Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (PN) in six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), PN, stomatal conductance (gs), and the ratio intercellular/ambient. CO2 concentration (Ci/Ca) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water. Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher PN than the others at low water potential (Ψ). The ratios of PN/gs and Ci/Ca showed that differences in photosynthetic inhibition between genotypes at low Ψ were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Osmotic Drought Stress Induced by a Combination of NaCl and Polyethylene Glycol on Leaf Water Status,Photosynthetic Gas Exchange,and Water Use Efficiency of Pistacia khinjuk and P. mutica

Leaf water potential, leaf osmotic potential, chlorophyll a and b contents, stomatal conductance, net photosynthetic rate, and water use efficiency were determined in two pistachio species (Pistacia khinjuk L. and P. mutica L.) grown under osmotic drought stress induced by a combination of NaCl and polyethylene glycol 6000. A decrease in values for all mentioned variables was observed as the osmotic potential of the nutrient solution (_s) decreased. The osmotic adjustment () of the species increased by decreasing _s. Thus P. khinjuk had a higher osmotic drought stress tolerance than P. mutica.     

Influence of Potassium Nutrition on Gas Exchange Characteristics and Water Relations in Cotton (Gossypium hirsutum L.)

The effects of potassium nutrition [0, 6.25, 12.50, 25.00 g(K) m^–2 of K₂SO₄ or KCl] on gas exchange characteristics and water relations in four cultivars (CIM-448, CIM-1100, Karishma, S-12) of cotton were assessed under an arid environment. Net photosynthetic rate (P _N) and transpiration rate (E) increased with increased K supply. The leaf pressure potential (_p) increased significantly by the addition of 25.00 g(K) m^–2 compared to zero K level. The water use efficiency (P _N/E) was improved by 24.6 % under the highest K dose compared to zero K. There were positive correlations (0.99^**, 0.98^**, 0.95^**, 0.97^**) between K-doses and P _N, E, _p, and P _N/E, respectively.     

土壤水分胁迫下沙漠葳的光合生理特征

以从美国西部引进的沙生灌木——沙漠葳（Chilopsis linearis）的2年生实生苗为材料,通过盆栽试验于7-9份进行轻度、中度和重度土壤水分胁迫处理并分析其光合生理响应特征.结果显示：（1）60 d中度或重度土壤水分胁迫使沙漠葳的净光合速率（Pn）、水分利用效率（WUE）和光补偿点（LCP）显著降低,暗呼吸速率（DRR）减弱,而气孔导度（Cs）增大,气孔限制值（Ls）变小.（2）Pn日变化在7月份的轻度和中度土壤水分胁迫下表现为双峰曲线,其余月份的胁迫处理均为单峰曲线,同期内各胁迫处理Pn峰值出现的时间基本相同,而且8月份各水分胁迫的Pn值显著高于其它月份;WUE的日变化趋势和Pn日变化相似,而且土壤水分胁迫越严重,其水分利用效率越低;各水分胁迫处理的Pn和Tr光响应拟合曲线均基本呈抛物线形或倒抛物线形.（3）在轻度和中度土壤水分胁迫的初期,Pn降低主要受气孔限制因素的影响,随着胁迫期的延长和胁迫的加重,Pn降低由气孔限制为主逐步转向以非气孔限制为主.研究表明,沙漠葳对干旱胁迫具有一定的适应能力,但长期中度或重度干旱胁迫都会影响沙漠葳的正常生长发育,使其光合生产力大大降低.     

Physiological significance of proline and glycinebetaine: Maintaining photosynthesis during NaCl stress in wheat

Experiments on the physiological significance of accumulation of proline and glycinebetaine (GB) in sustaining photosynthesis during salt stress in wheat in vivo showed that pre-treatment with GB, but not proline, alleviated NaCl-induced stomatal and non-stomatal inhibition of photosynthesis completely. A permeating and non-dissociating osmoticum, 3-orthomethyl-glucopyranose, also alleviated NaCl-induced perturbations of photosynthesis, suggesting that GB may work by maintaining chloroplast volume and not by specific effects on photosynthetic processes.     

Photosynthetic characteristics in Brassica carinata hybrids and their parents as influenced by moisture stress

The response of Brassica carinata hybrids and their parents to moisture stress at different growth stages was studied. B. carinata 226 was found to be susceptible to stress at pre-flowering and post-flowering stages while B. carinata 241 at flowering stage. Neither the changes in stomatal conductance nor in chlorophyll content could fully explain the reduction in net photosynthetic rate (P_N) induced by stress. B. carinata 241 had higher leaf water potential (ψ_w) although, it had lower P_N compared to B. carinata 226. Both the parents had lower P_N as well as leaf ψ_w. The stress response of PN in hybrids followed that in their respective female parents. This revised version was published online in July 2006 with corrections to the Cover Date.     

