Characteristics Of Water Consumption Through Transpiration And Evaluation Of Adaptability Mechanism Of Main Trees For Vegetation Restoration In The Dry-Hot River Valley

Taking tree species for vegetation in Jinsha River dry-hot river valley locating the up segment of Changjiang River as study object, in the view of ecophysiology, this paper deeply studied the characteristics of water consumption by transpiration, photosynthesis and water physiology of the main tree species through potted plant trial and plantation survey. Aiming at the special environment that changes from dry to dry and hot then to wet weather in one year, this paper systematically analyzed adaptation mechanism of ecophysiology for tested tree species. The practical growth condition of tested tree species was surveyed. Based on the index of ecophysiology and growth, the comprehensive index was built to scientifically evaluate the adaptation quality of tree species for vegetation restoration, and provide theoretical and practical base for ecological forestation in the Valley. The main conclusions were below:(1) Characteristics of water consumption by transpiration of main tree species for vegetation restorationCharacteristics of water consumption by transpiration of 29 tree species for vegetation restoration in Jinsha River dry-hot river valley were firstly systematically analyzed through potted plant weight method. Under the normal water condition, the daily changes of water consumption by transpiration and transpiration rate of different seedlings presented typical single peak distribution, and with the drough stress getting deep, the peaks of water consumption by transpiration and transpiration rate moved up. For the absolutely most tree species, the dry and hot stress make the range of daily change of water consumptation by transpiration get smaller, and one-peak types have the trend of transition to two-peaks type. The water consumption by transpiration in day time of seedlings decreased with the decline of soil water content and water potential, but the rate and extent of decline was different for different seedlings. With the soil drough stress getting deep, transpiration rate of seedlings gradually decreased, and at the early stage of drough stress, the rate of decreasing was more big, then had the trend of degression during the anaphase.Accoring to the quantity of water consumption by transpiration in whole day, the tested tree species could be classified to four sorts: Acacia mearnsii De. Wild., Eucalyptus globulus Labill. > Acacia auriculiformis A. Cunn., Leucaena leucoephala cv. Salvador, Cupressus duclouxiana Hickel., Sophora xanthantha C.Y. Ma. > Carallia longipes, Eucalyptus camaldolensia Dehn., Cupressus lusitanica Mill., Eucalyptus urophylla S.T. Blake., Ficus racemosa L., Casuarina equisetifolia, Dodonaea viscose (L.) Jacq., Acacia glauca (L.) Moelichl, Sabina chinensis (L.) Ant., Ligustrun lucidum Ait., Phyllanthus emblica L., Nerium indicum Mill., Ziziphus mauritiana Lam > Acacia mangium, Tephrosia candida DC., Schleichera oleosa Iour., Albizia kalkora Roxb., Bombax malabaricum DC., Pinus yunnanensis Franch. According to the mathematical relationship between transpiration rate in day time and soil potential, systematical classification method was applied to devide 29 kinds of tree species into four sorts:①high transpiration rate and middle drought sensitivity tree species, including Casuarina equisetifolia, Ziziphus mauritiana Lam, Ficus racemosa L. and Sophora xanthantha C.Y.;②sub-high transpiration rate and weak drought sensitivity tree species, including Bombax malabaricum DC., Tephrosia candida DC., Dodonaea viscose L., Acacia glauca L., Albizia kalkora Roxb., Azadirachta indica A. Juss and Cajanus cajan (L.) Mill.③Sub-low transpiration rate tree species, including middle drought sensitivity type and weak drought sensitivity type, the former have Pinus yunnanensis Franch., Tamarindus indica L., Acacia mangium, Cupressus duclouxiana and Phyllanthus emblica L., the latter include Eucalyptus camaldolensia and Schleichera oleosa Iour.④Low transpiration rate tree species, including strong drought sensitivity type, middle drought sensitivity type and weak drought sensitivity type, in which, strong drought sensitivity type include Nerium indicum Mill., Eucalyptus globulus Labill., Acacia mearnsii De. Wild., Eucalyptus urophylla S.T. and Carallia longipes, middle drought sensitivity type include Leucaena leucoephala cv., Cupressus lusitanica, Ligustrun lucidum Ait., Acacia auriculiformis A. and Sabina chinensis (L.) Ant., Jatropha curcas L. belongs to weak drought sensitivity type.The phenomenon of"sleep at noon"of water consumption by transpiration and transpiration rate of seedlings is controlled by the condition of soil water, while soil water stress takes place, the phenomenon of"sleep at noon"appears at once, which is independent of drough stress from atmosphere.Whether dry and hot season or wet season, the day and night change of trunk sap flow density of Azadirachta indica A. Juss had strong law, and presented one wide peak. When the environmental changes from dry and hot season to wet season, the trunk sap flow density of Azadirachta indica A. Juss got decreasing, the maximum of daily changes of sap flow density for five-year-old Azadirachta indica A. Juss respectively arrived to 27.21, 21.61 and 19.35 cm3·cm-2·h-1, the average values of daily changes respectively were 12.11, 7.48 and 6.90cm3·cm-2·h-1. Water consumption by transpiration of individual stem in dry and hot season had great passivity, however, water consumption by transpiration of individual stem in wet season presented initiative and balance quality.