Photosynthesis In Wheat Research Articles

Comparison of effects of salt and alkali stresses on the growth and photosynthesis of wheat

The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na2SO4 = 1: 1) and alkali-stress (AS, molar ratio of NaHCO3: Na2CO3 = 1: 1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (P N), stomatal conductance (g s), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, P N, g s, and E decreased sharply with rising salinity. The decrease of g s might cause the obvious decreases of E and intercellular CO2 concentration, and the increase of water use efficiency under both stresses. The Na+ content and Na+/K+ ratio in shoot increased and the K+ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na+ and K+ caused by the high pH at AS might be the reason of the decrease of P N and g s and of the destruction of photosynthetic pigments.

Cadmium effects on carbonic anhydrase, photosynthesis, dry mass and antioxidative enzymes in wheat (Triticum aestivum) under low and sufficient zinc

Leaf carbonic anhydrase (CA) activity, net photosynthetic rate (PN), stomatal conductance (gS) and plant dry mass (DM) exhibited a dose-dependent response to cadmium (Cd) in wheat (Triticum aestivum L.) grown under low and sufficient zinc (Zn) levels at 30 d after seedling emergence in sand culture. Cadmium at 10 µM concentration enhanced CA, PN and DM at low Zn level but these remain unaltered at sufficient Zn. Stomatal conductance decreased with increasing CdCl2 concentration at both the Zn levels. Cd higher than 10 µM inhibited the characteristics irrespective of Zn level. The activity of superoxide dismutase (SOD) was not saturated the with highest Cd concentration (50µM) at both the Zn levels. However, the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) increased up to 25 µM Cd and decreased at 50 µM Cd at both the Zn levels. It is suggested that CA activity was induced at low Cd (10 µM) under low Zn level increasing the photosynthesis. The synergies among the activities of antioxidative enzymes helped to maintain CA and thus photosynthesis and plant DM at low Cd concentration under low Zn level.

Heat-shock effects on photosynthesis and sink-source dynamics in wheat ( Triticum aestivum L.)

To assess the mechanisms causing genotypic differences in heat tolerance of wheat ( Triticum aestivum L.), physiological responses to a heat shock in a vegetative (‘end of tillering’) or a reproductive (‘early grain filling’) stage were studied. Three cultivars — Lavett, Ciano-79 and Attila — differing in adaptation to heat were grown in a glasshouse at a day/night temperature regime of 15/10 °C and a 12-h daylength from sowing to ‘end of tillering’ and next at two day/night regimes of 25/20 and 18/13 °C under natural daylength. The heat-shock treatment consisted of an exposure of plants to temperatures raised gradually over a time-span of 12 hours to above 30 °C with a maximum of 38 °C during three hours at midday for three days either at the ‘end of tillering’ or at ‘grain filling’. A heat shock at the ‘end of tillering’ strongly reduced the rate of leaf photosynthesis. A similar heat shock during ‘grain filling’ decreased both rate of photosynthesis (source) and grain growth (sink). The rate of leaf photosynthesis was decreased by 40 to 70%, depending on cultivar and developmental stage. Photosynthesis fully recovered within 4 days after the heat-shock treatment was ended. The effects of the heat shock on biomass yield were more pronounced for treatments at ‘early grain filling’ than at ‘end of tillering’. However, the impact of a 3-day heat shock on biomass yield was less than the effects of the pre- and post-treatment growing temperature.

Future CO2 concentrations, though not warmer temperatures, enhance wheat photosynthesis temperature responses

The temperature dependence of C3 photosynthesis is known to vary according to the growth environment. Atmospheric CO2 concentration and temperature are predicted to increase with climate change. To test whether long-term growth in elevated CO2 and temperature modifies photosynthesis temperature response, wheat (Triticum aestivum L.) was grown in ambient CO2 (370 micromol mol(-1)) and elevated CO2 (700 micromol mol(-1)) combined with ambient temperatures and 4 degrees C warmer ones, using temperature gradient chambers in the field. Flag leaf photosynthesis was measured at temperatures ranging from 20 to 35 degrees C and varying CO2 concentrations between ear emergence and anthesis. The maximum rate of carboxylation was determined in vitro in the first year of the experiment and from the photosynthesis-intercellular CO2 response in the second year. With measurement CO2 concentrations of 330 micromol mol(-1) or lower, growth temperature had no effect on flag leaf photosynthesis in plants grown in ambient CO2, while it increased photosynthesis in elevated growth CO2. However, warmer growth temperatures did not modify the response of photosynthesis to measurement temperatures from 20 to 35 degrees C. A central finding of this study was that the increase with temperature in photosynthesis and the photosynthesis temperature optimum were significantly higher in plants grown in elevated rather than ambient CO2. In association with this, growth in elevated CO2 increased the temperature response (activation energy) of the maximum rate of carboxylation. The results provide field evidence that growth under CO2 enrichment enhances the response of Rubisco activity to temperature in wheat.

