Response Of Photosynthetic Rate Research Articles

Fitting mitochondrial respiration rates under light by photosynthetic CO<inf>2</inf> response models

Aims The objective of this study was to compare the values of respiration under light derived by fitting a photosynthetic CO2 response model and measurements, in order to provide information for model optimization. Methods Using combined gas exchange measurements and a low O2 (2% O2) method, the responses of photosynthetic rate (Pn) to CO2 at different light intensities (2 000, 1 500, 1 000 and 500 μmol·m·s) in the flag leaves of wheat were measured. The measured data were fitted by a biochemical model, a rectangular hyperbola model and a modified rectangular hyperbola model of the photosynthetic response to intercellular CO2 concentration (A/Ci) and air CO2 concentration (A/Ca), aiming to approach the reasonability of the fitted results obtained from the models. Important finding The sequence of fitting effect of the three CO2 response models in descending order was as follows: modified rectangular hyperbola model > rectangular hyperbola model > biochemical model. Fitted values of A/Ca curve was more reasonable than A/Ci curve, because the photorespiration and mitochondrial respiration under light (Rd) estimated by the former better matched the measured values. However, there were significant differences in the whole between the fitted and measured values. The reason could be that the effect of CO2 concentrations on Rd and apparent photorespiration (Rpa) is neglected in all the current CO2 response models. Our results showed that CO2 concentration had a marked effect on Rpa and Rd. With increasing CO2 concentration, Rpa and Rd increased first, and then decreased sharply. Take 2 000 μmol·m·s for example, Rpa varied between 5.035 and 11.670 μmol CO2·m·s, and Rd varied between 0.491 and 2.987 μmol CO2·m·s. Regression analyses 康华靖等: 植物光合 CO2响应模型对光下(暗)呼吸速率拟合的探讨 1357 doi: 10.3724/SP.J.1258.2014.00130 indicated that Rpa and Rd were well related to CO2 concentrations at different light intensities.

The responses of photosynthetic rate and stomatal conductance of Fraxinus rhynchophylla to differences in CO<sub>2</sub> concentration and soil moisture

The photosynthetic parameters in leaves of three-year-old seedlings of Fraxinus rhynchophylla L. were studied under different soil water conditions and CO2 concentrations ([CO2]) with a LI-COR 6400 portable photosynthesis system. The objective was to investigate the response of photosynthesis and stomatal conductance (g s) to various [CO2] and soil water conditions, and to understand the adaptability of F. rhynchophylla to such conditions. The results showed that the soil water content (RWC) required to maintain high photosynthetic productivity in F. rhynchophylla was 49.5-84.3%; in this range, net photosynthetic rate (P N) rose with [CO2] increasing from 500 to 1,400 μmol mol-1. Outside this RWC range, P N decreased significantly. The apparent maximum photosynthetic rate (P max,c) and carboxylation velocity (V c) increased with increasing RWC and remained relatively high, when RWC was between 49.5 and 96.2%. CO2 compensation points and photorespiration rate exhibited a trend opposite to that of P max,c and V c, indicating that moderate water stress was beneficial for increasing plant assimilation, decreasing photorespiration, and increasing production of photosynthates. g s declined significantly with increasing [CO2] under different water supplies, but the RWC range maintaining high g s increased. g s reached its maximum, when RWC was approximately 73% and then decreased with declining RWC. The maximal g s was found with increasing RWC. Thus, based on photosynthetic characteristics in artificial, vegetation construction in semiarid loess hill and gully area, F. rhynchophylla could be planted in habitats of low soil water content.

On the role of plant mitochondrial metabolism and its impact on photosynthesis in both optimal and sub-optimal growth conditions

Given that the pathways of photosynthesis and respiration catalyze partially opposing processes, it follows that their relative activities must be carefully regulated within plant cells. Recent evidence has shown that the components of the mitochondrial electron transport chain are essential for the proper maintenance of intracellular redox gradients, to allow considerable rates of photorespiration and in turn efficient photosynthesis. Thus considerable advances have been made in understanding the interaction between respiration and photosynthesis during the last decades and the potential mechanisms linking mitochondrial function and photosynthetic efficiency will be reviewed. Despite the fact that manipulation of various steps of mitochondrial metabolism has been demonstrated to alter photosynthesis under optimal growth conditions, it is likely that these changes will, by and large, not be maintained under sub-optimal situations. Therefore producing plants to meet this aim remains a critical challenge. It is clear, however, that although there have been a range of studies analysing changes in respiratory and photosynthetic rates in response to light, temperature and CO2, our knowledge of the environmental impact on these processes and its linkage still remains fragmented. We will also discuss the metabolic changes associated to plant respiration and photosynthesis as important components of the survival strategy as they considerably extend the period that a plant can withstand to a stress situation.

