Gas exchange characteristics and water relations in two cultivars of <Emphasis Type="Italic">Hibiscus esculentus</Emphasis> under waterlogging

Thirty-day-old plants of two okra cultivars, Sabzpari and Chinese-red, were subjected for 30 d to normal watering or continuous flooding. Continuous flooding did not cause any adverse effect on shoot fresh and dry biomass. Leaf water potential and pressure potential of both cultivars increased significantly due to waterlogging, but there was a slight increase in leaf osmotic potential. Chlorophyll a and b contents decreased significantly and chlorophyll a/b ratio increased. Waterlogging caused a significant reduction in net photosynthetic rate, water use efficiency and intrinsic water use efficiency, but stomatal conductance and intercellular CO₂/ambient CO₂ ratio remained unchanged.     

Tolerance to Water Stress in Tomato Cultivars

The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), osmotic adjustment, and crop water stress index (CWSI) were investigated. Osmotic adjustment was the highest in cv. Arka Meghali, followed by cv. RFS-1. CWSI was lowest in cv. Arka Meghali and highest in cv. Pusa Ruby. Significant reduction in g _s, E, and P _N was observed in all the cultivars. The maximum reduction in E was observed in cv. Arka Saurabh during the fruiting stage (62.4 %) and maximum reduction in P _N at the flowering stage in Pusa Ruby (53.1 %). Maximum P _N was observed in Arka Meghali under water stress. The values of internal CO₂ concentration (C _i) did not follow the decrease in g _s which might be taken as an indication of mesophyll (non-stomatal) limitation to P _N. Magnitude of P _N decrease accompanying g _s reductions varied in the four cultivars. Arka Meghali which had highest rate of gas exchange efficiency (P _N/g _s) under water deficits can be recommended for rainfed cultivation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO₂ assimilation rate (P _N), stomatal conductance (g _s), and transpiration rate (E) declined, and intercellular CO₂ concentration (C _i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P _N and g _s coupled with a better C _i and water use efficiency (WUE) than the sensitive cultivar. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rehydration of Sugar Beet Plants after Water Stress: Effect of Cytokinins

The possibility to improve the recovery of sugar beet plants after water stress by application of synthetic cytokinins N⁶-benzyladenine (BA) or N⁶-(m-hydroxybenzyl)adenosine (HBA) was tested. Relative water content (RWC), net photosynthetic rate (P_N), transpiration rate (E), stomatal conductance (g_s), chlorophyll (Chl) a and Chl b contents, and photosystem 2 efficiency characterized by variable to maximal fluorescence ratio (F_v/F_m) were measured in control plants, in water-stressed plants, and after rehydration (4, 8, 24, and 48 h). Water stress markedly decreased parameters of gas exchange, but they started to recover soon after irrigation. Application of BA or HBA to the substrate or sprayed on leaves only slightly stimulated recovery of P_N, E, and g_s in rehydrated plants, especially during the first phases of recovery. Chl contents decreased only under severe water stress and F_v/F_m ratio was not significantly affected by water stress applied. Positive effects of BA or HBA application on Chl content and F_v/F_m ratio were mostly not observed.     

Photosynthesis and the Enzymes of Photosynthetic Carbon Reduction Cycle in Mulberry During Water Stress and Recovery

Net photosynthetic rate (P _N), stomatal conductance (g _S), transpiration rate (E), intercellular CO₂ concentration (C _i), leaf water potential (_w), leaf area, chlorophyll (Chl) content, and the activities of photosynthetic carbon reduction cycle (PCR) enzymes in two mulberry (Morus alba L.) cultivars (drought tolerant Anantha and drought sensitive M-5) were studied during water stress and recovery. During water stress, P _N, g _S, and E declined whereas C _i increased. P _N, g _S, and E were less affected in Anantha than in M-5, which indicates tolerance nature of Anantha over M-5. Activities of ribulose-5-phosphate kinase, NAD- and NADP-glyceraldehyde-3-phosphate dehydrogenases, and 3-phosphoglycerate kinase decreased with increasing stress in both the cultivars. The enzyme activities less affected in tolerant (Anantha) than in sensitive cultivar (M-5) were restored after re-watering to almost initial values in both the cultivars. Re-watering of the plants led to an almost complete recovery of P _N, E, and g _S, indicating that a short-term stress brings about reversible effect in these two cultivars of mulberry.     

