Steduto P, Albrizio R, Giorio P, Sorrentino G
CIHEAM-IAMB, via Ceglie 9, 70010 Valenzano, Bari, Italy
Environ Exp Bot. 2000 Nov 1;44(3):243-255. doi: 10.1016/s0098-8472(00)00071-x.
Sunflower (Helianthus annuus) was grown in both open-field and outdoor potted conditions in Southern Italy, and irrigated with water having electrical conductivity ranging between 0.9 and 15.6 dS m(-1) obtained by different NaCl concentrations. The aim of the work was to study the leaf area and photosynthetic responses of sunflower to mild salt stress. The response curve (A/c(i)) of assimilation (A) to leaf internal CO(2) concentration (c(i)) was used to determine leaf gas-exchange parameters, in order to evaluate stomatal and non-stomatal limitations to photosynthesis in relation to salt stress. In the field, a reduction of 19% in leaf area expansion occurred, while no correlation was observed between Psi(l) and stomatal conductance to water vapour (g(sw)) ranging between 0.76 and 1.35 mol m(-2) s(-1). This result was also evident at a higher salinity level reached in the pot experiment where leaf osmotic potential (psi(s)) varied from -1.35 to -2.67 MPa as compared with the field experiment, where psi(s) ranged from -1.15 to -1.42 MPa. Considering the two experiments as a unique data set, the assimilation rate, the stomatal conductance to CO(2) (g(sc)) and the sensitivity of A to c(i) variation (g*) were not significantly influenced by salinity in the whole range of psi(s). As a consequence, the stomatal and non-stomatal limitations to photosynthesis were not affected by salt treatment, averaging around 20 and 80%, respectively. The variation in A (from 44 to 29 µmol m(-2) s(-1)) was paralleled by the variation in g(sc) (from 0.47 to 0.84 mol m(-2) s(-1)), with a remarkable constancy of both c(i) (200+/-12.5 µmol mol(-1)) and normalized water-use efficiency (5+/-0.7 µmol mmol(-1) kPa), showing the optimal behaviour of the plant processes. These findings indicate that, under mild salt stress, the same as observed under water deficit, sunflower controls assimilation mainly by modulating leaf area rather than by stomatal closure, and that non-stomatal limitation of photosynthesis was not affected at all by the level of salinity reached in this study.
向日葵（Helianthus annuus）在意大利南部的露天田地和室外盆栽条件下种植，并用通过不同NaCl浓度获得的电导率在0.9至15.6 dS m(-1)之间的水进行灌溉。这项工作的目的是研究向日葵对轻度盐胁迫的叶面积和光合响应。利用同化作用（A）对叶片内部CO₂浓度（c(i)）的响应曲线（A/c(i)）来确定叶片气体交换参数，以便评估与盐胁迫相关的光合作用的气孔和非气孔限制。在田间，叶面积扩展减少了19%，而在0.76至1.35 mol m(-2) s(-1)之间的叶水势（Ψ(l)）与气孔导度（g(sw)）之间未观察到相关性。在盆栽试验中达到的较高盐度水平下，这一结果也很明显，与田间试验中叶渗透势（ψ(s)）在-1.15至-1.42 MPa之间相比，盆栽试验中叶渗透势（ψ(s)）在-1.35至-2.67 MPa之间变化。将这两个试验视为一个独特的数据集，在整个ψ(s)范围内，同化速率、气孔导度（g(sc)）以及A对c(i)变化的敏感性（g*）均未受到盐度的显著影响。因此，光合作用的气孔和非气孔限制不受盐处理的影响，分别平均约为20%和80%。A的变化（从44至29 µmol m(-2) s(-1)）与g(sc)的变化（从0.47至0.84 mol m(-2) s(-1)）平行，c(i)（200±12.5 µmol mol(-1)）和归一化水分利用效率（5±0.7 µmol mmol(-1) kPa）均保持显著恒定，表明植物过程具有最佳表现。这些发现表明，在轻度盐胁迫下，与水分亏缺时观察到的情况相同，向日葵主要通过调节叶面积而非气孔关闭来控制同化作用，并且本研究中达到的盐度水平对光合作用的非气孔限制没有任何影响。