(2)Adaptation mechanism of main tree species for vegetation restorationThrough discussing the photosynthesis law of tested tree species in dry season, dry and hot season and wet season, this paper studied the effect of different altitude region, different slope location, different mixture mode and different water condition on photosynthesis of tree species. The daily changes of leaf water potential of main tree species for vegetation restoration all had an obvious peak in different seasons, and absolutely most tree species presented one-peak concavity distribution. At the stage of dry and hot stress, the peak time of daily changes net photosynthesis rate of most tree species moved up, the phenomenon of"sleep at noon"of photosynthesis got weaken or not obvious, while dry and hot stress was relieved and wet season came, most tree species presented typical one-peak or two-peak curve again. The daily changes of transpiration rate of tree species were identical to net photosynthesis rate.The daily change of water using efficiency (WUE) of most tree species presented a two-peak or mutil-peak curve in dry March, the peak value of daily change of WUE was made come ahead with the dry and hot stress getting deep, which was identical to net photosynthesis rate. Independent of tree species and seasons, the daily changes of photochemistry efficiency Fv/Fm always presented the characteristics of descending first then ascending, available photochemistry efficiency of PSⅡ(Fmv/Fms) was more sensitive to environment condition than Fv/Fm, however, non-photochemistry efficiency extinguishment parameter NPQ presented convexity distribution of ascending first then descending, which showed that the startup of heat dissipation mechanism is an ordinary strategy of self-protection of photosynthesis organ for tree species in the dry- hot Valley.The leaf water potentials of tested tree species in Yuanmou County arrived to the minimum in dry-hot May, with dry-hot stress getting deep, water potentials of different tree species became more diverse, and the diversity could be relieved with the coming of wet season. The net photosynthesis rate and stoma conductance of most tree species were decreased by dry-hot stress. Transpiration rate and water using efficiency of tested tree species had some changes with the conversion of seasons. The control capacity of water losing of tree species had great difference in different seasons. The seasonal change direction of transpiration rate of tested tree species had the inconsistent phenomenon with stoma conductance, so we think the seasonal increasing and decreasing of transpiration rate might be action result of two different controlment form, one was priority to stoma factor, the other was priority to non-stoma factors. Comparing with dry season, the range of daily changes of minimal fluorescence parameter Fo was more small in wet season, which showed that wet environment was benefit to make photosynthesis organ keep a good reaction state, consequently improve photosynthesis production, which was identical with the phenomenon that tree species often had higher net photosynthesis rate in wet season. Wet environment benefited to relieve the photo restrain by light for tree species in dry-hot river valley.The sustaining and deepening of dry-hot stress strengthen the difference of net photosynthesis rate and transpiration between two different altitude region. With the deeping of dry-hot stress, the effect of altitude region on physiological index of different tree species had great change. Comparing with relatively high slope location, lower slope location was in favor of making leaf water potential, net photosynthesis rate and transpiration rate keep a relative high level, but this improved effect from low slope location was affected by tree species and its action was more obvious in dry-hot season. When mixing with Leucaena glauca (L.)Benth., Azadirachta indica A.Juss had the highest net photosynthesis rate, while mixing with Acacia auriculiformis, Azadirachta indica A.Juss had the highest leaf water potential. In dry-hot river valley, adaptive shade was benefit for photosynthesis capacity and efficiency of Azadirachta indica A.Juss, excessive press could restrict its formal physiological reaction. Irrigation could relieve the dry-hot stress and photosynthesis restrict of tree species in May. The rainfall in dry season increased net photosynthesis rate, transpiration rate and water using efficiency of most tested tree species, and the effect on different tree species had some difference. Rainfall in dry season had important sense for selection and physiological activity of tree species for vegetation restoration in dry-hot river valley.At the stage of dry stress turning to dry-hot stress, the photosynthesis restriction of most tree species became more early and strong. While wet season coming, the restriction extent of net photosynthesis rate relieved or disappeared. The photosynthesis of 12 tested tree species simultaneously had two dominant factors of stoma restriction and non-stoma restriction. The strengthening of dry-hot stress led to stoma restriction taking place more early, and presenting more non-stoma restriction. Generally, at the two successive course of dry-hot stress strengthening and relieving, the photosynthesis of tested tree species experienced two courses: stoma restriction decreasing and stoma restriction increasing. The improvement of cell photosynthesis activity might be main factor that caused net photosynthesis rate of tested tree species increased in the morning. High temperature obviously induced the taking place of photosynthesis restriction that took non-stoma restriction as main factor.(3)Comprehensive evaluation of adaptability of main tree species for vegetation restorationThe comprehensive indexes of physiological characteristics and growth had good correla -tion, Comprehensive index built by net photosynthesis rate, water using efficiency, transpira -tion rate and maximal photochemical efficiency of PSⅡcould make a reasonable evaluation for the adaptability of tree species for vegetation restoration. Water using efficiency had good direction.