Gas Exchange Characteristics of the Flue-Cured Tobacco (Nicotiana Tabacum L.) Cultivars Grown under Two Production Systems

The net photosynthetic rate (P _N), intercellular CO₂ concentration (C _i), stomatal conductance (g _s), transpiration rate (E), water use efficiency (WUE), and leaf biomass production of four American flue-cured tobacco (Nicotiana tabacum L.) cultivars K 326, K 358, and Speight G 28 were compared with three local Indian cultivars 16/103, Special FCV, and PCT-7, during 1994 and 1995 crop seasons under irrigated and rainfed production systems (Northern light soils, NLS, and Karnataka light soils, KLS) in India. By comparison, the American tobacco cv. K 326 showed the highest P _N and g _s. A positive correlation was found between P _N and biomass production in all the varieties tested (r = 0.55 in NLS and 0.73 in KLS). The American cultivars were superior than the local cultivars in their biomass production and P _N under Indian farming conditions.     

Effects of Drought Stress Induced by Polyethylene Glycol on Pigment Content and Photosynthetic Gas Exchange of Pistacia Khinjuk and P. Mutica

The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (P _N), stomatal conductance (g _s), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ₁), leaf osmotic potential (Ψ_π), leaf osmotic adjustment (ΔΨ_π), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. P _N, g _s, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthesis and Growth Responses of Parthenocissus quinquefolia (L.) Planch to Soil Water Availability

Photosynthesis and growth characteristics of Parthenocissus quinquefolia were measured under differing soil water availability within a pot. Decreased soil moisture significantly reduced the leaf relative water content (RWC) and the above- and below-ground biomass. However, more biomass was allocated to the root than to the leaf. Net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were also significantly decreased but water use efficiency (WUE) was increased. Midday depressions in P _N and g _s were not evident for the well-irrigated plants. With the lower water availability, midday reductions in P _N and g _s were much more marked and the duration of the depression was longer. Additionally, the P _N-irradiance response curves also indicated that water supply affected photosynthesis capacity. The growth and photosynthetic response of P. quinquefolia to water supply indicated that this species could resilient to water availabilities and adapt to Hunshandak conditions very well.     

Photosynthetic Response to Soil Water Contents of an Annual Pioneer C4 Grass (Agriophyllum squarrosum) in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and leaf water potential (Ψ_l) of an annual pioneer C₄ grass (Agriophyllum squarrosum) were compared under different simulated precipitation events in a field of Hunshandak Sandland, China. The increase of soil water content (SWC) had significant effect on these physiological traits (p<0.001). In the vegetative stage, the values of P _N, E, and g _s went up sharply when SWC increased at the beginning, while they went down with continuous increase of SWC. P _N, E, and g _s increased 1.4, 1.7, and 1.7 fold, respectively, with SWC range from 6.7 to 11.6 %. In the reproductive stage, similar trends were found, except for the climate with a higher SWC. This indicated that A. squarrosum was very sensitive to the small increment of SWC which might have a large photosynthetic potential. Ψ_l increased by about 8 % as the SWC changed from 6.7 to 8.8 %, and then maintained a steady level when the SWC was higher than 8.8 %, while the values of P _N, E, and g _s kept increasing even after this SWC. This might indicate that the adjustment of Ψ_l response to the changes of SWC lagged that of the photosynthetic parameters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Growth and Photosynthetic Characteristics in Pearl Millet under Water Stress and Different Potassium Supply

