Photosynthesis and yield responses of ozone-polluted winter wheat to drought

Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80–85 % (O₃+W) or drought treated (SWC 35–40 %, O₃+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (P _N) of winter wheat. Under good SWC, P _N of the O₃-treated plant was similar to that of control on 2 d after O₃-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O₃ exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O₃+W was significantly decreased. P _N of O₃+D was further notably decreased and green flag leaf area was reduced more than that in O₃+W. Consequently, substantial yield loss of O₃+D was observed compared to that of O₃+W. Although P _N was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (F_v/F_m), electron transport rate (ETR), photochemical quenching (q_P), as well as content of chlorophyll, suggesting that the depression of P _N was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O₃ pollution.     

Effects of water stress and nitrogen supply on leaf gas exchange and fluorescence parameters of <Emphasis Type="Italic">Sophora davidii</Emphasis> seedlings

Two-month-old seedlings of Sophora davidii were subjected to a randomized complete block design with three water (80, 40, and 20 % of water field capacity, i.e. FC₈₀, FC₄₀, and FC₂₀) and three N supply [N0: 0, Nl: 92 and Nh: 184 mg(N) kg⁻¹(soil)] regimes. Water stress produced decreased leaf area (LA) and photosynthetic pigment contents, inhibited photosynthetic efficiency, and induced photodamage in photosystem 2 (PS2), but increased specific leaf area (SLA). The decreased net photosynthetic rate (P _N) under medium water stress (FC₄₀) compared to control (FC₈₀) might result from stomatal limitations, but the decreased P _N under severe water deficit (FC₂₀) might be attributed to non-stomatal limitations. On the other hand, N supply could improve photosynthetic capacity by increasing LA and photosynthetic pigment contents, and enhancing photosynthetic efficiency under water deficit. Moreover, N supply did a little in alleviating photodamages to PS2 caused by water stress. Hence water stress was the primary limitation in photosynthetic processes of S. davidii seedlings, while the photosynthetic characters of seedlings exhibited positive responses to N supply. Appropriate N supply is recommended to improve photosynthetic efficiency and alleviate photodamage under water stress.     

Photosynthetic response of Podophyllum hexandrum Royle from different altitudes in Himalayan ranges

Plants of Podophyllum hexandrum, collected from lower, mid, and upper distribution limits in alpine Himalaya were studied under greenhouse conditions to evaluate the photosynthetic response. Net photosynthetic rates (P _N), stomatal conductance (g _s), and efficiency of carbon uptake increased with altitude. The maximum P _N and g _s were measured in the considered population during the 3–6^th week of development. P _N and g _s decreased on an average by 58 and 48 % from maximum rates reached around 4^th week to the 10^th week of growth, respectively. The photosynthetic response in the three ecotypes appeared to be genetically controlled.     

Characterization of photosynthesis of Populus euphratica grown in the arid region

Net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (L_s) of Populus euphratica grown at different groundwater depths in the arid region were measured. g _s of the trees with groundwater depth at 4.74 m (D₄) and 5.82 m (D₅) were lower and a little higher than that at 3.82 m (D₃), respectively. Compared with C _i and L_s of the D₃ trees, C _i decreased and L_s increased at 4.74 m, however, Ci increased and L_s decreased at D₅. Hence photosynthetic reduction of P. euphratica was attributed to either stomatal closure or non-stomatal factors depending on the groundwater depths in the plant locations. P _N of the D₃ trees was significantly higher than those at D₄ or D₅. The trees of D₄ and D₅ did not show a significant difference in their P _N, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.     

Interactions of Elevated CO2 Concentration and Drought Stress on Photosynthesis in Eucalyptus Cladocalyx F. Muell

Response of net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (c _i), and photosynthetic efficiency (F_v/F_m) of photosystem 2 (PS2) was assessed in Eucalyptus cladocalyx grown for long duration at 800 (C₈₀₀) or 380 (C₃₈₀) μmol mol^-1 CO₂ concentration under sufficient water supply or under water stress. The well-watered plants at C₈₀₀ showed a 2.2 fold enhancement of P _N without any change in g _s. Under both C₈₀₀ and C₃₈₀, water stress decreased P _N and g _s significantly without any substantial reduction of c _i, suggesting that both stomatal and non-stomatal factors regulated P _N. However, the photosynthetic efficiency of PS2 was not altered. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temperature-Dependent Gas Exchange and Stomatal/Non-Stomatal Limitation to CO2 Assimilation of Quercus Liaotungensis under Midday High Irradiance

