Characteristics Of Betula Platyphylla Sap Flow Over Day And Night And Its Influencing Factors In The South Part Of Daxing’an Mountains

Water consumption and transpiration to trees has an important impact on ecohydrology.In recent years,global temperature has been rising and precipitation pattern has been changing,which affected the growth of trees.In this thesis,as one of dominant tree species in the southern part of Daxing’an Mountains,Betula platyphylla was taken as the research object.The TDP thermal probe method was used to continuously measure the sap flow in the growing season,and simultaneously the data of solar radiation（Rn）,atmospheric temperature（Ta）,atmospheric relative humidity（RH）,wind speed（WS）and soil water content（SWC）were collected,and analyzed different weather conditions.The relationship between daytime and nighttime flow rate characteristics of time-scale trunks and their relationship with environmental factors was studied.The results show that:1.On a typical sunny day,the daily variation of Betula platyphalla was basically a single-peak curve.Sap flow velocity in relation to different weather conditions,in descending order,was sunny,cloudy,and rainy days.The ratio of transpiration to precipitation in the growing season was 34.47%-64.76%.The stand transpiration in the middle growing season was greater than that in the early and late growing season.2.There was a significant nighttime liquid flow during the growing season of Betula platyphalla.From May to September,the nighttime sap flow was 2017（11.43mm）>2019（10.01mm）>2018（9.01mm）,the rate of contribution of the sap flow at night to that of whole of day is fluctuating from 1.32 to 14.67.The sap flow in the first half of the night was more active than that in the second half of the night.The sap flow in the first half of the night accounted for 52.23%-73.84%of the sap flow at night,and the sap flow in the second half of the night accounted for 26.16%-47.77%of the sap flow at night.In July and August,the sap flow at night was the largest,and the differences of sap flow between the whole day and night are extremely significant.3.Under different weather conditions,there are differences in environmental factors affecting day-night sap flow.RH and Ta were the main environmental factors that promoted the transpiration in the daytime.RH inhibited the transpiration in the daytime and sap flow at night during rainy and cloudy days.SWC is an important environmental factor affecting nighttime sap flow.SWC_0-40cmwas the main source of sap flow on sunny and rainy days and nights.SWC_20-40cmwas the main source of transpiration during cloudy days,and SWC_0-20cmwas the main source of sap flow at night on cloudy days.In terms of the influence mode,RN and Ta were positively correlated with sap flow in various weather.RH was negatively correlated with transpiration.WS promoted sap flow rate in daytime and inhibited sap flow rate at night.Seeing from the whole day,the determination coefficient R²of multiple regression equation between environmental factors and sap flow is sunny day（0.869）>rainy day（0.805）>cloudy day（0.794）.Conversely,seeing from the day and night,the effect of explanation is higher during the day and night than at night.