Photosynthetic stimulation under long-term CO2 enrichment and fertilization is sustained across a closed Populus canopy profile (EUROFACE)

The long-term response of leaf photosynthesis to rising CO2 concentrations [CO2] depends on biochemical and morphological feedbacks. Additionally, responses to elevated [CO2] might depend on the nutrient availability and the light environment, affecting the net carbon uptake of a forest stand. After 6 yr of exposure to free-air CO2 enrichment (EUROFACE) during two rotation cycles (with fertilization during the second cycle), profiles of light, leaf characteristics and photosynthetic parameters were measured in the closed canopy of a poplar (Populus) short-rotation coppice. Net photosynthetic rate (A(growth)) was 49% higher in poplars grown in elevated [CO2], independently of the canopy position. Jmax significantly increased (15%), whereas leaf carboxylation capacity (Vcmax), leaf nitrogen (N(a)) and chlorophyll (Chl(a)) were unaffected in elevated [CO2]. Leaf mass per unit area (LMA) increased in the upper canopy. Fertilization created more leaves in the top of the crown. These results suggest that the photosynthetic stimulation by elevated [CO2] in a closed-canopy poplar coppice might be sustained in the long term. The absence of any down-regulation, given a sufficient sink capacity and nutrient availability, provides more carbon for growth and storage in this bioenergy plantation.     

柚树叶片CO2驯化的光合参数变化

柚树(Citrus grandis)幼树生长在砂和磋石的生长介质,每周供给0.05mmol P(正常P,P)和0．1mmol P(高磷,2P)的营养液．植株分别生长在空气CO2分压(约39Pa)和倍增CO2分压(81±5Pa)下45d,利用CI-301PS(CID,Inc)光合作用测定系统在较高光强(1150μmol·m^-2·s^-1)下测定叶片光合速率并得出的Pn-Pi关系曲线和在较高CO2分压(PCO2,56Pa)下得出Pn-PAR关系曲线计算有关光合参数。结果表明,大气CO2分压下2P植株最大光合速率较P植株高13．3％,倍增CO2分压下,无论P或2P植株最大光合速率较大气CO2分压下相应植株低,但在倍增CO2分压下2P植株较P植株高,且2P植株有较P植株高的表观量子产率和光能利用效率(P<0．05),但并不改变г^*、Rd和Rubisco羧化速率(Vc)和氧速率的比率(P>0．05)在大气CO2分压下2P植株的Vcmax和Jmax较P植株分别高83％和12．5％,在倍增CO2分压下2P植株的Vcmax和Jmax均较P植株高,柚树在高CO2驯化中改变叶N在Rubisco和捕光组分分配系数,但不改变叶N在光合电子传递链的分配系数,结果表明,增加P供给可以促进高CO2分压下光合碳循环中P的周转,提高倍增CO2分压下植株的光合速率,调节柚树叶片的CO2驯化的光合参数。     

空气NH3增高情况下不同形式氮源对荫香光合作用和氮利用的影响

 生长在供给NO-3 N、NH+4 N和NH4NO3 N氮源下的荫香（Cinnamomum burmanni）幼树暴露在增高空气NH3浓度下30 d。利用气体交换测定和氮分析研究了植株的光合作用、氮利用和氮在光合过程一些组分中的分配,根据Farquhar-von Caemmerer模式得出相关光合参数。结果表明在增高空气NH3下生长于NO-3 N的植株Rubisco最大羧化速率（Vcmax）和最大光合电子传递速率（Jmax）较正常空气下的高,但生长于NH+4 N和NH4NO3 N的植株则较正常空气下的低。无论生长于何种形式氮下的植株,在空气NH3增高下以单位叶面积为基准的叶氮含量（Na）显著增高（p<0.05）。在增高空气NH3下,生长于NO-3 N下的植株,其类囊体氮量（NT）、Rubisco氮（NR）和结合于光合电子传递链的氮（NE）的含量较正常空气下的增高（p<0.05）;而生长于NH+4 N和NH4NO3 N下的植株则较正常空气下的低。表明在空气NH3增高下生长于NO－3 N的植株能有效地利用氮合成光合过程必要的组份,而生长于NH+4 N和NH4NO－3 N的植株氮在NT、NR和NE的分配受到部分限制。在空气NH3增高下生长于NO－3 N和NH4NO3 N的植株,其以单位干重为基准的有机氮量较正常空气下的高,但生长于NH+4 N的植株则较正常空气下的低,此外在空气NH3增高下生长于NO－3 N的植株的可溶性蛋白氮较正常空气下增高,而生长在NH+4 N的植株亦见降低。结果表明空气NH3增高可能有利于NO－3 N下生长的荫香植株利用空气中的氮,促进叶片光合速率提高,而空气NH3增高能抑制NH+4 N或NH4NO3 N下生长的荫香植株光合作用和氮的利用和再分配。     

