Abstract:Based on the experimental factors like soil moisture, air temperature, relative humidity and solar radiation, a composite quadratic orthogonal regressive rotation design of four factors and five levels was adopted to characterize the co-ordination of environmental factors in driving and regulating transpiration rate of greenhouse grown muskmelon. Soil moisture was maintained by using weighing method, and environmental factors were controlled by the chamber of a portable photosynthesis system (Li-6400; LI-COR). Transpiration rate and stomatal conductance were measured under different combinations of environmental factors. Characterizations of main effect, single effect and marginal effect for each environmental factor were determined by using the environmental data. The results showed that: all of the environmental factors were positively correlated with transpiration rate except relative humidity. Correlation between transpiration rate and soil moisture, temperature can be described in a linear function, respectively. But solar radiation and relative humidity exhibited parabolic functions with transpiration rate. Soil moisture and temperature showed a stable positive marginal effect on transpiration rate with increasing treatment levels, while solar radiation and relative humidity showed linear functions with a positive and negative slope, respectively. Marginal effects of solar radiation and relative humidity were divided into positive and negative with threshold treatment levels of -0.69 and -1.49. Considering the tight coordination between environmental factors in regulating transpiration rate, a quantitative framework was presented to characterize and quantify pathways of each environmental factor. Vapour pressure deficit (VPD) was an important intermediary factor in modulating driving force of other environment factors, which performed a dominant role in determining leaf transpiration rate at the instantaneous scale.
