光合作用对光和二氧化碳响应的观测方法探讨

用便携式光合仪LI-6400观测自然条件下生长的盆栽蚕豆叶片光合作用对光和二氧化碳的响应发现：（1）用未经过光合诱导的叶片观测光合作用对光的响应会得到即使在全太阳光强下光合作用仍然不饱和的假象;（2）利用某些经验方程计算的饱和光强远低于实际观测值;（3）在观测光合作用对CO2的响应过程中,每一次CO2浓度变化都应当伴随一次光合仪的匹配步骤,否则所得结果偏差很大;（4）在不饱和光下观测光合作用对CO2的响应,会导致对叶片光合能力的低估。     

Effects of O(2) Tension and Temperature during Light Uptake of CO(2) on the Dark Release of CO(2) by Excised C(3) and C(4) Leaves

A study was conducted on a C₄ (Panicum maximum) and a C₃ (Panicum bisulcatum) species to determine the nature of the dark release of ¹⁴CO₂ with respect to its responses to changes in temperature and O₂ tension during light CO₂ uptake of ¹⁴CO₂.     

Photosynthetic Responses of Turf-forming Red Macroalgae to High CO2 Conditions

Seaweeds are important components of near-shore ecosystems as primary producers, foundation species, and biogeochemical engineers. Seaweed communities are likely to alter under predicted climate change scenarios. We tested the physiological responses of three perennial, turf-building, intertidal rhodophytes, Mastocarpus stellatus, Osmundea pinnatifida, and the calcified Ellisolandia elongata, to elevated pCO₂ over 6 weeks. Responses varied between these three species. E. elongata was strongly affected by high pCO₂, whereas non-calcified species were not. Elevated pCO₂ did not induce consistent responses of photosynthesis and respiration across these three species. While baseline photophysiology differed significantly between species, we found few clear effects of elevated pCO₂ on this aspect of macroalgal physiology. We found effects of within-species variation in elevated pCO₂ response in M. stellatus, but not in the other species. Overall, our data confirm the sensitivity of calcified macroalgae to elevated pCO₂, but we found no evidence suggesting that elevated pCO₂ conditions will have a strong positive or negative impact on photosynthetic parameters in non-calcified macroalgae.     

Dynamic Balancing of Isoprene Carbon Sources Reflects Photosynthetic and Photorespiratory Responses to Temperature Stress

