| The accurate regulation of greenhouse environmental factors and intelligent and accurate water management have gradually become the development direction of modern smart agriculture,which are important measures to achieve efficient cultivation of protected agriculture.Light radiation drives water transport in soil-plant-atmosphere continuum（SPAC）.Light radiation affects crop growth in many ways,including the amount of light radiation,light time,and change period.Many studies have investigated water transport in plants,while the effects of light radiation on diurnal dynamics of transpiration and water transport remain unclear.In present study,tomatoes were used as test materials.Different light radiation amount,light time,and the period of increased light radiation amount were set.We systematically investigated the response mechanism of tomato transpiration and water transport to light radiation in greenhouses,as well as the interactions between various factors in the SPAC system,aiming to provide decision-making basis for accurate,efficient and intelligent irrigation of facility water.The main findings are as follows:（1）The effects of light radiation amount on diurnal dynamics of water consumption and water productivity on tomatoes in the greenhouse were determined.During the daytime,the increase of light radiation amount significantly improved the leaf water potential,stomatal conductance,and hydraulic conductance of plants before dawn and at noon.The stomatal conductance and hydraulic conductance were increased by 21.78%and 50.53%,respectively.With the increase of the amount of light radiation,the transpiration and stem flow of plants increased steadily,while the higher the amount of light radiation,the smaller the upward trend.Increasing the amount of light radiation could also significantly enhance the hydraulic structure of roots,stems,leaves and stomata of plants,improve the water conductivity of plants,strengthen the relationship between various factors of SPAC system,and ultimately improve the dry matter accumulation,yield and water use efficiency of plants.Compared with the control,adding 6.48/12.96 MJ m-2 radiation on sunny day and cloudy day respectively increased the yield by 38.42%.On both sunny and cloudy days,the supplementation of4.32/8.64 MJ m-2 light radiation increased the water use efficiency by 28.60%.（2）The effect of light time on the dynamics of water circadian rhythm and water transport on greenhouse tomatoes was revealed.The results showed that moderate extension of light time could improve the adaptability of leaf water state to the environment,improve the stomatal and hydraulic conductance,and enhance the power of water transport.Among them,the stomatal(0.64 mol m-2 s-1)and hydraulic conductance(9.87 mmol m-2 s-1MPa-1)in 16h treatment were the highest.In the natural light period,the daily transpiration water consumption of plants was higher at 12 h and 16 h treatments,and the transpiration and stem flow were most active at 20 h treatment during the extended light period.Prolonged treatment enhanced the hydraulic structure of the plants,and the maximum stomatal conductance and stem and leaf duct area were the largest at 16 h treatment.The analysis results of structural equation model showed that the effect of light radiation on transpiration and stem flow was the highest at 16 h treatment,and the model has the best effect.The dry matter accumulation,yield and water utilization of 16 h treatment were significantly higher than those of other treatments,and the light energy utilization of 12 h and 16 h treatments was the highest.（3）The effect of temporal variation of light radiation on diurnal dynamic tradeoff of water transport and photosynthesis on greenhouse tomato was elucidated.Increasing the amount of light radiation at different times of the day had significant effects on plant hydraulics and photosynthetic capacity.Increasing the amount of light radiation at 6:00～10:00,16:00～20:00and 20:00～24:00 could improve the leaf water potential and hydraulic conductivity of plants.Among them,the increase of light radiation from 16:00 to 20:00 had the greatest effect on the increase of hydraulic conductivity of plants,which was 19.54%higher than that of the control,and effectively enhanced the water conductivity of plants.Increasing the amount of light radiation improved the transpiration and stem flow of plants at all time periods.Increasing the amount of light radiation from 16:00 to 20:00 had the greatest improvement on the transpiration and stem flow,and increasing the amount of light radiation from 20:00 to 24:00would increase the transpiration and water consumption of plants from 0:00 to 6:00 at night.In terms of plant photosynthetic capacity,the increase of light radiation amount from 16:00 to20:00 had the greatest effect on net photosynthetic rate and stomatal conductance of plants,and had the most significant effect on mesophysial conductance,maximum carboxylation rate,maximum electron transfer rate and triose phosphate utilization rate of plants,and enhanced the structural parameters related to hydraulic and photosynthesis of plants.Increasing the amount of light radiation between 16:00 and 20:00 could enhance the coordination between hydraulics and photosynthesis.The improvement of water use efficiency and yield was the highest,which were 23.28%and 32.74%higher than that of control,respectively.（4）The time-lag effect of greenhouse tomato water transport under different light radiation amount and irrigation quantity was quantified.Hysteresis effect is common in each stage of SPAC.Under high radiation conditions,the lag effect of transpiration on light radiation and stem flow on transpiration is strong,and the maximum lag time in a day is 60min.Compared with the basal stem flow in the middle,the upper stem flow had a greater fluctuation in the lag time of the middle stem flow in one day,and their maximum lag time was 50 min and 60 min,respectively.Stem diameter,fruit diameter and substrate water content lagged behind stem flow for 60 min,70 min and 50 min,respectively.Under high radiation and sufficient irrigation conditions,plant transpiration was significantly higher than stem flow from 10:00 to 18:00.Under the condition of high radiation and light water stress,plant transpiration was significantly higher than stem flow from 10:00 to 16:00.When the time-lag effect of plant transpiration and water transport were added to the structural equation model,the path coefficients between most variables were improved,and the overall effect of the model in each treatment was enhanced.（5）An irrigation decision model of greenhouse tomato based on different water physiological states and transpiration time-lag effect was constructed.Based on the different effects of light radiation on the physiological state of water,transpiration water consumption of plants was divided into"growth water"which promoted the physiological growth of plants and"maintenance water"which maintained the basic survival of crops.The time-lag effect between transpiration and light radiation was introduced,and the transpiration estimation model of plant and half an hour scale was established.The advance decision of crop transpiration water consumption was realized.The simulation accuracy of the model is reasonable,and it can be well applied to the simulation of plant transpiration in the complex environment of greenhouse.Compared with the control model,the standard error is reduced by 45.03%and the relative error is reduced by 11.08%.In conclusion,when the supplement of light radiation amount on sunny and cloudy days was 4.32 and 8.64 MJ m-2,the daily light time was 16 h,and the light radiation amount was increased from 16:00 to 20:00.The plant water transport capacity was improved by enhancing the stomatal conductance,hydraulic conductance and hydraulic structure of the plant.Moreover,the dynamic relationship among factors in the SPAC system was strengthened,which ultimately improved yield and water use efficiency.The regulation of light in production should be coordinated with economic cost and other environmental factors.The water transport process of plants is affected by the"water clock"and the time lag effect.The single plant and the half-hour scale transpiration model based on these two points could effectively improve the prediction accuracy of plant water consumption.It can provide basis for intelligent high-frequency and precise water management of tomato.It can provide decision basis for intelligent high frequency and precise water management of plant tomatoes. |
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