Characteristics of trunk SAP flow and its relationship with environmental factors during growth and development in Hongyang kiwifruit

Abstract: 【Objective】At present, the situation of water shortage in China is becoming more and more serious, especially in the arid areas of northwest China. The lack of water resources has been considered as a serious obstacle to agricultural development. With the change of industrial structure, the planting ar-ea of fruit industry in China is increasing, but the irrational use of water resources leads to a sharp in-crease in water consumption. Therefore, how to make effective use of limited water resources and pro-duce high-quality, stable and high-yield fruits with increasing the income of local farmers and promot-ing the effective circulation of ecological environment has become a scientific problem to be solved ur-gently. In view of the large spatial and temporal differences in rainfall in Miluo Town, Shuicheng Coun-ty, Guizhou province, the water consumption and environmental factors of kiwifruit in different growth stages were measured and systematically analyzed. The water consumption of kiwifruit in different growth stages was discussed in order to provide scientific basis for water management and rational utili-zation of kiwifruit in this district.【Methods】The experiment was carried out from March 1 to August 31, 2020. The flow rate of stem fluid of 5-year-old kiwifruit Hongyang was measured by thermal diffu-sion flow probe method, and the environmental factors were monitored synchronously by small meteo- rological stations. After selecting the representative sample wood, the compass was employed to deter-mine the sample wood north direction, the dead skin at the diameter with breast height (1.3 m) was scraped off, and sodium hypochlorite was used to clean out the drill, which was fit to the sensor hole. The probe was inserted into it, paying attention to the depth of the probe, and plasticine was applied to seal the joints after insertion, and tools such as foam and tape were used to fix the probe. Finally, the outer layer was wrapped around the PVR shield and sealed with waterproof tape. The seal was coated with glass glue to prevent water from entering, which worked normally after connecting the power sup-ply. Average data were calculated and stored for every 30 min. The measurement method was set for point continuous observation.【Results】Daily average water consumption at different growth stages was as follows: the fruit expansion period (3.02 kg) > fruit maturity period (2.94 kg) > flowering and fruit setting period (0.99 kg) > bud break and leaf expansion period (0.77 kg). The daily maximum aver- age water consumption in fruit expansion period was 4 times more than that in bud break and leaf ex-pansion period. It was worth noting that the daily water consumption of kiwifruit mainly showed a trend of“low- high- low”. The daily maximum average water consumption at the fruit enlargement growth stage was 4 times more than that at the bud break and leaf expansion stage, and notably, the dai-ly water consumption of kiwifruit mainly showed a“low-high-low”trend. The water consumption of ki-wifruit mainly occurred between 8׃00 and 16׃00, which represented“high in the day and low in the night”, and there was a less water consumption at night. In terms of the monthly scale, the water con-sumption of kiwifruit increased gradually from March to July, reaching the maximum in July, while slightly decreasing in August, and the overall trend was as follows: July (90.60 kg)>August (86.96 kg)>June (66.20 kg)>May (53.35 kg)>April (41.21 kg) >March (25.29 kg). The total water consumption at different growth stages was as follows: The fruit swell stage (326.33 kg) > the fruit maturing stage (88.13 kg) > the flowering and fruit-setting stage (24.71 kg) > the bud break and leaf expansion stage (18.36 kg), and the maximum water consumption at the fruit swell stage was 17.78 times more than that at the fruit maturing stage. There was a significant correlation between SAP flow rate and environmen-tal factors at different growth stages of kiwifruit. In addition, the solar radiation, air temperature, wind speed, soil temperature and soil moisture were significantly and positively correlated with diurnal varia-tion of SAP flow of kiwifruit at different growth stages, while negatively correlated with relative humid-ity. Furthermore, the diurnal variation trend of environmental factors such as solar radiation, air temper-ature, wind speed and soil temperature was similar to that of SAP flow rate of kiwifruit. Moreover, tak-ing RN, VPD, VT and TS as independent variables and SAP flow rate as dependent variables, the multi-ple regression analysis was conducted, and the bud break and leaf expansion stage was obtained: F=60.985+0.055Rn+11.844VPD+1.043VT-3.119Ts (R2=0.918), the flowering and fruit-setting stage was F=-301.524+0.336Rn-77.366VPD+2.529VT+22.777Ts (R2=0.962), the fruit swell stage was F=643.830+0.124Rn+26.082VPD+1.683VT+29.093Ts (R2=0.968), and the fruit maturing stage was F=-1955.991-1.845Rn+175.061VPD+17.850VT+81.869Ts (R2=0.973). The coefficient of determination for the fit of the four factors was 0.973. It was worth noting that the four environmental factors of RN, VPD, VT and TS had a good explanation for the changes in SAP traffic. There were differences in SAP flow rate un-der different weather conditions during the prime period of kiwifruit. In addition, the daily variation of SAP flow was as follows: Sunny day > cloudy day > rainy day. The SAP flow rate of kiwifruit trunk showed a single or bimodal trend of“low-high-low”on cloudy days and sunny days, while it showed a multi-peak pattern on rainy days, which was mainly caused by the environmental factors that fluctuated greatly in rainy days. Furthermore, with Rn, VPD, VT and TS as independent variables and SAP flow  rate as dependent variable, the multiple regression analysis was carried out. The fitting equation under sunny conditions was F=-943.776+0.260Rn+49.647VPD+1.7558VT+42.698Ts (R 2=0.956), and that under overcast conditions was F=-476.655+3.643Rn+228.831VPD+0.566VT-1.854Ts (R2=0.674). The fit-ting determinants of sunny, cloudy and rainy days were 0.965, 0.751 and 0.674, respectively. The fluctu-ation of environmental factors was the largest in rainy days, while the fitting determinants were the low-est.【Conclusion】According to the multiple relationships among water consumptions in different growth stages of kiwifruit, the water consumption ratio in different phenological stages was determined synthetically. Combined with soil moisture index, the corresponding water storage facilities were estab-lished, and the problem of uneven spatial and temporal distribution of rainfall was compensated.