Senescence and hyperspectral reflectance of cotton leaves exposed to ultraviolet-B radiation and carbon dioxide

The objectives of this study were to determine the effects of UV-B radiation and atmospheric carbon dioxide concentrations ([CO(2)]) on leaf senescence of cotton by measuring leaf photosynthesis and chlorophyll content and to identify changes in leaf hyperspectral reflectance occurring due to senescence and UV-B radiation. Plants were grown in controlled-environment growth chambers at two [CO(2)] (360 and 720 micro mol mol(-1)) and three levels of UV-B radiation (0, 7.7 and 15.1 kJ m(-2) day(-1)). Photosynthesis, chlorophyll, carotenoids and phenolic compounds along with leaf hyperspectral reflectance were measured on three leaves aged 12, 21 and 30 days in each of the treatments. No interaction was detected between [CO(2)] and UV-B for any of the measured parameters. Significant interactions were observed between UV-B and leaf age for photosynthesis and stomatal conductance. Elevated [CO(2)] enhanced leaf photosynthesis by 32%. On exposure to 0, 7.7 and 15.1 kJ of UV-B, the photosynthetic rates of 30-day-old leaves compared with 12-day-old leaves were reduced by 52, 76 and 86%, respectively. Chlorophyll pigments were not affected by leaf age at UV-B radiation of 0 and 7.7 kJ, but UV-B of 15.1 kJ reduced the chlorophylls by 20, 60 and 80% in 12, 21 and 30-day-old leaves, respectively. The hyperspectral reflectance between 726 and 1142 nm showed interaction for UV-B radiation and leaf age. In cotton, leaf photosynthesis can be used as an indicator of leaf senescence, as it is more sensitive than photosynthetic pigments on exposure to UV-B radiation. This study revealed that, cotton leaves senesced early on exposure to UV-B radiation as indicated by leaf photosynthesis, and leaf hyperspectral reflectance can be used to detect changes caused by UV-B and leaf ageing.     

大气CO2浓度升高对香蕉光合作用及光合碳循环过程中叶氮分配的影响

生长在高CC2浓度(700±56μl     

Low stomatal and internal conductance to CO2 versus Rubisco deactivation as determinants of the photosynthetic decline of ageing evergreen leaves

A novel A-Ci curve (net CO2 assimilation rate of a leaf -An- as a function of its intercellular CO2 concentration -Ci) analysis method (Plant, Cell & Environment 27, 137-153, 2004) was used to estimate the CO2 transfer conductance (gi) and the maximal carboxylation (Vcmax) and electron transport (Jmax) potentials of ageing, non-senescing Pseudotsuga menziesii leaves in relation to their nitrogen (N) content and protein and pigment composition. Both gi and the stomatal conductance (gsc) of leaves were closely coupled to Vcmax, Jmax and An with all variables decreasing with increasing leaf age. Consequently, both Ci and Cc (chloroplastic CO2 concentration) remained largely conserved through successive growing seasons. The N content of leaves, as well as the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and other sodium dodecyl sulfate-soluble proteins, increased during the first three growing seasons, then stabilized or decreased only slightly afterwards. Thus, the age-related photosynthetic nitrogen use efficiency (PNUE) decline of leaves was not a consequence of decreased allocation of N towards Rubisco and other proteins involved in bioenergetics and light harvesting. Rather, loss of photosynthetic capacity was the result of the decreased activation state of Rubisco and proportional down-regulation of electron transport towards the photosynthetic carbon reduction (PCR) and photorespiratory (PCO) cycles in response to a reduction of CO2 supply to the chloroplasts' stroma. This study emphasizes the regulatory potential and homeostaticity of Cc- rather than photosynthetic metabolites or Ci- in relation to the commonly observed correlation between photosynthesis and gsc.     

