Photosynthetic Gas Exchange Characteristics Research Articles

Do mutations modifying the leaf area (nr3) and the number of potential seeds (dfc) influence photosynthetic gas exchange characteristics in common buckwheat Fagopyrum esculentum Moench?

Contemporary buckwheat breeding in Russia is based mainly on a Mendelian mutation det. Some additional mutations are being considered for inclusion in buckwheat breeding programs. Among them are the nr3 (narrow leaf 3) and dfc (determinate floret cluster). We evaluated the effects of the mutations on both the characteristics of photosynthetic gas exchange and the number of seeds per plant. The nr3 reduces the leaf surface area by 1.4 times. The mutant plants show some compensatory increase in photosynthesis rate, which, however, is not enough to reach the level of the source ability as in the wild type since the number of seeds per plant is significantly decreased. The possibility of using this mutation in buckwheat breeding depends on the accumulation of modifiers that increase either leaf size or photosynthesis rate. The reduced number of flowers of the dfs mutation is compensated by an increase in flower fertility, and the number of seeds per plant does not change compared to the wild type. It explains the absence of differences between the dfs and wild type in terms of the photosynthesis rate. This experiment did not reveal any problems for using the dfc mutation in breeding. In general, the results of the work support the photosynthesis rate in buckwheat is regulated based on the source-sink ratio.

Photosynthetic and grain yield responses to intercropping of two common bean lines with maize under two types of fertilizer applications in the colombian amazon region

Acid soils in the Amazon region are characterized by low fertility and high aluminum saturation causing reduced crop yields. Improving genetic adaptation of crop genotypes together with suitable agronomic management practices can mitigate the impact on crop production in acid soils. The objective of the present study was to determine the photosynthetic and grain yield responses of two common bean lines to intercropping with maize under two types of fertilizer applications in the Colombian Amazon region. A randomized complete block design (RCBD) with 3 replications in a nested trifactorial arrangement was used consisting of two advanced bean lines of BFS 10 and ALB 121 (main plots); three cropping system patterns of monoculture, intercropping pattern 1, intercropping pattern 2 (subplots); and two types of fertilizer applications, chemical and organic (sub-subplots) for a total of 12 treatments. The experiment was conducted in two growing seasons and the effects of the treatments were evaluated during two growth stages within a cropping season. Measurements included photosynthetic gas exchange characteristics, chlorophyll fluorescence, specific leaf area, viability of pollen and grain yield. Mean values from two growing seasons were presented. Photosynthetic response of BFS 10 was superior to ALB 121 under both monoculture and intercropping patterns with either chemical or organic fertilizer application. Both bean lines showed an increase in apparent quantum efficiency and maximum rate of ribulose-1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) carboxylation (Vcmax) during pod filling growth stage when grown in association with maize, particularly with organic fertilizer application. Small farmers in the Amazon region can benefit from either one of the two bean lines by growing them as intercrops with maize, using organic fertilizer application.

Influence of nitrogen supply on gas exchange, chlorophyll fluorescence and grain yield of breeding lines of common bean evaluated in the Amazon region of Colombia

The common bean (Phaseolus vulgaris L.) is a food crop that provides fiber, vitamins and carbohydrates and it is produced by smallholders in developing countries under nitrogen (N)-depleted and low-fertility soil conditions. Soil acidity and the associated aluminum toxic and phosphorus deficient conditions are known to reduce symbiotic N-fixing ability of common bean. Breeding lines of common bean have been developed to adapt to acid-soil and high-temperature conditions in the Amazon region but the response of these lines to N application was not determined. The present study was conducted with an objective to identify genotypic differences among ten common bean breeding lines (4 Andean, 5 Mesoamerican, 1 interspecific) in their physiological characteristics (gas exchange, chlorophyll fluorescence and photosynthetic efficiency) and their contribution to superior agronomic performance under three different levels of N (0, 60 and 120 kg N ha−1; N0, N60 and N120) supply. We tested the hypothesis that common bean genotypes that combine greater capacity to assimilate carbon with improved ability to mobilize photosynthates to developing pods and seeds could enhance their agronomic performance at different levels of N supply under high-temperature and acid soil-stress conditions in the field. A randomized complete block design with factorial arrangement (3 levels of N × 10 genotypes) in three replications was used for the study. Measurements included photosynthetic gas exchange characteristics (light and CO2-saturated photosynthesis), chlorophyll fluorescence, viability of pollen, leaf N concentration, photosynthetic N use efficiency and grain yield. The increase in supply of N had a significant effect on grain yield and on different photosynthetic characteristics. Results showed that lines with indeterminate growth habit responded better to increase in N supply through their physiological response in improving grain yield. Among the genotypes evaluated, two lines (BFS 10 and SEF 10) were outstanding in their agronomic performance due to greater photosynthetic capacity combined with greater ability to mobilize photosynthates to grain with increase in N supply. These two lines can serve as parents for further improvement in resource use efficiency and multiple-stress resistance of common bean in the tropics.

