黑麦草幼苗对NaCl和NaHCO_3胁迫的光合响应差异

Difference in Photosynthetic Response of Ryegrass Seedling to NaCl and NaHCO_3 Stress

为了探讨牧草光合功能对盐、碱胁迫的响应差异,采用营养液砂培方法,分别研究了不同浓度(0、50、100、150、200mmol.L-1)NaCl和NaHCO3胁迫对黑麦草幼苗生长、叶片光合色素含量、气体交换和叶绿素荧光参数、叶绿体Hill反应活力和ATPase活性的影响。结果表明:①随着处理浓度的增加,黑麦草幼苗全株干重、叶片叶绿素和类胡萝卜素含量、净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)明显下降。当NaCl浓度小于100mmol.L-1时,胞间CO2浓度(Ci)显著降低,气孔限制值(Ls)明显增加,随着NaCl浓度进一步增大,Ci显著增加,Ls显著减小;NaHCO3胁迫下Ci随着处理浓度增大而显著增加,Ls则显著减小。但NaHCO3胁迫下各指标下降或增加的幅度大于NaCl胁迫。②随着NaCl和NaHCO3胁迫强度的增大,黑麦草幼苗荧光参数PSⅡ最大光化学效率(Fv/Fm)、实际光化学效率(ΦPSⅡ)、光化学淬灭(qP)及叶绿体Hill反应和ATPase活性明显下降,非光化学淬灭(NPQ)显著提高,叶片吸收的光能中用于光化学反应的比例(P)显著减小,天线热耗散的比例(D)显著增大。在相同浓度下,NaHCO3胁迫的各荧光参数及Hill反应和ATPase活性的变幅大于NaCl胁迫,说明NaHCO3胁迫对幼苗的伤害程度大于NaCl胁迫。由此表明,黑麦草对碱的耐性低于盐,这可能与碱的高pH值更多引起光合色素含量下降和光合机构受到严重伤害有关。

To explore the differences of photosynthetic responses of forage to saline stress and alkaline stress, ryegrass seedlings were exposed to Hoagland＇s nutrient solution at five NaC1 or NaHCO3 levels （0, 50, 100, 150, 200 mmol. L^-1）, and the effects of NaCl and NaHCO3 stress on plant growth, photosynthetic pigment content, gas exchange and chlorophyll fluorescence parameters, and the activities of Hill reaction and ATPase in chloroplast of ryegrass seedling leaves were investigated by a sandy culture in greenhouse. Results show： （1） With increase of NaCl and NaHCO3 concentration, the whole plant dry weight, the leaf chlorophyll and carotenoid contents, net photosynthetic rate （Pn）, stomatal conductance （Gs）, and transpiration rate （Tt） of the ryegrass seedlings decrease significantly. Intercellular CO2 concentration （Ci） decreases significantly and stomatal limited value （Ls） increases significantly with increasing of NaCl concentration when the NaCl concentration is below 100 mmol. L 1, and the Ci increases significantly and Ls decreases significantly with further increase of NaCI concentration. While the Ci increases significantly and L s decreases significantly with the increasing of NaHCO3 concentration. The decrements or increments of all the indexes under NaHCO3 stress were greater than under NaCI stress. （2） The PSII maximal photochemical efficiency （Fv/Fm）, actual photochemical efficiency （ФesⅡ）, photochemical quenching （qp）, and the activities of Hill reaction and ATPase in chloroplast of ryegrass seedling leaves decrease significantly with increasing of NaC1 and NaHCOa stress intensity, while PSII non-photochemical quenching （NPQ） increases significantly, and the ratio of absorbed light energy allocating to the photochemical reaction of PS 11 （P） reduces significantly, meanwhile, the proportion allocated in antenna heat dissipation （D） increases signifi- cantly. At the same concentration of treatments, the decreases of the Fv/Fm, ФPsⅡ, qP, P, Hill reaction and ATPase activities, and the increases of NPQ and D are higher in NaHCO3 stress than in NaC1 stress, suggesting that the injury of NaHCO3 stress to ryegrass seedlings is greater than NaCl stress. All the results show that the tolerance of ryegrass to alkaline stress is lower than to saline stress, which may be concerned with the greater decrease of photosynthetic pigment and the more serious injury of photosynthetic system caused by high pH of alkaline stress.