Effect of oxygen on photosynthesis by spinach leaf protoplasts

The photosynthetic CO₂ fixation by spinach leaf (Spinacia oleracea L. var. Kyoho) protoplasts was inhibited by substituting an atmosphere of N₂ with one of either air (21% O₂) or 100% O₂. The inhibitory effect of 100% O₂ was greater than that of air. The mode of inhibition by 100% O₂ and air was competitive with respect to CO₂; Ki(O₂) value was 0.32 mM at pH 7 and 0.28 mM at pH 8.5 The labeling patterns of compounds in protoplasts exposed to ¹⁴CO₂ in light after transferring them from N₂ to O₂ atmospheres were examined. There was no detectable ¹⁴CO₂ incorporation into glycolate under anaerobic and O₂ atmospheres; a more marked labeling of glycine occurred under an oxidative environment compared to that under the anaerobic condition, presumably because of a rapid transformation of glycolate to glycine in the protoplasts.     

Responses of soybean to oxygen deficiency and elevated root-zone carbon dioxide concentration

Root flooding is damaging to the growth of crop plants such as soybean (Glycine max L.). Field flooding for 3 d often results in leaf chlorosis, defoliation, cessation of growth and plant death. These effects have been widely attributed solely to a lack of oxygen in the root-zone. However, an additional damaging factor may be CO(2), which attains levels of 30 % (v/v) of total dissolved gases. Accordingly, the effects of root-zone CO(2) on oxygen-deficient soybean plants were investigated in hydroponic culture. Soybean plants are shown to be very tolerant of excess water and anaerobiosis. No oxygen (100 % N(2) gas) and low oxygen (non-aerated) treatments for 14 d had no effect on soybean survival or leaf greenness, but plants became severely chlorotic and stunted when the roots were exposed to no oxygen together with CO(2) concentrations similar to those in flooded fields (equilibrium concentrations of 30 %). When root-zone CO(2) was increased to 50 %, a quarter of soybean plants died. Those plants that survived showed severe symptoms of chlorosis, necrosis and root death. In contrast, rice (Oryza sativa L.) plants were not affected by the combination of no oxygen and elevated root-zone CO(2.) A concentration of 50 % CO(2) did not affect rice plant survival or leaf colour. These results suggest that the high susceptibility of soybean to soil flooding, compared with that of rice, is an outcome of its greater sensitivity to CO(2).     

Effects of irradiance and leaf water deficit on net carbon dioxide assimilation and mesophyll and transport resistances

Rate of net CO₂ assimilation by soil-grown soybean plants were studied over a range of relative leaf water contents at each of four levels of irradiance. There was a large interaction between light level and leaf water deficit on the rate of CO₂ assimilation. The effect of leaf water deficit on assimilation became larger as irradiance increased. Both stomatal resistance to CO₂ transport and mesophyll resistance to CO₂ assimilation increased as leaf-water deficit increased. The increase in both resistance with changing leaf-water content was largest at high irradiance and became smaller as irradiance decreased. Relief of soil-moisture stress by watering induced large oscillations of CO₂ assimilation, stomatal resistance, and mesophyll resistance. The oscillation of the mesophyll resistance occurred in the absence of changes in relative water content and appeared to be related to oscillations in leaf temperature. The observed increase in mesophyll resistance with decreasing leaf-water content under nonoscillative conditions may be caused by changes in leaf temperature rather than leaf water content.     

Responses of cotton and wheat photosynthesis and growth to cyclic variation in carbon dioxide concentration