Priming with 5-aminolevulinic acid (ALA) attenuates UV-B induced damaging effects in two varieties of Cajanus cajan L. seedlings by regulating photosynthetic and antioxidant systems

The objective of this study is to investigate whether pre-treatment (priming) of chlorophyll precursor 5-aminolevulinic acid (ALA) assumes a huge part in moderating harms caused by UV-B exposure on two varieties of Cajanus cajan L. seedlings namely BAHAR and KB-17. Healthy seeds were primed with two doses of ALA (lower dose: ALA1; 25µM and higher dose: ALA2; 100 µM) for 24 h at 25±2 °C and thereafter 17-day old seedlings were exposed to an enhanced dose of UV-B radiation i.e. 2.2 kJ m−2d−1. Results showed that UV-B exposure significantly declined growth attributes, photosynthetic pigments (chlorophyll a, b and carotenoids contents), photosynthetic gas exchange characteristics (A, Ci, Gs, E, and WUE). This decrease was also accompanied by the accumulation of reactive oxygen species: superoxide radical (SOR; O₂˙ˉ), hydrogen peroxide (H2O2), and lipid peroxidation (MDA contents). The antioxidative enzyme activities: catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST), and peroxidase (POD) and non-enzymatic antioxidants: total phenolics content (TPC) and total flavonoids content (TFC) were increased. On contrary to this, damaging effects of UV-B radiations were markedly alleviated with the exogenous application (priming) of ALA by enhancing plant growth and growth-regulating parameters. Furthermore, ALA application decreased the UV-B induced oxidative stress in Cajanus cajan L. seedlings by further improving the activity of enzymatic and the contents of non-enzymatic antioxidants of test plant defense system. Furthermore, priming with ALA decreased the germination time and increased the germination index which additionally served as a significant purpose behind the improvement in the harvest quality and amount. The BAHAR variety of Cajanus cajan was discovered to be more tolerant against UV-B stress due to its more efficient defense system with a higher rate of antioxidant enzyme activities. On the other hand, KB-17 variety of Cajanus cajan was discovered to be sensitive against UV-B stress due to its feeble defense system with higher accumulation of reactive oxygen species. Thus, these findings suggest that priming of seeds with ALA act as a sustainable remedial strategy in reducing the hazardous effects of UV-B induced stress on crop productivity of Cajanus cajan seedlings by triggering the up-regulation of photosynthesis and antioxidant system to counterbalance the ROS-mediated damage to macromolecules.

Effects of shading on the growth, development and yield of winged bean (Psophocarpus tetragonolobus)

ABSTRACT: An experiment was conducted to investigate the effects of different shading regimes [i.e., 60% (heavy), 30% (moderate), and 0% (control)] on 25 traits associated with the morphological features, photosynthetic gas exchange and agronomic characteristics of winged bean (Psophocarpus tetragonolobus), an underutilized protein-rich legume from the tropics. Collectively, 80% of the studied variables displayed significant differences (P<0.05) between at least two shade treatments. Shading generally showed most pronounced effect on the physiological traits of the legume, whereby the stomatal conductance, photosynthetic and transpiration rate differed significantly among plants for all treatments. The non-shaded plants were observed to have superior growth and physiological responses than the shaded plants. Interestingly, the moderately shaded plants exhibited the highest yield per plant, which significantly differed from the non-shaded and heavily shaded plants. This indicated that winged bean can adapt to partial canopy cover, making it a potential nitrogen-fixing cash crop which can be planted together with fruit or oil trees in commercial plantations.