The effects of varying leaf temperature (T ₁) on some ecophysiological characteristics of photosynthesis for Quercus liaotungensis Koiz. under ambient radiation stress around midday on clear summer days were investigated using an IRGA equipped with a temperature-controlled cuvette. Net photosynthetic rate (P _N) decreased as T ₁ increased from 30 to 35 °C as a result of stomatal closure, whereas non-stomatal limitation led to decreased P _N in the T ₁ range of 35–45 °C. Decreased transpiration rate (E) and stomatal conductance (g _s) at leaf temperatures above 30 °C were interpreted as a combined feedward effect as a result of enhanced leaf-air vapour pressure deficit (VPD) and stomatal closure. Changes in E from T ₁ 30 to 20 °C depended on VPD when g _s was maintained constant. Water use efficiency (WUE) varied inversely with T ₁ by following a hyperbola. A decrease in intercellular CO₂ concentration (C _i) occurred as a result of stomatal closure and a relatively high carboxylation capacity, whereas inactivation of mesophyll carboxylation in combination with photorespiration might be associated with the observed increase in C _i in the T ₁ range of 40 to 45 °C.     

Effects of foliar application of nitrogen on the photosynthetic performance and growth of two fescue cultivars under heat stress

The effects of nitrogen fertilization on the growth, photosynthetic pigment contents, gas exchange, and chlorophyll (Chl) fluorescence parameters in two tall fescue cultivars (Festuca arundinacea cv. Barlexas and Crossfire II) were investigated under heat stress at 38/30 °C (day/night) for two weeks. Shoot growth rate of two tall fescue cultivars declined significantly under heat stress, and N supply can improved the growth rates, especially for the Barlexas. Chl content, leaf net photosynthetic rate, stomatal conductance, water use efficiency, and the maximal efficiency of photosystem 2 photochemistry (F_v/F_m) also decreased less under heat stress by N supply, especially in Crossfire II. Moreover, cultivar variations in photosynthetic performance were associated with their different response to heat stress and nitrogen fertilization, which were evidenced by shoot growth rate and photosynthetic pigment contents.     

Changes in effects of ozone exposure on growth,photosynthesis, and respiration of <Emphasis Type="Italic">Ginkgo biloba</Emphasis> in Shenyang urban area

An open-top chamber experiment was carried out from April through October 2006 to examine the effects of elevated (80 nmol mol⁻¹) atmospheric O₃ on Ginkgo biloba (4-years-old) in urban area. The air with ambient O₃ (AA, ≈ 45 nmol mol⁻¹) was used as control. The leaf mass and size, leaf area index, net photosynthetic rate (P _N), apparent quantum yield, transpiration rate, and stomatal conductance were decreased by elevated O₃ (EO) exposure. Visible foliar injury, which is light-brown flecks, was observed in the EO OTCs after 90 d of exposure. Carboxylation efficiency (Φ_CO2) and photorespiration and dark respiration rates were enhanced by EO exposure in the first half of the season, but all of them turned to be lower than those of the AA control at the end of experiment. Stomata limitation of photosynthesis was significantly higher than control in the whole season (p<0.05). Chlorophyll (Chl) content was lower in EO variant than in the control and the difference became more and more apparent through the season. Hence the decrease in P _N of G. biloba exposed to EO was the result of both stomatal and non-stomatal limitations. In the early season, the inhibition of photosynthesis was mainly caused by the stomatal limitation, and the earliest response was photoprotective down-regulation of photosynthesis but not photodamage. However, at the end of the season, the non-stomatal limiting factors such as decrease in Chl content, decrease in Φ_CO2, and anti-oxidative enzyme activity became more important.     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.This revised version was published online in March 2005 with corrections to the page numbers.     