Growth under elevated CO2 concentration affects the temperature response of photosynthetic rate

In this study, we tested the hypothesis that an elevated CO2 concentration leads to a shift of the temperature optimum of the photosynthetic rate in trees. Since the elevated CO2 treatment usually leads to a significant decrease in stomatal conductance and consequently to decrease in transpiration followed by an increase in leaf temperature, we hypothesized that elevated CO2 results in the acclimation of photosynthetic apparatus to the higher temperature.We studied the two most common species in the Czech Republic – European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karsten). The eight-year-old trees were grown in glass domes at the experimental research site Bílý Kříž in the Beskydy Mts. and they were exposed to ambient (AC; 385 µmol CO2 mol-1) and elevated CO2 concentrations (EC; 700 µmol CO2 mol-1). Based on the gas-exchange and fluorescence techniques we determined the basic photosynthetic characteristics in the range of leaf temperatures from 10 to 45 °C. The changes in temperature acclimation of tree species studied were evaluated on the basis of the shift of temperature optima. EC treatment led indeed to an increase of leaf temperature up to 3.5 °C in both species studied. The temperature optimum of the light-saturated rate of CO2 assimilation, measured at the growth CO2 concentration (i.e. 385 for AC and 700 µmol CO2 mol-1 for EC trees), was higher by 3 °C in both tree species of the EC variant. Although the shift in photosynthetic temperature optimum disappeared when the AC plants were exposed to an elevated CO2 concentration, an acclimation of Rubisco carboxylation and electron transport to higher temperature was observed.

Using combined measurements of gas exchange and chlorophyll fluorescence to investigate the photosynthetic light responses of plant species adapted to different light regimes

One broad-leaved pioneer tree, Alnus formosana, two broad-leaved understory shrubs, Ardisia crenata and Ardisia cornudentata, and four ferns with different light adaptation capabilities (ranked from high to low, Pyrrosia lingus, Asplenium antiquum, Diplazium donianum, Archangiopteris somai) were used to elucidate the light responses of photosynthetic rate and electron transport rate (ETR). Pot-grown materials received up to 3 levels of light intensity, i.e., 100%, 50% and 10% sunlight. Both gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously by an equipment under constant temperature and 7 levels (0-2,000 μmol m-2 s-1) of photosynthetic photon flux density (PPFD). Plants adapted to-or acclimated to high light always had higher light-saturation point and maximal photosynthetic rate. Even materials had a broad range of photosynthetic capacity [maximal photosynthetic rate ranging from 2 to 23 μmol(CO2) m-2 s-1], the ratio of ETR to gross photosynthetic rate (P G) was close for A. formosana and the 4 fern species when measured under constant temperature, but the PPFD varied. In addition, P. lingus and A. formosana grown under 100% sunlight and measured at different seasonal temperatures (15, 20, 25, and 30°C) showed increased ETR/P G ratio with increasing temperature and could be fitted by first- and second-order equations, respectively. With this equation, estimated and measured P G were closely correlated (r 2 = 0.916 and r 2 = 0.964 for P. lingus and A. formosana, respectively, p<0.001). These equations contain only the 2 easily obtained dynamic indicators, ETR and leaf temperature. Therefore, for some species with near ETR/P G ratio in differential levels of PPFD, these equations could be used to simulate dynamic variation of leaf scale photosynthetic rate under different temperature and PPFD conditions.

