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.     

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.     

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.     

两个品种转基因抗虫棉光合生理的CO2响应

栽培环境条件的改变会对转基因作物产生深远影响。以2种不同转基因棉花及其亲本对照为材料,研究了盆栽种植条件下不同棉花品种在蕾期和吐絮期光合生理特性CO2响应特征。结果表明,与各自的常规棉对照比较,两种转基因抗虫棉单叶净光合速率CO2响应的特征参数表观初始羧化效率(CE)、表观暗呼吸速率(Rd)和最大净光合速率(Pmax,c)虽有一定程度的变化,但其差异均未达到显著水平。在高CO2浓度范围内(700μmol.mol-1),转基因抗虫棉单叶净光合速率和水分利用率(WUE)的CO2响应曲线特征发生变化,且与品种及生育时期有关。两种转基因抗虫棉在不同生育时期的气孔导度(Gs)对CO2浓度的响应特征与其常规棉对照相似,短期CO2浓度增高对转基因抗虫棉的气孔导度没有显著性影响。     

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.     

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.     

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.     

Gas exchange in leaves of the root hemiparasitemelampyrum arvense L. before and after attachment to the host plant

Gas exchange characteristics of a hemiparasiteMelampyrum arvense L. before and after attachment to the hostCapsella bursa pastoris (L.) Med. were compared. The net photosynthetic rates (P_N) on a leaf area basis were extremely low and in comparison to the value obtained for the host were about 15 % and 23 % for the unattached and attached hemiparasite, respectively. Also the concentration of photosynthetic pigments was low (as compared with the host the content of chlorophylls was about 33 % and 49 % and of carotenoids about 38 % and 36 % in the unattached and attached hemiparasite, respectively). On the other hand the rates of respiration were high (about 1.8 and 2.6 times higher in the unattached and attached hemiparasite, respectively, than in the host). In darkness stomatal conductance (g_S) of the host and the unattached hemiparasite was rapidly reduced to 10 % of the value obtained in light, g_S of the attached hemiparasite was decreased only by about 30%. A total reduction of g_S occurred at relative water content (RWC) of 85 %, 75% and 45 % for the unattached hemiparasite, the host, and the attached hemiparasite, respectively. The transpiration (E) rate in the preparasitic stage was very low, being 2.6 and 4.5 times smaller than in the host and the attached hemiparasite, respectively. In the attached hemiparasite WUE was 7.5 and 3 times poorer than in the host and in the preparasitic stage, respectively.     

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.     

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.     

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.     

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.     

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.     

The Effect of Phyllode Temperature on Gas Exchange and Chlorophyll Fluorescence of Acacia mangium

The optimum temperature for photosynthetic CO₂ assimilation of A. mangium phyllodes was 30–32 °C. Photosystem 2 (PS 2) exhibited high tolerance to high temperature. Gas exchange and the function of PS2 of A. mangium were adapted to the temperature regime of the tropical environment and this might be the contributing factor to their fast growth under tropical conditions.     

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.     

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.     

Leaf Gas Exchange of Pachyrhizus ahipa and P. erosus Under Water and Temperature Stress

Gas exchange, water relations, and leaf traits were studied in the tuberous-root producing legumes ahipa (Pachyrhizus ahipa) and yambean (P. erosus) under different environmental conditions. Differences in leaf traits (hairiness, leaf area, areal leaf mass, stomatal density) and paraheliotropism were found between ahipa and yambean. Under sufficient water supply, the increase in air temperature and decrease in air humidity increased stomatal conductance (g _s) and net photosynthetic rate (P _N) in yambean but reduced them in ahipa. In a drying soil (14 d after irrigation), inter-specific variation in gas exchange was only observed in the early morning, and yambean showed a greater sensitivity to water restriction than ahipa. High g _s at low humidity increased P _N of P. erosus but resulted in lower water-use efficiency (WUE). However, long-term WUE, estimated by leaf carbon isotope discrimination, showed little variation between species. Daily-irrigated ahipa and yambean grown in the greenhouse did not show significant differences in gas exchange. However, leaf temperature was significantly greater in yambean than in ahipa while a steepper relationship between E and P _N and g _s was observed in ahipa.     

Gas exchange inHardwickia binata after water stress and rewatering

The net photosynthetic rate (P_N), stomatal conductance (g_s) and transpiration (E) ofHardwickia binata Roxb. leaves were reduced due to decrease in the leaf water potential (ψ_w) from -2.0 to - 5.7 MPa. P_N partially recovered in the treated plants upon rewatering. Decrease in g_s due to water stress may be the main factor for reduction of P_N. This work was supported by a financial grant from the MNES, India to KP.     

Leaf gas exchange capacity in relation to leaf position on the stem in field grown teak (Tectona grandis L.f.)

Leaf gas exchange patterns in relation to leaf positions on stems were studied in field grown forest tree, teak (Tectona grandis L.f.) during first year growth under intensive culture plantation. Net photosynthetic rates (PN) were low in immature leaves (1-2 from shoot apices), increased basipetally on shoot, peaked in leaves (3rd or 4th leaves from shoot apices) which had recently reached full expansion, and thereafter declined in lower crown leaves. High PN found in fully expanded young leaves was associated with increased dark respiration rate (RD) and high radiation saturation as well as compensating irradiance for PN when compared to those of aged leaves. Intercellular CO2 concentrations (Ci) determined at ambient CO2 concentration and saturating irradiance were apparently low for leaves exhibiting high PN when compared to those of aged leaves. Differences in stomatal conductance (gs) and the rate of transpiration (E) were not apparent between leaves after full expansion. The relationship of PN with Ci recorded for leaves at different positions on stems and under natural ambient CO2 concentrations showed a linear decrease in PN with marked increasing Ci and suggested that increase in mesophyll limitations could cause decline in PN during aging of teak leaves after full expansion. Highly significant positive linear correlation was found between PN and Ci determined at below ambient CO2 concentrations and saturating irradiance for both fully expanded young and aged leaves. The estimate of linear relationship between PN and Ci, often considered as carboxylation efficiency, was higher for fully expanded young leaves characterised by high PN than for aged leaves exhibiting low PN. Hence, the increase in mesophyll limitations or decrease in carboxylation efficiency could explain gradual reduction in photosynthetic potential with leaf age after maturation in teak. This revised version was published online in June 2006 with corrections to the Cover Date.