Influence of supra-optimal concentrations of K on growth, water relations, and photosynthetic capacity in pearl millet under severe water deficit conditions was assessed in a glasshouse. Nineteen-days-old plants of two lines, ICMV-94133 and WCA-78, of Pennisetum glaucum (L.) R.Br. were subjected for 30 d to 235.0, 352.5, and 470.0 mg(K) kg^–1(soil) and two water regimes (100 and 30 % field capacity). Increasing K supply did not alleviate the effect of water deficit on the growth of two lines of pearl millet since additional amount of K in the growth medium had no effect on shoot dry mass, relative growth rate, plant leaf area, net assimilation rate, or leaf area ratio, although there was significant effect of drought stress on these variables. Soil moisture had a significant effect on net photosynthetic rate (P _N), transpiration rate, stomatal conductance, and water use efficiency of both pearl millet lines, but there was no significant effect of varying K supply on these variables. In WCA-78 an ameliorative effect of increasing supply of K on P _N was observed under water deficit. Chlorophyll (Chl) a and b contents increased significantly in both lines with increase in K supply under well watered conditions, but under water deficit they increased only in ICMV-94133. Chl a/b ratios were reduced significantly in WCA-78 with increasing K supply under both watering regimes, but by contrast, in ICMV-94133 this variable was decreased only under water stress. Leaf water potential and osmotic potential of both lines decreased significantly with the imposition of drought. Leaf pressure potential in both lines increased with increase in K supply under water stress. Contents of total free amino acids in the leaves of both pearl millet lines increased significantly with increase in K supply under water stress. Potassium supply had no effect on leaf soluble sugars or soluble proteins. Considerable osmotic adjustment occurred in pearl millet plants experiencing water deficit under high K supply.     

Physiological divergences between two rhizomatous grasses from a desertification steppe,North China

The inter-and intra-specific physiological differences, e.g. rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), and water use efficiency (WUE), were compared between two grasses, Calamagrostis epigeios (L.) Roth. and Psammochloa villosa (Trin.) Bor., and between their leaf types in a desertification steppe in North China. The two species had a similar habitat, but differed in leaf area and rhizome depth. Leaf P _N, E, and g _s for P. villosa were significantly greater than those for C. epigeios in the growing season, but WUE for the former species was only 50 and 80 % of that for the latter one in dry and rainy seasons, respectively. In general, leaf P _N, E, g _s, and WUE for both vegetative and reproductive shoots of the two species exhibited little variations between leaf types or with leaf age, even though there were some remarkable differences between dry and rainy seasons. The mean leaf P _N and E in reproductive shoots of P. villosa were significantly lower than those in its vegetative shoots in rainy season, while these differences were much smaller for those of C. epigeios. P. villosa with deeper rhizome roots has relative higher leaf P _N, E, and g _s, but a smaller WUE in the arid desertification steppe region.     

Leaf Gas Exchange and Water Relations of Grapevines Grown in Three Different Conditions

Diurnal and seasonal changes in the leaf water potential (), stomatal conductance (g _s), net CO₂ assimilation rate (P _N), transpiration rate (E), internal CO₂ concentration (C _i), and intrinsic water use efficiency (P _N/g _s) were studied in grapevines (Vitis vinifera L. cv. Touriga Nacional) growing in low, moderate, and severe summer stress at Vila Real (VR), Pinhão (PI), and Almendra (AL) experimental sites, respectively. In VR and PI site the limitation to photosynthesis was caused more by stomatal limitations, while in AL mesophyll limitations were also responsible for the summer decline in P _N.     

Photosynthesis Parameters in Two Cultivars of Mulberry Differing in Salt Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (salt tolerant cv. S1 and salt sensitive cv. ATP) were subjected to different concentrations of NaCl for 12 d. Leaf area, dry mass accumulation, total chlorophyll (Chl) content, net CO₂ assimilation rate (P _N), stomatal conductance (g _s), and transpiration rate (E) declined, and intercellular CO₂ concentration (C _i) increased. The changes in these parameters were dependent on stress severity and duration, and differed between the two cultivars. The tolerant cultivar showed a lesser reduction in P _N and g _s coupled with a better C _i and water use efficiency (WUE) than the sensitive cultivar.     