Physiological Response to Heat Stress During Seedling and Anthesis Stage in Tomato Genotypes Differing in Heat Tolerance

AbstractTomato cultivars differ in their sensitivity to heat stress, and the sensitivity depends on the developmental stage of the plants. It is less known how heat stress affects tomato at the anthesis stage in terms of leaf physiology and fruit set and whether the ability of tomato to tolerate heat at different developmental stages is linked. To investigate photosynthetic gas exchange characteristics, carbohydrate content and fruit set during heat stress, a thermo‐tolerant cultivar (‘LA1994’) and a thermo‐sensitive cultivar (‘Aromata’) were studied at the seedling and anthesis stage. The photosynthetic parameters, maximum quantum efficiency of photosystem II (Fv/Fm), chlorophyll content, carbohydrate content and fruit set were determined in plants grown at 26/18 °C (control) and 36/28 °C (heat stress). The physiological responses including net photosynthetic rate (PN), chlorophyll content and Fv/Fm decreased in ‘Aromata’ at both developmental stages during heat stress, whereas they were unaltered in ‘LA1994’ during heat stress as compared to the respective control. This was accompanied by lower contents of glucose and fructose in mature leaves of ‘Aromata’ at the seedling stage under heat stress. In contrast, the glucose content increased while the fructose content was unaltered in mature leaves of ‘LA1994’ at the seedling stage under heat stress. High temperature induced a similar change in carbohydrate content in the young leaves of both cultivars at anthesis. The fructose and sucrose content were unaffected in the mature leaves of ‘Aromata’ but significantly increased in ‘LA1994’ under heat stress at anthesis. The heat stress treatment decreased pollen viability and inhibited fruit set due to flower wilting and abnormal abscission in ‘Aromata’, whereas fruit set was not inhibited in ‘LA1994’. A decrease in chlorophyll content, photosynthesis and carbohydrate content in the mature leaves of tomato could be related to fruit set failure at high temperature. The results show that physiological responses to heat stress at the seedling stage correspond with the responses at the anthesis stage, demonstrating that screening for heat stress sensitivity can be carried out in young plants.

Elevated CO2atmosphere significantly increased photosynthesis and productivity in a fast growing tree species,Gmelina arboreaRoxb.

Sequestering atmospheric carbon and storing it in the terrestrial biosphere is one of the option that has been proposed to compensate greenhouse gas emissions. Young fast growing tree species are believed to be a major potential sinks and could absorb large quantities of CO2. The ongoing enrichment of the atmosphere with CO2 found to stipulate a positive effect on tree species due to increasing availability of carbon. The present study dissects out the CO2 fertilisation effects on photosynthetic gas exchange characteristics, key responses of photosynthetic enzymes consorted with overall plant growth performance in a fast growing tree species, Gmelina arborea Roxb (Verbenaceae). Gmelina plants were grown under ambient (360 μmol/mol) and CO2-enriched conditions (460 μmol/mol) in open top chambers and studied for two marked growth seasons subsequently for 3 years (2006 to 2008). Growth characteristics string along with biochemical measurements were carried out at regular intervals. Photosynthetic rates (Pn) were correlated with other leaf gas exchange and biochemical variables to localise bottlenecks for acclimatory response. Carbonic anhydrase (CA; EC 4. 2. 1. 1) activity showed positive linear correlation (r2 = 0.947) with Pn and RUBP case activity (r2 = 0.952). Gmelina plants were harvested and biomass measured at the end of two growth seasons for three consecutive years. Gmelina significantly responded to CO2 enrichment with periodic and potential increase in biomass, which was also espied with almost 32% higher Pn and a radical increase in CA (60.82%). Our findings clearly demonstrate that Gmelina plants are highly suitable for agroforestry projects for efficient long-term carbon sequestration and to mitigate elevated CO2 levels in the near unprecedented global climate change.