The carbon dioxide concentration in free air carbon dioxide enrichment (FACE) systems typically has rapid fluctuations. In our FACE system, power spectral analysis of CO₂ concentration measured every second with an open path analyzer indicated peaks in variation with a period of about one minute. I used open-top chambers to expose cotton and wheat plants to either a constant elevated CO₂ concentration of 180 ??mol mol^?1 above that of outside ambient air, or to the same mean CO₂ concentration, but with the CO₂ enrichment cycling between about 30 and 330 ??mol mol^?1 above the concentration of outside ambient air, with a period of one minute. Three short-term replicate plantings of cotton were grown in Beltsville, Maryland with these CO₂ concentration treatments imposed for 27-day periods over two summers, and one winter wheat crop was grown from sowing to maturity. In cotton, leaf gas-exchange measurements of the continuously elevated treatment and the fluctuating treatment indicated that the fluctuating CO₂ concentration treatment consistently resulted in substantial down-regulation of net photosynthetic rate (P _N) and stomatal conductance (g _s). Total shoot biomass of the vegetative cotton plants in the fluctuating CO₂ concentration treatment averaged 30% less than in the constantly elevated CO₂ concentration treatment at 27 days after planting. In winter wheat, leaf gas-exchange measurements also indicated that down-regulation of P _N and g _s occurred in flag leaves in the fluctuating CO₂ concentration treatment, but the effect was not as consistent in other leaves, nor as severe as found in cotton. However, wheat grain yields were 12% less in the fluctuating CO₂ concentration treatment compared with the constant elevated CO₂ concentration treatment. Comparison with wheat yields in chambers without CO₂ addition indicated a nonsignificant increase of 5% for the fluctuating elevated CO₂ concentration treatment, and a significant increase of 19% for the constant elevated treatment. The results suggest that treatments with fluctuating elevated CO₂ concentrations could underestimate plant growth at projected future atmospheric CO₂ concentrations.     

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C₃ species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C₃ species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 °C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 – 25 °C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 °C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

Study of CO2 exchange processes,resistances to carbon dioxide and chlorophyll content during leaf ontogenesis in poplar

Net photosynthetic (P _N) and dark respiration (R _D) rate, stomatal (rs′) and internal (ri′) resistances to carbon dioxide were measured by gas exchange methods on leaves of different ages, expressed in leaf plastochron index units (LPI) for a fast growing poplar cultivar Unal 2. Although the optimal leaf age differs slightly for the different gas exchange parameters, leaf ontogeny is reflected in the same way in these different parameters. MaximalP _N and minimalrs′ and ri′ values were found at LPI between 6 and 10. Chlorophyll concentrations were lowest at LPI lower than 10 although an increase in two steps was found, when leaf age increases up to maturity.     

A model of leaf photosynthesis and respiration for predicting carbon dioxide assimilation in different environments

Summary A model of leaf photosynthesis and repiration was developed which adequately predicted carbon dioxide assimilation responses by a C ₃ species, Atriplex patula, to light, [CO₂], [O₂] and temperature in controlled environments. Methods were developed for estimating input parameters using laboratory, controlled environment and field data.     

Effect of carbon dioxide concentration on microbial respiration in soil

In order to assess the validity of conventional methods for measuring CO₂ flux from soil, the relationship between soil microbial respiration and ambient CO₂ concentration was studied using an open-flow infra-red gas analyser (IRGA) method. Andosol from an upland field in central Japan was used as a soil sample. Soil microbial respiration activity was depressed with the increase of CO₂ concentration in ventilated air from 0 to 1000 ppmv. At 1000 ppmv, the respiration rate was less than half of that at 0 ppmv. Thus, it is likely that soil respiration rate is overestimated by the alkali absorption method, because CO₂ concentration in the absorption chamber is much lower than the normal level. Metabolic responses to CO₂ concentration were different among groups of soil microorganisms. The bacteria actinomycetes group cultivated on agar medium showed a more sensitive response to the CO₂ concentration than the filamentous fungi group.     

Effect of oxygen concentration on photosynthesis and respiration in two hypersaline microbial mats

The effects of oxygen concentration on photosynthesis and respiration in two hypersaline cyanobacterial mats were investigated. Experiments were carried out on mats from Eilat, Israel, with moderate photosynthetic activity, and mats from Mallorca, Spain, with high photosynthetic activity. The oxygen concentration in the overlying water above the mats was increased stepwise from 0% to 100% O2. Subsequent changes in oxygen concentration, gross photosynthetic rates, and pH values inside the mats were measured with microelectrodes. According to published reports on the regulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the key enzyme in the CO2-fixation pathway of phototrophs, we expected photosynthetic activity to decrease with increasing oxygen concentration. Gross photosynthetic and total respiration rates in both mats were highest when the O2 concentration was at 0% in the overlying water. Net oxygen production rates under these conditions were the same as under air saturation (21% O2), while gross photosynthetic and respiration rates were lowest at air saturation. In both mats, gross photosynthetic and respiration rates increased upon gradually increasing the oxygen concentration in the overlying water from 21% to 100%. These results contradict the expectation that photosynthesis decreases with increasing oxygen concentration. Increased photosynthetic rates at oxygen concentrations above 21% were probably caused by enhanced oxidation of organic matter and concomitant CO2 production due to the increased oxygen availability. The cause of the high respiration rates at 0% O2 in the overlying water was presumably the enhanced excretion of photosynthetic products during increased photosynthesis. We conclude that the effect of the O2/CO2 concentration ratio on the activity of Rubisco as demonstrated in vitro on enzyme extracts cannot be extrapolated to the situation in intact microbial mats, because the close coupling of the activity of primary producers and heterotrophic bacteria plays a major role in this ecosystem.     

