不同辐射条件下苹果叶片净光合速率模拟

以富士苹果(Malus domestica Borkh.cv.‘Fuji’)为试材,将C3植物光合生化模型、气孔导度半机理模型、叶片最大光合速率和相对光合有效辐射(RPAR)之间的经验公式相耦合,能够模拟出不同RPAR(或树冠不同部位)下叶片净光合速率(Pn)对小气候因子和叶水势(Ψl)的响应,及Pn日变化。模拟表明,不同RPAR下Pn变化主要依赖于光合有效辐射(PAR)大小,并对CO2浓度有很高敏感性。不同RPAR下叶片Pn最适温度约为20—30℃,并随PAR或CO2浓度的升高而升高。相对湿度(RH)和Ψl对不同RPAR下叶片Pn影响不大,Pn只随RH和Ψl的减小而略有降低。数值模拟表明,当RPAR减小时Pn随之迅速减小,从冠层3 m到1 m处,叶片RPAR从57.18%减少到16.22%,而最大Pn从16.65μmol.m-.2s-1减小到4.24μmol.m-.2s-1。在平均气象条件下,树冠顶部单位面积叶片每天固定CO2为420 mmol.m-.2d-1,而下层叶片只有40 mmol.m-.2d-1。当苹果树冠内叶片接受RPAR低于12%时,全天净光合总量为0,这类叶片可称为无效叶,其所在树冠空间为无效光区。果树整形修剪的主要目的就是尽量减少无效枝叶,利用该模型可确定出这类枝叶在树冠中的位置。

The simulation of leaf net photosynthtic rates in different radiation in apple canopy

The study of leaf photosynthesis in different canopy positions of fruit tree is very important,which can be applied to solving various theoretical and applied tasks,e.g.the study of canopy physiological dynamic,orchard density,pruning and fruit load control.Coupled model of net photosynthetic rate(Pn) of the apple leaves was presented which was developed on the basis of the biochemical model of C3 photosynthesis and semi-mechanistic model of stomatal conductance.We used an experiential equation to describe the relationship of Amax between the top,mature,sunlit leaves,and others in the canopy.The sensitivity of Pn to microclimatic factors and leaf water potential(Ψl) in different RPAR was assessed systemically.The experiment was carried out in a ’Fuji’ apple(Malus domestica Borkh.cv.’Fuji’) orchard from 2006 to 2008.The orchard is in the farm of The Ming Tombs(latitude 40°13′north,longitude 116°13′east,altitude 79m) in Changping county of Beijing. The simulation showed that leaves Pn in different RPAR were highly sensitive to variations in CO2 concentration at the leaf surface,and was a function of PAR.The optimum Ta of Pn was about 20—30℃ in different RPAR and shifted to a higher temperature as PAR or CO2 increased.The influence of RH and Ψl on Pn occurred through the stomata,which closed with the decrease in RH and Ψl.Only slight effects of RH and Ψl on Pn were found in different RPAR.The results indicated that Pn decreased rapidly with the decrease in RPAR interception by the leaves.When the canopy radiation decreased from 3 m to 1 m,the average RPAR and maximal Pn of leaves decreased by 57.18% to 16.22% and by 16.65 to 4.24 μmol·m-2·s-1,respectively.The diurnal variations in Pn depended mostly on PAR,represented as double-peak curves when RPAR excessed 60%.During a whole day(24 h),a unit leaf area fixed 420 mmol of CO2 on average weather data to upper leaves,and only 40 mmol of CO2 when leaves RPAR was about 30%.When leaves RPAR decreased to 12% in apple canopy,the net photosynthetic rate in a whole day decreased to 0 with meteorological data.The area of canopy where total Pn is zero in growth season can be called useless radiation area.The main aim of tree pruning is to remove useless shoots and leaves,and identification of these parts can be conveniently determined by our model.In conclusion,the coupled model performed well in predicting Pn for leaves in different RPAR(or canopy position).And the model has simple input and output parameters and can be widely used as a module in the fruit simulation model.