Stem flow of mature jujube trees during dormancy in arid area of northwest China

Abstract:【Objective】A jujube orchard about 6.67 hm² was selected in the South Industrial Park of Ak- su, Xinjiang, for this study. The jujube trees were planted in 2000. Because the jujube trees in this area are mostly flood irrigated, a lot of water is lost due to evaporation and soil leakage. The evapotranspira-tion of jujube is mainly composed of transpiration and soil evaporation. In order to prevent the evapora-tion and soil leakage, micro sprinkler irrigation was used in this study. Through the fixed-point monitor-ing of stem flow rate of mature jujube trees for two consecutive years, the water consumption of mature jujube trees in the growth and dormancy period was accurately measured, which provided a theoretical basis for high-efficiency water-saving irrigation for mature jujube trees.【Methods】In this experiment, three healthy mature gray jujube trees with similar vigor were randomly selected in the orchard. The stem flow was monitored with thermal diffusion probe method. The probes of 3 tree species were locat-ed at the same height and the distance between two probes on each tree was the same. The heating probe was 40 cm from the ground, and the other probe 12 cm above the heating probe, which was fixed by foam board, wrapped with reflective and heat-insulating film, and the top of the probe was wrapped adhesive tape to protect the sensors from the downward water flow along the stem. The correlation be-tween the stem flow rate and meteorological factors during the dormancy period was analyzed, and mul-tiple linear regression models of stem flow rate against meteorological factors were established.【Re-sults】Based on the analysis of stem flow, it was found that the sap flow still occurred in the dormancy period, and there were great differences in start-up time, maximum increase range, maximum decrease range, peak value and diurnal variation pattern of stem flow. The sap flow activity of mature jujube trees was obvious at night during dormancy period, which fluctuated in the range of 50-490 mL·h^-1. The peak range of stem flow rate varied with stages of dormancy, and the peak value of stem flow rate shift-ed from 7:00—10:00 in C1, C2 and C3 stages to 10:00—13:00 in C4 and C5 stages. The peak value of stem flow rate fluctuated between 7:00 and 12:00, and it was higher in the early dormancy stage (C1)and dormancy breaking stage (C5), and lowest in mild dormancy stage (C3). The daily cumulative wa-ter consumption in dormancy period decreased first and then increased, which was opposite to that in the growth stage. Daily cumulative water consumption was 4.99 L in C1 stage, 4.22 L in C2 stage, 4.00 L in C3 stage, 4.88 L in C4 stage, and 5.53 L in C5 stage in the season of 2018—2019; and 5.23 L, 4.99 L,4.01 L, 4.91 L and 5.19 L in the corresponding stages in the season of 2019—2020. The correlation co-efficients between stem flow rate and air humidity were 0.770**, 0.818**, 0.660**, 0.549** and 0.769** for C1, C2, C3, C4 and C5 stages, respectively. The correlation degree between stem flow rate and meteorological factors was in the order of air humidity > air temperature > solar radiation in C1, C2 and C3 stages, and was air temperature > air humidity > solar radiation in C4 stage. The multiple linear regression models of jujube stem flow rate and meteorological factors in dormancy period were estab-lished. The regression coefficient and correlation coefficient test showed that the multiple linear regres-sion equation reached significant level.【Conclusion】The ratio of water consumption of mature jujube trees in dormancy period to the total water consumption of the whole year was 22.19% to 23.31%. Air humidity was the most significant meteorological factor affecting stem flow rate during dormancy period.