The volatile gas isoprene is emitted in teragrams per annum quantities from the terrestrial biosphere and exerts a large effect on atmospheric chemistry. Isoprene is made primarily from recently fixed photosynthate; however, alternate carbon sources play an important role, particularly when photosynthate is limiting. We examined the relative contribution of these alternate carbon sources under changes in light and temperature, the two environmental conditions that have the strongest influence over isoprene emission. Using a novel real-time analytical approach that allowed us to examine dynamic changes in carbon sources, we observed that relative contributions do not change as a function of light intensity. We found that the classical uncoupling of isoprene emission from net photosynthesis at elevated leaf temperatures is associated with an increased contribution of alternate carbon. We also observed a rapid compensatory response where alternate carbon sources compensated for transient decreases in recently fixed carbon during thermal ramping, thereby maintaining overall increases in isoprene production rates at high temperatures. Photorespiration is known to contribute to the decline in net photosynthesis at high leaf temperatures. A reduction in the temperature at which the contribution of alternate carbon sources increased was observed under photorespiratory conditions, while photosynthetic conditions increased this temperature. Feeding [2-¹³C]glycine (a photorespiratory intermediate) stimulated emissions of [¹³C_1–5]isoprene and ¹³CO₂, supporting the possibility that photorespiration can provide an alternate source of carbon for isoprene synthesis. Our observations have important implications for establishing improved mechanistic predictions of isoprene emissions and primary carbon metabolism, particularly under the predicted increases in future global temperatures.Many plant species emit isoprene (2-methyl-1,3-butadiene [C₅H₈]) into the atmosphere at high rates (Sharkey and Yeh, 2001). With an estimated emission rate of 500 to 750 teragram per year by terrestrial ecosystems (Guenther et al., 2006), isoprene exerts a strong control over the oxidizing capacity of the atmosphere. Due to its high reactivity to oxidants, it fuels an array of atmospheric chemical and physical processes affecting air quality and climate, including the production of ground-level ozone in environments with elevated concentrations of nitrogen oxides (Atkinson and Arey, 2003; Pacifico et al., 2009) and the formation/growth of organic aerosols (Nguyen et al., 2011). At the plant level, isoprene provides protection from stress, through stabilizing membrane processes (Sharkey and Singsaas, 1995; Velikova et al., 2011) and/or reducing the accumulation of damaging reactive oxygen species in plant tissues under stress (Loreto et al., 2001; Vickers et al., 2009b; Velikova et al., 2012). While the mechanism(s) are still under investigation, isoprene may directly or indirectly stabilize hydrophobic interactions in membranes (Singsaas et al., 1997), minimize lipid peroxidation (Loreto and Velikova, 2001), and directly react with reactive oxygen species (Kameel et al., 2014), yielding first-order oxidation products methyl vinyl ketone and methacrolein (Jardine et al., 2012, 2013). The two main environmental drivers for global changes in isoprene fluxes are light and temperature (Guenther et al., 2006). Isoprene production is closely linked to net photosynthesis, and both isoprene emissions and net photosynthesis are controlled by light intensity (Monson and Fall, 1989). There is also a positive correlation between net photosynthesis and isoprene emissions as leaf temperatures increase up to the optimum temperature for net photosynthesis (Monson et al., 1992).Despite the close correlation between photosynthesis and isoprene emissions, plant enclosure observations and leaf-level analyses have both shown that the fraction of net photosynthesis dedicated to isoprene emissions is not constant. During stress events that decrease net photosynthetic rates, isoprene emissions are often less affected or even stimulated; this results in an increase in relative isoprene production from 1% to 2% of net photosynthesis under normal conditions to 15% to 50% under extreme stress (Goldstein et al., 1998; Fuentes et al., 1999; Kesselmeier et al., 2002; Harley et al., 2004). In severe stress conditions such as drought, isoprene emissions can even continue in the complete absence of photosynthesis (Fortunati et al., 2008). An uncoupling of isoprene emissions from net photosynthesis has also been observed in a number of other studies where the optimum temperature for isoprene emissions was found to be substantially higher than that of net photosynthesis; under the high-temperature conditions, isoprene emissions can account for more than 50% of net photosynthesis (Sharkey and Loreto, 1993; Lerdau and Keller, 1997; Harley et al., 2004; Magel et al., 2006).Analyses of carbon sources using ¹³CO₂ leaf labeling have revealed that under standard conditions (i.e. leaf temperature of 30°C and photosynthetically active radiation [PAR] levels of 1,000 µmol m^–2 s^–1), isoprene is produced primarily (70%–90%) using carbon directly derived from the Calvin cycle (Delwiche and Sharkey, 1993; Affek and Yakir, 2002; Karl et al., 2002) via the chloroplastic methylerythritol phosphate (MEP) isoprenoid pathway (Zeidler et al., 1997). The relative contributions of photosynthetic and alternate carbon sources for isoprene are now recognized as being variable under different environmental conditions. Changes in net photosynthesis rates under drought stress (Funk et al., 2004; Brilli et al., 2007), salt stress (Loreto and Delfine, 2000), and changes in ambient O₂ and CO₂ concentrations (Jones and Rasmussen, 1975; Karl et al., 2002; Trowbridge et al., 2012) alter their relative contributions. Under heat stress-induced photosynthetic limitation in Populus deltoides (a temperate species), an increase in the relative contribution of alternate carbon sources was also observed (Funk et al., 2004). However, our current understanding of the responses of isoprene carbon sources to changes in temperature and light levels is poor, and the connection(s) of these responses to changes in leaf primary carbon metabolism (e.g. photosynthesis, photorespiration, and respiration) remains to be determined.Studies over the last decade have shown or suggested that potential alternate carbon sources include refixation of respired CO₂ (Loreto et al., 2004), intermediates from the cytosolic mevalonate (MVA) isoprenoid pathway (Flügge and Gao, 2005; Lichtenthaler, 2010), and intermediates from central carbon metabolism, including pyruvate (Jardine et al., 2010), phosphoenolpyruvate (Rosenstiel et al., 2003), and Glc (Schnitzler et al., 2004). Over 40 years ago, it was also proposed that photorespiratory carbon could directly contribute to isoprene production in plants (Jones and Rasmussen, 1975); however, subsequent studies (Monson and Fall, 1989; Hewitt et al., 1990; Karl et al., 2002) have concluded that photorespiration does not contribute to isoprenoid production.In this study, we examined the carbon composition of isoprene emitted from tropical tree species under changes in light and temperature, the two key environmental variables that affect isoprene emissions. Using a novel real-time analytical approach, we were able to observe compensatory changes in carbon source contribution to isoprene during thermal ramping at high temperatures, despite the overall isoprene emissions remaining relatively stable. By conducting leaf temperature curves under variable ¹³CO₂ concentrations and applying [2-¹³C]Gly leaf labeling, we also reopen the discussion on the role of photorespiration as an alternate source of carbon for isoprenoid formation.     

