Simulation Of The Transpiration Of Mountain Apple Trees With The RATP Structural-functional Model

Most apple varieties planted in the Loess Plateau are Fuji apples,which have a high water demand.Thus,the study of tree transpiration is of great importance for the growth and development of apple trees.At present,measurement of transpiration of fruit trees mainly depends on stem flowmeters.However,this method is expensive and could cause damages to tree trunks.Therefore,it is necessary to find a new method to study the transpiration and water consumption of Fuji apple trees,which could accurately simulate the physiological and ecological processes of apple trees without destroying the tree body.This new method is expected to provide practical guidance for the production of fruit trees in the Loess Plateau in China.In this study,an orchard in the Miaogou Village,Baota District,Yan’an City,Shaanxi Province of China was chosen as the experimental site.First,three-dimensional(3D)digital technology was used to obtain the 3D spatial coordinates of fruit trees’ branches.Then the growth relationship of branches and leaves and the Euler Angle of leaves were combined to construct the 3D virtual plants of apple trees.The response curves of stomatal conductance to photosynthetically active radiation(PAR),temperature(T),atmospheric vapor pressure difference(VPD),and CO2 were measured with photosynthesiometer.Then,the parameters of the structural-functional model of RATP(Radiation absorption,Transpiration and Photosynthesis)were fitted based on the Jarvis empirical stomatal conductance model and Farquhar photosynthetic model.Finally,based on the 3D virtual plants of apple trees,the meteorological data,functional model parameters and non-functional parameters of leaves were input into the model to simulate the transpiration and net photosynthetic rate of apple trees.At the same time,the transpiration dynamics of apple trees were compared with the measured transpiration values with stem flowmeter.Some main results were obtained as follows.(1)Based on the 3D digital technology,the six types of branch shape parameters were successfully fitted for the structure of apple tree body.The results showed that the correlationships between total leaf number and the lengths of nutrition short shoot,fruit set,and secondary shoot of fruit set were very weak,of fruit trees,while the correlationships among the other allometric growth parameters were strong(The relationship between the length of a branch and its total leaf area,the relationship between the length of a branch and its petiole length,the relationship between the length of a branch and its leaf area,the relationship between the length of a branch and its leaf area,the relationship between the length of a branch and its leaf width)and the regression equations were significantly correlated.At the same time,the Mapple model was used to construct the front view,left view,and back view of the virtual plants of apple trees.From the three views,it was found that the constructed virtual plants of apple trees was good since the differences between the virtual trees and the actual apple trees were small.(2)The functional parameters and non-blade functional parameters of the RATP model were fitted.The relationships among different functional parameters of tree leaf were revealed(The linear relationship between maximum stomatal conductance,maximum carboxylation rate,respiration rate,photosynthetically active radiation and leaf area nitrogen content,the relationship between the ratio of stomatal conductance to maximum stomatal conductanceand temperature,the difference of saturated water pressure and photosynthetically active radiation).The results showed that the maximum stomatal conductance,maximum carboxylation rate,respiration rate,and photosynthetically active radiation had a significantly linear relationship with leaf area nitrogen content,which could be used as parameters in the RATP structural-functional model to simulate the physiological process of apple trees.(3)The RATP structural-functional models of Fuji apple trees were constructed in this study.The RATP model simulated the transpiration and net photosynthetic rate of selected Fuji apple trees in the Loess Plateau and the simulation results were compared with the measured transpiration with stem flowmeter to evaluate the simulation accuracy of the RATP model.It was found that the differences between the simulated transpiration with RATP model and the measured transpiration were small.Based on the digital plant data of the model,it is found that when the structure of apple trees was at a medium level,the accuracy of simulated transpiration with RATP model was the highest.At the same time,combined with the measurement data with stem flow-meters,it was found that the transpiration of apple trees followed an obvious single-peak curve both for simulated and measured transpiration values,Diurnal variations of photosynthetic rate of apple trees followed bimodal curves.To sum up,three-dimensional digital technology can model apple tree body well,and leaf functional parameters can well reflect the physiological process of fruit trees and the fitting effect is very good.Therefore,fruit tree structure module and leaf functional module can be combined to build RATP functional model,the transpiration of fruit trees can be well simulated.