Water deficit as a regulatory switch for legume root responses

Plant roots perceive declining soil water potential as an initial signal which further triggers an array of physiological, morphological and molecular responses in the whole plant. Understanding the root responses with parallel insights on protein level changes has always been an area of interest for stress biologists. In a recent study, we reported drought stress-induced changes among certain structural and functional root proteins involved in reactive oxygen species (ROS) detoxification, primary and secondary metabolite biosynthetic pathways as well as proteins associated with cell signalling in an economically important legume crop Vigna radiata (L.) Wilczek. We also demonstrated photosynthetic gas exchange characteristics and root physiology under varying levels of water-deficit and recovery. In this report, we depict a closer analysis of the expression patterns of the identified proteins which were categorized into five major functional groups. These proteins represent a unique coherence and networking with each other as well as with the overall physiological and metabolic machinery in the plant cell.

Effects of LaCl 3 on photosynthesis and the accumulation of tanshinones and salvianolic acids in Salvia miltiorrhiza seedlings

The effects of LaCl 3 on the growth, photosynthetic gas-exchange characteristics, chlorophyll fluorescence, and the accumulation of tanshinones and salvianolic acids in Salvia miltiorrhiza seedlings were investigated. The results showed that the increase in photosynthesis induced by LaCl 3 might be attributed to the enhanced stomatal conductance of the leaves and the increased level of the photochemical efficiency of PS II. The accumulation of tanshinone IIA and cryptotanshinone was markedly increased with the application of LaCl 3 at 20 and 60 mg/L, while tanshinone I was only slightly increased. The content of salvianolic acid B was, however, decreased with the treatment of LaCl 3 at 200 mg/L.

Effects of growth temperature on photosynthetic gas exchange characteristics and hydraulic anatomy in leaves of two cold-climate Poa species.

How plastic is hydraulic anatomy with growth temperature, and how does this relate to photosynthesis? These interrelationships were studied in subantarctic Poa foliosa Hook. f. and alpine Poa hothamensis Vickery grown under 7/4°C and 12/9°C day/night temperatures, reflecting summer temperatures in their respective habitats. Conduit radii were smaller in P. foliosa than in P. hothamensis, consistent with greater avoidance of freeze/thaw-induced embolism. Despite its origins in an environment with relatively little temperature variation, P. foliosa exhibited greater plasticity in hydraulic anatomy than P. hothamensis, increasing the size and density of conduits when grown under the warmer temperature regime. Both species had similar anatomical capacities for water transport when grown at 12/9°C, but stomatal conductance was lower in P. foliosa than P. hothamensis, suggesting hydraulic limitations not explained by leaf vascular anatomy. However, greater photosynthetic capacity and foliar nitrogen contents enabled P. foliosa to achieve the same assimilation rate as P. hothamensis under the 12/9°C growth conditions. Our results showed that nitrogen plays a central role in maintaining assimilation rates when constrained either by enzymatic activity at low temperatures or by hydraulic limitations at high temperatures and evaporative demands. Interspecific differences in nitrogen and water use may influence how subantarctic and alpine vegetation responds to climate warming.

Impact of Low Concentration of Cadmium on Photosynthesis and Growth of Pea and Barley

Photosynthetic gas exchange and growth characteristics were examined in pea and barley plants using 1 mM Cd treatment. Plants were sown into neutral peat substrate and at a leaf development stage were treated with 1 mM cadmium concentration solution. Gas exchange parameters (photosynthetic rate; intercellular CO 2 concentration; transpiration rate; water use efficiency) were measured with portable photosynthesis system LI-6400 on the fifth day after Cd treatment. Under Cd stress the photosynthetic rate of pea and barley plants decreased by 16.7 % (p 2 concentration decreased by 27.4 % (p 2 reduction processes of Cd treated pea leaves increased (because intercellular CO 2 concentration decreased), but that had no positive effect on a photosynthetic rate, and the photosynthetic rate of pea decreased by 4 % more than that of barley. The changes of dry biomass of cadmium treated plants were weak and statistically insignificant.