Involvement of Photosynthetic Carbon Reduction Cycle Intermediates in CO(2) Fixation and O(2) Evolution by Isolated Chloroplasts

The photosynthetic carbon reduction cycle intermediates can be divided into three classes according to their effects on the rate of photosynthetic CO₂ evolution by whole spinach (Spinacia oleracea) chloroplasts and on their ability to affect reversal of certain inhibitors (nigericin, arsenate, arsenite, iodoacetate, antimycin A) of photosynthesis: class I (maximal): fructose 1, 6-diphosphate, dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, ribose-5-phosphate; class 2 (slight): glucose 6-phosphate, fructose 6-phosphate, ribulose-1, 5-diphosphate; class 3 (variable): glycerate 3-phosphate. While class 1 compounds influence the photosynthetic rate, they do not lower the Michaelis constant of the chloroplast for bicarbonate or affect strongly other photosynthetic properties such as the isotopic distribution pattern. It was concluded that the class 1 compounds influence the chloroplast by not only supplying components to the carbon cycle but also by activating or stabilizing a structural component of the chloroplast.     

野生与栽培黄花蒿净光合速率对光强和CO2浓度的响应

比较了相同种源的野生和栽培黄花蒿(Artemisia annua L.)净光合速率对光强和CO2浓度的响应特性。结果表明,野生和栽培黄花蒿的光饱和点(LSP)分别为1 183和1 564μmol m-2s-1,光补偿点(LCP)为17和18μmol m-2s-1,最大净光合速率(Pmax)为18.78和22.38μmol m-2s-1,表观量子效率(AQY)为0.08和0.075μmol m-2s-1,表明黄花蒿的光合能力强,能够利用很高的光强,且对弱光的适应性也较强。栽培黄花蒿的Pmax、LSP和最大羧化速率(Vcmax)显著高于野生黄花蒿,两者的LCP、不包括光下呼吸的CO2补偿点、AQY、光下呼吸速率和最大电子传递速率(Jmax)差异不显著。强光下栽培黄花蒿主要通过提高Vcmax和Jmax等来增强光合能力,强的光合能力有利于黄花蒿的生长,因此在人工栽培黄花蒿的过程中应选择阳光充足的开阔生境。     

Red Light-Dependent CO(2) Uptake and Oxygen Evolution in Guard Cell Protoplasts of Vicia faba L.: Evidence for Photosynthetic CO(2) Fixation

Suspensions of dark-adapted guard cell protoplasts of Vicia faba L. alkalinized their medium in response to irradiation with red light. The alkalinization peaked within about 50 minutes and reached steady state shortly thereafter. Simultaneous measurements of O₂ concentrations and medium pH showed that oxygen evolved in parallel with the red light-induced alkalinization. When the protoplasts were returned to darkness, they acidified their medium and consumed oxygen. Both oxygen evolution and medium alkalinization were inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). In photosynthetically competent preparations, light-dependent medium alkalinization is diagnostic for photosynthetic carbon fixation, indicating that guard cell chloroplasts have that capacity. The striking contrast between the responses of guard cell protoplasts to red light, which induces alkalinization, and that to blue light, which activates proton extrusion, suggests that proton pumping and photosynthesis in guard cells are regulated by light quality.     

Photosynthetic CO(2) Fixation at Air Levels of CO(2) by Isolated Spinach Chloroplasts

A system has been developed for the study of photosynthetic CO₂ fixation by isolated spinach chloroplasts at air levels of CO₂. Rates of CO₂ fixation were typically 20 to 60 micromoles/milligrams chlorophyll per hour. The rate of fixation was linear for 10 minutes but then declined to less than 10% of the initial value by 40 minutes. Ribulose 1,5-bisphosphate (RuBP) levels remained unchanged during this period, indicating that they were not the cause for the decline. The initial activity of the RuBP carboxylase in the chloroplast was high for 8 to 10 minutes and then declined similar to the rate of CO₂ fixation, suggesting that the decline in CO₂ fixation may have been caused by deactivation of the enzyme.     