Genotypic variation in the photosynthetic competence of Sorghum bicolor seedlings subjected to polyethylene glycol-mediated drought stress

Eleven varieties of Sorghum bicolor, subjected to PEG-mediated drought stress were compared for their photosynthetic performance. The varieties differed in their relative water content over a range of PEG concentrations (0-25%). CO2 assimilation, stomatal conductance and the quantum yield of PSII electron transport decreased with increasing PEG concentrations in all varieties. However the intercellular CO2 concentration showed a nonlinear PEG concentration-dependent change. At lower PEG concentrations there was a decrease in the levels of intercellular CO2 concentration in all varieties that could be attributed to stomatal closure. At higher PEG concentrations, some varieties showed an increase in the intercellular CO2 concentration, indicating an inhibition of photosynthetic activity due to non-stomatal effects, while others did not. It was seen that the varieties differed in the stress thresholds at which stomatal and metabolic limitations to photosynthesis occur. These differences in the photosynthetic adaptation of Sorghum varieties could be useful in identifying genotypes showing large differences in photosynthetic adaptation, which could be useful in mapping photosynthetic traits for drought stress tolerance.     

Diurnal and Seasonal Changes in Photosynthetic Characteristics in Different Olive (Olea europaea L.) Cultivars

Diurnal and seasonal changes in photosynthetic characteristics, leaf area dry mass (ADM), and reducing sugar and total chlorophyll (Chl) contents of leaves of Frantoio, Leccino, and Maurino olive cultivars were investigated in Central Italy. Leaf net photosynthetic rate (P _N) per unit leaf area changed during the growing season and during the day, but the cultivar did not significantly influence the changes. In both young and one-year-old leaves the highest P _N values were observed in October, while the lowest values were recorded in August and December; during the day the highest P _N values were generally found in the morning. The pattern of photosynthetic response to photosynthetic photon flux density (PPFD) of leaves was similar in the three genotypes. Sub-stomatal CO₂ concentration (C _I) tended to increase when P _N decreased. The increase in C _I was accompanied by a stomatal conductance to water vapor (g _S) decrease. In general, P _N and dark respiration rate (R _D) were correlated. Transpiration rate (E), with no differences between the cultivars, increased from April to July, decreased greatly in August, then increased in October and finally decreased again in December. Leaf water content increased from April to June, remained high until mid July, decreased significantly in August, remaining constant until December with no differences associated with the cultivar. In both young and one-year-old leaves, the leaf water content per unit leaf area was slightly greater in Frantoio than in the other two cultivars. The one-year-old leaves had a higher Chl content than the young ones. The cultivar did not substantially influence the leaf reducing sugar content which decreased from April to August, when it reached the lowest level, then increased rapidly until October. During the day the reducing sugar content did not change significantly. The leaf ADM was slightly higher in Frantoio than in the other cultivars and one-year-old leaves had higher values than the young ones. Leaf ADM decreased from April to June and then tended to increase until December. During the day there were no substantial variations.     

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 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.     

Comparison of Some Photosynthetic Characters Between Two Hybrid Rice Combinations Differing in Yield Potential

Photosynthetic characteristics of two hybrid rice combinations, Peiai 64S/E32 and Shanyou 63, were compared at the panicle differentiation stage. As compared with Shanyou 63, the new combination Peiai 64S/E32 showed a significantly higher net photosynthetic rate (P _N), apparent quantum yield of carbon assimilation (_c), carboxylation efficiency (CE), and photorespiratory rate (R _P) as well as leaf chlorophyll content, but a significantly lower dark respiration rate (R _D) and compensation irradiance (I _c). It also showed a slightly higher photochemical efficiency (F_v/F_m and F/F_m) of photosystem 2, a lower non-photochemical quenching (q_N), and a similar CO₂ compensation concentration () as compared to Shanyou 63.     

Clonal Differences in Photosynthesis in Hevea Brasiliensis Müll. Arg.

