Relationships between stem sap flow rate of litchi trees and meteorological parameters

The stem sap flow rates in Guiweilitchi trees and the meteorological conditions in the litchi orchard were observed continuously and synchronously from 2011 to 2012,using a Dynamax sap flow measuring system and an automatic weather station system,respectively. The temporal patterns of stem sap flow rates and the response to meteorological parameters were analyzed in order to establish a model of the relationship between these two variables. The principle results were as follows:( 1) the stem sap flow rate followed a diurnal pattern,whereby rates were high during the day and low during the night. Seasonal variations in stem sap flow rates were observed,with higher average flow rates in the period of fruit maturation,from May to July. The average stem sap flow rate in 2011 was significantly higher than that in 2012.( 2) On sunny days,the daily variation in stem sap flow-rate was characterized by a single-peak with a large amplitude of variation,while on rainy days the flow-rate was characterized by multiple peaks with a smaller amplitude of variation. On sunny days,the average value of stem sap flow-rate was twice as high as that on rainy days.( 3) The regression equation based on stem sap flow rates and meteorological conditions showed that for a certain range of values,a positive correlation existed between the stem sap flow rates and solar radiation,and between the stem sap flow rates and air temperature,while a negative correlation existed between the stem sap flow rates and relative air humidity. On both sunny and rainy days,solar radiation and air temperature were the most important controls on stem sap flow rates,in terms of meteorological conditions.