Use of the response of photosynthesis to oxygen to estimate mesophyll conductance to carbon dioxide in water-stressed soybean leaves

Methods of estimating the mesophyll conductance (g_m) to the movement of CO₂ from the substomatal airspace to the site of fixation are expensive or rely upon numerous assumptions. It is proposed that, for C₃ species, measurement of the response of photosynthesis to [O₂] at limiting [CO₂], combined with a standard biochemical model of photosynthesis, can provide an estimate of g_m. This method was used to determine whether g_m changed with [CO₂] and with water stress in soybean leaves. The value of g_m estimated using the O₂ response method agreed with values obtained using other methods. The g_m was unchanged over the tested range of substomatal [CO₂]. Water stress, which decreased stomatal conductance (g_s) by about 80%, did not affect g_m, while the model parameter V_Cmax was reduced by about 25%. Leaves with g_s reduced by about 90% had g_m values reduced by about 50%, while V_Cmax was reduced by about 64%. It is concluded that g_m in C₃ species can be conveniently estimated using the response of photosynthesis to [O₂] at limiting [CO₂], and that g_m in soybean was much less sensitive to water stress than g_s, and was somewhat less sensitive to water stress than V_Cmax.     

Effect of mycorrhizal-enhanced leaf phosphate status on carbon partitioning, translocation and photosynthesis in cucumber

An assessment of the effects of arbuscular mycorrhizal (AM) infection on photosynthesis, carbon (C) allocation, translocation and biomass production of cucumber, grown in sand culture, was made using a previously determined phosphorus (P) supply (0·13 mol m^?3 P) which had a significant impact on AM infection. Separation of a direct effect of AM infection from an indirect one due to an enhanced leaf P status was achieved using a comparable non‐mycorrhizal treatment (NAM + P) supplemented with extra P (0·19 mol m^?3 P). Total leaf P concentration, specific leaf mass, photosynthetic capacity, and incorporation of ¹⁴C into non‐structural carbohydrate pools were dependent on leaf age. Both maximum and ambient photosynthetic rates were significantly higher in the youngest fully expanded leaves from AM and NAM + P plants which also had the higher leaf P concentrations. There were no differences in the total concentrations of starch, sucrose, raffinose or stachyose in young or old leaves among AM, non‐mycorrhizal (NAM) and NAM + P treatments. However, younger leaves of NAM plants showed a shift in ¹⁴C‐partitioning from stachyose and raffinose synthesis to starch accumulation. Determination of ADP‐glucose pyrophosphorylase (AGPase), sucrose synthase and sucrose phosphate synthase enzyme activities revealed that only AGPase activity was correlated with the increased incorporation rate of ¹⁴C into starch in young leaves of NAM plants. Although there were significant AM‐specific effects on C translocation to the root system, AM plants had similar rate of photosynthesis to NAM + P plants. These results suggest that the increase in photosynthetic rate in leaves of AM‐infected cucumber was due to an increased P status, rather than a consequence of a mycorrhizal ‘sink’ for assimilates.     

“光合作用需要二氧化碳”实验的改进

用无色透明的塑料袋代替锥形瓶,套在实验用的叶片上并抽出其中的空气：用锥形瓶、分液漏斗和橡胶塞等组装成“去除空气中二氧化碳装置”;在装置内用氢氧化钠与二氧化碳反应的方式去除空气中二氧化碳;经分液漏斗向锥形瓶内注水．并将排出的“空气”注入部分套有叶片的塑料袋中,另一部直接注入空气。     

The role of carbon dioxide and oxygen in determining chlorophyll fluorescence quenching during leaf development