Photosynthetic acclimation to elevated CO2 in a sunflower canopy

Sunflower canopies were grown in mesocosom gas exchange chambers at ambient and elevated CO2 concentrations (360 and 700 ppm) and leaf photosynthetic capacities measured at several depths within each canopy. Elevated [CO2] had little effect on whole-canopy photosynthetic capacity and total leaf area, but had marked effects on the distribution of photosynthetic capacity and leaf area within the canopy. Elevated [CO2] did not significantly reduce the photosynthetic capacities per unit leaf area of young leaves at the top of the canopy, but it did reduce the photosynthetic capacities of older leaves by as much as 40%. This effect was not dependent on the canopy light environment since elevated [CO2] also reduced the photosynthetic capacities of older leaves exposed to full sun on the south edge of the canopy. In addition to the effects on leaf photosynthetic capacity, elevated [CO2] shifted the distribution of leaf area within the canopy so that more leaf area was concentrated near the top of the canopy. This change resulted in as much as a 50% reduction in photon flux density in the upper portions of the elevated [CO2] canopy relative to the ambient [CO2] canopy, even though there was no significant difference in the total canopy leaf area. This reduction in PFD appeared to account for leaf carbohydrate contents that were actually lower for many of the shaded leaves in the elevated as opposed to the ambient [CO2] canopy. Photosynthetic capacities were not significantly correlated with any of the individual leaf carbohydrate contents. However, there was a strong negative correlation between photosynthetic capacity and the ratio of hexose sugars to sucrose, consistent with the hypothesis that sucrose cycling is a component of the biochemical signalling pathway controlling photosynthetic acclimation to elevated [CO2].     

空气 NH3增高和不同氮源供应下大叶相思叶片光合参数的变化

生长在空气 NH3增高下 45 d的 NOˉ3- N大叶相思植株 ,其光饱和光合速率较对照的植株高 ;而生长在空气 NH3增高下的 NH 4- N和 NH4 NO3- N的大叶相思 ,当光强在 70 0 μmol·m- 2 ·s- 1左右时 Pn 达到最大值 ,较对照植株的要高。而当光强 >70 0 μmol·m- 2·s- 1时 ,Pn 降低 ,且较生长在对照条件下的低。表明在空气 NH3增高下生长的 NH 4- N和 NH4 NO3- N植株 ,其净光合速率 Pn会受到强光抑制。空气 NH3增高并不明显改变光呼吸 ( Rd)和无光呼吸下的 CO2 补充点 (Γ* )。无论生长在何种氮源下的大叶相思 ,其最大Ru BP饱和羧化速率 ( Vcmax)和最大电子传递速率 ( Jmax)均较生长在对照植株的高 ( P<0 .0 5 ) ,其叶氮含量亦较高 ( P<0 .0 5 ) ,其碳氮比较对照的低。在空气 NH3增高下 ,无论何种氮源生长的大叶相思 ,其 PR和 PB明显高于对照的植株 ,表明大叶相思能从空气 NH3中摄取和同化氮 ,增加氮积累和有利于 Rubisco和电子传递组分的合成 ,增高光合速率。空气 NH3增高可能有利于 Rubisco和电子传递组分的合成 ,在较低光强下能增高光合速率。空气 NH3增高可能有利于退化生态系统的生态恢复过程中的氮积累和先锋植物的早期生长。     