The Feasibility Analysis of PVX and TRV Vectors as the VIGS Tool for Studying the Gene Function

Abstract A method of virus-induced post-transcriptional gene silencing for studying rbcS gene function was established and optimized using tobacco rattle virus vector and potato X virus vector as materials in this study. The following analyses were conducted: phenotypic characterization of rbcS gene silenced plants, transcription levels of rbcS gene by RT-PCR, and protein levels of rbcS by the antibodies of rbcS. For feasibility assessment of the PVX and TRV vectors on the VIGS for studying gene function, the statistical analysis was first employed in which it contained the two-factor variance analysis model and F-test based upon a large amount of data of the response of photosynthetic rates, the photosynthetic active radiation intensity and CO2 concentrations generated from the rbcS silenced and control plants. Our findings suggested that TRV vector was superior to PVX vector.

In vivo cytochrome and alternative pathway respiration in leaves of Arabidopsis thaliana plants with altered alternative oxidase under different light conditions

The in vivo activity of the alternative pathway (ν(alt)) has been studied using the oxygen isotope fractionation method in leaves of Arabidopsis thaliana modified for the expression of the AtAOX1a gene by anti-sense (AS-12) or overexpression (XX-2). Under non-stressful conditions, ν(alt) was similar in all plant lines regardless of its different alternative pathway capacities (V(alt)). Total leaf respiration (V(t)) and V(alt) were directly related to growth light conditions while electron partitioning between the cytochrome pathway (CP) and alternative pathway (AP) was unchanged by light levels. Interestingly, the AP functioned at full capacity in anti-sense plants under both growth light conditions. The role of the AP in response to a high light stress induced by short-term high light treatment (HLT) was also studied. In wild type and XX-2, both CP and AP rates increased proportionally after HLT while in AS-12, where the AP was unable to increase its rate, the CP accommodated all the increase in respiration. The results obtained under high light stress suggest that flexibility in the response of the mitochondrial electron transport chain is involved in sustaining photosynthetic rates in response to this stress while the saturated AP in AS-12 plants may contribute to the observed increase in photoinhibition.

Comparisons of anatomical structure, component and photosynthetic capacity of leaves at different apple canopy positions

以富士苹果(<i>Malus domestica</i> Borkh. cv. ‘Fuji’)树冠不同部位叶片为试材, 对其解剖结构、内含物和光合能力进行了比较研究。苹果叶片光合速率对小气候因子的响应是根据C₃植物光合机理模型模拟, 其中气孔导度由气孔的半机理模型模拟。结果表明, 树冠中、上部叶片比下部叶片分别厚31.8%和37.0%, 栅栏组织分别厚44.8%和62.7%; 中、上部叶片的叶绿素含量比下部叶分别高18.0%和20.6%, 可溶性糖分别高25.2%和38.8%, 脯氨酸分别高11.7%和29.0%。树冠不同部位叶片光合能力差异和叶片结构及叶绿素等内含物差异一致。苹果叶片净光合速率的变化主要由光合有效辐射的变化引起, 同时对CO₂浓度的变化也非常敏感。模拟显示, 从树冠上部到下部, 叶片净光合总量晴天从约400 mmol·m^-2·d^-1减少到130 mmol·m^-2·d^-1, 减少67%, 阴天从约170 mmol·m^-2·d^-1减少到22 mmol·m^-2·d^-1, 减少87%, 叶片的最大光合速率相应减少67%。

Differences in drought sensitivities and photosynthetic limitations between co-occurring C3 and C4 (NADP-ME) Panicoid grasses.

The success of C4 plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C4 grasses are not necessarily less sensitive to drought than C3 grasses and are proposed to respond with greater metabolic limitations, while the C3 response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C3 and C4 NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response. Six species of locally co-occurring grasses, C3) species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C4 (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO2 concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types. Leaves of C4 species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C4 photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO2 assimilation, whereas, in the C3 species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C4 plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C3 plants which recovered a greater proportion of photosynthesis through increased stomatal conductance. Within the Panicoid grasses, C4 (NADP-ME) species are metabolically more sensitive to drought than C3 species and recover more slowly from drought.

