Modeling Leaf Photosynthesis And Stomatal Conductance Of Greenhouse Grown Cut-lily In Response To Drought And Nitrogen Stress Combinations

Leaf photosynthesis and transpiration are two imporatant eco-physiological processes affecting crop growth and water use efficiency.Water and nitrogen are two important environmental factors affecting leaf photosynthesis and transpiration.Crops grown in the field and low-investment greenhouses frequently encounter drought and nitrogen stress due to inappropriate crop management.Therefore,accurately modelling leaf photosynthesis and transpiration in response to different water and nitrogen conditions is the first step towards predicting crop growth and yield,optimizing water and nitrogen management,and accessing yield loss under drought and nitrogen stress.The photosynthetic biochemical model of Farquhar,von Caemmerer and Berry(the FvCB model)has been widely used to study photosynthesis in response to environmental changes.The FvCB model is always coupled with the stomatal conductance model of Ball,Woodrow and Berry(the BWB model).How to adjust parameters in the FvCB model and BWB model according to environmental conditions is of vital importance for model application.In this study,experiments on cut-lily with different water and nitrogen treatments were conducted in Nanjing,China from 2009 to 2013.Key parameters in the FvCB model and BWB-Leuning-Yin model(a revised version of the BWB model)were estimated.The relationships between model parameters and leaf nitrogen content were quantified,and these relationships were incorporated with the FvCB model and BWB-Leuning-Yin model to develop a coupled FvCB and BWB-Leuning-Yin model that can be used to predict leaf photosynthetic rate(An)and stomatal conductance(gs)under different water and nitrogen conditions.The coupled model was validated using independent experimental data.Main results were listed below:1.The effects of drought and nitrogen stress combinations on the FvCB model parameters were clarified,and the linear relationships between FvCB model parmeters and leaf nitrogen content were quantified.Key biochemical parameters in the FvCB model,including maximal electron transport rate(Jmax25),the conversion efficiency between light and electron under limiting light condition(?2LL),maximal Rubisco carboxylation rate(Vcmax25)and mitochondrial respiration during daytime(Rd25),and the activation energy for Jmax25 and Vcmax25(i.e.EJmax and EVcmax)were estimated by fiiting the gas exchange data and chlorophyll florescence data obtained in the combined water and nitrogen stress experiments to the FvCB model equations.Results showed that drought,nitrogen stress and their combination decreased Jmax25,K2LL,Vcmax25 and Rd25,whereas EJmax and Evcmax were not affected by water and nitrogen treatments.Linear relationships existed between key biochemical parameters(Jmax25,?2LL,Vcmax25,Rd25)and leaf nitrogen content.2.The effects of drought and nitrogen stress combinations on mesophyll conductance and BWB-Leuning-Yin model parameters were clarified,and the linear relationships between mesophyll conductance and leaf nitrogen content and between g0(a parameter in the BWB-Leuning-Yin model)and leaf nitrogen content were quantified.Mesophyll conductance(gm25)and BWB-Leuning-Yin model parameters,including stomatal conductance when light level approaches to zero(g0),the ratio between intercellular CO2 concentration Ci and ambient CO2 concentration Ca under saturating vapour pressure defict(a1)and the decreasing slope of the Ci/Ca with vapour pressure deficit(b1),were estimated by fitting gas exchange data and chlorophyll florescence data obtained in the combined water and nitrogen stress experiments to the equations describing mesophyll conductance and the BWB-Leuning-Yin model.Results showed that drought,nitrogen stress and their combination decreased gm25 and g0.a1 and b1 were decreased by drought but were not affected by nitrogen treatments.Linear relationships existed between gm25 and leaf nitrogen content,and between g0 and leaf nitrogen content,whereas no obvious linear relationships existed between a1 and leaf nitrogen content,and between b1 and leaf nitrogen content.3.A coupled model of leaf photosynthesis and stomatal conductance for cut-lily grown under different water and nitrogen conditions was developed,and the model was validated using independent experimental data.The linear relationships between FvCB model parameters(Jmax25,?2LL,Vcmax25,Rd25)and leaf nitrogen content,between gm25 and leaf nitrogen content,and between g0 and leaf nitrogen content were incorporated with the FvCB model and BWB-Leuning-Yin model to develop a coupled FvCB and BWB-Leuning-Yin model that can be used under different water and nitrogen conditions.The coupled model was validated using independent experimental data.Results showed that the coupled model was able to satisfactorily predict leaf photosynthetic rate(An)and stomatal conductance(gs)within a certain range of soil water potential(for drought happened in leaf expansion stage and flower bud break stage in cut-lily,this range for soil water potential was-4?-50 kPa and-4?-30 kPa,respectively).When applying the coupled model,a1 and b1 need to be adjusted according to water condition,otherwise,gs was underestimated by 9%under non-water stress and was overestimated by 13%under water stress.The underestimation of gs under non-water stress did not affect the prediction of An whereas the overestimation of gs under water stress led to a 9%overestimation of An.The coupled FvCB and BWB-Leuning-Yin model developed in this study can be used to predict leaf photosynthesis and transpiration under different water and nitrogen conditions,can facilitate the development of yield loss accessing model under drought,and can be used to optimize crop water and nitrogen management.