The variation characteristics of sap flow of Chinese fir in the Yangtze River Delta

This study was designed to analyze the changing rules of the sap flow rate of Chinese fir( Cunninghamia lanceolata) based on the 12 months continuous located observation of the sap flow rate and environment factors by using sap flow meter and ECH2O system from February 2012 to January 2013 in Dongshanqiao Forest Farm of Nanjing. The results indicated that the sap flow rate of Chinese fir showed distinct diurnal changing rhythms both in sunny and cloudy days in different seasons. The change of the sap flow showed a single-peak curve. The crest values of the sap flow rate in spring, summer,autumn and winter were 0. 71- 1. 44,1. 45- 3. 49,0. 55- 1. 91 and 0. 30- 0. 85 kg / h,respectively. The crest value of summer was the highest,that of the winter was the lowest. The greater rainfall,the earlier the sap flow rate starting and the higher peak,the longer of impact. In winter,the sap flow rate increased rapidly when it rained,after the rain the sap flow rate would decrease soon. In summer,the sap flow rate would show obvious rise in the daytime after the rain,and in the later days it would decrease gradually to the original level. There existed seasonal differences for the main environmental factors that influenced the sap flow rate. The main environmental factors of spring,summer,autumn and winter were VPD(0. 884),air relative humidity(- 0. 882),VPD(0. 798) and solar radiation in field(0. 621). Soil temperature was an important environmental factor that influenced the average daily sap flow rate of Chinese fir.