CO2增长对杉木中龄林针叶光合生理生态的影响

通过对１７ａ生杉木人工林小枝的活体测定,研究了大气ＣＯ２增长对杉木中龄林净光合、呼吸、气孔导度和水分利用效率等生理生态特性的影响。结果表明,在ＣＯ２浓度为４５μｍｏｌ／Ｌ左右时,杉木针叶净光合速率比正常大气ＣＯ２下提高１倍以卢,气孔导度和蒸速率有不同程度的降低,水分利用效率提高约１￣２倍;同时使光补偿点降低,饱和点和光抑制点提高,光量子效率提高４０％￣２９５％且阳酝 大于阴枝,针叶暗呼吸降低２０％     

CO_2增长对杉木中龄林针叶光合生理生态的影响

通过对 1 7a生杉木人工林小枝的活体测定 ,研究了大气 CO2 增长对杉木中龄林净光合、呼吸、气孔导度和水分利用效率等生理生态特性的影响。结果表明 ,在 CO2 浓度为 4 5μmol/ L左右时 ,杉木针叶净光合速率比正常大气 CO2 下提高 1倍以上 ,气孔导度和蒸腾速率有不同程度的降低 ,水分利用效率提高约 1～ 2倍 ;同时使光补偿点降低 ,饱和点和光抑制点提高 ,光量子效率提高 4 0 %～ 2 95%且阳枝大于阴枝 ,针叶暗呼吸降低 2 0 %～ 72 %。随着 CO2 浓度的增加 ,针叶净光合速率和水分利用效率呈线性上升 ,约到 4 5μmol/ L以后 ,增加速率减慢 ,但 CO2 饱和点可达 1 1 6μmol/ L以上。杉木针叶对CO2 增长的这种反应 ,对大气 CO2 不断增长的条件下杉木生长是有利的 ,但对其长期反应还有待进一步研究。     

两个品种转基因抗虫棉光合生理的CO2响应

栽培环境条件的改变会对转基因作物产生深远影响。以2种不同转基因棉花及其亲本对照为材料,研究了盆栽种植条件下不同棉花品种在蕾期和吐絮期光合生理特性CO2响应特征。结果表明,与各自的常规棉对照比较,两种转基因抗虫棉单叶净光合速率CO2响应的特征参数表观初始羧化效率(CE)、表观暗呼吸速率(Rd)和最大净光合速率(Pmax,c)虽有一定程度的变化,但其差异均未达到显著水平。在高CO2浓度范围内(700μmol.mol-1),转基因抗虫棉单叶净光合速率和水分利用率(WUE)的CO2响应曲线特征发生变化,且与品种及生育时期有关。两种转基因抗虫棉在不同生育时期的气孔导度(Gs)对CO2浓度的响应特征与其常规棉对照相似,短期CO2浓度增高对转基因抗虫棉的气孔导度没有显著性影响。     

Moderate water stress affects tomato leaf water relations in dependence on the nitrogen supply

The responses of water relations, stomatal conductance (g_s) and growth parameters of tomato (Lycopersicon esculentum Mill. cv. Royesta) plants to nitrogen fertilisation and drought were studied. The plants were subjected to a long-term, moderate and progressive water stress by adding 80 % of the water evapotranspirated by the plant the preceding day. Well-watered plants received 100 % of the water evapotranspirated. Two weeks before starting the drought period, the plants were fertilised with Hoagland’s solution with 14, 60 and 110 mM NO₃ ⁻ (N14, N60 and N110, respectively). Plants of the N110 treatment had the highest leaf area. However, g_s was higher for N60 plants and lower for N110 plants. At the end of the drought period, N60 plants showed the lowest values of water potential (Ψ_w) and osmotic potential (Ψ_s), and the highest values of pressure potential (Ψ_p). N60 plants showed the highest Ψ_s at maximum Ψ_p and the highest bulk modulus of elasticity.     

Blue light effects on rose photosynthesis and photomorphogenesis

Through its impact on photosynthesis and morphogenesis, light is the environmental factor that most affects plant architecture. Using light rather than chemicals to manage plant architecture could reduce the impact on the environment. However, the understanding of how light modulates plant architecture is still poor and further research is needed. To address this question, we examined the development of two rose cultivars, Rosa hybrida‘Radrazz’ and Rosa chinensis‘Old Blush’, cultivated under two light qualities. Plants were grown from one‐node cuttings for 6 weeks under white or blue light at equal photosynthetic efficiencies. While plant development was totally inhibited in darkness, blue light could sustain full development from bud burst until flowering. Blue light reduced the net CO₂ assimilation rate of fully expanded leaves in both cultivars, despite increasing stomatal conductance and intercellular CO₂ concentrations. In ‘Radrazz’, the reduction in CO₂ assimilation under blue light was related to a decrease in photosynthetic pigment content, while in both cultivars, the chl a/b ratio increased. Surprisingly, blue light could induce the same organogenetic activity of the shoot apical meristem, growth of the metamers and flower development as white light. The normal development of rose plants under blue light reveals the strong adaptive properties of rose plants to their light environment. It also indicates that photomorphogenetic processes can all be triggered by blue wavelengths and that despite a lower assimilation rate, blue light can provide sufficient energy via photosynthesis to sustain normal growth and development in roses.     

