Studies On Characteristics Of Transpiration And Water Consumption Of Ginkgo Biloba L. And Its Regulating And Controlling Mechanism In Given Urban Environment

It is very important for water uptake,transport,movement,and evapotranspiration in Soil-Plant-Atmosphere Continum(SPAC).The characteristics of sapflow,tissue and organ water content,water potential,water capacitance reflect the tree water status.By studying on their characteristics and their coordination relationship with the water consumption,we may further explore and promulgate the laws of water consumption and their internal controlling mechanisms in tree species for providing a theoretical foundation and technique instructor for the scientific water management of tree species ecologically and economically.Sap flow velocity(V_sf),twig and leaf absoluteness Absoluteness Water Content(AWC),water potential(Ψ) and water capacitance(C) were measured using thermal dissipation sap flow velocity probe(TDP) and pressure chamber on the campus of Beijing Forestry University(N 39°46′,E 116°19′) to understand transpiration and water consumption fluctuations of Ginkgo biloba L.and its regulating and controlling mechanism in given urban plantation,and for scientific water management and higher water use efficiency in ueban greenland water management.The results showed that1) The diurnal fluctuation of Ginkgo biloba L.sap flow velocity(V_sf) was a single-peaked curve in Spring and Summer,and a double-peaked curve in Autumn.The sap flow velocity of Ginkgo biloba L. was not significant differences in Spring,Summer,and Autumn,but the appearing time of V_sf peak value was different in three seasons.2) Sap flow velocity,which was effected by environmental,in general was positively effected by solar radiation,air temperature,wind speed and soil temperature and negatively effected by relative humidity of air.However,the relevance between sap flow and various factors of environment was different at different specific period and it was better to conduct the research on the basis of different time periods in order to establish more precise regression models.3) Net photosynthetic rate(Pn),transpiration rate(Tr),and stomatal Conductance(gs),of Ginkgo biloba L.presented similar tendencies of daily variation with differences from season to season. Diurnal and seasonal variation of Ginkgo biloba L.Water Use Efficiency(WUE) was not a regular pattern.Seen from the seasonal average rates,it was higher in spring than in autumn and in autumn higher than in summer,which was the same with the seasonal changing of Sap flow velocity.The results also showed that Vapor Pressure Deficit based on Leaf Temperature(VpdL)is clearly and positively connected with the sapflow,which meaned the sapflow of Ginkgo biloba L.was as well effected by VDPL besides the environmental factors such as solar radiation,air temperature,wind speed,soil temperature,air relative humidity,and SPAC hydraulic potential gradient,etc.4)In urban plantation,the daily changing tendencies of Absoluteness Water Content(AWC),water potential(Ψ) and water capacitance(C) of Gingko twigs and leaves were the same but show different daily changing patterns from season to season and different daily changing degrees which jointly effects the evaporation of gingko.The research revealed that water potential contribute more than water content to water capacitance.Meanwhile,in the process of adjusting tree evaporation,the effects of different factors and parts of trees can be illustrated as follows:water capacitance＞water potential＞absoluteness water content;twigs＞leaves.5)The daily and seasonal variation of water capacitance of gingko branches and leaves had similar changing rules and co-adjust the evaporation of trees,presenting a different changing pattern from sapflow.The fact that twig water capacitance(0.38 g·cm^-3·MPa^-1±0.02 g·cm^-3·MPa^-1) was far greater than leaf water capacitance(0.0058g·cm^-3·MPa^-1±0.0019 g·cm^-3·MPa^-1),while the relevance between twig water capacitance and sapflow was also greater than leaf water capacitance indicates a channel to minimize the instantaneous imbalance of water supply and consumption was to use water kept in the pant tissues near the parts of water evaporation and dehydration.