沙尘胁迫对阿月浑子光合作用及叶绿素荧光特性的影响

Influence of dust stress on the photosynthetic and chlorophyll fluorescence characteristics of Pistacia vera L.

为了探讨长期沙尘胁迫下阿月浑子叶片光合性能的变化机制,以室内盆栽阿月浑子为材料,对叶片进行覆盖厚度为2mg/cm2(轻度),9 mg/cm2(重度)的沙尘处理,无沙尘覆盖为对照,并分别在处理后第7天、14天、28天和42天,测定叶片光合CO2同化速率,叶绿素含量以及叶绿素荧光特性等参数。结果表明,阿月浑子叶片的净光合速率(Pn)和气孔导度(Gs)随沙尘处理时间延长而下降,重度沙尘处理下Pn和Gs下降幅度比轻度大,胞间CO2浓度(Ci)处理前期增加而后期下降,重度沙尘处理下Ci增幅比轻度小;叶绿素a(Chl-a)、叶绿素b(Chl-b)和总叶绿素含量均随处理时间的延长而下降,在重度沙尘处理下下降幅度比轻度沙尘处理大,Chl-a的下降速率大于Chl-b,叶绿素a和b的比值(Chl-a/Chl-b)在重度沙尘处理下逐渐下降,而在轻度沙尘处理下呈升-降-升趋势;PSⅡ最大光化学效率(Fv/Fm)不同程度下降,在重度沙尘处理下下降幅度比轻度沙尘处理大;轻度沙尘覆盖下实际光化学效率(ΦPSⅡ)及非环式电子传递效率(ETR)在处理第42天显著下降,而重度覆盖处理先急剧下降,后期逐渐恢复;非光化学荧光猝灭(NPQ)在轻度胁迫下先下降而后逐步上升,在重度处理下则在处理前期就迅速上升。从而得出结论,阿月浑子轻度沙尘胁迫条件下前期其光合作用非气孔限制贡献率大于气孔限制,随胁迫时间气孔限制逐渐占优势,并且随处理时间的延长其吸收的光能用于保护性耗散量逐渐增加,使其光合CO2同化效率下降。

In plants, photosynthesis is one of the physiological processes that are sensitive to sand-dust stress. The leaves of sand-dust stressed plants show decreases in net photosynthetic rate and chlorophyll pigment content, and changes in chlorophyll fluorescence parameters because of decreased leaf-absorbed solar radiation, physical blockage of stomata and physical leaf epidermis damage by sand-dust particles. Photosystem Ⅱ （PSⅡ） is the most sensitive component of the photosynthetic apparatus to environmental stresses. Analyses of chlorophyll fluorescence dynamics are useful to determine the effects of environmental stresses on PSⅡ structure, and to study the response mechanisms of the photosynthetic machinery. Pistacia vera L. is often subjected to drought and salt stress during its growth season in planted areas. However, little is known about chlorophyll pigment content and the physiological mechanisms underlying changes in the photochemical activity of PSⅡ in Pistacia vera under sand-dust stress. This experiment was designed to study the adaptive photosynthetic mechanism and chlorophyll fluorescence characteristics of Pistacia vera under dust stress and was carried out in a greenhouse at the experimental site of Xinjiang Agricultural University. Plant materials were grown in flowerpots in the greenhouse and the stress treatment was performed by covering plant leaves with 2 mg/cm^2 （mild sand-dust cover） or 9 mg/cm2 （severe sand-dust cover） dust, with 0 mg/cm^2 as a control. Photosynthesis, chlorophyll pigment content and chlorophyll fluorescence parameters were measured at 7, 14, 28 and 42 d after treatment. The results showed that prolonged dust stress led to decreases in net photosynthetic rate （Pn） and stomatal conductance （Gs）, and that Pn and Gs decreased more under severe dust treatment than mild dust treatment, while the intercellular CO2 concentration （Ci） increased at the beginning but later declined, and was increased less under severe dust treatment than mild dust treatment. Chlorophyll-a （Chl-a）, chlorophyll-b （Chl-b） and total chlorophyll contents decreased with increasing treatment time, and decreased more in the severe dust treatment than the mild. The rate of Chl-a decrease was higher than that of Chl-b, which resulted in a decrease in Chl-a/Chl-b ratio. The Fv/Fm gradually decreased under mild and severe stress conditions, and decreased more under severe sand-dust cover compared with mild sand-dust cover. While the quantum efficiency of photosystem Ⅱ （ΦPSⅡ） and the nonlinear electron transport rate （ETR） were decreased after 42 d in the mild dust treatment, they rapidly decreased until the 14th day of treatment under severe stress conditions and then increased to the levels of the control by the 42^nd day. Non-photochemical quenching （NPQ） was decreased at first and then continually increased under mild stress conditions, whereas it was maintained at a high level during the entire treatment period under severe stress. In conclusion, the contribution of non-stomatal inhibition to the photosynthetic rate was greater than stomatal inhibition at the beginning, but stomatal inhibition became the main factor at later stages under mild sand-dust stress, because of the increased adaptive dissipation of absorbed photoenergy by the photosynthetic machinery, and caused a decrease in photosynthetic CO2 assimilation rate in Pistacia vera leaves.