Study of physiological parameters in sustainable winter wheat (Triticum aestivum L.) production

Introduction Wheat is currently the world’s most important food crop and it has determinative part in Hungarian crop production too (Kutasy et al., 2005). Yield levels of winter wheat were determined mostly by climatic effects of the cropyears limited primarily by water deficiency (Hoffmann-Burucs, 2005), the actual quantity of precipitation prevails in interaction with other external factors (Hoffmann et al., 2006). Light and nutrients are two essential factors that plants must have to grow and forming yield (Csajbok et al., 2005). Among the corns for fertilization one of the most exacting and best reacting is the winter wheat (Szentpetery, 2004). Nitrogen is one of the most important elements in the nutrition of higher plants, wheat grain yields have always been strongly linked to available N nutrition (Szentpetery et al., 2005). Our small grain cereals belongs to C3 plants. This means that their photosynthesis is limited even under the best conditions. Although the correlation between leaves’ photosynthesis and productivity of wheat is not always positive, but under circumstances of arable land the photosynthesis is a factor that defines the higher production potential of genotypes (Pajevic et al., 1999). Reynolds et al., (2000) were measured net photosynthetic rate (An) on wheat cultivars at booting, anthesis and grain filling and found significant correlation between An and grain yield at all developmental stages. Pepo (2005) experiments showed, that the dry matter production and LAI have determined basically the yield of the examined genotypes.

Photosynthesis in Wheat at the Grain Filling Stage Is Altered by Larval Wheat Stem Sawfly (Hymenoptera: Cephidae) Injury and Reduced Water Availability

The impact of larval feeding by wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), and reduced water availability on the photosynthesis and primary metabolism of wheat, Triticum aestivum (L.), was evaluated at the grain-filling developmental stage. Photosynthetic parameters measured included photosynthesis (Ps), stomatal conductance (gs), and transpiration (E) in the flag leaves. The parameters were measured at 4 wks after the treatments were imposed. Additional concomitant chlorophyll a fluorescence measurements were taken using both dark- and light-adapted tests. Photosynthesis was significantly affected by C. cinctus injury and suboptimal water availability. However, no significant interaction was observed between the two treatment factors. Plants under a reduced or suboptimal watering regime had Ps rates that were 43.7% lower than plants that were watered daily. We also observed a 12% higher Ps rate in uninfested plants compared to plants infested by C. cinctus. Several chlorophyll a fluorescence parameters also were affected by C. cinctus. Specifically, reductions in the photochemical efficiency of photosystem II (PSII) of C. cinctus infested plants were observed for plants under reduced water availability. This study demonstrates that wheat plants at the grain filling stage have reduced photosynthetic capacity when watered less frequently or when subjected to C. cinctus larval feeding injury. Less frequent watering and larval feeding injury did not have significant impacts on yield in this greenhouse study.

The effects of UV-B radiation on photosynthesis in relation to Photosystem II photochemistry, thermal dissipation and antioxidant defenses in winter wheat (Triticum aestivum L.) seedlings at different growth temperatures.