Effect of fruit load and girdling on leaf photosynthesis in Mangifera indica L

Leaf nitrogen concentration (Nm), mass-to-area ratio, amount of nitrogen per unit leaf area (Na), non-structural carbohydrate concentration (TNCa), maximal rate of carboxylation (Vcmax), light-saturated rate of photosynthetic electron transport (Jmax), dark respiration (Rd), net photosynthetic assimilation (Anet), quantum yield of photosystem II (PhiPSII), and intercellular CO2 concentration (Ci) were measured in Mangifera indica L. leaves on three types of fruit-bearing branches (non-girdled, NG; girdled with high (HFL) and low (LFL) fruit load), experiencing similar light exposure. TNCa, Vcmax/Na, Jmax/Na, Rd/Na, Ci, and the initial quantum yield of photosynthetic electron transport (alpha) were similar in both HFL and NG treatments, but Nm, Na, and photosynthetic capacity parameters (Vcmax and Jmax) were lower in the HFL than in the NG treatment. The strong depressing effect of girdling on leaf nitrogen concentration cannot therefore be attributed to a change in TNCa. By contrast, Na and TNCa were lower and higher, respectively, in the LFL than in the HFL treatment, suggesting that carbohydrate content may become the driving force behind photosynthetic acclimation to changing source-sink relationships, like the ones resulting from the presence of developing fruits. Vcmax/Na and Jmax/Na were lower in the LFL than in the HFL treatment, while Rd/Na, Ci, and alpha were not affected by fruit load. It is concluded that girdling and high fruit load affect photosynthesis permanently by decreasing and increasing, respectively, leaf nitrogen concentration. Fruit load, moreover, may have an additional effect on photosynthetic capacity by affecting the relationship between Vcmax and Jmax, and Na.     

Acclimation of peanut (Arachis hypogaea L.) leaf photosynthesis to elevated growth CO2 and temperature

Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO₂ concentrations ([CO₂]) of 360 μmol mol⁻¹ (ambient) and 720 μmol mol⁻¹ (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO₂] and temperature, and to assess whether elevated [CO₂] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO₂] had higher midday photosynthetic CO₂ exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO₂]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO₂]. Declines in Rubisco under elevated growth [CO₂] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO₂], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO₂] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO₂] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO₂] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO₂]. Under elevated [CO₂], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO₂] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO₂]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO₂] and temperature as predicted for this century.     

Elevated CO(2) induces biochemical and ultrastructural changes in leaves of the C(4) cereal sorghum

We analyzed the impact of growth at either 350 (ambient) or 700 (elevated) microL L(-1) CO(2) on key elements of the C(4) pathway (photosynthesis, carbon isotope discrimination, and leaf anatomy) using the C(4) cereal sorghum (Sorghum bicolor L. Moench.). Gas-exchange analysis of the CO(2) response of photosynthesis indicated that both carboxylation efficiency and the CO(2) saturated rate of photosynthesis were lower in plants grown at elevated relative to ambient CO(2). This was accompanied by a 49% reduction in the phosphoenolpyruvate carboxylase content of leaves (area basis) in the elevated CO(2)-grown plants, but no change in Rubisco content. Despite the lower phosphoenolpyruvate carboxylase content, there was a 3-fold increase in C isotope discrimination in leaves of plants grown at elevated CO(2) and bundle sheath leakiness was estimated to be 24% and 33%, respectively, for the ambient and elevated CO(2)-grown plants. However, we could detect no difference in quantum yield. The ratio of quantum yield of CO(2) fixation to PSII efficiency was lower in plants grown at elevated CO(2), but only when leaf internal was below 50 microL L(-1). This suggests a reduction in the efficiency of the C(4) cycle when [CO(2)] is low, and also implies increased electron transport to acceptors other than CO(2). Analysis of leaf sections using a transmission electron microscope indicated a 2-fold decrease in the thickness of the bundle sheath cell walls in plants grown at elevated relative to ambient CO(2). These results suggest that significant acclimation to increased CO(2) concentrations occurs in sorghum.     

