Study on sap flow characteristics of grape and its environment influencing factors in cold regions of northeastern China

Transpiration of plants is a complex process, it not only affected by its own characteristics, but also affected by the surrounding environmental factors. In order to explore the characteristics of grape sap flow and its relationships with environment factors in the cold areas in northeastern China, grape sap flow rate and meteorological factors were monitored and analyzed systematically. Results showed that the daily transpiration of grape sap flow and daily transpiration in the whole growing period showed a trend of single peak changes, intraday peak values occurred between 10:30-13:00, the peak values reached 406.32 g/h at the most vigorous August. Under the clear weather condition, the flow in each month showed a clear trend of single peak change. The sap flow rates in rainy, cloudy and sunny days were 64.81, 67.42 and 127.00 g/h, respectively. Due to the difference in solar radiation, the fluid flow and fluctuation ranges of three weather conditions showed differences. The daily transpiration of grape was the most severe at August during the whole growth period, and the daily average transpiration exceeded 4 mm/d. From the mean value of transpiration for each growth period, the value reached 2.41-2.91 mm/d during the fruit ripening period and the coloring period, while the average daily transpiration decreased to 0.79 mm/d during the late growth period of grape, and the maximum daily transpiration during the growth period was 4.10 mm/d. The changes of daily grape transpiration in the whole growth period showed obvious seasonality, and overall presented a high-low-high trend. From the daily changes of the sap flow during the growth period (May-October), the monthly variation of the sap flow rate from the largest to the smallest was: August>July>September>June>May>October. The positive correlation between grape sap flow rate and PAR, VPD, VT (variable of transpiration) were significant (P<0.01), and the negative correlation between sap flow rate and RH (relative humidity) (P<0.01). The main influencing factors of instantaneous flow rate and daily transpiration were PAR and VPD. At month scale, the most important influence factor changed between PAR and VT. The main influencing factors of sap flow during the whole growth period were PAR and VT, however, the coefficient of determination would decrease as the study time scale increases. Constructing regression equations of sap flow and PAR, VT, VPD, PAR and VPD during the whole growth period, and the coefficient of determination were 0.60, 0.58, 0.40 and 0.53. The results showed that in different meteorological factors and sap flow, the time lag varied obviously, there is a significant time lag between the sap flow rate and PAR, VPD. PAR start-up time and stop time were ahead of the sap flow, the peak time was behind sap flow, the longest time lag of PAR was 1.5 hour. VPD lags behind the flow fully.