To study the UV-B effect on photosynthesis in winter wheat at different day/night temperatures, biologically effective UV-B radiation at 4.2 (LUVB) and 10.3 (HUVB) kJ m-2 d-1 was provided on the seedlings at 25/20°C or 10/5°C. UV-B radiation inhibited net photosynthesis rate (Pn) by enhanced intensity and decreased temperature without change of intercellular CO2 concentrations (Ci). Decreased maximal quantum yield of Photosystem II (Fv/Fm) and increased minimum fluorescence (Fo) were observed in HUVB at both temperatures and LUVB at 10/5°C. HUVB increased total pool size (VAZ) of xanthophyll cycle pigments, but decreased the de-epoxidation state (DEPS) of these pigments at both temperatures, while LUVB only decreased DEPS at 10/5°C. The activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) and the redox states of ascorbate and glutathione (AsA/DAsA and GSH/GSSG) were enhanced at 25/20°C, while there were increased SOD and CAT, unaltered APX activities and AsA/DHA, as well as decreased GR activity and GSH/GSSG in LUVB and HUVB at 10/5°C. UV-B radiation resulted in higher H2O2 and thiobarbituric acid reactive substance (TBARS) concentrations at 10/5°C than 25/20°C. It appears that low temperature alone did not influence photosynthesis but aggravated UV-B induced photoinhibition, which was associated with PSII photochemistry rather than stomatal limitation. Xanthophyll cycle pigments failed to provide photoprotection through thermal dissipation. The antioxidant system was up-regulated in LUVB and HUVB at 25/20°C, but was impaired at 10/5°C. Low temperature intensified UV-B induced photoinhibition and damage by weakening the antioxidant system.

Photosynthetic Responses of Wheat, <I>Triticum aestivum</I> L., Plants to Simulated Insect Defoliation During Vegetative Growth and at Grain Fill

The impact of different levels of whole plant partial defoliation (WPPD) on the photosynthesis and primary metabolism of wheat,Triticumaestivum L., was evaluated at the vegetative and reproductive (grain-Þlling) developmental stages. Photosynthetic parameters such as photosyn- thesis, stomatal conductance, and transpiration, chlorophyll a suorescence, and plant morphological parameters, such as main stem height, sag-leaf and undefoliated leaf areas, and number of tillers, were recorded 1 h and 1, 9, and 12 d after defoliation in 2004 and 1 h, 3 d, and 6 d after defoliation in 2005. Plants with high defoliation levels (i.e., defoliation 75%) had 21 and 20% greater photosynthesis rates compared with control and low defoliation level treatments, respectively. Our data show that stomatal conductance for sag leaves was not signiÞcantly affected by WPPD. In addition, we did not observe a signiÞcant effect of defoliation on intercellular CO2 concentrations or on transpiration rates remaining sag leaf tissue. Similar responses were observed for the overall photosynthesis of defoliated plants during vegetative stages. Whole plant source-sink manipulation of wheat by WPPD during the major plant developmental stages (i.e., vegetative and reproductive) did not elicit any signiÞcant long-term modiÞcations to growth, morphological, or primary physiological characteristics of wheat plants.

Photosynthetic Responses of Wheat, Triticum aestivum L., Plants to Simulated Insect Defoliation During Vegetative Growth and at Grain Fill

The impact of different levels of whole plant partial defoliation (WPPD) on the photosynthesis and primary metabolism of wheat, Triticum aestivum L., was evaluated at the vegetative and reproductive (grain-filling) developmental stages. Photosynthetic parameters such as photosynthesis, stomatal conductance, and transpiration, chlorophyll a fluorescence, and plant morphological parameters, such as main stem height, flag-leaf and undefoliated leaf areas, and number of tillers, were recorded 1 h and 1, 9, and 12 d after defoliation in 2004 and 1 h, 3 d, and 6 d after defoliation in 2005. Plants with high defoliation levels (i.e., defoliation > 75%) had ≈21 and 20% greater photosynthesis rates compared with control and low defoliation level treatments, respectively. Our data show that stomatal conductance for flag leaves was not significantly affected by WPPD. In addition, we did not observe a significant effect of defoliation on intercellular CO2 concentrations or on transpiration rates remaining flag leaf tissue. Similar responses were observed for the overall photosynthesis of defoliated plants during vegetative stages. Whole plant source-sink manipulation of wheat by WPPD during the major plant developmental stages (i.e., vegetative and reproductive) did not elicit any significant long-term modifications to growth, morphological, or primary physiological characteristics of wheat plants.

