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.     

Growth and Leaf Gas Exchange Characteristics in Dalbergia sissoo Roxb. and D. latifolia Roxb. Under Water Deficit

Forty two-month-old plants of Dalbergia sissoo and D. latifolia were subjected for 56 d to water deficit induced by withholding water. Drought stress caused a significant reduction in plant height, stem diameter, net photosynthetic rate (P _N), transpiration rate (E), and stomatal conductance (g _s) in both species, but the reduction was greater in D. sissoo than in D. latifolia. Water use efficiency (P _N/E) was adversely affected due to water stress only in D. latifolia, and intrinsic water use efficiency (P _N/g _s) was increased in both species. There was a slight effect of water stress on variable to maximum fluorescence (F_v/F_m) (quantum yield of photosystem 2) in both species, but the species did not differ significantly in this attribute.     

Leaf Gas Exchange and Water Relations in Polylepis tarapacana at Extreme Altitudes in the Bolivian Andes

Stress-induced restrictions to carbon balance, growth, and reproduction are the causes of tree-line formation at a global scale. We studied gas exchange and water relations of Polylepis tarapacana in the field, considering the possible effects of water stress limitations imposed on net photosynthetic rate (P _N). Daily courses of microclimatic variables, gas exchange, and leaf water potential were measured in both dry-cold and wet-warm seasons at an altitude of 4 300 m. Marked differences in environmental conditions between seasons resulted in differences for the dry-cold and wet-warm seasons in mean leaf water potentials (–1.67 and –1.02 MPa, respectively) and mean leaf conductances (33.5 and 58.9 mmol m^–2 s^–1, respectively), while differences in mean P _N (2.5 and 2.8 mol m^–2 s^–1, respectively) were not as evident. This may be related to limitations imposed by water deficit and lower photon flux densities during dry and wet seasons, respectively. Hence P. tarapacana has coupled its gas exchange characteristics to the extreme daily and seasonal variations in temperature and water availability of high elevations.     

Interspecific Differences of Leaf Gas Exchange and Water Relations of Three Evergreen Mediterranean Shrub Species

Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (P _N) and stomatal conductance (g _s) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum P _N and g _s, although P _N was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (₁) during the drought period (–3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as ₁. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of ₁ at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus.     

Effects of Osmotic Drought Stress Induced by a Combination of NaCl and Polyethylene Glycol on Leaf Water Status,Photosynthetic Gas Exchange,and Water Use Efficiency of Pistacia khinjuk and P. mutica

Leaf water potential, leaf osmotic potential, chlorophyll a and b contents, stomatal conductance, net photosynthetic rate, and water use efficiency were determined in two pistachio species (Pistacia khinjuk L. and P. mutica L.) grown under osmotic drought stress induced by a combination of NaCl and polyethylene glycol 6000. A decrease in values for all mentioned variables was observed as the osmotic potential of the nutrient solution (_s) decreased. The osmotic adjustment () of the species increased by decreasing _s. Thus P. khinjuk had a higher osmotic drought stress tolerance than P. mutica.     

Interrelationship between Leaf Gas-Exchange Characteristics,Area Leaf Mass,and Yield in Soybean (Glycine max L. Merr) Genotypes

Variability in leaf gas-exchange traits in thirteen soybean (Glycine max L. Merr) genotypes was assessed in a field experiment conducted at high altitude (1 950 m). Leaf net photosynthetic rate (P ^N) exhibited a high degree of variability at all the growth stages studied. P _N and other gas-exchange parameters exhibited a seasonal pattern that was similar for all the genotypes. P _N rate was highest at seed filling stage. P _N was positively and significantly associated with aboveground dry matter and seed yield. The area leaf mass (ALM) exhibited a strong positive association with leaf P _N, aboveground dry matter, and seed yield. The positive association between ALM, P _N, and seed yield suggests that this simple and easy to measure character can be used in breeding programmes as a surrogate for higher photosynthetic efficiency and eventually higher yield.     

Biomass Partitioning and Gas Exchange in Dalbergia sissoo seedlings under water stress

Biomass, leaf water potential (_l), net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), leaf to air temperature difference (T _diff), and instantaneous water use efficiency (WUE) were measured in the seedlings of Dalbergia sissoo Roxb. grown under irrigation of 20 (W₁), 14 (W₂), 10 (W₃), and 8 (W₄) mm. Treatments were maintained by re-irrigation when water content of the soil reached 7.4% in W₁, 5.6% in W₂, 4.3% in W₃, and 3.2% in W₄. Seedlings in a control (W₅) were left without irrigation after maintaining the soil field capacity (10.7%). Seedlings of W₁ had highest biomass that was one tenth in W₅. Biomass allocation was highest in leaf in W₂ and in root in W₄ and W₅ treatments. Difference between predawn leaf water potential (_Pd) and midday (_mid) increased with soil water stress and with vapour pressure deficit (VPD) in April and May slowing down the recovery in plant leaf water status after transpiration loss. P _N, E, and g _s declined and T _diff increased from W₁ to W₅. Their values were highly significant in April and May for the severely stressed seedlings of W₄ and W₅. P _N increased from 08:00 to 10:00 and E increased until 13:00 within the day for most of the seedlings whereas g _s decreased throughout the day from 08:00 to 17:00. P _N and E were highest in March but their values were low in January, February, April, and May. Large variations in physiological variables to air temperature, photosynthetically active radiation, and vapour pressure deficit (VPD) indicated greater sensitivity of the species to environmental factors. WUE increased from W₁ to W₂ but decreased drastically at high water stress particularly during hot summer showing a kind of adaptation in D. sissoo to water stress. However, low biomass and reduced physiological functions at <50% of soil field capacity suggest that this species does not produce significant biomass at severe soil water stress or drought of a prolonged period.     