Enhancement of morphological, anatomical and physiological characteristics of seedlings of the mangrove Avicennia marina inoculated with a native phosphate-solubilizing isolate of Oceanobacillus picturae under greenhouse conditions

One hundred and twenty-nine rock phosphate (RP) solubilizing bacteria were isolated from the mangrove Avicennia marina rhizosphere sediment deficient in available phosphorus (P), in the United Arab Emirates (UAE). Among these isolates, an outstanding isolate of Oceanobacillus picturae grown in Pikovskaya’s liquid medium amended with RP, caused the highest percentage of RP solubilization (97%), the most pronounced drop in the medium pH and produced a variety of organic acids, as well as acid and alkaline phosphatases. Greenhouse experiments were carried out to investigate the effect of sediment inoculation with O. picturae (Op) with or without RP amendment on the growth, nutrient uptake, conducting tissue and photosynthetic gas exchange characteristics of mangrove seedlings. The application of Op to sediments amended with RP significantly promoted the growth of roots and shoots of seedlings compared with those grown in sediment amended with RP only. O. picturae significantly increased available sediment P, decreased sediment pH, positively enhanced nutrient uptake parameters in roots and shoots, increased stem circumference, number of xylem vessels, mean xylem diameter, and the hydraulically weighted xylem vessel diameter, compared with plants grown in non-inoculated sediment amended with only RP. Mechanistic analysis of A:Ci response curves (Assimilation versus sub-stomatal CO2 concentration) showed that photosynthetic gas exchange characteristics were significantly enhanced by Op + RP treatment compared with RP alone or control treatment. The maximal Rubisco-catalyzed carboxylation velocity (Vc,max), increased by more than two fold in plants treated with RP + Op, over the control. Application of Op + RP greatly increased the maximal electron transport rate values (Jmax) by 185%, over the control plants. In addition, the triose phosphate utilization rate (VTPU) increased three fold in plants treated with RP + Op over the control. To the best of our knowledge, this is the first published report of Op from mangrove sediments and also the first report of this organism as a phosphate-solubilizing bacterium. These results have clearly shown that Op has the potential to be applied as an effective and economical treatment in association with RP amendment for mangrove reforestation programs in arid environments such as those found in the UAE.

Effects of exogenous putrescine on gas-exchange characteristics and chlorophyll fluorescence of NaCl-stressed cucumber seedlings

The effects of 10 mM putrescine (Put) treated by spraying on leaves on growth, chlorophyll content, photosynthetic gas-exchange characteristics, and chlorophyll fluorescence were investigated by growing cucumber plants (Cucumis sativus L. cv. ChangChun mici) using hydroponics with or without 65 mM NaCl as a salt stress. Salt stress caused the reduction of growth such as leaf area, root volume, plant height, and fresh and dry weights. Furthermore, net photosynthesis rate (P(n)), stomatal conductance (g(s)), intercellular CO(2) concentration (C(i)), and transpiration rate (T(r)) were also reduced by NaCl, but water use efficiency (WUE; P(n)/T(r)) showed a tendency to be enhanced rather than reduced by NaCl. However, Put alleviated the reduction of P (n) by NaCl, and showed a further reduction of C (i) by NaCl. The reduction of g(s) and T(r) by NaCl was not alleviated at all. The enhancement of WUE by NaCl was shown to have no alleviation at day 1 after starting the treatment, but after that, the enhancement was gradually reduced till the control level. Maximum quantum efficiency of PSII (F(v)/F(m)) showed no effects by any conditions based on the combination of NaCl and Put, and in addition, kept constant values in plants grown in each nutrient solution during this experimental period. The efficiency of excitation energy capture by open photosystem II (PSII) (F(v)'/F(m)'), actual efficiency of PSII (Phi(PSII)), and the coefficient on photochemical quenching (qP) of plants with NaCl were reduced with time, and the reduction was alleviated till the control level by treatment with Put. The F(v)'/F(m)', Phi(PSII), and qP of plants without NaCl and/or with Put showed no variation during the experiment. Non-photochemical quenching of the singlet excited state of chlorophyll a (NPQ) showed quite different manner from the others as mentioned above, namely, continued to enhance during the experiment.