Solar UV-B Exclusion Effects on Growth and Photosynthetic Characteristics of Wheat and Pea

Increased UV-B radiation on the earth's surface due to depletion of stratospheric ozone layer is one of the changes of current climate-change pattern. A field experiment was conducted to study the effects of solar ultraviolet-B (UV-B) radiation on growth parameters, net photosynthesis and biochemical characteristics of wheat (Triticum aestivum) and pea (Pisum sativum) crop species. Plants grown under ambient UV-B radiation were compared with those grown without UV-B by excluding ambient UV-B radiation. To exclude solar ambient UV-B, the sunlight was filtered through a polyester film that selectively absorbed UV-B. For ambient UV-B effects, plants were grown under polyvinyl chloride (PVC) filters that transmitted the complete light spectrum. The results indicate increased shoot length, leaf area, dry matter accumulation, leaf area ratio and specific leaf weight in plants of both the crops grown without UV-B compared with those grown under ambient UV-B. The effect of UV-B exclusion was clearer in pea compared with that in wheat.Similarly, the rate of photosynthesis (measured as CO2 exchange rate), chlorophyll content, nitrate reductase (NR) enzyme activity and sugar content were significantly higher in pea plants grown without UV-B radiation, while changes in wheat plants were marginal and insignificant. We conclude that monocot species may be less sensitive to increased solar UV-B due to ozone depletion compared with dicots.

Simulation of diurnal variations of CO 2, water and heat fluxes over winter wheat with a model coupled photosynthesis and transpiration

A model was developed that couples canopy photosynthesis and transpiration of winter wheat. The model combined a two-layer evapotranspiration model with a coupled photosynthesis–stomatal conductance model to study the diurnal variations of CO 2, water and heat fluxes of winter wheat. Field experiments were conducted in Yucheng Comprehensive Experimental Station in the North China Plain to evaluate the model. Half-hourly data of weather variables and CO 2, water and heat fluxes were measured by the eddy covariance method in 2002–2003. An analysis of measured flux data showed that there was an evident midday depression of photosynthesis, caused by stomatal closure due to high vapor water deficit and canopy temperature though the soil was well irrigated. There was a close agreement between simulated and measured net radiation, CO 2 flux, sensible and latent heat fluxes, which proved the predictive power of the coupled photosynthesis and transpiration model. The response of CO 2 flux, canopy conductance and latent heat flux to changes in climatic factors was discussed, which indicated the model could be used to predict CO 2, water and heat fluxes of wheat not only in the North China Plain, but also in other climatic regions in China.

Nitrogen source and water regime effects on durum wheat photosynthesis and stable carbon and nitrogen isotope composition

Water stress and nitrogen (N) availability are the main constraints limiting yield in durum wheat (Triticum turgidum L. var. durum). This work investigates the combined effects of N source (ammonium–NH4+, nitrate–NO3– or a mixture of both–NH4+:NO3–) and water availability (well‐watered vs. moderate water stress) on photosynthesis and water‐use efficiency in durum wheat (cv. Korifla) flag leaves grown under controlled conditions, using gas exchange, chlorophyll fluorescence and stable carbon isotope composition (δ13C). Under well‐watered conditions, NH4+‐grown plants had lower net assimilation rates (A) than those grown with the other two N forms. This effect was mainly due to lower stomatal conductance (gs). Under moderate water stress, differences among N forms were not significant, because water regime (WR) had a stronger effect on gs and A than did N source. Consistent with lower gs, δ13C and transpiration efficiency (TE) were the highest in NH4+ leaves in both water treatments. These results indicate higher water‐use efficiency in plants fertilized with NH4+ due to stomatal limitation on photosynthesis. Moreover, leaf δ13C is an adequate trait to assess differences in photosynthetic activity and water‐use efficiency caused by different N sources. Further, the effect of these growing conditions on the nitrogen isotope composition (δ15N) of flag leaves and roots was examined. Water stress increased leaf δ15N in all N forms. In addition, leaf δ15N increased as root N decreased and as leaf δ13C became less negative. Regardless of WR, the leaf δ15N of NO3–‐grown plants was lowest. Based on stepwise and canonical discriminant analyses, we conclude that plant δ15N together with δ13C and other variables may reflect the conditions of N nutrition and water availability where the plants were grown. Thus well‐watered plants grown with NH4+:NO3– resembled those grown with NO3–, whereas under water stress they were closer to plants grown with NH4+.