Growth at elevated CO(2) delays the adverse effects of drought stress on leaf photosynthesis of the C(4) sugarcane

Sugarcane (Saccharum officinarum L. cv. CP72-2086) was grown in sunlit greenhouses at daytime [CO(2)] of 360 (ambient) and 720 (elevated)mumolmol(-1). Drought stress was imposed for 13d when plants were 4 months old, and various photosynthetic parameters and levels of nonstructural carbohydrates were determined for uppermost fully expanded leaves of well-watered (control) and drought stress plants. Control plants at elevated [CO(2)] were 34% and 25% lower in leaf stomatal conductance (g(s)) and transpiration rate (E) and 35% greater in leaf water-use efficiency (WUE) than their counterparts at ambient [CO(2)]. Leaf CO(2) exchange rate (CER) and activities of Rubisco, NADP-malate dehydrogenase, NADP-malic enzyme and pyruvate P(i) dikinase were marginally affected by elevated [CO(2)], but were reduced by drought, whereas activity of PEP carboxylase was reduced by elevated [CO(2)], but not by drought. At severe drought developed at day 12, leaf g(s) and WUE of ambient-[CO(2)] stress plants declined to 5% and 7%, while elevated-[CO(2)] stress plants still maintained g(s) and WUE at 20% and 74% of their controls. In control plants, elevated [CO(2)] did not enhance the midday levels of starch, sucrose, or reducing sugars. For both ambient- and elevated-[CO(2)] stress plants, severe drought did not affect the midday level of sucrose but substantially reduced that of starch. Nighttime starch decomposition in control plants was 55% for ambient [CO(2)] and 59% for elevated [CO(2)], but was negligible for stress plants of both [CO(2)] treatments. For both ambient-[CO(2)] control and stress plants, midday sucrose level at day 12 was similar to the predawn value at day 13. In contrast, sucrose levels of elevated-[CO(2)] control and stress plants at predawn of day 13 were 61-65% of the midday values of day 12. Levels of reducing sugars were much greater for both ambient- and elevated-[CO(2)] stress plants, implying an adaptation to drought stress. Sugarcane grown at elevated [CO(2)] had lower leaf g(s) and E and greater leaf WUE, which helped to delay the adverse effects of drought and, thus, allowed the stress plants to continue photosynthesis for at least an extra day during episodic drought cycles.     

Effects of Rubisco kinetics and Rubisco activation state on the temperature dependence of the photosynthetic rate in spinach leaves from contrasting growth temperatures

Recently, several studies reported that the optimum temperature for the initial slope [IS(Ci)] of the light-saturated photosynthetic rate (A) versus intercellular CO2 concentration (Ci) curve changed, depending on the growth temperature. However, few studies compare IS(Ci) with ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) properties. Here, we assessed Rubisco activation state and in vitro Rubisco kinetics, the main determinants of IS(Ci), in spinach leaves grown at 30/25 [high temperature (HT)] and 15/10 degrees C [low temperature (LT)]. We measured Rubisco activation state and A at a CO2 concentration of 360 microL L(-1) (A360) at various temperatures. In both HT and LT leaves, the Rubisco activation state decreased with increasing temperatures above the optimum temperatures for A360, while the activation state remained high at lower temperatures. To compare Rubisco characteristics, temperature dependences of the maximum rate of ribulose 1,5-bisphosphate (RuBP) carboxylation (Vcmax), specificity factor (Sc/o) and thermal stability were examined. We also examined Vcmax, and thermal stability in the leaves that were transferred from HT to LT conditions and were subsequently kept under LT conditions for 2 weeks (HL). Rubisco purified from HT, LT and HL leaves are called HT, LT and HL Rubisco, respectively. Thermal stabilities of LT and HL Rubisco were similar and lower than that of HT Rubisco. Both Vcmax and Sc/o in LT Rubisco were higher than those of HT Rubisco at low temperatures, while these were lower at high temperatures. Vcmax in HL Rubisco were similar to those of LT Rubisco at low temperatures, and to those of HT Rubisco at high temperatures. The predicted photosynthetic rates, taking account of the Rubisco kinetics and the Rubisco activation state, agreed well with A360 in both HT and LT leaves. This study suggests that photosynthetic performance is largely determined by the Rubisco kinetics at low temperature and by Rubisco Kinetics and the Rubisco activation state at high temperature.     

