Effects Of Root Zone Temperature On Growth And Development And Physiological And Biochemical Metabolism Of Cucumber In Solar Greenhouse

In accordance with the question of low root zone temperature appearing in sorlar greenhouse, two cucumber (cucwnis sativus L.) cultivars Jinchun No.2(J2) and Jinchun No.3 (J3), which had different resistance to coldness stress, were used as materials in the experiments. Effects of root zone temperature(optimal temperature CK is 21-23 "C; sub-optimal temperature is 14-16 "C; low temperature is 8-10 "C) on growth and development and physiological and biochemical metabolism of cucumber seedlings cultivated in sand were studied in winter and spring in solar greenhouse. The results provided theoretical bases for understanding the important effects of root zone tempereture on growth and development of cucumber and further practical guides for reasonable choice of cultivars and better improvement of root zone temperature of cucumber in solar greenhouse in low temperature season. The main results were as follows:1. Lowering root zone temperature reduced growth vigour of cucumber seedlings; reduced dry matter accumulations of shoots and winter treatment' s roots, increased dry matter accumulations of roots of spring and successive treatments, increased of root:shoot ratios; reduced pnotosynthetic pigment contents and photosynthetic parameters in leaves; effects of the post-effect of lowing root zone temperature of spring treatment in seedling period postponed blooming of female flower, reduced fruit number and yield per plant.2. Lowering root zone temperature reduced contents of N(winter treatment), P(winter treatment), Ca, Fe, Mn, Cu, Zn in roots of cucumber seedlings, contents of P, Mn, Cu, Zn of stems, and contents of N, P, Ca, Mg, Fe, Mn, Cu, Zn in leaves; increased of contents of N(spring treatment), P(spring treatment), K, Mg in roots, contents of N, K, Ca, Mg, Fe of stems, K content in leaves, the changes of N and P contents played an important role indry matter accumulations of roots; reduced total absorption amounts of mineral elements; increased great majority of distribution percentages of N, P, K, Ca, Mg, Fe, Mn, Zn in roots, increased great majority of distribution percentages of N, Ca, Fe, Cu, Zn in stems, reduced great majority of distribution percentages of N, P, K, Ca, Mg, Fe, Mn, Cu, Zn in leaves.3. Lowering root zone temperature of winter treatment reduced volume, total and active absorbent areas, and percentage of active area of roots, increased area:volume ratio of roots, while effects of on above indexs were reverse in spring treatment; increasd activities of succinic dehydrogenase and nitrate reductase in roots, reduced activities of nitrate reductase in leaves.4. Lowering root zone temperature reduced activities of most protective enzymes in cucumber seedlings, only increased activities of superoxide dismutase(SOD) and catalase(CAT) in roots of spring treatment; resulted in accumulations of active oxyzon species, increase of membrance-lipid peroxidation and malondiadehyde(MDA) contents, destruction of intact membrance structure , and increase of relative electric conductance in cucumber seedlings; increased contents of proline(Pro), soluble protein(Pr), and soluble sugar in cucumber seedlings, which was beneficial to enhancing resistance of cucumber seedlings to coldness stress.5. Lowering root zone temperature increased contents of gibberellic acid(GA), indol-3yl-acetic acid(IAA), and zeatin riboside(ZR) in roots of cucumber seedlings, reduced contents of GA, IAA, ZR in leaves; increased contents of abscisis acid(ABA) in leaves and winter treatment' s roots, reduced contents of ABA in roots of spring treatment.6. Cucumber cultivar with different resistance to coldness stress had different susceptibility to low root zone temperature stress. Cultivar with higher resistance to coldness stress should be chosen in solar greenhouse production in low temperature season.7. Improvement of root zone temperature in winter night had better effect than in spring night, which could reduce harmful effects of low root zone temperature on growth...