr6 expression was detected under both salt and alkali stresses for two consecutive years, suggesting it may have a key role in salt-alkali tolerance breeding. OsGLYII-2, which is a salt tolerant gene located in the mapping interval of major QTLs qPn3-2 and qCc3, was sequenced to verify the additive effect orientation of the two QTLs. The sequenced result showed that the OsGLYII-2 allele of extremely salt-tolerant RIL lines was consistent with that of the tolerant parent CB10 and showed that the positive alleles of qPn3-2 and qCc3 originated from CB10. The information obtained in this study may be useful for understanding the genetic basis of salt-alkali tolerance; it also provides an important base for the fine mapping and map-based cloning of the QTLs for photosynthetic-related traits under salt-alkali stress. [ABSTRACT FROM AUTHOR]