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.     

Influence of Potassium Nutrition on Gas Exchange Characteristics and Water Relations in Cotton (Gossypium hirsutum L.)

The effects of potassium nutrition [0, 6.25, 12.50, 25.00 g(K) m^–2 of K₂SO₄ or KCl] on gas exchange characteristics and water relations in four cultivars (CIM-448, CIM-1100, Karishma, S-12) of cotton were assessed under an arid environment. Net photosynthetic rate (P _N) and transpiration rate (E) increased with increased K supply. The leaf pressure potential (_p) increased significantly by the addition of 25.00 g(K) m^–2 compared to zero K level. The water use efficiency (P _N/E) was improved by 24.6 % under the highest K dose compared to zero K. There were positive correlations (0.99^**, 0.98^**, 0.95^**, 0.97^**) between K-doses and P _N, E, _p, and P _N/E, respectively.     

Different Patterns of Gas Exchange and Photochemical Efficiency in Three Desert Shrub Species Under Two Natural Temperatures and Irradiances in Mu Us Sandy Area of China

Field studies of gas exchange and chlorophyll fluorescence of three desert shrub species, Hedysarum fruticosum var. mongolicum, Artemisia ordosia, and Salix pasmmophylla, showed different patterns under different leaf temperature (T₁) and incident photosynthetic photon flux density (PPFD). H. fruticosum var. mongolicum and A. ordosia exhibited higher P _N and g _s than S. pasmmophylla, especially under very high T₁ (>46 °C) and high PPFD (>2 100 µmol m^–2 s^–1) in hot summer. The decreases of P _N with the diurnal course were due mainly to stomata closure. However, P _N of S. pasmmophylla was seriously depressed by very high temperature from midday to evening as shown by the negative P _N in hot summer, whereas none of such depression was found in spring. Maximal spring photochemical efficiency of photosystem 2 (PS2), i.e, F_v/F_m, was the lowest at 16:00, indicating the injury of PS2 by heat at this stage. In hot summer again, all the three shrubs underwent pronounced midday depression of P _N and g _s, while in spring they showed a one-peak response. And the first peak appeared 2 h earlier in hot summer than in spring for all the three shrubs. It was the high temperature that led to the different patterns of gas exchange and the serious depression of P _N in S. pasmmophylla. H. fruticosum var. mongolicum and A. ordosia were much more tolerant to heat and high irradiance than S. pasmmophylla, which fixed most of CO₂ at the fast growing stage in spring. Nevertheless, in hot summer it had to survive the severe hot environment through strong respiration and storage of CO₂ only in the early morning.     

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.     

Effects of Reddening of Cotton (Gossypium hirsutum L.) Leaves on Functional Activity of Photosynthetic Apparatus

Strong inhibition of rates of CO₂ assimilation and transpiration, stomatal conductance, and water use efficiency as well as photosystem 2 (PS2) photochemical activity were related to the severity of reddening. The inhibition of photosynthesis in red cotton leaves was due to both decreased photochemical activity and stomatal limitation. Lowered photosynthetic capacity could be one of the main factors of reduced yield in reddening cotton.     

Participation of Phytohormones in the Stomatal Regulation of Gas Exchange During Water Stress

Almost all processes in the life of a plant are directly or indirectly affected by both stresses and phytohormones. Nevertheless, apart from abscisic acid, the role of phytohormones in plant response to water stress is far from being fully elucidated. This review tries to answer the question whether interactions between abscisic acid and some other phytohormones might be important in the regulation of stomatal opening during water stress and subsequent rehydration. Firstly, it describes the changes in the contents of individual endogenous phytohormones during water stress. Then, it deals with the effects of applied phytohormones on stomatal opening, and on transpiration and photosynthetic rates in different plants species. Finally, it focuses on the alleviation or stimulation of absicic acid-induced stomatal closure by application of other phytohormones. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gas Exchange Characteristics and Water Relations in Some Elite Okra Cultivars Under Water Deficit

Thirty-days-old plants of two cultivars of okra (Hibiscus esculentus L.), Sabzpari and Chinese-red, were subjected for 30 d to two water regimes (100 and 60 % field capacity). Leaf water potential and osmotic potential of both lines decreased significantly with the imposition of drought. Both the leaf pressure potential and osmotic adjustment were much lower in Chinese-red than those in Sabzpari. Chlorophyll (Chl) b content increased, whereas Chl a content remained unchanged and thus Chl a/b ratios were reduced in both lines. Drought stress also caused a significant reduction in net photosynthetic rate (P _N), transpiration rate (E), stomatal conductance (g _s), and water use efficiency (WUE) especially in cv. Sabzpari. The lines did not differ in intrinsic WUE (P _Ng_s) or intercellular/ambient CO₂ ratio. Overall, the growth of two okra cultivars was positively correlated with P _N, but not with g _s or P _N/E, and negatively correlated with osmotic adjustment.     

