Path Analysis of the Main Control Factors of Transpiration in Greenhouse, Drip-Irrigated Grapes in Cold Areas of Northeast China

To investigate the characteristics of grape transpiration water consumption and its environmental coupling mechanism in a greenhouse growing environment in cold areas of Northeast China, the dynamic monitoring of greenhouse grape sap flow and microenvironmental factors in a greenhouse was carried out for two years. Correlation analysis and path analysis were used to study the characteristics of grape transpiration environmental factors at different temporal scales (instantaneous, daily, and growth period) and the influence mechanisms on greenhouse grape transpiration. The results of correlation analysis by growth period showed that, on the instantaneous scale, the correlation between each meteorological factor and grape transpiration reached a significant level (coefficient of determination R-2 ranged from 0.25 to 0.84). On the daily scale, the correlation of solar radiation (R-s) was the best except for the new growth period (R-2 ranged from 0.49 to 0.89). The results of the split-fertility path analysis showed that the total effects of R-s on instantaneous transpiration were the largest at all stages of fertility, with decision coefficients (R) ranging from 0.69 to 0.90. On the daily scale, the total and direct effects of R-s on daily transpiration were the largest (R ranged from 0.70 to 0.94), except for the new growth period. The results of the whole growth period path analysis showed that R-s had the greatest effect on instantaneous transpiration, with R of 0.86. On the daily scale, R-s was also the most influential factor in grape transpiration, with R of 0.81. On the growth period scale, only air temperature (T-a) and leaf area index (LAI) were significantly correlated with transpiration (p < 0.05), and R-s had the largest total effect on transpiration with R of 0.68. To sum up, on each time scale, R-s was always the most important factor influencing grape transpiration. However, as the time scale increased, the effects of LAI and soil water content (SW) on transpiration increased while the effects of R-s, T-a, RH, and VPD on transpiration gradually decreased.