Diurnal and Seasonal Patterns of Water Potential,Photosynthesis, Evapotranspiration and Water Use Efficiency of Clusterbean

Diurnal patterns of leaf water potential (_W), canopy net photosynthetic rate (P _N), evapotranspiration rate (E), canopy temperature (T_c), and water use efficiency (WUE) of clusterbean [Cyamopsis tetragonoloba (L.) Taub., cv. Desi] were studied at six phenological stages of plant development under field conditions at CCS Haryana Agricultural University, Hisar. The highest P _N, E, and WUE were observed at pod initiation stage (61 DAS). Daily maxima of P _N were usually between 11:00 to 14:00 h while those of E and WUE between 12:30 and 16:00 h. P _N was mainly dependent on photosynthetically active radiation and E on air temperature (T_a) but the relationships varied at different growth stages. WUE declined with the increase in T _a. At mid-day, _W was highest during pod initiation.     

Effect of water stress on leaf photosynthesis,chlorophyll content,and growth of oriental lily

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C_i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P _max) and dark respiration rates (R _D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P _n, E, g _s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P _n)-PAR response curve. Drought stress increased LCP and R _D and decreased LSP and P _max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P _n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.     

Diurnal and seasonal trends in photosynthetic performance of <Emphasis Type="Italic">Dalbergia sissoo</Emphasis> Roxb. and <Emphasis Type="Italic">Hardwickia binata</Emphasis> Roxb. from a semi-arid ecosystem

Diurnal and seasonal trends in net photosynthetic rate (P _N), stomatal conductance (g), transpiration rate (E), vapour pressure deficit, temperature, photosynthetic photon flux density, and water use efficiency (WUE) were compared in a two-year-old Dalbergia sissoo and Hardwickia binata plantation. Mean daily maximum P _N in D. sissoo ranged from 21.40±2.60 μmol m⁻² s⁻¹ in rainy season I to 13.21±2.64 μmol m⁻² s⁻¹ in summer whereas in H. binata it was 20.04±1.20 μmol m⁻² s⁻¹ in summer and 13.64±0.16 μmol m⁻² s⁻¹ in winter. There was a linear relationship between daily maximum P _N and g _s in D. sissoo but there was no strong linear relationship between P _N and g _s in H. binata. In D. sissoo, the reduction in g _s led to a reduction in both P _N and E enabling the maintenance of WUE during dry season thereby managing unfavourable environmental conditions efficiently whereas in H. binata, an increase in g _s causes an increase of P _N and E with a significant moderate WUE.     

Physiological Effects of Plant Hormones in Cotton Under Drought

Effects of plant hormones indole-3-yl-acetic acid (IAA), gibberellic acid (GA), benzylaminopurine (BAP), abscisic acid (ABA) and ethrel (ETH) in 5 M concentration on gas exchange, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39) activity, pigment content and yield in cotton (Gossypium hirsutum L. cv. H-777) under drought were studied. At reproductive stage (55 – 60 d after sowing) these hormones were sprayed on shoots one day prior to stress imposition by withholding irrigation. The soil moisture of control plants was kept at field capacity. Net photosynthetic rate (P_N), stomatal conductance (g_s), transpiration rate (E), carboxylation efficiency (CE), water use efficiency (WUE), RuBPCO activity, boll number per plant, seed number per plant and lint mass per plant significantly decreased at drought while chlorophyll (Chl) b content and flower number per plant increased. ABA and ETH significantly reduced gas exchange parameters, Chl a and Chl b content. Detrimental drought effect on P_N, g_s, E, CE, RuBPCO and lint mass per plant was significantly alleviated by BAP and also its effect on seed number and lint mass per plant was significantly alleviated with the ABA treatment.     

