Temporal and spatial diurnal dynamics of the hysteresis of weighed transpiration and water transport in tomatoes

Abstract

In studies of terrestrial water cycles and farmland irrigation management, plant transpiration is an important reference data source. There is a hysteresis effect between plant transpiration and meteorological factors, which is important for predicting plant transpiration. However, the hysteresis effect in diurnal dynamics (time) and between the processes of water from soil to air in the soilplantatmosphere continuum (SPAC) system (space) remains unclear. In this study, the intensity of light radiation (high radiation, HR; low radiation, LR) and the amount of water used for irrigation (high irrigation, HW; low irrigation, LW) were used to form four treatments (HRHW, HRLW, LRHW, and LRLW) on tomato plants in a greenhouse. The diurnal dynamics of the transpiration of the whole plant by weighting (weighted transpiration, WT), sap flow (SF), and lag time in the process of water transport in tomato plants were analyzed by the data of every 10 min. The results showed that the WT exceeded the SF in the HRHW during 10:00–18:00 and in the HRLW during 10:00–16:00. In the HRHW, the proportion of SF in the upper part to the lower part of the plants was significantly lower than that in the other treatments during the daytime. The hysteresis effect was prevalent in the process of water transport from soil through plants to the atmosphere during the daytime. The lag time of WT to net radiation (Rn) and SF to WT changed more dramatically during the daytime under HR- conditions, and the maximum lag time was 60 min. Compared with the hysteresis of middle SF to low SF of plants, the lag time of top SF to middle SF had a greater fluctuation, with a maximum of 50 min (LRLW) and 60 min (HRHW and HRLW), respectively. The longest times at which of stem diameter (SD), fruit diameter (FD) and substrate water content (SWC) lagged behind SF were 60 min (LRHW), 70 min (HRHW and LRHW) and 50 min (HRHW and HRLW), respectively. After temporal and spatial dynamic hysteresis were added to the structural equation modeling (SEM), the path coefficients between most variables were improved, and the overall effect of the model was enhanced in all treatments. This provides a valuable direction for the future improvements in transpiration models, irrigation efficiency, and crop yield.