Response of Wheat Seedlings to Ni Stress: Effects of Supplemental Calcium

The effect of excess Ni (1 mM Ni) on wheat plants as well as the role of Ca (1 mM Ni+5000 microM Ca) for amelioration of toxicity and recovery of growth and photosynthesis in Ni-stressed wheat was evaluated. Growth, nutrient status (Ca, Mg, Fe, K, Na), and photosynthesis showed a distinct decrease strictly related to the period of treatment. Calcium ameliorated to a certain extent toxic symptoms of Ni, due to antagonistic action between Ni and Ca ions. Since chlorophyll content and variable fluorescence (Fv) decreased significantly, but Fo did not particularly change, the decrease of t1/2 with increasing duration of Ni exposure indicates negative changes on the acceptor side of PSII, which also may result from diminution of Calvin cycle. The maximum quantum yield for energy trapping was also suppressed. Plant transfer to Hoagland solution+5000 microM Ca caused recovery to plant morphology and physiology. Even in control plants, during recovery period an increased Ca concentration in plant tissues with concomitant increased rates of growth and morphology was observed. Ni concentration in plants exposed to 1 mM Ni+5000 microM Ca was lower than in plants exposed to 1 mM Ni. In all treatments a certain increase of plant nutrients was observed during recovery.

Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis of dwarf wheat

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21-24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 micromol m(-2) s(-1)) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 micromol m(-2) s(-1)) and CO(2) (4000 micromol mol(-1)) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at approximately 280 micromol m(-2) s(-1) were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO(2) compensation (121 vs. 118 micromol mol(-1)) and PPF compensation (85 vs. 81 micromol m(-2) s(-1)) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.

Role of calcium ion in protection against heat and high irradiance stress-induced oxidative damage to photosynthesis of wheat leaves

Cross stress of heat and high irradiance (HI) resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus of wheat leaves during grain development. Pre-treatment with calcium ion protected the photosynthetic system from oxidative damage by reducing O-.2 production, inhibiting lipid peroxidation, and retarding electrolyte leakage from cell. Therefore, high Fv/Fm [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], Fm/F0 (another expression for the maximal photochemical efficiency of PS2), ΦPS2 (actual quantum yield of PS2 under actinic irradiation), qP (photochemical quenching coefficient), and PN (net photosynthetic rate) were maintained, and lower qNP (non-photochemical quenching coefficient) of the leaves was kept under heat and HI stress. EGTA (a chelant of calcium ion) and LaCl3 (a blocker of Ca2+ channel in cytoplasmic membrane) had the opposite effect. Thus Ca ion may help protect the photosynthetic system of wheat leaves from oxidative damage induced by the cross stress of heat and HI.

Apparent quantum yield of photosynthesis of winter wheat and its response to temperature and intercellular CO_2 concentration under low atmospheric pressure on Tibetan Plateau

The Tibetan Plateau is characterized by lower atmospheric pressure, lower air temperature and high daily and seasonal variation due to high elevation. The photosynthesis of plants is significantly influenced by these alpine environmental factors. Apparent quantum yield (alpha A) is one of the basic parameters of photosynthesis and mass production. Its accuracy determination is of significance to model photosynthesis Of C-3 plants and global change on the plateau. In the Lhasa Plateau Ecological Station with 65.4 kPa of atmospheric pressure at an elevation of 3688 m, U-Cor 6400 portable photosynthesis system was used to measure light response curves of winter wheat in different temperatures and intercellular CO2 concentration (C). The slope of light response curve in weak light area of PFD from 0 to 150 mu mol m(-2) s(-1) was used to evaluate the value of alpha(A). The dependence of alpha(A) on temperature and intercellular concentration was analyzed. In 30 degrees C, the average value of alpha(A) was 0.0476 +/- 0.0038. It is not quite different from the values in low elevation areas. alpha(A) is influenced both by temperature and by the ratio Of CO2 and O-2 partial pressure ([CO2]/[O-2]). The measured values in the previous study were much lower. This might be due to systematic errors from instrument and data processing methods. The values of alpha(A) decreased linearly with temperature. It decreased 0.0007 in every 1 degrees C increase of temperature. The decrease slope is similar to those Of C-3 plants in the previous researches. While [O-2] is constant, alpha(A) increases with Ci with a hyperbolic relationship. In comparison with low elevation areas, the alpha(A) on the Tibetan Plateau is more sensitive to increase Of CO2.

