Stem Sap Flow in Different Measurement Positions of Triploid Populus tomentosa

In order to clarify the relationship between sap flow and the probe directions and environmental factors of triploid Populus tomentosa fast-growing pulpwood,sap flow velocity(Vsp),environmental factors such as wind direction and velocity,solar radiation,rainfall,air temperature and humidity,soil moisture and temperature were measured using thermal dissipation sap flow velocity probe(TDP) and automatic weather station in Gaotang County(36°58′N,116°14′E),Shandong Province in August,2008.The results showed that:(1)The Vsp diurnal variation was similar at different directions,i.e.east,south,west,and north,which showed the double-peak curve in sunny day,and the single-peak curve in cloudy and rainy day.There was no obvious difference among the four directions Vsp in sunny and cloudy days(P0.05),but in rainy day,Vsp at east was significantly higher than that at south which was 0.906 cm/s and 0.267 cm/s respectively.(2)Sap flow velocities of triploid P.tomentosa at four orientations were highly positively correlated with each other,and the regression equations of sap flow velocity at four orientations was highly significant.(3)Correlative and path analysis showed that Vsp of triploid P.tomentosa was affected by environmental factors such as solar radiation,air temperature and relative humidity,wind velocity,soil water content and temperature at 10 cm.However,the predominate factors were varying as the time and weather changing.(4)Nocturnal sap flow of triploid P.tomentosa was obvious according to the accumulative nocturnal Vsp which accounting for 18.84%,19.13% and 40.77% of total day accumulative Vsp respectively in sunny,cloudy,and rainy day.