盐碱土条件下马蔺幼苗渗透调节物质和光合特性对干旱的响应

Responses of Osmotic Adjustment and Photosynthetic Characteristics to Drought for Seedlings of Iris lactea Pall. var chinensis koidz Grown in Saline and Alkaline Soil

以马蔺(耐盐碱和抗干旱的植物)为材料,在盐碱化土壤的条件下进行干旱处理,研究了马蔺抗旱的渗透调节和光合特性。结果表明:12 d干旱处理,马蔺叶片的水势(Ψw)、渗透势(Ψs)和相对含水量(RWC)分别从-0.61 MPa,-1.21 MPa和90%降低到-2.52 MPa,-2.53 MPa和76%。在干旱期间,可溶性糖和脯氨酸含量明显增加,淀粉含量降低,说明渗透调节物质提高了马蔺的抗旱性。干旱6 d,光合速率(Pn)和气孔导度(Gs)下降,细胞间隙CO2浓度(Ci)下降,而气孔限制值(Ls)升高,说明盐碱化土壤上马蔺Pn的降低主要是气孔因素;干旱6 d后,Ci升高,Ls下降,说明Pn的降低主要是非气孔因素。干旱期间,叶片PS最大光化学效率(Fv/Fm)变化不大,说明干旱情况下光合效率没有受到影响。复水后,Ψw和RWC恢复到对照水平,但Ψs仍然保持较低的水平,说明渗透调节物质起着非常重要的作用。据此,马蔺在盐碱化土壤上具有较强的渗透调节能力,使叶片的保水能力增强,维持了净光合速率和PS光化学活性,具有较强的抗旱性,是盐碱化土壤地区植被恢复可供选择的抗旱性植物。

Osmotic adjustment and photosynthetic characteristics were investigated using seedlings of Iris lactea Pall. var chinensis koidz grown in salt and alkali soil during single water stress cycles. This species is tolerant of drought and alkaline salt conditions. In this experiment, during a 12 d drying cycle, leaf water potential（ Ψw ）, osmotic potential（ Ψs ） and relative water content （RWC） in droughted plants declined from -0. 61 MPa, -1.21 MPa and 90% to -2.52 MPa,-2.53 MPa, 76%, respectively. Within 6 d drought, net photosynthetic rate （Pn）, stomatal conductance （Gs）and intercellular CO2 concentration （Ci）decreased, stomatal limitation （Ls） increased, thus indicating that the decrease in Pn during drought was probably due to stomatal closure rather than non-stomatal limitations. After 6 d drought, Ci decreased and Ls increased, thus indicating that the decrease in Pn was probably due to non-stomatal limitations. Maximal PSII photochemistry in dark-adapted leaves （Fv/Fm） was unchanged under water stress, suggesting that photosynthetic efficiency was not affected by drought. During drought stress, changes in sugar metabolism were associated with significant increases in concentrations of soluble sugars and proline, suggesting that altered solute partitioning may be an important factor in the drought tolerance of Iris lactea Pall. var chinensis koidz. After rewatering at 12 d, Ψw and RWC recovered fully, but Ψs remained depressed relative to control values, indicating that osmolytes played an important role in osmotic adjustment during the drought cycle in salt-alkali soil. These findings indicate that Iris lactea Pall. var chinensis koidz, resists to drought in salt-alkali soil by increasing the capacity of osmotic adjustment to maintain Pn and Fv/Fm. This plant species could be selected for vegetation restoration in salt-alkali soil under drought conditions.