Chlorophyll fluorescence emission at 680 nm (F680) and the rate of CO₂ fixation were measured simultaneously in sections along the length of wheat and maize leaves. These leaves possess a basal meristem and show a gradation in development towards the leaf tip. The redox state of the primary electron acceptor, Q, of photosystem II was estimated using a non-invasive method. Distal mature leaf sections displayed typical F680 induction curves which were generally anti-parallel with CO₂ fixation and during which Q became gradually oxidised. In leaf-base sections net assimilation of CO₂ was not detectable, F680 quenched slowly and monotonously without displaying any of the oscillations typical of mature tissue and Q remained relatively reduced. Sections cut from mid-regions of the leaf showed intermediate characteristics. There were no major differences between the wheat and maize leaf in the parameters measured. The results support the hypothesis that generation of the transthylakoid proton gradient and associated ATP production is not a major limitation to photosynthesis during leaf development in either C₃ or C₄ plants. Removal of CO₂ from the mature leaf sections caused little change in steady-state F680 and produced about 50% reduction of Q. When O₂ was then removed, F680 rose sharply and Q became almost totally reduced. In immature tissue unable to assimilate CO₂, removal of O₂ alone caused a similar large rise in F680 and reduction of Q whilst removal of CO₂ had negligible effects on F680 and the redox state of Q. It is concluded that in leaf tissue unable to assimilate CO₂, either because CO₂ is absent or the tissue is immature, O₂ acts as an electron acceptor and maintains Q in a partially oxidised state. The important implication that O₂ may have a role in the prevention of photoinhibition of the photochemical apparatus in the developing leaf is discussed.Abbreviations F680 chlorophyll fluorescence emission at 680 nm - PSI photosystem I - PSII photosystem II - Q PSII primary electron acceptor - pH transthylakoid proton gradient     

Sagebrush and grasshopper responses to atmospheric carbon dioxide concentration

Summary Seed- and clonally-propagated plants of Big Sagebrush (Artemisia tridentata var.tridentata) were grown under atmospheric carbon dioxide regimes of 270, 350 and 650 μl l⁻¹ and fed toMelanoplus differentialis andM. sanguinipes grasshoppers. Total shrub biomass significantly increased as carbon dioxide levels increased, as did the weight and area of individual leaves. Plants grown from seed collected in a single population exhibited a 3–5 fold variation in the concentration of leaf volatile mono- and sesquiterpenes, guaianolide sesquiterpene lactones, coumarins and flavones within each CO₂ treatment. The concentration of leaf allelochemicals did not differ significantly among CO₂ treatments for these seed-propagated plants. Further, when genotypic variation was controlled by vegetative propagation, allelochemical concentrations also did not differ among carbon dioxide treatments. On the other hand, overall leaf nitrogen concentration declined significantly with elevated CO₂. Carbon accumulation was seen to dilute leaf nitrogen as the balance of leaf carbon versus nitrogen progressively increased as CO₂ growth concentration increased. Grasshopper feeding was highest on sagebrush leaves grown under 270 and 650 μl l⁻¹ CO₂, but varied widely within treatments. Leaf nitrogen concentration was an important positive factor in grasshopper relative growth but had no overall effect on consumption. Potential compensatory consumption by these generalist grasshoppers was apparently limited by the sagebrush allelochemicals. Insects with a greater ability to feed on chemically defended host plants under carbon dioxide enrichment may ultimately consume leaves with a lower nitrogen concentration but the same concentration of allelochemicals. Compensatory feeding may potentially increase the amount of dietary allelochemicals ingested for each unit of nitrogen consumed.     

Photosynthetic acclimation to rising atmospheric carbon dioxide concentration

With rising level of CO2 in the atmosphere plants are expected to be exposed to higher concentration of CO2. Since, CO2 is a substrate limiting photosynthesis particularly in C3 plants in the present atmosphere, the impact of elevated CO2 would depend mainly on how photosynthesis acclimates or adjusts to the long term elevated level of CO2. Photosynthetic acclimation is a change in photosynthetic efficiency of leaves due to long term exposure to elevated CO2. This change in photosynthetic efficiency could be a biochemical adjustment that may improve the overall performance of a plant in a high CO2 environment or it could be due to metabolic compulsions as a result of physiological dysfunction. Acclimation has generally become synonymous with the word response, if long term exposure to elevated CO2 decreases the photosynthesis rate (Pn) at a given CO2 level, it is called negative acclimation, if it stimulates Pn at a given CO2 level, it is called positive acclimation. Photosynthetic acclimation is clearly revealed by comparing Pn of ambient and elevated CO2 grown plants at same level of CO2. Species level differences in acclimation to elevated CO2 have been reported. The physiological basis of differential photosynthetic acclimation to elevated CO2 is discussed in relation to the regulation of photosynthesis and photosynthetic carbon partitioning at cellular level.