Leaf expansion and development of PHOTOSYNTHETIC CAPACITY AND PIGMENTS IN Liquidambar styraciflua (Hamamelidaceae)—EFFECTS OF UV-B RADIATION

In order to perform their functions as photosynthetic organs, leaves must cope with excess heat and potentially damaging ultraviolet radiation. Possible increases in the UV-B portion of the solar spectrum may place an additional burden on leaves, and this could be particularly important for young expanding leaves with poorly developed UV-B defense mechanisms. We evaluated the effects of supplemental UV-B radiation on leaf expansion and the development of photosynthetic capacity and pigments in sweetgum (Liquidambar styraciflua L.) seedlings. Seedlings were grown in the field under either ambient or ambient plus 3 or 5.0 kJ of biologically effective supplemental UV-B radiation. Although final leaf size was unaffected, the rate of leaf elongation and accumulation of leaf area was slower in leaves exposed to the lower supplemental UV-B irradiance. In contrast, chlorophyll accumulation and the development of photosynthetic capacity was more rapid in plants exposed to the higher, compared to the lower supplemental UV-B irradiance. The accumulation of anthocyanins and other putative flavonoids or UV-absorbing compounds was scarcely affected by exposure to supplemental UV-B radiation. These results suggest that the UV-B portion of the solar spectrum may, in the absence of gross affects on biomass, exert subtle influences on leaf ontogeny and the development of photosynthetic pigments and capacity in sweetgum.     

Combined effects of chronic ozone and elevated CO2 on Rubisco activity and leaf components in soybean Glycine max

Content and activity of Rubisco and concentrations of leaf nitrogen, chlorophyll and total non-structural carbohydrates (TNC) were determined at regular intervals during the 1993 and 1994 growing seasons to understand the effects and interactions of [O3] and elevated [CO2] on biochemical limitations to photosynthesis during ontogeny. Soybean (Glycine max var. Essex) was grown in open-top field chambers in either charcoal-filtered air (CF, 20 nmol mol^-1) or non-filtered air supplemented with 1.5 x ambient [O3] (c. 80 nmol mol^-1) at ambient (AA, 360 mol mol^-1) or elevated [CO2] (700 mol mol^-1). Sampling period significantly affected all the variables examined. Changes included a decrease in the activity and content of Rubisco during seed maturation, and increased nitrogen (N), leaf mass per unit area (LMA) and total non-structural carbohydrates (TNC, including starch and sucrose) through the reproductive phases. Ontogenetic changes were most rapid in O2-treated plants. At ambient [CO2], O3 decreased initial activity (14-64% per unit leaf area and 14-29% per unit Rubisco) and content of Rubisco (9-53%), and N content per unit leaf area. Ozone decreased LMA by 17-28% of plants in CF-AA at the end of the growing season because of a 24-41% decrease in starch and a 59-80% decrease in sucrose. In general, elevated CO2], in CF or O3-fumigated air, reduced the initial activity of Rubisco and activation state while having little effect on Rubisco content, N and the chlorophyll content, per unit leaf area. Elevated CO2 decreased Rubisco activity by 14-34% per unit leaf area and 15-25% per unit Rubisco content of plants in grown CF-AA, nd increases LMA by 27-74% of the leaf mass per unit area in CF-AA because of a 23-148% increase in starch. However, the data suggest that, at elevated [CO2], increases in starch and sucrose are not directly responsible for the deactivation of Rubisco. Also, there was little evidence of an adjustment of Rubisco activity in response to starch and sucrose metabolism. Significant interactions between elevated [CO2] and [O3] on all variables examined generally resulted in alleviation or amelioration of the O3 effects at elevated CO2. These data provide further support to the idea that elevated atmospheric CO2 will reduce or prevent damage from pollutant O3.     