Stomatal Limitation to Carbon Gain in Paphiopedilum sp. (Orchidaceae) and Its Reversal by Blue Light

Leaves from Paphiopedilum sp. (Orchidaceae) having achlorophyllous stomata, show reduced levels of stomatal conductance when irradiated with red light, as compared with either the related, chlorophyllous genus Phragmipedium or with their response to blue light. These reduced levels of stomatal conductance, and the failure of isolated Paphiopedilum stomata to open under red irradiation indicates that the small stomatal response measured in the intact leaf under red light is indirect.

The overall low levels of stomatal conductance observed in Paphiopedilum leaves under most growing conditions and their capacity to increase stomatal conductance in response to blue light suggested that growth and carbon gain in Paphiopedilum could be enhanced in a blue light-enriched environment. To test that hypothesis, plants of Paphiopedilum acmodontum were grown in controlled growth chambers under daylight fluorescent light, with or without blue light supplementation. Total photosynthetic photon flux density was kept constant in both conditions. Blue light enrichment resulted in significantly higher growth rates—of up to 77%—over a 3 to 4 week growing period, with all evidence indicating that the blue light effect was a stomatal response. Manipulations of stomatal properties aimed at long-term carbon gains could have agronomic applications.

     

Photosynthetic Electron Transport in Plants of Sitka Spruce Subjected to Differing Light Environments during Growth

Seedlings of Picea sitchensis (Bong.) Carr. (Sitka spruce) have been grown in four different light regimes in growth chambers. Chloroplast fragments have been isolated from the needles and Photosystem I and Photosystem II activities measured. Measurements were made at eight photon flux densities giving light response curves for photosystem activity in needles grown in the four different light regimes. Chlorophyll concentration was higher in needles from the low cultivation light environments than in those from the high light environments. Photosystem activity was higher in needles from the high cultivation light environments. Evidence that Photosystem I was limiting photosynthesis in needles grown in the high light environments was obtained.     

Morphological and Physiological Responses of Hawaiian Hibiscus tiliaceus Populations to Light and Salinity

Hibiscus tiliaceus (Hau) is a pantropical mangrove associate that usually occurs in coastal ecosystems where substrate salinity is relatively high, but it also inhabits upland habitats in Hawaii. Cuttings from three populations on the island of Oahu, Hawaii, were collected and grown in the glasshouse under two levels of substrate salinity (0 and 335 mOsm kg-1) and three light treatments (0%, 50%, and 90% shade). Photosynthetic gas exchange, biomass allocation, and accumulation were studied in relation to salinity and light. Salinity reduced net CO2 assimilation in the upland population but had no effect or stimulated photosynthesis in the coastal populations, whereas increasing salinity decreased stomatal conductance in all populations and therefore increased water-use efficiency. The degree to which photosynthesis was inhibited by salinity was inversely proportional to the salinity of the source population, indicating a loss of salinity tolerance in upland plants. Light had a stronger effect on leaf area ratio (LAR) and leaf mass per area (LMA), whereas salinity had a stronger effect on leaf water content, internode length, and plant biomass. Salinity reduced total new biomass by 58%, 50%, and 34% in full sun, 50% shade, and 90% shade, respectively, but this response did not differ between populations. Salinity reduced the photosynthesis, but not growth, of upland plants because increased allocation to photosynthetic tissue increased LAR to compensate for inhibition of photosynthesis by salinity.     

Photosynthetic CO2 Uptake and Whole Plant Growth as Related to Plant Water Relations

Morphological features of arid region plant life forms are described and interpreted as adaptations to drought although this cannot be easily quantified. Functional adaptations, however, can be measured, and using the annual crop plant Vigna unguiculata (L.) Walp. responses to drought are described at the leaf and the whole plant level. In the first step of this analysis theoretical criteria are developed to define optimal water use. In the second step experimental data are used to test to what extent Vigna follows a theoretically optimal regulation of water and carbon relations. The analysis indicates that the ecological adaptation of regulatory processes may be quantified at a functional level.     