Interspecific differences in photosynthetic gas exchange characteristics and acclimation to soil moisture stress among shrubs of a semiarid grassland

Woody plants generally exhibit more conservative water-use characteristics than herbaceous perennials and annuals, including lower stomatal conductance, net photosynthesis, and transpiration, but higher photosynthetic water-use efficiency. Under soil moisture stress, stomatal conductance usually decreases more than net photosynthesis, resulting in lower ratios of internal to atmospheric CO2 concentrations and higher photosynthetic water-use efficiency. However, we found that shrubs of a semiarid grassland employed opportunistic water-use strategies, which likely evolved due to the short duration of soil moisture availability. We measured photosynthetic gas exchange, leaf reflectance, and foliar stable carbon isotope composition in Artemisia cana, Prunus Virginiana, Rhus trilobata, and Ribes aureum in southern Alberta. Under moist conditions, net photosynthesis was very high in A. cana, R. trilobata, and R. aureum, but less so in P. virginiana. Declining volumetric soil moisture caused stomatal conductance to decrease in proportion with net photosynthesis in 3 of 4 species (P. virginiana, R. aureum, and R. trilobata). Consequently, ratios of internal to atmospheric CO2 were unaffected by soil moisture depletion, and photosynthetic water-use efficiency declined. At the leaf level, the normalized difference vegetation index did not vary with season in these species, while the chlorophyll index decreased only slightly and the photochemical reflectance index showed a small mid-season peak. A. cana had the lowest stable carbon isotope ratio, highest stomatal conductance, highest late-season net photosynthesis, and highest leaf nitrogen (% dry weight). As soil moisture decreased, A. cana exhibited a decline in ratios of internal to atmospheric CO2 concentrations but no change in photosynthetic water-use efficiency. This study shows that even long-lived, woody species of a semiarid grassland have evolved traits facilitating rapid water-use to maximize carbon gain during brief periods of soil moisture availability.

Physiological acclimation of Pinus flexilis to drought stress on contrasting slope aspects in Waterton Lakes National Park, Alberta, Canada

Photosynthetic gas-exchange characteristics were measured in Pinus flexilis James (limber pine) during two drought years in a xeric, subalpine ecosystem of the Rocky Mountains. Limber pine exhibited conservative water-use traits, including low specific leaf area, leaf nitrogen, stomatal conductance, transpiration (E), and light-saturated net photosynthesis (Amax), but exhibited high needle longevity, water-use efficiency (Amax/E), and stable carbon isotope composition. Net photosynthesis declined strongly with leaf-to-air vapour pressure deficit, resulting in a bimodal seasonal pattern of Amax. Although very little gas exchange was observed in late summer, photosynthetic activity extended into October. The avoidance of gas exchange during high atmospheric demand maximized whole-season water-use efficiency. Leaf temperature and leaf-to-air vapour pressure deficit were higher on south-facing slopes during both moderate (2006) and severe (2007) drought. Severe drought caused lower stomatal conductance and E on the southeast-facing slope, but neither Amax nor canopy reflectance indices differed among slope aspects. Although Amax was lower in 2007 than 2006, branch-length increment did not differ. Foliar stable carbon isotope composition was higher in needles produced in dry years but did not vary among slope aspects. These results indicate that physiological acclimation to water stress prevented among-aspect differences in Amax and that shoulder-season photosynthesis may become increasingly important in a warmer climate.

Seasonal photosynthetic gas exchange and leaf reflectance characteristics of male and female cottonwoods in a riparian woodland

