Responses of Trunk Sap Flow of Armeniaca sibirica to Varied Environmental Factors in Different Weather Conditions

The sap flow rate of Armeniaca sibirica, environmental factors including meteorological factors, soil moisture, and soil temperature were monitored simultaneously in the growing season of 2019 in a loess hilly area of Ningxia. The relationships between the sap flow rate and environmental factors were analyzed under different weather conditions, and the contributions of each main environmental factor to the sap flow variation were quantified separately. The results showed that in sunny days, solar radiation was the greatest conctributor to the sap flow variation(80.8%), then were the saturation vapor pressure deficit(2.7%) and wind speed(1.4%). In cloudy days, solar radiation, air temperature and soil temperature contributed 44.9%, 9.3% and 13.7% to the sap flow varation respectively. In rainy days, the contribution of solar radiation was 60.4%, and the saturation vapor pressure deficit was 4.7%. From sunny, cloudy, to rainy days, the total contribution of environmental factors to the sap flow variatoin decreased in turn, the correlation between sap flow rate and air relative humidity and saturation vapor pressure deficit gradually increased, and the correlation between sap flow rate and air temperature, soil moisture and soil temperature gradually decreased. Under the 3 weather conditions, solar radiation was the main meteorological factor controlling the sap flow variation, then were the saturation vapor pressure deficit, air temperature, soil temperature, and wind speed. The results provide a theoretical basis for a detailed characterization of vegetation transpiration response to environmental factors and a better understanding of relevant driving mechanisms.