Effects Of Environmental Factors On Sap Flow And Radial Growth Of Poplar Plantation

As one of the commonly used afforestation tree species in the north,Populus euramericana is widely used in timber forests,ecological forests and landscape forests.It is also concerned about its transpira?tion and water consumption.In this paper,the poplar tree in Shunyi Gonglin Forest Farm of Beijing was taken as the research object.The TDP thermal probe method and the strip radial growth instrument were used to continuously measure the sap flow and trunk radial variation of poplar trees in the growing sea-son,and analyzed different weather conditions.The relationship between daytime and nighttime flow rate characteristics of time-scale trunks and their relationship with environmental factors,the relation-ship between radial variation of trunks and environmental factors such as meteorology and soil moisture was studied.The results show that:(1)The small breast diameter sample tree responds more quickly to changes in the surrounding environment.On a typical sunny day,the daily variation of poplars with dif-ferent breast diameter is basically a single-peak curve.The peak value of the sap flow is 0.0067g/cm2· s,and the peak value of the sap flow on sunny days is about 1.3 times that of the cloudy day.On a typical rainy day,the daily variation of the sap flow of different breast diameter sample trees are not obvious,but the sap flow at night is more active.(2)There was obvious nighttime sap flow during the growing season of poplar,and it was significantly active in the middle of the night before midnight.The ratio of nighttime sap flow to total transpiration is May>September>June>July>August,with May reaching a maximum of 8.5%,followed by September at 8.4%,and the average contribution rate is 7.2%,the pro-portion of nighttime transpiration in the early and late growth seasons is greater than that in the middle of the growing season.(3)Within a certain range,the larger the crown of the breast diameter tree,the greater sap flow rate at night.At night,there is a high correlation between the sap flow and the envi-ronmental factors in the month when the rainfall is less.At this time,part of the night flow is used for hydration for a part of transpiration,while in the month of heavy rainfall,the sap flow is more for stem water recharge.The amount of water recharge depends on the required water replenishment capacity determined by the soil moisture content and the degree of tree water deficit caused by the daily transpi-ration intensity.Nighttime transpiration existed in the first half of the night.(4)The influence of mete?orological factors on sap flow is solar radiation>saturated water vapor pressure deficit>air tempera-ture>air relative humidity>wind speed,solar radiation has the direct effect on sap flow,and saturated water vapor pressure difference has the greatest indirect effect on sap flow rate.Within a certain range,the daily transpiration of the stand increases with the increase of solar radiation,but in the case of low soil water content,the stand transpiration remains at a lower level of saturated water vapor pressure dif-ference for transpiration activities.Within a certain range,with the increase of saturated water vapor pressure difference,the transpiration of stand stands also increases.When the saturated water vapor pressure difference exceeds a certain value,t:he stand transpiration is inhibited.(5)The stem growth of poplar showed obvious diurnal changes,which were mainly divided into systolic,expansion and growth stages.Poplar stems exhibit a tortuous growth during the growing season.The amount of daytime con-traction of the wood increased from May to November,and the maximum value is 272.24?m.The av-erage daily expansion decreased gradually from the early to the end of the growing season.The nighttime expansion of the trunk was 159.43?203.47?m at the beginning of the growing season,and the nighttime expansion was 30.09?36.79?m at the end of the growing season.The diameter of the small breast diameter tree was larger than that of the large breast diameter tree.(6)The radial diurnal contrac-tion of poplar trunks was significantly positively correlated with solar radiation intensity,saturated wa-ter vapor pressure difference,daily average temperature and maximum temperature,and negatively correlated with air relative humidity and soil water content.The radial contraction between the two de-pends on the amount of water loss caused by the transpiration of the trees.The radial nighttime expan-sion of the trunk is positively correlated with the nighttime average temperature,the lowest temperature,the highest temperature,the saturated water vapor pressure difference,the rainfall,and the nighttime liquid flux,but negatively correlated with the nighttime relative humidity,and the nighttime liquid flux is a certain degree.It can explain the change in the amount of radial expansion of the trunk.The cumu-lative growth process of trunk diameter and the power function y= axd have the best fitting results.Prin-cipal component analysis and partial correlation analysis show that the daily minimum temperature,solar radiation and saturated vapor pressure difference are the main meteorological factors affecting the radial growth of the trunk.A linear regression model was established.