Cottonwoods (Populus spp.) are dioecious phreatophytes of hydrological and ecological importance in riparian woodlands throughout the Northern Hemisphere. In streamside zones of southern Alberta, groundwater and soil water typically decline between May and September. To understand how narrowleaf cottonwoods (Populus angustifolia James) are adapted to this seasonal decrease in water availability, we measured photosynthetic gas exchange, leaf reflectance, chlorophyll fluorescence and stable carbon isotope composition (delta(13)C) in trees growing in the Oldman River valley of southern Alberta during the 2006 growth season. Accompanying the seasonal recession in river flow, groundwater table depth (Z(gw)) declined by 1.6 m, but neither mean daily light-saturated net photosynthetic rate (A(max)) nor stomatal conductance (g(s)) was correlated with this change. Both A(max) and g(s) followed a parabolic seasonal pattern, with July 24 maxima of 15.8 micromol m(-2) s(-1) and 559 mmol m(-2) s(-1), respectively. The early summer rise in A(max) was related to an increase in the chlorophyll pool during leaf development. Peak A(max) coincided with the maximum quantum efficiency of Photosystem II (F(v)/F(m)), chlorophyll index (CI) and scaled photochemical reflectance index (sPRI), but occurred one month after maximum volumetric soil water (theta(v)) and minimum Z(gw). In late summer, A(max) decreased by 30-40% from maximum values, in weak correlation with theta(v) (r(2) = 0.50). Groundwater availability limited late-season water stress, so that there was little variation in mean daily transpiration (E). Decreasing leaf nitrogen (% dry mass), CI, F(v)/F(m) and normalized difference vegetation index (NDVI) were also consistent with leaf aging effects. There was a strong correlation between A(max) and g(s) (r(2) = 0.89), so that photosynthetic water-use efficiency (WUE; A(max)/E) decreased logarithmically with increasing vapor pressure deficit in both males (r(2) = 0.75) and females (r(2) = 0.95). The male:female ratio was unequal (2:1, chi(2) = 16.5, P < 0.001) at the study site, but we found no significant between-sex differences in photosynthetic gas exchange, leaf reflectance or chlorophyll fluorescence that might explain the unequal ratio. Females tended to display lower NDVI than males (P = 0.07), but mean WUE did not differ significantly between males and females (2.1 +/- 0.2 versus 2.5 +/- 0.2 mmol mol(-1)), and delta(13)C remained in the -28.8 to -29.3 per thousand range throughout the growth season, in both sexes. These results demonstrate changes in photosynthetic and water-use characteristics that collectively enable vigorous growth throughout the season, despite seasonal changes in water supply and demand.

Mechanisms of Enhancing Photosynthetic Gas Exchange in Date Palm Seedlings (Phoenix dactylifera L.) under Salinity Stress by a 5-Aminolevulinic Acid-based Fertilizer

Photosynthetic gas exchange characteristics, salt uptake, pigment contents, and electrolyte leakage were examined in date palm seedlings (Phoenix dactylifera L.) subject to seawater treatments at 1-, 15-, and 30-mS cm−1 salinity levels in the presence or absence of 0.08% ALA-based (5-aminolevulinic acid-based) functional fertilizer commercially known as Pentakeep-v. Date palm seedlings accumulated significant amounts of Na+ in the foliage with increasing salinity, about a threefold increase in the accumulated Na+ between the control and 30-mS cm−1salinity treatment. Electrolyte leakage indicated a significant reduction in membrane integrity as salinity increased. A strong linear correlation was observed between the chlorophyll (chl) a/b ratio and assimilation rate throughout salinity treatments. The slope (b) and the correlation coefficient between the chl a/b ratio and assimilation suggested that salinity reduced assimilation predominantly via the reduction in chlorophyll a contents (r2 = 0.885 and b = 1.77, P < 0.05). Plants treated with Pentakeep-v showed a similar response with increasing salinity but at higher levels of both chl a/b ratios and assimilation rates. Mechanistic analysis of A:Ci response curves showed that photosynthetic gas exchange in seedlings of the date palm was significantly reduced with increasing salinity due to gas phase limitation (SL) as evident by stomatal conductance (gs) values. Salinity did not induce any change in the carboxylation efficiency of the rubisco enzyme (Vc,max), or in the rate of electrons supplied by the electron transport system for ribulose 1,5-bisphosphate (RuBP) regeneration (Jmax). Accelerated carbon loss through respiration has significantly contributed to the described reduction in assimilation and increased CO2 compensation point (Γ). Only at the 30-mS cm−1 salinity level did treatment with Pentakeep-v reduce Na+ accumulation in the leaves, and caused a reduction in K+ selective uptake, leading to a concomitant reduction in K+/Na+ ratios. Pentakeep-v significantly improved chl a contents in all treatments, which was subsequently reflected in total chlorophyll and chl a/b ratios. The non-gas-phase components of the photosynthetic process (biochemical factors limiting gas exchange) were significantly improved by Pentakeep-v applications. Specifically, Pentakeep-v enhanced the biochemical efficiency of carbon fixation (Vc,max) and the rate of electron transport required for RuBP regeneration (Jmax) by 37.4% and 17.8%, respectively, over untreated plants at a salinity level of 15 mS cm–1. In addition, Pentakeep-v reduced SL to values similar to those of control plants (9.07%) and lowered CO2 compensation points by reducing respiratory CO2 loss, with increasing salinity to 30 mS cm−1. We, therefore, conclude that the ALA-based fertilizer Pentakeep-v improves salt tolerance in date palm seedlings by increasing photosynthetic assimilation. The latter is mediated via boosting light-harvesting capabilities of the treated plants by increasing chl a content and by reducing stomatal limitation to photosynthetic gas exchange.