Induction of HCO(3) Transporting Capability and High Photosynthetic Affinity to Inorganic Carbon by Low Concentration of CO(2) in Anabaena variabilis

The apparent affinity of photosynthesis for inorganic carbon in Anabaena variabilis strain M-3 increased during the course of adaptation from high to low CO₂ concentration (5% and 0.03% v/v CO₂ in air, respectively). This was attributed to an increased ability of the cells to accumulate inorganic carbon during the course of adaptation to low CO₂ conditions. The release of phycobiliproteins was used to evaluate the sensitivity of the cells to lysozyme treatment followed by osmotic shock. High CO₂-grown cells were more sensitive to this treatment than were low CO₂ ones. The efflux of inorganic carbon from cells preloaded with radioactive bicarbonate is faster in high than it is in low CO₂-adapted cells. It is postulated that the cell wall or membrane components undergo changes during the course of adaptation to low CO₂ conditions. This is supported by electron micrographs showing differences in the cell wall appearance between high and low CO₂-grown cells. The increasing ability to accumulate HCO₃⁻ and the lessened sensitivity to lysozyme during adaptation to low CO₂ conditions depends on protein synthesis. The increase in affinity for inorganic carbon during the adaptation to low CO₂ conditions is severely inhibited by the presence of spectinomycin. Incubation in the light significantly lessens the time required for the adaptation to low CO₂ conditions.     

Limitation of Photosynthesis by Carbon Metabolism : II. O(2)-Insensitive CO(2) Uptake Results from Limitation Of Triose Phosphate Utilization

The occurrence of O₂-insensitive photosynthesis at high quantum flux and moderate temperature in Spinacia oleracea was characterized by analytical gas exchange measurements on intact leaves. In addition photosynthetic metabolite pools were measured in leaves which had been rapidly frozen under defined gas conditions. Upon switching to low O₂ in O₂-insensitive conditions the ATP/ADP ratio fell dramatically within one minute. The P-glycerate pool increased over the same time. Ribulose bisphosphate initially declined, then increased and exceeded the pool size measured in air. The pools of hexose monophosphates and UDPglucose were higher at a partial pressure of O₂ of 21 millibars than at 210 millibars. These results are consistent with the hypothesis that the rate of sucrose synthesis limited the overall rate of assimilation under O₂-insensitive conditions.     

Enhancement of CO(2) Uptake in Avena Coleoptiles by Fusicoccin

When Avena coleoptile segments are immersed in a solution containing H¹⁴CO₃⁻, the appearance of label in the tissue is stimulated approximately 3-fold by fusicoccin application. This effect is rapid (1-2 minutes lag time), dependent upon respiratory energy, inhibited by carbonyl cyanide m-chlorophenylhydrazone, but not appreciably altered by cycloheximide treatment. A large percentage of the cellular radioactivity is found in the form of malate. Preliminary experiments indicate that CO₂, as opposed to HCO₃⁻, is the favored species of “CO₂” taken up by the segments. These results are consistent with the notion that CO₂, presumably by virtue of its fixation and conversion to malic acid, participates in the early events associated with fusicoccin-enhanced acidification of the cell wall region leading to the stimulation of cell extension growth.     

Responses of Photosynthetic Electron Transport in Stomatal Guard Cells and Mesophyll Cells in Intact Leaves to Light, CO2, and Humidity

High-resolution images of the chlorophyll fluorescence parameter Fq'/Fm' from attached leaves of commelina (Commelina communis) and tradescantia (Tradescantia albiflora) were used to compare the responses of photosynthetic electron transport in stomatal guard cell chloroplasts and underlying mesophyll cells to key environmental variables. Fq'/Fm' estimates the quantum efficiency of photosystem II photochemistry and provides a relative measure of the quantum efficiency of non-cyclic photosynthetic electron transport. Over a range of light intensities, values of Fq'/Fm' were 20% to 30% lower in guard cell chloroplasts than in mesophyll cells, and there was a close linear relationship between the values for the two cell types. The responses of Fq'/Fm' of guard and mesophyll cells to changes of CO2 and O2 concentration were very similar. There were similar reductions of Fq'/Fm' of guard and mesophyll cells over a wide range of CO2 concentrations when the ambient oxygen concentration was decreased from 21% to 2%, suggesting that both cell types have similar proportions of photosynthetic electron transport used by Rubisco activity. When stomata closed after a pulse of dry air, Fq'/Fm' of both guard cell and mesophyll showed the same response; with a marked decline when ambient CO2 was low, but no change when ambient CO2 was high. This indicates that photosynthetic electron transport in guard cell chloroplasts responds to internal, not ambient, CO2 concentration.     

