Influence of dust stress on the photosynthetic and chlorophyll fluorescence characteristics of Pistacia vera L.
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 (PS Ⅱ) 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 PS Ⅱ 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 PS Ⅱ 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/cm2(mild sand-dust cover) or 9 mg/cm2 (severe sand-dust cover) dust,with 0 mg/cm2 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 42ndday.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.
Pistacia vera L.dust stressphotosynthetic characteristicschlorophyll fluorescence characteristics
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