Effects of Drought Stress Induced by Polyethylene Glycol on Pigment Content and Photosynthetic Gas Exchange of Pistacia Khinjuk and P. Mutica

The effects of drought stress induced by polyethylene glycol, PEG (molecular mass 6000) on some ecophysiological characteristics of two wild pistachio species, Mastic and Khinjuk (P. mutica and P. khinjuk) selected as root stocks for production of edible pistachio trees (P. vera) in Iran and Turkey, were studied. Net photosynthetic rate (P _N), stomatal conductance (g _s), chlorophyll (Chl) fluorescence parameters, leaf water potential (Ψ₁), leaf osmotic potential (Ψ_π), leaf osmotic adjustment (ΔΨ_π), and Chl a and b were measured. All parameters were influenced by increase in concentra-tion of PEG in the nutrient solutions. P _N, g _s, and Chl a were significantly higher in P. mutica than in P. khinjuk but, compared to the control treatment, P. khinjuk showed a higher resistance to drought stress than P. mutica. This revised version was published online in August 2006 with corrections to the Cover Date.     

Salinity effects on CO2 assimilation and diffusive conductance of cowpea leaves

The effect of NaCl salinity at concentrations of 43–173 mM in nutrient solution on net gas exchange of attached cowpea [Vigna unguiculata (L.) Walp cv. California Black-eye No. 5 (CB5)] leaves was investigated under both greenhouse and growth chamber conditions.
There was a marked decrease in leaf conductance to water vapor after exposure to low salinity levels and a slighter decrease when salinity levels were higher. The decrease in net assimilation was much more gradual throughout the entire salinity range. The altered responses of net assimilation and leaf conductance to salinity were more evident at a high light intensity. A decrease in intercellular partial CO₂ pressure [p(CO₂)] was found at the low and intermediate salinity levels but not at the high level. These findings suggest that CO, assimilation was mainly controlled by stomatal conductance and the fixation of CO, might have been increased due to stimulated biochemical activity or to higher chlorophyll concentration per unit leaf area. A decrease in assimilation was already found one day after salinization and pro-ceeded up to 4 days when it was inhibited by 50% at 43 mM NaCl and up to 85% at 173 mM. The decrease in transpiration was larger than the decrease in net assimila-tion, and both were attributed to osmotic stress. Partial recovery was found thereaf-ter and new steady-state rates, in the range of 55 to 100% of the control, were then obtained for salinity levels between 43 and 130 mM. Inhibition of net CO, assimila-tion at this stage was attributed partly to a specific sodium effect and partly to plant water status. A linear relationship between leaf sodium content and net photosynthe-sis was also evident at this stage. Net CO, assimilation recovered more completely than transpiration when salt stress was removed, but at 173 mM NaCl recovery was neglible.     

植物气孔导度对CO2响应模型的构建

构建一个普适性的植物叶片气孔导度(g_s)对CO₂浓度响应(g_s-C_a)的模型, 对定量研究植物叶片g_s对CO₂浓度的响应变化尤为必要。该研究运用便携式光合仪(LI-6400)测量了大豆(Glycine max)和小麦(Triticum aestivum)光合作用对CO₂的响应曲线(A_n-C_a), 在比较传统的Michaelis-Menten模型(M-M模型)和叶子飘构建的CO₂响应模型拟合大豆和小麦A_n-C_a效果的基础上, 构建了g_s-C_a响应新模型。然后用新构建的模型拟合大豆和小麦的g_s-C_a曲线, 并将拟合结果与传统模型的拟合结果, 以及与其对应的观测数据进行比较, 以判断所构建模型是否合理。结果显示: 叶子飘构建的A_n-C_a模型可较好地拟合大豆和小麦的A_n-C_a曲线, 确定系数(R²)均高达0.999。M-M模型拟合大豆和小麦的A_n-C_a曲线时的R²虽然也较高, 但在较高CO₂浓度时的拟合曲线偏离观测曲线。因此, 基于叶子飘的A_n-C_a模型构建g_s-C_a模型更为可行。新构建的g_s-C_a模型可较好地拟合大豆和小麦的g_s-C_a曲线, R²分别为0.995和0.994, 而且还可以直接给出最大气孔导度(g_s-max)、最小气孔导度(g_s-min), 以及与g_s-min相对应的CO₂浓度值(C_s-min)。拟合得到大豆和小麦的g_s-max分别为0.686和0.481 mol·m^-2·s^-1, 与其对应的观测值(分别为0.666和0.471 mol·m^-2·s^-1)之间均不存在显著差异; 同样, 拟合得到的大豆和小麦的g_s-min分别为0.271和0.297 mol·m^-2·s^-1, 与其对应的观测值(分别为0.279和0.293 mol·m^-2·s^-1)之间也均不存在显著差异; 此外, 新构建的g_s-C_a模型给出大豆和小麦的C_s-min值分别为741.45和1 112.43 μmol·mol ^-1, 与其对应的观测值(732.78和1 200.34 μmol·mol ^-1)也不存在显著差异。由此可见, 该研究新构建的g_s-C_a模型可作为定量研究植物叶片气孔导度对CO₂浓度变化的有效数学工具。