The objective of the present investigation was to examine the extent of variations in single leaf net photosynthetic rate (P_N) and its relative dependence on stomatal conductance (g_s) and the mesophyll capacity to fix carbon in 12 clones of the natural rubber plant. There were significant variations in P_N measured at low and saturating photon flux density (PFD); the extent of variation was larger at low than at saturating PFD. The compensation irradiance (CI) and apparent quantum yield of CO₂ assimilation (φ_c) calculated from the P_N/PFD response curves showed significant variations among the clones. P_N at low irradiance was positively correlated with φ_c. Thus a clone with large P_N at low irradiance, high φ_c, and low CI may tolerate shade better and thus produce a high tree stand per hectare. A strong positive correlation existed between P_N saturated with radiant energy (P_sat) and carboxylation efficiency (CE) estimated from the response curves of P_N on intercellular CO₂ concentration (C_i), but g_s showed a poor correlation with P_sat High CO₂ compensation concentration (Γ) led to low CE in Hevea clones. A clone with large P_sat, high CE, low g_s, and low Γ is the one in which photosynthesis is more dependent on the mesophyll factors than stomata. Such a clone may produce relatively high biomass and maintain high water use efficiency. This revised version was published online in September 2006 with corrections to the Cover Date.     

Photoprotective function of photorespiration in Reaumuria soongorica during different levels of drought stress in natural high irradiance

Diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem 2 (PS2) as well as H₂O₂ content were analyzed in Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub. The rate of photorespiration was estimated by combined measurement of gas exchange and Chl fluorescence. The rate of photorespiration increased with the increasing drought stress (DS). The ratio of carboxylation electron flow to oxygenation electron flow (J_c/J_o) and the maximal photochemical efficiency of PS2 (variable to maximum fluorescence ratio, F_v/F_m) decreased with the increasing DS. F_v/F_m in isonicotinic acid hydrazide (INH)-sprayed plants was lower than that in normal plants under moderate DS, but no significant difference was observed under severe DS. H₂O₂ content in INH-sprayed plants was significantly lower than that in normal plants under severe DS. Taken together, photorespiration in R. soongorica consumed excess electrons and protected photosynthetic apparatus under moderate DS, whereas it accelerated H₂O₂ accumulation markedly and induced the leaf abscission under severe DS.     

Photosynthetic and stomatal responses of two tropical and two temperate trees to atmospheric humidity

The effects of leaf to air vapour pressure differences (ΔW) on net photosynthetic rate (P_N) and stomatal conductance (g_s) were examined in the leaves of two tropical rain forest trees, Eugenia grandis and Pongamia pinnata, and two temperate evergreen trees, Viburnum awabuki and Daphniphyllum macropodum. A single leaf was set inside a small chamber and ΔW was varied from 7 to 24 mmol mol^-1 at 25 and 500 μmol m^-2 s^-1 of photon flux density. P_N and g_s of the two tropical rain forest trees decreased with increasing ΔW, while the two temperate evergreen trees were not highly responsive to ΔW. P. pinnata was more sensitive to ΔW in its stomatal response, and had a higher stomatal density and higher stomatal index than did the two temperate trees and another tropical tree. Significant reductions i n g_s and intercellular CO₂ concentrations in the two tropical trees at high ΔW suggest that the decline of P_N was due to the decrease in g_s. The responses of P_N and g_s indicated that the tropical trees were more sensitive to ΔW than were the temperate ones. This revised version was published online in September 2006 with corrections to the Cover Date.     

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.     

Partitioning of photosynthetic electron flow between CO<Subscript>2</Subscript> assimilation and O<Subscript>2</Subscript> reduction in sunflower plants under water deficit

In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (P _N) and stomatal conductance (g _s) of attached leaves decreased as leaf water potential (Ψ_w) declined from −0.3 to −2.9 MPa. Although g _s decreased over the whole range of Ψ_w, nearly constant values in the intercellular CO₂ concentrations (C _i) were observed as Ψ_w decreased to −1.8 MPa, but C _i increased as Ψ_w decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased with water deficit, whereas non-photochemical quenching (q_NP) increased progressively. A highly significant negative relationship between q_NP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content suggesting metabolic impairment. At a photon flux density of 550 μmol m⁻² s⁻¹, the allocation of electrons from photosystem (PS) 2 to O₂ reduction was increased by 51 %, while the allocation to CO₂ assimilation was diminished by 32 %, as Ψ_w declined from −0.3 to −2.9 MPa. A significant linear relationship between mean P _N and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas q_P declined only at very severe stress and the excess photon energy was dissipated by increasing q_NP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation of PS2 and supported the protective role of q_NP against photoinhibition in sunflower.