Investigation on dynamic changes of photosynthetic characteristics of 10 wheat ( Triticum aestivum L.) genotypes during two vegetative-growth stages at water deficits

Drought is a worldwide problem, seriously influencing plant (crop) productivity. Wheat is a stable food for 35% of the world population, and moreover, about 60% of land area on the globe belongs to arid and semiarid zone. Wheat drought resistance is a multi-gene controlling quantitative character and wheat final production in field is realized mainly by physiological regulation under the condition of multi-environmental factor interaction. Exploring drought resistance physiological mechanisms for different wheat genotypes is of importance to finding new drought resistance gene resources and conventional breeding, and the basis for wheat drought resistance biotechnological breeding and platform. Photosynthesis is the main component for physiological machinery of wheat assimilates conversion and wheat production. Investigation on photosynthetic characteristics of different wheat genotypes at soil water deficits also has other implications for refine physiological regulation of photosynthesis in fields and field management of crops in arid and semiarid areas. By pot-cultivating experiments, investigation of photosynthesis for 10 wheat genotypes at seedling stage and tillering stage at soil water deficits (75%FC, 55%FC and 45%FC, respectively) was conducted. The main results were as followed: developmental stages influenced wheat photosynthesis greatly and tillering stage played more roles; there were significant difference in the main photosynthetic parameters, photosynthesis rate (Photo), stomatal conductance (Cond) and transpiration rate (Tr), among 10 wheat genotypes; general photosynthesis and drought resistance in different wheat genotypes was related much to their domesticated origin soil water environment and selected generations and there was a photosynthetic threshold effect in terms of different wheat genotypes at soil water deficits.

Effect of elevated CO2and high temperature on the photosynthesis and yield of wheat

Effect of elevated CO₂and high temperature on the photosynthesis and yield of wheat

Photosynthesis, root respiration, and grain yield of spring wheat in response to surface soil drying

The aims of this research were to test the influence of surface soil drying on photosynthesis, root respiration and grain yield of spring wheat (Triticum aestivum), and to evaluate the relationship between root respiration and grain yield. Wheat plants were grown in PVC tubes 120 cm in length and 10 cm in diameter. Three water regimes were employed: (a) all soil layers were irrigated close to field water capacity (CK); (b) upper soil layers (0–40 cm from top) drying (UD); (c) lower soil layer (80–120 cm from top) wet (LW). The results showed that although upper drying treatment maintained the highest root biomass, root respiration and photosynthesis rates at anthesis, the root respiration of the former was significantly (P < 0.05) lower than the latter at the jointing stage. There were no differences in water use efficiency or harvest index between plants from the upper drying and well-watered treatment. However, the grain weight for plants in the upper drying treatment was significantly (P< 0.05) higher than that of in well-watered control. The results suggest that reduced root respiration rate and the amount of photosynthates utilized by root respiration in early season growth may also have contributed to improve crop production under soil drying. Reduced root activity and root respiration rate, in the early growth stage, not only increased the photosynthate use efficiency (root respiration rate: photosynthesis ratio), but also grain yield. Rooting into a deeper wet soil profile before grain filling was crucial for spring wheat to achieve a successful seedling establishment and high grain yield.

Interactive effects of elevated CO 2, temperature and nitrogen on photosynthesis of wheat grown under temperature gradient tunnels

The effects of increased CO 2, temperature and nitrogen on leaf photosynthesis of wheat were investigated in two field experiments under temperature gradient tunnels in a Mediterranean environment. Ambient and 700 μmol mol −1 CO 2, ambient and 4 °C warmer temperatures, and 80 and 120 kg nitrogen per hectare were compared. Although rising CO 2 concentrations increased photosynthesis, measurements at the same CO 2 concentration showed decreased photosynthesis and stomatal conductance in plants grown at elevated CO 2. Elevated growth CO 2 decreased photosynthesis for any given value of intercellular CO 2 concentration. Downward acclimation of photosynthesis was decreased at temperatures 4 °C above ambient and high nitrogen supply, under both photorespiratory and non-photorespiratory measurement conditions. Growth in elevated CO 2 decreased the quantum yield of photosystem II (PSII) electron transport and the efficiency of energy capture by open PSII centres. At later stages of leaf growth, warm temperatures decreased maximal photochemical efficiency ( F v/ F m) at low, but not at high nitrogen supply. F v/ F m increased with nitrogen application, although the quantum yield of electron transport in the light remained unchanged.