Influence of varying light regimes on photosynthesis and related variables on tree seedlings of Warburgia ugandensis Sprague and Polyscias fulva (Hiern) harms

The physiology of seedlings of Warburgia ugandensis and Polyscias fulva were studied at varying light levels. Photosynthesis was significantly higher in P. fulva(1.4 mmols CO2 m-2 s-1) than in W. ugandensis (0.3 mmols CO2 m-2s-1) when grown in full sunlight. However, photosynthesis was not significantly (P > 0.05) different under moderate and dense shades (PPFD about 600 mmols m-2s-1 and 350 mmols m-2s-1 respectively) for both species (and ranged between 0.4 and 0.5 mmols CO2 m-2s-1). Generally, P. fulva seedlings had significantly (P < 0.05) greater reductions (from 1.0 to 0.4 mmols CO2 m-2s-1) in photosynthetic rates in response to increasing shade than did W. ugandensis (0.6 to 0.4 mmols CO2 m-2s-1). However, W. ugandensis attained significantly (P < 0.05) higher photosynthetic rates under shade conditions (0.6 mmols CO2 m-2s-1) than full sunlight conditions (0.3 mmols CO2 m-2s-1). Leaf temperatures were highest (30°C) in full sunlight and lowest (27°C) in dense shade for both species. Generally, stomatal conductance, transpiration and water use efficiency showed significantly (P < 0.05) higher values for shade grown W. ugandensis and full sunlight grown P. fulva. Water use efficiency for P. fulva (2.3 mmols CO2 mmol-1 H2O) was significantly (P < 0.05) higher that for W. ugandensis (1.5 mmols CO2 mmol-1 H2O) in full sunlight than. It was concluded that P. fulva was also less adapted to growth at low light intensity while W. ugandensis was better adapted to growth at low light levels because of its significantly greater ability to maintain higher rates of photosynthesis in low light intensity. Therefore in East Africa P fulva can be a better agroforestry species than W. ugandensis. Key words: Net carbon exchange, forest tree seedlings, shade, Warburgia ugandensis, Polyscias fulva

Photosynthetic response to low sink demand after fruit removal in relation to photoinhibition and photoprotection in peach trees

Diurnal variations in photosynthesis, chlorophyll fluorescence, xanthophyll cycle, antioxidant enzymes and antioxidant metabolism in leaves in response to low sink demand caused by fruit removal (-fruit) were studied in 'Zaojiubao' peach (Prunus persica (L.) Batch) trees during the final stage of rapid fruit growth. Compared with the retained fruit treatment (+fruit), the -fruit treatment resulted in a significantly lower photosynthetic rate, stomatal conductance and transpiration rate, but generally higher internal CO(2) concentration, leaf-to-air vapor pressure difference and leaf temperature. The low photosynthetic rate in the -fruit trees paralleled reductions in maximal efficiency of photosystem II (PSII) photochemistry and carboxylation efficiency. The midday depression in photosynthetic rate in response to low sink demand resulting from fruit removal was mainly caused by non-stomatal limitation. Fruit removal resulted in lower quantum efficiency of PSII as a result of both a decrease in the efficiency of excitation capture by open PSII reaction centers and an increase in closure of PSII reaction centers. Both xanthophyll-dependent thermal dissipation and the antioxidant system were up-regulated providing protection from photo-oxidative damage to leaves during low sink demand. Compared with the leaves of +fruit trees, leaves of -fruit trees had a larger xanthophyll cycle pool size and a higher de-epoxidation state, as well as significantly higher activities of antioxidant enzymes, including superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase and a higher reduction state of ascorbate and glutathione. However, the -fruit treatment resulted in higher hydrogen peroxide and malondialdehyde concentrations compared with the +fruit treatment, indicating photo-oxidative damage.

An estimation of CO2 fixation capacity in mangrove forest using two methods of CO2 gas exchange and growth curve analysis

