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Accueil du site → Doctorat → Chine → 2008 → Study on the Response and Adaptation Mechanism of Greenhouse Cucumber (Cucumis Sativus L.) to Drought Stresses and Elevated CO2 Concentration

Northwest University of Science and Technology (2008)

Study on the Response and Adaptation Mechanism of Greenhouse Cucumber (Cucumis Sativus L.) to Drought Stresses and Elevated CO2 Concentration

Li Qing Ming

Titre : Study on the Response and Adaptation Mechanism of Greenhouse Cucumber (Cucumis Sativus L.) to Drought Stresses and Elevated CO2 Concentration

Auteur : Li Qing Ming

Grade : Doctoral Dissertation 2008

Université : Northwest University of Science and Technology

Résumé partiel
Drought stress is a prevalent problem for agriculture in the world. The elevation of CO2 concentration around the world has obtained great attention in recent years, and CO2 can be used as fertilizer in greenhouse. Based on the two points, this study was deployed with cucumber (JinYou No.1) in two adjacent identical test greenhouses located at Northwest A & F University during 2006-2007. Under both elevated CO2 concentration and ambient CO2 concentration, this study focused on several aspects, such as the growth and development of cucumber seedlings, microstructure and ultrastructure of cucumber leaves, photosynthetic gas exchange, photochemistry efficiency, metabolism of nonstructural carbon hydrate and the activity of involved enzymes, reactive oxygen species (ROS) and protective system of anti-oxide and so on. The major results are as follows:1. The effects of drought stresses and elevated CO2 concentration on the growth and development of cucumber seedlingsUnder drought stress, the plant height, leaf area, leaf area ratio and relative growth rate of cucumber seedlings were declined significantly, whereas the root/shoot ratio, growth index were raised. The growth and development of seedlings were impaired by severe drought stress, and the accumulation of dry matter was changed to a large extent. The rise of root/shoot ratio was caused by the decrease of shoot dry mass, instead of the greater accumulation of dry matter for root. Under elevated CO2 environment, the height of seedlings, leaf area, shoot dry mass and relative growth rate (RGR) increased significantly, although the diameter of stem, root dry mass, root/shoot ratio was not changed significantly.2. The effects of drought stresses and elevated CO2 concentration on the microstructure and ultrastructure of cucumber leavesThe thickness of cucumber leaf declined under drought stressed, but increased under elevated CO2 concentration. The number of chloroplast decreased but the size of chloroplast increased significantly under drought stresses. The number of chloroplast increased significantly and the size had no changes under elevated CO2. The starch grain accumulated and the size of which were increased by both drought stresses and elevated CO2 concentration. Under drought stresses conditions, choloroplast swelled, stroma became thin, the thickness and number of grana decreased significantly, thylakoid swelled, lamella of grana and stroma became blurry, some of membrane broke and disorganized, many big plastoglobules appeared. Elevated CO2 stimulated thylakoid development through increasing the thickness of grana and the number lamella to some extent. The density of stomata was increased, but the ratio of aperture stomata, stomata aperture were lowered by drought stresses. However, elevated CO2 not only decreased the density of stomata, but also decreased the ratio of aperture stomata and stomata aperture. At the same time, the density of stomata and the ratio of aperture stomata of abaxial surface were higher significantly than adaxial surface.3. The effects of drought stresses and elevated CO2 concentration on photosynthetic gas exchange of cucumber seedlingsThe photosynthetic rate, transpiration rate, stomata conductance and intercellular CO2 concentration of cucumber seedlings decreased with treatment of drought stresses. However, the water use efficiency was raised by the cooperation between the increase of photosynthetic rate and decrease of transpiration rate. Under drought stress, apparent quanta efficiency, CO2 assimilation maximum depressed significantly. Light compensatory points and CO2 compensatory points were enhanced. At the same time, carboxylation efficiency, respiration rate, CO2 assimilation maximum, light saturated electron transport rate [1], triose phosphate utilization (TPU) and mesophyll conductance (gm) decrease significantly. Contrarily, the parameters about photosynthesis went the opposite direction under elevated CO2 environment, i.e. elevated CO2 promoted photosynthesis of cucumber seedlings. Therefore, the factor of stomata and non-stomata resulted in the decrease of photosynthesis when cucumber seedlings subjected to drought stress. Nevertheless, under elevated CO2 environment, photosynthesis of cucumber seedlings was promoted through the adjustment of stomata and non-stomata factor, in order to keep metabolism and energy circulation running well, and alleviate or avoid the impair of drought stress. 4. The effects of drought stresses and elevated CO2 concentration on photochemical efficiency of cucumber seedlingsThe photosynthetic ability and electron transport rate decreased when cucumber seedlings subjected to drought stresses. However, elevated [CO2] alleviated the negative effects of drought stresses to a certain extent mainly by increasing Fv/Fm, qP and PPFDsat, and decreasing NPQ. Furthermore, the above four parameters could be used to evaluate the interactive effects of drought stresses and elevated [CO2] on photochemistry efficiency of cucumber seedlings.5. The effects of drought stresses and elevated CO2 concentration on metabolism of nonstructural carbonhydrate and involved activity of enzymes of cucumber seedlingsUnder elevated CO2 environment, nonstructural carbonhydrate of cucumber leaves increased, including glucose, fructose, sucrose, stachyose. Hence, the osmotic potential decreased subsequently, avoiding the severe dehydration of cells, maintaining turgor pressure of cells, and the ability of seedlings resisting drought stress was improved. During drought stress of 7 days, sucrose synthase (SS), soluble acid invertase and alkaline invertase of leaves climbed up firstly, and then declined ; soluble acid invertase and alkaline invertase of root system increased gradually, whereas sucrose phosphate synthase increased firstly and then decreased.

Mots clés : cucumber drought stresses elevated CO2 concentration morphological characteristic physiochemical characteristic

Présentation (Dissertation topics)

Page publiée le 9 avril 2014, mise à jour le 10 janvier 2018