Effects of different irradiances on the photosynthetic process during ex-vitro acclimation of Anoectochilus plantlets

Six months old in vitro-grown Anoectochilus formosanus plantlets were transferred to ex-vitro acclimation under low irradiance, LI [60 μmol(photon) m⁻² s⁻¹], intermediate irradiance, II [180 μmol(photon) m⁻² s⁻¹], and high irradiance, HI [300 μmol(photon) m⁻² s⁻¹] for 30 d. Imposition of II led to a significant increase of chlorophyll (Chl) b content, rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), electron transfer rate (ETR), quantum yield of electron transport from water through photosystem 2 (Φ_PS2), and activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBPCO, EC 4.1.1.39). This indicates that Anoectochilus was better acclimated at II compared to LI treatment. On the other hand, HI acclimation led to a significant reduction of Chl a and b, P _N, E, g _s, photochemical quenching, dark-adapted quantum efficiency of open PS2 centres (F_v/F_m), probability of an absorbed photon reaching an open PS2 reaction centre (F_v′/F_m′), ETR, Φ_PS2, and energy efficiency of CO₂ fixation (Φ_CO2/Φ_PS2). This indicates that HI treatment considerably exceeded the photo-protective capacity and Anoectochilus suffered HI induced damage to the photosynthetic apparatus. Imposition of HI significantly increased the contents of antheraxanthin and zeaxanthin (ZEA), non-photochemical quenching, and conversion of violaxanthin to ZEA. Thus Anoectochilus modifies its system to dissipate excess excitation energy and to protect the photosynthetic machinery.     

Diurnal changes in leaf gas exchange and validation of a mathematical model for coffee (<Emphasis Type="Italic">Coffea arabica</Emphasis> L.) canopy photosynthesis

Diurnal variations in net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), internal CO₂ concentration (C _i), and water use efficiency (WUE) were studied on individual leaves of coffee plants to determine the effect of climatic factors on photosynthetic capacity. P _N and E showed bimodal behaviour with the maximum values of P _N at mid-morning. At noon, under saturating photosynthetically active radiation (PAR) and high leaf temperature (T _l), P _N declined. In the afternoon (14:00), P _N slightly recovered in association with a decrease in Tl and in leaf-to-air vapour pressure deficit (VPD). Reductions in E during the morning were associated with decreases in g _s. Higher WUE in the morning was related to higher P _N and lower E. The reverse occurred in the afternoon. Goudriaan's simulation model, adapted for coffee canopy photosynthesis, was tested at the level of whole plant (P _pl). Three methods were used: (a) Whole plant net photosynthesis (P _pl) under semi-controlled conditions in a chamber. (b) P _pl estimation following Goudriaan's method (Gaussian integration) of instantaneous P _N in single leaves at three canopy depths and at three different hours assuming a photosynthesis unimodal behaviour. (c) P _pl using Goudriaan's method but at five different hours according to the bimodal behaviour reported above. Results of P _pl estimates using Goudriaan's model adapted for coffee canopy confirm the observed P _pl bimodal behaviour with high fitness degree of the measured whole plant photosynthesis. The high fitness found among observed and simulated data indicates that the modified model may be used as a subroutine for the general simulation model of coffee crop growth.     

Diurnal Gas Exchange and Superior Resources Use Efficiency of Typical C4 Species in Hunshandak Sandland,China

Net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), leaf water potential (ψ_leaf), leaf nitrogen content, and photosynthetic nitrogen use efficiency (PNUE) were compared between a typical C₄ plant, Agriophyllum squarrosum and a C₃ plant, Leymus chinensis, in Hunshandak Sandland, China. The plant species showed different diurnal gas exchange patterns on June 12–14 when photosynthetic photon flux density (PPFD), air temperature (T _air), and water potential were moderate. P _N, E, and g _s of A. squarrosum showed distinct single peak while those of L. chinensis were depressed at noon and had two peaks in their diurnal courses. Gas exchange traits of both species showed midday depression under higher photosynthetic photon flux density (PPFD) and T _air when Ψ_leaf was significantly low down on August 6–8. However, those of A. squarrosum were depressed less seriously. Moreover, A. squarrosum had higher P _N, Ψ_leaf, water use efficiency (WUE), and PNUE than L. chinensis. Thus A. squarrosum was much more tolerant to heat and high irradiance and could utilise the resources on sand area more efficiently than L. chinensis. Hence species like A. squarrosum may be introduced and protected to reconstruct the degraded sand dunes because of their higher tolerance to stress and higher resource use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.