Analysis of sap flow characteristics and plant growth and development status of Kyoho grapevines based on row orientation

【Objective】This study aimed to investigate the effects of row orientation on stem sap flow characteristics and plant growth and development of Kyoho grapevines, in order to determine the transpiration amount and the optimal row orientation for grapevines in the arid and semi- arid regions of Northern Xinjiang. The goal was to establish precise irrigation schedules based on transpiration, utilize row orientation to create suitable canopy microclimate conditions, improve fruit quality and yield, and provide a theoretical basis for irrigation decision-making and cost-effective efficiency enhancement in grape production.【Methods】Using the main fresh grape cultivar Kyoho in the arid region of Xinjiang as the research material, this study employed the wrapped stem flow gauge (heat balance principle) and soil moisture sensors to monitor real-time grape stem sap flow velocity and soil temperature and humidity. Meteorological factor data were collected from a weather station, while yield and quality-related indicators during plant growth and development were also measured.【Results】The results showed that un-der different weather conditions, grape sap flow velocity exhibited an "inverted U-shaped" pattern, being highest on sunny days and lowest on rainy days (though sap flow on rainy days with sufficient sunlight could exceed that on cloudy days). On sunny days, sap flow velocity displayed a bimodal curve; on cloudy days, a multimodal curve; and on rainy days, no clear pattern was observed. Grapevines planted in the east-west (E-W) row orientation exhibited higher sap flow rates than those in the north-south (N- S) orientation, indicating stronger transpiration and a greater need for irrigation to prevent water stress. Across different growth stages, sap flow velocity followed the order: Berry expansion stage＞ maturation stage＞harvest stage, with E-W rows consistently showing higher mean values. Under varying weather conditions, daily cumulative sap flow exhibited an“S- shaped”trend, with the magnitude ordered as: Sunny days＞moderate rain days＞cloudy days＞light rain days. Transpiration in E-W rows was 6.2%, 10.4%, 21.5%, and 5.36% higher than in N-S rows on sunny, moderate rain, cloudy, and light rain days, respectively. Significant differences in transpiration were observed between row orientations, and within the same orientation, transpiration varied significantly among sunny, cloudy, and moderate rain days, but not between cloudy and light rain days. On a diurnal scale, sap flow initiation occurred earlier on sunny days than on cloudy days, while peak flow and cessation times were later. Under both cloudy and sunny conditions, peak sap flow in E-W rows occurred 15 and 30 minutes later, respectively, compared to N-S rows. During moderate rain, sap flow could initiate prematurely due to active root water uptake, potentially starting during the night when rainfall was heavy. Comparative analysis revealed that sap flow velocity in E-W rows was significantly higher than in N-S rows, with both initiation and cessation times delayed. Sap flow velocity showed highly significant positive correlations with sunshine duration, vapor pressure deficit, and mean air temperature (correlation coefficients: 0.89, 0.88, and 0.85, respectively), and highly significant negative correlations with air relative humidity and soil temperature (coefficients: - 0.71 and - 0.77, respectively). A significant negative correlation was observed with soil moisture (coefficient: -0.38). The order of correlation strength with meteorological factors was: Air temperature＞vapor pressure deficit＞sunshine duration＞soil temperature＞air relative humidity＞soil moisture＞wind speed. After fruit set, berry longitudinal diameter increased rapidly in the early stage, entering a rapid expansion phase 45 days after flowering, during which transverse diameter growth dominated. By 55 days after flowering, berries entered the color change and sugar accumulation stage, with size growth slowing. After 65 days, berry size stabilized, and sugar accumulation and flavor compound formation became dominant. E-W rows outperformed N-S rows in berry size, dry matter accumulation, soluble solid content, and yield, with most indicators showing significant differences. However, E-W rows were inferior in fruit quality uniformity and leaf dry matter accumulation.【Conclusion】In conclusion, under the arid and semi-arid climate conditions in northern Xinjiang, Kyoho grapes are more suitable for east-west row orientation planting. However, it should be noted that the irrigation volume required for this row orientation is higher than that for the south-north row orientation.