Water relations and photosynthesis in Cucumis sativus L. leaves under salt stress

Hydroponically grown cucumber plants were exposed to 14-d period of salinity (0, 50, 100 mM NaCl). NaCl caused reduction in the relative water content in the leaves. The Na⁺ content increased and the K⁺ content decreased. The net photosynthetic rate, stomatal conductance and transpiration rate were markedly decreased by all of the salt treatments. Salinity decreased also the maximum quantum efficiency of photosystem 2 (PS 2) determined as the variable to maximum fluorescence ratio, the photochemical quantum yield of PS 2 and the photochemical fluorescence quenching, while the non-photochemical quenching increased. Above results indicate that NaCl affects photosynthesis through both stomata closure and non-stomatal factors.     

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.     

Photosynthesis and Water Use Efficiency in Twenty Tropical Tree Species of Differing Succession Status in a Brazilian Reforestation

Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (P _NA) or a dry mass (P _NM) basis, differed among species. P _NA and P _NM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 mol m^–2 s^–1) for P _NA, and 5-fold (from 50 to 275 mol kg^–2 s^–1) for P _NM. The highest P _NA (23 mol m^–2 s^–1) and P _NM (275 mol kg^–2 s^–1) values were recorded in PS Croton urucurana, while the lowest P _NA (7 mol m^–2 s^–1) and P _NM (50 mol kg^–2 s^–1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (g _s), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest g _s and E. P _NM was highly correlated with ALM in both PS and LS (r=–0.75 and –0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUE_i) were also observed in the PS when compared with the LS.     

Effect of Benzyladenine and Hydroxybenzyladenosine on Gas Exchange of Bean and Sugar Beet Leaves

Using bean seedlings, the effects of benzyladenine (BA) on stomatal conductance (g_s), transpiration rate (E), and net photosynthetic rate (P_N) were examined in order to find out dose and time responses. In bean seedlings, BA appli roots in concentrations of 1, 5, 10, and 20 µM increased g_s and P_N of leaves already 1 h after application. E was not markedly affected and water use efficiency (WUE) was increased. However, the effects were mostly transient and after 24 h P_N only at 1 and 5 µM BA was increased, and other parameters were not affected or even decreased. In sugar beet seedlings, the effects of hydroxybenzyladenosine (HBA) in addition to those of BA on the same parameters were determined. The both cytokinins were applied in 1, 5, 10, and 20 µM concentrations either to roots or sprayed on leaves However, the effects were inconsistent and the positive effect was observed only after 24 h on P_N in plants with roots immersed in 5 and 10 µM BA, or 10 µM HBA, and on E in plants sprayed with 5 µM BA or 10 µM HBA. Thus the stimulation of gas exchange by exogenously applied cytokinins is rather exceptional than general.     

Leaf Gas Exchange and Chlorophyll Fluorescence Parameters in Phaseolus Vulgaris as Affected by Nitrogen and Phosphorus Deficiency

The effects of N and P deficiency, isolated or in combination, on leaf gas exchange and fast chlorophyll (Chl) fluorescence emission were studied in common bean cv. Negrito. 10-d-old plants grown in aerated nutrient solution were supplied with high N (HN, 7.5 mol m⁻³) or low N (LN, 0.5 mol m⁻³), and also with high P (HP, 0.5 mol m⁻³) or low P (LP, 0.005 mol m⁻³). Regardless of the external P supply, in LN plants the initial fluorescence (F₀) increased 12 % in parallel to a quenching of about 14 % in maximum fluorescence (F_m). As a consequence, the variable to maximum fluorescence ratio (F_v/F_m) decreased by about 7 %, and the variable to initial fluorescence ratio (F_v/F₀) was lowered by 25 % in relation to control plants. In LP plants, F_v/F_m remained unchanged whilst F_v/F₀ decreased slightly as a result of 5 % decline in F_m. Under N deficiency, the net photosynthetic rate (P _N) halved at 6 d after imposition of treatment and so remained afterwards. As compared to LN plants, P _N declined in LP plants latter and to a less extent. From 12 d of P deprivation onwards. P _N fell down progressively to display rates similar to those of LN plants only at the end of the experiment. The greater P _N in LP plants was not reflected in larger biomass accumulation in relation to LN beans. In general, P and N limitation affected photosynthesis parameters and growth without showing any synergistic or additive effect between deficiency of both nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.