Stomatal, biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment

The effect of salinity on leaf area and the relative accumulation of Na + and K + in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities ≥ 40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities ≤ 30‰ were negatively correlated with the total leaf area per plant ( r 2 = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves ( r 2 = 0.94). Selective uptake of K + over Na + declined sharply with increasing salinity, where K +/Na + ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis V c,max (from 50.4 to 18.4 μmol m −2 s -1), J max (from 118.0 to 33.8 μmol photons m −2 s −1), and V TPU (from 6.90 to 2.30 μmol m −2 s −1), while stomatal limitation to gas phase conductance ( S L) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor ( S L) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.

Photosynthetic gas exchange characteristics in three different almond species during drought stress and subsequent recovery

Three different drought stress levels (water potential of the nutrient solution, Ψ s = −0.6, −1.2 and −1.8 MPa, respectively), and a control treatment ( Ψ s = −0.1 MPa), were applied during 2 weeks to three almond species, followed by 3 weeks of recovery. The selected test species were Prunus dulcis (Miller) D.Webb (bitter almond) and two wild almond species, P. lycioides (Spach) C.K. Schneider and P. scoparia (Spach) C.K. Schneider. All three are species native to Iran, and can be used as rootstock, but only P. dulcis is actually used for commercial almond production. In the absence of drought stress, maximum net assimilation rate ( A max) is highest for P. scoparia and lowest for P. dulcis. For all species A max was above 16 μmol CO 2 m −2 s −1. A similar relationship between A max and dark respiration rate ( R d), was observed for all species. This relationship suggests that optimisation of the carbon budget is independent of species. The three investigated species seem to have a different reaction to a similar stress, indicating different drought stress coping strategies. P. scoparia lost all its leaves during the experiment, while P. lycioides only kept some leaves, however, the remaining leaves were almost totally wilted and did not allow for any photosynthesis measurement. P. scoparia did not recover during the experiment, as no new leaves were developed once Ψ s was restored to pre-drought stress levels. However, this species has green stems, indicating that stem photosynthesis might play an important role in the plants’ overall carbon balance. This species is an opportunistic one ( sensu [Higgins, S.S., Larsen, F.E., Bendel, R.B., Radamaker, G.K., Bassman, J.H., Bidlake, W.R., Alwir, A., 1992. Comparative gas-exchange characteristics of potted, glasshouse-grown almond, apple, fig, grape, olive, peach and Asian pear. Sci. Hortic. 52 (4), 313–329]), where assimilation is seriously limited by non-stomatal processes as evidenced by measurements of intercellular CO 2 concentration, eventually resulting in total leaf loss. All P. lycioides leaves almost completely wilted during the experiment, but this species recovered rather quickly. Leaves, newly formed at the end of the experiment, obtained maximal assimilation rates under control Ψ s levels, equivalent to those measured in the control treatment. Finally, P. dulcis did keep at least part of its leaves during drought stress. However, assimilation rates after 2 weeks of drought treatment and 3 weeks of recovery were only about half of those measured in the control treatment. Of the three investigated species, non-stomatal limitation of assimilation seems to be the least important in P. dulcis. Intrinsic water use efficiency, defined as the ratio of assimilation rate over stomatal conductance, increased for P. dulcis with increasing drought stress, while a different pattern was observed for P. lycioides and P. scoparia, indicating non-stomatal processes prevail over stomatal limitations of the assimilation process. It was concluded that P. dulcis is the species most tolerant to drought. P. scoparia tries to avoid drought, whereas P. lycioides has an intermediate behaviour. Besides P. dulcis, also P. lycioides seems to have some potential for use as rootstock for commercial almond production.

Photosynthetic Gas Exchange Characteristics, Leaf Area and Dry Matter Accumulation of Two Blackgram Cultivars

Photosynthetic Gas Exchange Characteristics, Leaf Area and Dry Matter Accumulation of Two Blackgram Cultivars