Photosynthetic Acclimation to Elevated CO2 Occurs in Transformed Tobacco with Decreased Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content

Inhibition of net carbon assimilation rates during growth at elevated CO2 was studied in transgenic tobacco (Nicotiana tabacum L.) plants containing zero to two copies of antisense DNA sequences to the small subunit polypeptide (rbcS) gene of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). High- and low-Rubisco tobacco plants were obtained from the selfed progeny of the original line 3 transformant (S.R. Rodermel, M.S. Abbott, L. Bogorad [1988] Cell 55: 673-681). Assimilation rates of high- and low-Rubisco tobacco plants increased 22 and 71%, respectively, when transferred from 35- to 70-Pa CO2 chamber air at 900 [mu]mol m-2 s-1 photon flux density. However, CO2-dependent increases of net carbon assimilation rates of high- and low-Rubisco plants virtually disappeared after 9 d of growth in elevated CO2 chamber air. Total above-ground dry matter production of high- and low-Rubisco plants was 28 and 53% greater, respectively, after 9 d of growth at 70 Pa compared with 35 Pa CO2. Most of this dry weight gain was due to increased specific leaf weight. Rubisco activity, Rubisco protein, and total chlorophyll were lower in both high- and low-Rubisco plants grown in enriched compared with ambient CO2 chamber air. Soluble leaf protein also decreased in response to CO2 enrichment in high- but not in low-Rubisco tobacco plants. Decreased Rubisco activities in CO2-adapted high- and low-Rubisco plants were not attributable to changes in activation state of the enzyme. Carbonic anhydrase activities and subunit levels measured with specific antibodies were similar in high- and low-Rubisco tobacco plants and were unchanged by CO2 enrichment. Collectively, these findings suggested that photosynthetic acclimation to enriched CO2 occurred in tobacco plants either with or without transgenically decreased Rubisco levels and also indicated that the down-regulation of Rubisco in CO2-adapted tobacco plants was related to decreased specific activity of this enzyme.     

Does ear C sink strength contribute to overcoming photosynthetic acclimation of wheat plants exposed to elevated CO2?

Wheat plants (Triticum durum Desf., cv. Regallo) were grown in the field to study the effects of contrasting [CO(2)] conditions (700 versus 370 μmol mol(-1)) on growth, photosynthetic performance, and C management during the post-anthesis period. The aim was to test whether a restricted capacity of sink organs to utilize photosynthates drives a loss of photosynthetic capacity in elevated CO(2). The ambient (13)C/(12)C isotopic composition (δ(13)C) of air CO(2) was changed from -10.2‰ in ambient [CO(2)] to -23.6‰ under elevated [CO(2)] between the 7th and the 14th days after anthesis in order to study C assimilation and partitioning between leaves and ears. Elevated [CO(2)] had no significant effect on biomass production and grain filling, and caused an accumulation of C compounds in leaves. This was accompanied by up-regulation of phosphoglycerate mutase and ATP synthase protein content, together with down-regulation of adenosine diphosphate glucose pyrophosphatase protein. Growth in elevated [CO(2)] negatively affected Rubisco and Rubisco activase protein content and induced photosynthetic down-regulation. CO(2) enrichment caused a specific decrease in Rubisco content, together with decreases in the amino acid and total N content of leaves. The C labelling revealed that in flag leaves, part of the C fixed during grain filling was stored as starch and structural C compounds whereas the rest of the labelled C (mainly in the form of soluble sugars) was completely respired 48 h after the end of labelling. Although labelled C was not detected in the δ(13)C of ear total organic matter and respired CO(2), soluble sugar δ(13)C revealed that a small amount of labelled C reached the ear. The (12)CO(2) labelling suggests that during the beginning of post-anthesis the ear did not contribute towards overcoming flag leaf carbohydrate accumulation, and this had a consequent effect on protein expression and photosynthetic acclimation.     