Photosynthetic Carbon Metabolism in Photoautotrophic Cell Suspension Cultures Grown at Low and High CO(2)

Photosynthetic carbon metabolism was characterized in four photoautotrophic cell suspension cultures. There was no apparent difference between two soybean (Glycine max) and one cotton (Gossypium hirsutum) cell line which required 5% CO₂ for growth, and a unique cotton cell line that grows at ambient CO₂ (660 microliters per liter). Photosynthetic characteristics in all four lines were more like C₃ mesophyll leaf cells than the cell suspension cultures previously studied. The pattern of ¹⁴C-labeling reflected the high ratio of ribulosebisphosphate carboxylase to phosphoenolpyruvate carboxylase activity and showed that CO₂ fixation occurred primarily by the C₃ pathway. Photorespiration occurred at 330 microliters per liter CO₂, 21% O₂ as indicated by the synthesis of high levels of ¹⁴C-labeled glycine and serine in a pulse-chase experiment and by oxygen inhibition of CO₂ fixation. Short-term CO₂ fixation in the presence and absence of carbonic anhydrase showed CO₂, not HCO₃⁻, to be the main source of inorganic carbon taken up by the low CO₂-requiring cotton cells. The cells did not have a CO₂-concentrating mechanism as indicated by silicone oil centrifugation experiments. Carbonic anhydrase was absent in the low CO₂-requiring cotton cells, present in the high CO₂-requiring soybean cell lines, and absent in other high CO₂ cell lines examined. Thus, the presence of carbonic anhydrase is not an essential requirement for photoautotrophy in cell suspension cultures which grow at either high or low CO₂ concentrations.     

Responses to Light and Water Availability of Four Invasive Melastomataceae in the Hawaiian Islands

Plant invasion by Neotropical Melastomataceae is prominent in Hawaii. To understand life history traits of four successful invasive Melastomataceae, two shade-intolerant herbs (Arthrostema ciliatum and Tibouchina herbacea) and two shade-tolerant woody species (Clidemia hirta, a shrub, and Miconia calvescens, a tree) were subjected to three light levels and two watering regimes in a greenhouse. Plant height, leaf number and area, biomass allocation, relative growth rate (RGR), carbon assimilation (A), leaf nutrient content, leaf construction costs (CC), specific leaf mass (SLM), and leaf spectral properties were determined at the end of the experimental period. Plant size, total biomass, RGR, A, CC, and SLM decreased, whereas leaf light transmittance and leaf N increased under low light in all species. The effects of water stress were weaker than light-stress effects. Relative growth rate of herbs grown in sun and partial shade (0.046 and 0.033 g g-1 d-1, respectively) was higher than in the woody species (0.027 and 0.020 g g-1 d-1). Woody species allocated more biomass to leaf production than herbs, which allocated more biomass to stem production. Shade increased allocation of biomass to leaves, and water stress increased the root-shoot ratio in all species. Partial shade increased leaf area ratios more in the herbs (140%) than in woody species (68%). Miconia calvescens and C. hirta had higher leaf absorbance (92%) than both herbs (79%). Maximum A under all light treatments was similar in all species, and there was substantial acclimation to the different light levels. Leaf construction cost was higher in the apparently long-lived leaves of the woody species. Relative growth rate, carbon allocation, and SLM showed larger changes to light and water stress than A and related photosynthetic parameters. All species showed responses qualitatively similar to those of other tropical species including the high acclimation potential to light, but the herbs exhibited the largest quantitative responses. When compared with a large group of native species, the four melastomes appear to be better suited to capture and use light, which is consistent with their rapid spread in mesic and disturbed Hawaiian environments.     

CO(2)-Enhanced Yield and Foliar Deformation among Tomato Genotypes in Elevated CO(2) Environments

Yield increases observed among eight genotypes of tomato (Lycopersicon esculentum Mill.) grown at ambient CO₂ (about 350) or 1000 microliters per liter CO₂ were not due to carbon exchange rate increases. Yield varied among genotypes while carbon exchange rate did not. Yield increases were due to a change in partitioning from root to fruit. Tomatoes grown with CO₂ enrichment exhibited nonepinastic foliar deformation similar to nutrient deficiency symptoms. Foliar deformation varied among genotypes, increased throughout the season, and became most severe at elevated CO₂. Foliar deformation was positively related to fruit yield. Foliage from the lower canopy was sampled throughout the growing season and analysed for starch, K, P, Ca, Mg, Fe, and Mn concentrations. Foliar K and Mn concentrations were the only elements correlated with deformation severity. Foliar K decreased while deformation increased. In another study, foliage of half the plants of one genotype received foliar applications of 7 millimolar KH₂PO₄. Untreated foliage showed significantly greater deformation than treated foliage. Reduced foliar K concentration may cause CO₂-enhanced foliar deformation. Reduced K may occur following decreased nutrient uptake resulting from reduced root mass due to the change in partitioning from root to fruit.