Abstract:
To estimate the plant transpiration water consumption of urban greenland accurately and
conveniently, the response relationship between sap flow density and environmental factors of Ginkgo
biloba was studied in this paper. Based on relative efficiency soil water (REW), photo synthetically
active radiation (PAR), deficit vapor pressure(DVP), wind speed (W), the response relationship
between sap flow and environmental factors were analyzed. So as to analyze the interaction between each
factor and sap flow, and determine the key threshold, discrete statistical analysis was given to groups of
the environmental variable factors, which was excluded the influence of other environmental factors.
Finally, based upon the response process and empirical formula of sap flow-evaporation-stoma above to
environmental factors, the relational model of sap flow and environmental factors was built. The results
were as follows: 1) the effects of soil moisture on sap flow were restricted with specific threshold value.
When the relative extractable soil water REW was higher than 62%, soil moisture was unlimited to sap
flow of G. biloba. While when REW was lower than 62%, soil moisture was a limiting factor for sap flow,
and the relationship between sap flow and soil moisture can be described by half value empirical
functions. 2) Photo synthetically active radiation(PAR) was the driving factor for sap flow, with the
driving effect being stronger when PAR was lower than 0.39 mmol/(m2second), while it reached
saturation when PAR was higher than 0.8 mmol/(m2second). The relationship between sap flow and
PAR could be described by hyperbolic functions. 3)Deficient vapor pressure爷s function to sap flow was
dual, when DVP was lower than 3.2 kPa, it had driving effect and the relationship between them could
be described by hyperbolic functions. While DVP was higher than 3.2 kPa, it was restricting functions
which can be described by half value empirical functions. 4) Wind was a restricting factor for sap flow,
but it worked only when wind speed was 4 m/second. The relationship between sap flow and wind
speed could be described by half value empirical functions. 5) The accuracy of sap flow-environmental
factors model was tested. The results showed that the determination coefficient R2 of simulation on hourly
sap flow density was 0.799 8, and relative deviation was 17%, while the determination coefficient R2 of
simulation diurnal sap flow density was 0.895 2, and relative deviation was 10%.