In many coastal areas of South-East Asia, attempts have been made to revive coastal ecosystem by initiating projects that encourage planting of mangrove trees. Compared to the terrestrial trees, mangrove trees possess a higher carbon fixation capacity. It becomes a very significant option for clean development mechanism (CDM) program. However, a reliable method to estimate CO2 fixation capacity of mangrove trees has not been established. Acknowledging the above fact, we decided to set up an estimation method for the CDM program, using gas exchange analysis to estimate mangrove productivity, we put into consideration the net CO2 fixation of reforested Kandelia candel (5-, 10-, and 15-year-old stand). This was estimated by gas exchange analysis and growth curve analysis. In growth curve analysis, we drew a growth curve of a single stand using data of above- and below-ground biomass. In the gas exchange analysis, we calculated CO2 fixation capacity by (1) measuring respiration rate of each organ of stand and calculating respiratory CO2 emission from above- to below-ground biomass. (2) Measuring the single-leaf photosynthetic rate in response to light intensity and calculating the photosynthetic CO2 absorption. (3) We also developed a model for the diurnal changes in temperature, and monthly averages based on one-day estimation of CO2 absorption and emission, which we corrected by this model in order to estimate the net CO2 fixation capacity in response to temperature. Comparing the biomass accumulation of the two methods constructed for the same forest, the above-ground biomass accumulation of 10-year-old forest (34.3 ton ha−1 yr−1) estimated by gas exchange analysis was closely compared to those of growth curve analysis (26.6 ton ha−1 yr−1), suggesting that the gas exchange analysis was capable of estimating mangrove productivity. The validity of the estimated CO2 fixation capacity by the gas exchange analysis and the growth curve analysis was also discussed.

Increased photosynthesis following partial defoliation of field-grown Eucalyptus globulus seedlings is not caused by increased leaf nitrogen

Increased photosynthetic rates following partial defoliation may arise from changes in leaf biochemistry, water relations or nutrient status. Twelve-month-old field-grown Eucalyptus globulus Labill. seedlings were pruned from below to reduce the green crown depth by 50 (D50) or 70% (D70). Photosynthetic responses to light and CO2 concentration were examined before and one, three and five weeks after partial defoliation. One week after defoliation, photosynthetic rates were greater in seedlings in the D50 (21 micromol m(-2) s(-1)) and D70 (23 micromol m(-2) s(-1)) treatments than in control seedlings (15 micromol m(-2) s(-1)); however, there was little difference in photosynthetic rates between partially defoliated seedlings and control seedlings after 5 weeks. An analysis of the sensitivity of photosynthesis to biochemical parameters revealed that the transient increase in photosynthetic rate in response to partial defoliation was largely a function of the maximum rate of carboxylation (85-87%) and the maximum rate of RuBP regeneration (55-60%) rather than stomatal conductance (12-13%). Nitrogen increased in leaves following partial defoliation (increases of 0.6 and 1.2 g m(-2) for D50 and D70, respectively), but was accumulated in a non-photosynthetic form (i.e., there was no increase in nitrogen concentration of Rubisco or chlorophyll). Increased photosynthetic rates immediately following partial defoliation were primarily a result of increased activity rather than amount of photosynthetic machinery. There was no evidence that phosphorus was responsible for the increase in photosynthetic rates after partial defoliation.

Growth yield of Vicia faba L in response to microbial symbiotic associations

A multifactor experiment was undertaken to investigate the influence of Rhizobium and arbuscular mycorrhizal fungi (AMF) on biomass production, leaf area generation, whole plant photosynthetic and respiration rates, growth yield and maintenance respiration in Vicia faba L under low phosphorus (P) supply. Treatments consisted of low (LN) or high nitrogen (HN) supply with or without microbial symbiont(s). Plants were harvested at 54 (T 1) and 63 (T 2) days after planting. In all instances, plants colonized with both microbial symbionts had significantly higher total biomasses, leaf areas, whole plant photosynthesis and respiration rates than plants with only one or no microbial symbionts. Similarly, plants with both microbial symbionts also had significantly higher (≥ 0.7) growth yield ( Y g) values than all the other treatments. There were no significant differences in Y g values between harvest intervals within individual treatments. Maintenance respiration rates were also highest in plants with two microbial symbionts (> 30 CO 2 (g DM) − 1 d − 1 ). In LN plants colonized by both microbial symbionts there was evidence of compensatory increases in the photosynthetic rates in response to the carbon sink demands of the microbial symbionts. Finally, the results of this investigation are consistent with the hypothesis that the plant potential photosynthetic capacity exceeds the carbon demand of the Rhizobium–AMF symbiotic complex.