CO_2加富对UV-B辐射胁迫下亚心形扁藻光合作用和膜脂过氧化以及抗氧化酶活性的影响(英文)

在CO2浓度分别为当今CO2浓度(360 mL/L)和加富浓度(5 000 mL/L)条件下,研究了UV-B胁迫对亚心形扁藻(Platymonas subcordiformis (Wille) Hazen)的光合作用、膜脂过氧化和抗氧化酶活性的影响。实验结果表明:(1) UV-B单独作用下,亚心形扁藻的干重、光合速率、叶绿素a (Chl a)和类胡萝卜素(Car.)含量显著降低,CO2加富单独作用下,亚心形扁藻的干重和光合速率显著升高,叶绿素a和类胡萝卜素含量与对照相比没有显著变化,而UV-B与CO2共同作用则使亚心形扁藻的干重和光合速率与对照相比没有显著变化,叶绿素a和类胡萝卜素含量显著降低。(2) UV-B单独作用和CO2加富单独作用都使可溶性蛋白含量显著降低,UV-B与CO2共同作用下的可溶性蛋白含量比UV-B单独作用的要高。高CO2对藻的可溶性蛋白含量的变化在很大程度上归因于Rubisco蛋白的降低。(3)UV-B单独作用下,O2-. 产生速率、H2O2 含量和MDA含量显著升高,而CO2加富单独作用下,O2-. 产生速率、H2O2 含量和MDA含量显著降低,与UV-B单独作用相比,UV-B与CO2共同作用使O2-. 产生速率、H2O2 含量和MDA含量显著降低。说明CO2加富可以减少活性氧对亚心形扁藻的氧化胁迫,同时减少UV-B对亚心形扁藻的膜脂过氧化伤害。(4) UV-B单独作用下,SOD、POD、CAT、GR和GPX活性显著升高,高CO2     

Growth in Elevated CO2 Can Both Increase and Decrease Photochemistry and Photoinhibition of Photosynthesis in a Predictable Manner. Dactylis glomerata Grown in Two Levels of Nitrogen Nutrition

Biochemically based models of C(3) photosynthesis can be used to predict that when photosynthesis is limited by the amount of Rubisco, increasing atmospheric CO(2) partial pressure (pCO(2)) will increase light-saturated linear electron flow through photosystem II (J(t)). This is because the stimulation of electron flow to the photosynthetic carbon reduction cycle (J(c)) will be greater than the competitive suppression of electron flow to the photorespiratory carbon oxidation cycle (J(o)). Where elevated pCO(2) increases J(t), then the ratio of absorbed energy dissipated photochemically to that dissipated non-photochemically will rise. These predictions were tested on Dactylis glomerata grown in fully controlled environments, at either ambient (35 Pa) or elevated (65 Pa) pCO(2), and at two levels of nitrogen nutrition. As was predicted, for D. glomerata grown in high nitrogen, J(t) was significantly higher in plants grown and measured at elevated pCO(2) than for plants grown and measured at ambient pCO(2). This was due to a significant increase in J(c) exceeding any suppression of J(o). This increase in photochemistry at elevated pCO(2) protected against photoinhibition at high light. For plants grown at low nitrogen, J(t) was significantly lower in plants grown and measured at elevated pCO(2) than for plants grown and measured at ambient pCO(2). Elevated pCO(2) again suppressed J(o); however growth in elevated pCO(2) resulted in an acclimatory decrease in leaf Rubisco content that removed any stimulation of J(c). Consistent with decreased photochemistry, for leaves grown at low nitrogen, the recovery from a 3-h photoinhibitory treatment was slower at elevated pCO(2).