Photosynthetic and water-related physiological characteristics of Periploca sepium in response to changing soil water conditions in a shell sand habitat

This study was performed to observe the effects of water on photosynthesis and water-related physiology in dominant shrubs in shell sand habitats.Four-year-old Periploca sepium seedlings were used as model species.A gradient of 12 water levels was established by artificially supplying the shell sand with water up to saturation and then allowing natural evapotranspiration to occur.The photo synthetic,chlorophyll fluorescence and stem sap flow parameters of P.sepium were measured under a range of water conditions.The different soil water conditions were classified according to the responses of these parameters.(1)With the increase in the relative water content(RWC)of the shell sand,the parameters of leaf photosynthesis,chlorophyll fluorescence and water-related physiology in P.sepium showed significant critical responses.The net photo synthetic rate(Pn),transpiration rate(Tr),instantaneous water use efficiency(WUE),potential water use efficiency(WUEi),maximum photochemical efficiency(Fv/Fm),actual photochemical efficiency(ΦPSII)and daily accumulation of stem sap flow all increased first and then decreased with increasing RWC,but the corresponding water conditions associated with their maximum values were not the same.An RWC of 69.40%was determined to be the optimal water condition for photosynthesis and water-related physiological activity in P.sepium.At an RWC of 36.61%,the mechanism of photosynthetic inhibition in P.sepium changed from stomatal limitation to nonstomatal limitation;this was also the minimum water requirement for maintaining normal photo synthetic processes.An RWC of 50.27%resulted in the highest WUE in P.sepium,indicating that moderate drought stress increased WUE.(2)Based on the quantitative relationship between the photo synthetic parameters of P.sepium and the shell sand water gradient,the soil water availability was classified into 6 water grades.The RWC range for maintaining strong photosynthesis and high WUE in P.sepium was 63.22-69.98%.(3)Gas exchange in P.sepium was inhibited under drought and waterlogging stresses.Under these conditions,the photosynthetic electron transport chain was blocked,and the dissipation of light energy as heat increased,which ultimately led to a decline in photo synthetic productivity;moreover,transpiration and dissipation were aggravated,and water transmission and utilization processes in P.sepium were hindered.A significant negative feedback regulation mechanism in the photosynthetic and water-related physiological processes of P.sepium was observed;this mechanism allowed P.sepium growing in shell sand to be highly adaptable to water stress.

Preliminary Study on Water Physiological Characters of Male and Female Ginkgo biloba L.

[Objective] The experiment aimed to study the difference of water physiology of male and female Ginkgo biloba L. for discussing the strategy of water utilization as well as the important role of this difference during evolution process. [Method] The stem sap flow, stomatal conductance(Gs), transpiration rate(Tr) and water use efficiency (WUE) of male and female Ginkgo biloba L. were comparatively studied. [Result] The day-night processes of flow on male and female Ginkgo biloba L. were similar. The flow on male and female Ginkgo biloba L. in day were almost same while the flow at night on male Ginkgo biloba L. was bigger than that on female Ginkgo biloba L. The Tr and Gs of male and female Ginkgo biloba L. were high in morning and at night but low at noon ,while Tr and Gs of female Ginkgo biloba L. in morning and at night were higher than these of male Ginkgo biloba L. at the same time point. However, these indexes of female plant were lower than these of male plant from 11:00 to 14:00. WUE changing trends of male and female Ginkgo biloba L. were similar, while average water utilization rate of female Ginkgo biloba L. was slightly lower than that of male Ginkgo biloba L. [Conclusion] Compared with other companion plants, water physiology of male and female Ginkgo biloba L. had strong homoplasy. The phenomenon might be a survival strategy of dioecious plants under long term evolutionary pressure.

Effect of continuous negative pressure water supply on the growth, development and physiological mechanism of Capsicum annuum L.

Effects of continuous negative pressure water supply on water consumption, growth and development, as well as physiological mechanism and quality of Capsicum annuum L. were investigated in this paper. Meanwhile, the optimal negative pressure water supply conditions for growth of C. annuum L. were screened out to achieve the goals of water conservation, high yield and high quality, thus providing theoretical foundation for its field production. The pot experiment within the greenhouse was utilized; the continuous negative pressure water supply was adopted; the four treatments, artificial watering（CK）, –5 k Pa（T1）, –10 k Pa（T2）, and –15 k Pa（T3） were set; and the daily water consumption, yield, as well as the biomass, nitrate reductase, root activity, vitamin C, capsaicin, and nutrient uptakes of nitrogen（N）, phosphorus（P） and potassium（K） during various stages of its growth were determined. Compared with CK, when the water supply pressure was controlled at –5 to –15 k Pa in the experiment, the total water consumption of C. annuum L. reduced by 53.42 to 67.75%, the total water consumption intensity reduced by 54.29 to 67.14%, and the water use efficiency increased by 12.66 to 124.67%. The N accumulation in a single strain of C. annuum L. from the color turning stage to the red ripe stage increased by 15.99 to 100.55%, respectively, compared with that of CK; the P accumulation increased by 20.47 to 154.00% relative to that of CK, and the K accumulation increased by 64.92 to 144.9% compared with that of CK. Compared with CK, C. annuum L. yield was remarkably improved by 13.79% at T1, and contents of vitamin C, capsaicin as well as carotenoids at all growth stages were enhanced by 13.42–147.01%, 11.54–71.01%, and 41.1–568.06%, respectively. Nitrate reductase activity, root activity and chlorophyll（a＋b） were markedly increased by 335.78–500%, 79.6–140.68% and 114.95–676.19%, respectively, from immature stage to full ripe stage. Adopting the continuous negative pressure water supply for C. annuum L. has a significant water-saving effect, and the water supply pressure being stable at –5 k Pa contributes to its growth and development, improves yield, enhances root activity, promotes nutrient uptake, and improves its quality, thus achieving the effects of water conservation, high yield, high quality and high efficiency.

治沙植物旱生结构及生理特性的研究

研究植物的旱生结构和一理特性，为干旱沙区造林提供科学依据。供试的６种植物普遍具有典型的旱生结构和具有束缚水含量高、束缚水与自由水比值大，水势低，临界饱和亏值大等生理指标，但由于植物种的不同，这生理指标又各具有互为消长的特性。

Advances in Biological Water-saving Research:Challenge and Perspectives

Increasing the efficiency of water use by crops continues to escalate as a topic of concem because drought is a restrictive environmental factor for crop productivity woridwide .Greater yield per unit rainfall is one of the most important challenges in water-saving agriculture Besides water-saving by irrigation engineering and conservation tillage, a good understanding of factors limiting and/or regulating yleld now provides us with an opportunity to identify and then precisely seiect for physiciogical and breeding traits that increase the efficiency of water use and drought tolerance under water-limited conditions, biological water-saving is one means of achieving this goal, A definition of bilogical water-saving measures is proposed which embraces improvements in water use efficiency （WUE） and drought tolerance, by genetic improvement and physiological regulation. The preponderance of bilogical water-saving measures is discussed and strategies identified for working within natural resource constraints. The technology and future perspectives of bilogical water saving could provide not only new water-saving techniques but also a scientific base for application of water-saving irrigation and conservation tillage.