Intraspecific variation in temperature dependence of gas exchange characteristics among Plantago asiatica ecotypes from different temperature regimes

There are large inter- and intraspecific differences in the temperature dependence of photosynthesis, but the physiological cause of the variation is poorly understood. Here, the temperature dependence of photosynthesis was examined in three ecotypes of Plantago asiatica transplanted from different latitudes, where the mean annual temperature varies between 7.5 and 16.8 degrees C. Plants were raised at 15 or 30 degrees C, and the CO(2) response of photosynthetic rates was determined at various temperatures. When plants were grown at 30 degrees C, no difference was found in the temperature dependence of photosynthesis among ecotypes. When plants were grown at 15 degrees C, ecotypes from a higher latitude maintained a relatively higher photosynthetic rate at low measurement temperatures. This difference was caused by a difference in the balance between the capacities of two processes, ribulose-1,5-bisphosphate regeneration (J(max)) and carboxylation (V(cmax)), which altered the limiting step of photosynthesis at low temperatures. The organization of photosynthetic proteins also varied among ecotypes. The ecotype from the highest latitude increased the J(max) : V(cmax) ratio with decreasing growth temperature, while that from the lowest latitude did not. It is concluded that nitrogen partitioning in the photosynthetic apparatus and its response to growth temperature were different among ecotypes, which caused an intraspecific variation in temperature dependence of photosynthesis.

High temperature acclimation of C4 photosynthesis is linked to changes in photosynthetic biochemistry

With average global temperatures predicted to increase over the next century, it is important to understand the extent and mechanisms of C4 photosynthetic acclimation to modest increases in growth temperature. To this end, we compared the photosynthetic responses of two C4 grasses (Panicum coloratum and Cenchrus ciliaris) and one C4 dicot (Flaveria bidentis) to growth at moderate (25/20 degrees C, day/night) or high (35/30 degrees C, day/night) temperatures. In all three C4 species, CO2 assimilation rates (A) underwent significant thermal acclimation, such that when compared at growth temperatures, A increased less than what would be expected given the strong response of A to short-term changes in leaf temperature. Thermal photosynthetic acclimation was further manifested by an increase in the temperature optima of A, and a decrease in leaf nitrogen content and leaf mass per area in the high- relative to the moderate-temperature-grown plants. Reduced photosynthetic capacity at the higher growth temperature was underpinned by selective changes in photosynthetic components. Plants grown at the higher temperature had lower amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase and cytochrome f and activity of carbonic anhydrase. The activities of photosystem II (PSII) and phosphoenolpyruvate carboxylase were not affected by growth temperature. Chlorophyll fluorescence measurements of F. bidentis showed a corresponding decrease in the quantum yield of PSII (phi(PSII)) and an increase in non-photochemical quenching (phi(NPQ)). It is concluded that through these biochemical changes, C4 plants maintain the balance between the various photosynthetic components at each growth temperature, despite the differing temperature dependence of each process. As such, at higher temperatures photosynthetic nitrogen use efficiency increases more than A. Our results suggest C4 plants will show only modest changes in photosynthetic rates in response to changes in growth temperature, such as those expected within or between seasons, or the warming anticipated as a result of global climate change.

RESPONSE OF PHOTOSYNTHETIC RATE AND STOMATAL CONDUCTANCE OF RICE TO LIGHT INTENSITY AND CO2 CONCENTRATION IN NORTHERN CHINA

The response of photosynthetic rate and stomatal conductance of rice (Oryza sativa var. Japonica) to changes in light intensity and CO2 concentrations was studied using a Li-6400 in Northern China. In general, photosynthetic rates increased with light intensity and CO_(2) concentrations and could be expressed by a Michaelis-Menten function. Apparent quantum yield increased with CO_(2) concentrations but decreased slightly when CO_(2) concentrations exceeded 800 mol·mol~(-1). Similarly, apparent carboxylation efficiency increased with light intensity but decreased slightly when light intensity exceeded 1600 mol·m~(-2)·s~(-1). The response of stomatal conductance to light intensity can also be expressed by a Michaelis-Menten function, whereas the response to CO_(2) concentrations can be expressed by a hyperbola. If the combined effects of light intensity and CO_(2) concentrations are considered, the photosynthetic rate can be estimated by a Michaelis-Menten equation with a maximum photosynthetic rate of 71.74 mol·m~(-2)·s~(-1). Apparent quantum yield was 0.0560 mol CO_(2)·mol~(-1) photons and carboxylation rate was 0.1031 mol·m~(-2)·s~(-1)/mol·mol~(-1). The response of stomatal conductance (G_(sw)) to light intensity can be expressed by a Michaelis-Menten function too, but the response to CO_(2) concentrations (C_(s)) can be simulated by the equation: G_(sw)=G_(max,c)/(1+C_(s)/C_(s0)) where G_(max,c) is maximum stomatal conductance of stomatal response to CO_(2) under a defined light intensity and C_(s0) is a constant, because the stomatal conductance decreases with increases in CO_(2) concentrations, stomatal conductance can be estimated by G_(sw)=G_(max)(PFD/PFD_(c))/[(1+PFD/PFD_(c))(1+C_(s)/C_(s0))]+G_(ct) in response to the combined effects of CO_(2) concentration and light intensity (I). The potential maximum stomatal conductance, G_(max), can reach 0.6709 mol·m~(-2)·s~(-1) under saturated light levels and CO_(2) near 0 mol·mol~(-1). Ball-Berry model and its revised form can still be used to express the coupled relationship of stomatal conductance and photosynthesis. The simulation precision will be improved if saturation vapor pressure deficit, D_(s), at the leaf surface was used in the Ball-Berry model instead of relative humidity.

Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China

Soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum photosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation.

Inorganic Carbon Utilization of the Freshwater Red Alga Compsopogon coeruleus (Balbis) Montagne (Compsopogonaceae, Rhodophyta) Evaluated by in situ Measurement of Chlorophyll Fluorescence

To explore the inorganic carbon utilization of the freshwater red alga Compsopogon coeruleus, photosynthetic rates in response to increasing of bicarbonate concentration, the addition of alkaline HEPES buffer (pH 8.8), acid HEPES buffer (pH 4.0) and the extracellular carbonic anhydrase inhibitor (acetazolamide, AZ), respectively, were examined in situ by using a submersible pulse amplitude modulated (PAM) fluorometer. Among the treatments, adding acid HEPES buffer significantly reduced photosynthetic rates of the alga, while others showed no effect. Accordingly, we concluded that C. coeruleus had less or no inorganic carbon (Ci) limitation in its natural habitat. The alga might have higher affinity for bicarbonate and directly uptake bicarbonate as main Ci source without the aid of extracellular carbonic anhydrase.

Ecophysiological responses of two Mediterranean shrubs, Erica multiflora and Globularia alypum, to experimentally drier and warmer conditions

A new approach was used to experimentally dry and warm a Mediterranean shrubland. By means of automatically sliding curtains, the drought period was extended by excluding rain over the two growing seasons (spring and autumn), and passive warming was created by avoiding infra‐red dissipation at night over the whole year. The aim of the study was to test how a future extended drought period and an increase in temperatures could affect the photosynthetic and water use strategies of two co‐occurring Mediterranean shrubs, Erica multiflora and Globularia alypum, which are common species of the dry coastal shrublands. The shoot water potential, leaf gas exchange rates and chlorophyll a fluorescence of plants was monitored seasonally during two years (1999–2001). In addition we measured the photosynthetic response curves to light and CO2 in autumn 2001 and the foliar N concentration and leaf C and N stable isotopes in summer 1999 and 2000. Droughted plants of both shrub species showed lower shoot water potentials, transpiration rates and stomatal conductances than control plants, although there was a high seasonal variability. Drought treatment reduced significantly the overall leaf net photosynthetic rates of E. multiflora, but not of G. alypum. Droughted plants of E. multiflora also showed lower leaf net photosynthetic rates in response to light and CO2 and lower carboxylation efficiency than controls, but there was no significant effect of drought on its overall photosystem II (PSII) photochemical efficiency. Although warming treatment did not affect the leaf net photosynthetic rates of the two species overall the study, it increased significantly the carboxylation efficiency and leaf net photosynthetic rates of G. alypum plants in response to CO2 levels in autumn 2001. In addition, warming treatment increased the potential photochemical efficiency of PSII (Fv/Fm) of both species (but especially of G. alypum) at predawn or midday and mainly in autumn and winter. Thus, the results suggest that drier conditions might decrease the annual productivity of these Mediterranean shrubs, particularly of E. multiflora, and that future warming could alleviate the present low temperature constraints of the photosynthetic performance of the two studied species, but especially of G. alypum, during the colder seasons. Ultimately, drier and warmer conditions in the near future may change the competitive relationship among these species in such Mediterranean ecosystems.