Selection of light response models and comparative photosynthetic pa-rameters of Malus Jinxiu under different fertilization treatments

LI Hengkai; WANG Haichao; PEI Zhiyong; ZHANG Junyao; WANG Xinping; CHEN Congyu; ZHANG Yan; GU Yiming; BAO Chunming

doi:10.13925/j.cnki.gsxb.20250110

Abstract：[Objective]Malus Jinxiu is a key component of the characteristic forestry and fruit industry in Xing'an League,with considerable economic and ecological value.Due to its rich nutritional profile and unique medicinal properties,it is well-received by consumers and highly favored in the market.In addition to contributing to local income generation,the cultivation of M.Jinxiu also plays a vital role in maintaining regional biodiversity and promoting sustainable land use.However,despite the growing de-mand for M.Jinxiu,studies on its light response mechanisms remain relatively limited,particularly re-garding the effects of different fertilization treatments on its photosynthetic response and overall physio-logical performance.Understanding how varying nutrient inputs influence photosynthetic efficiency is essential for improving yield quality and ensuring optimal growth conditions.This study,therefore,aimed to identify the most suitable light response curve model for M.Jinxiu and to conduct a compara-tive analysis of its photosynthetic parameters under various fertilization treatments.By evaluating pho-tosynthetic gas exchange characteristics and model fitting accuracy,the study sought to provide a scien-tific basis for precise nutrient management.The results would offer theoretical guidance and data sup-port for optimizing cultivation strategies,enhancing plant productivity,and improving resource use effi-ciency in the context of ecological agriculture.[Methods]The experimental materials consisted of six-year-old dwarf M.Jinxiu trees grafted onto Malus baccata(L.)Borkh.rootstocks with GM256 as the in-terstock,grown in Group 10 of Ping'an Village,Horqin Right Front Banner,Xing'an League.And the trees had undergone three years of cultivation and acclimatization since their introduction,making them well-suited for studying long-term physiological responses under field conditions.To simulate realistic orchard management,a randomized block design was employed based on local fertilization practices.Four fertilization treatments were applied:T1(0.67 kg Shilomei macronutrient water-soluble fertilizer+2.66 kg organic water-soluble fertilizer for root protection and fruit expansion),T2(1 kg+4 kg),T3(1.33 kg+5.34 kg),and a control group(CK)that received no fertilization.Each treatment was replicat-ed to ensure statistical reliability.A Li-6800 portable photosynthesis system was used to measure the di-urnal variation in net photosynthetic rate and the photosynthetic light response curves under each fertil-ization regime.Key photosynthetic gas exchange parameters,including net photosynthetic rate(Pn),sto-matal conductance(Gs),transpiration rate(Tr),and intercellular CO2 concentration(Ci),were recorded and analyzed.To better understand how different fertilization levels affect photosynthetic performance,the light response data were fitted using four mathematical models:the rectangular hyperbola,non-rect-angular hyperbola,exponential,and modified rectangular hyperbola.The performance of each model was evaluated based on fitting accuracy indicators such as the coefficient of determination(R2),root mean square error(RMSE),and mean absolute error(MAE).Additionally,the accuracy of fitted photo-synthetic parameters-such as maximum net photosynthetic rate(Pn max),light saturation point(LSP),dark respiration rate(Rd),light compensation point(LCP),and apparent quantum efficiency(α)—was compared across models and treatments.This comprehensive analysis intended to provide insights into the photosynthetic characteristics and light response adaptability of M.Jinxiu under varying nutrient conditions,offering a scientific basis for the refinement of fertilization strategies and sustainable or-chard management practices.[Results]The diurnal variation of net photosynthetic rate(Pn)in M.Jinx-iu under all fertilization treatments exhibited a parabolic trend,characterized by a rapid increase from 8:00 to 10:00,a gradual decline from 10:00 to 16:00,and a sharp drop after 16:00.A certain degree of synchronization was observed in the diurnal patterns across different fertilization treatments.The photo-synthetic gas exchange parameters of the fertilized treatments displayed a bimodal curve pattern,where-as the control treatment(CK)showed a distinct unimodal curve.Increasing fertilization levels signifi-cantly enhanced the net photosynthetic rate(Pn),transpiration rate(Tr),and stomatal conductance(Gs),with the T3 treatment showing the most pronounced improvements in all three parameters.After fitting the light response curves of the four fertilization treatments,it was found that all treatments had coeffi-cients of determination(R2)greater than 0.99.Among the models tested,the non-rectangular hyperbola model achieved the highest fitting accuracy,while the rectangular hyperbola model had the lowest.The modified rectangular hyperbola model demonstrated superior parameter fitting for dark respiration rate(Rd),light compensation point(LCP),and maximum net photosynthetic rate(Pn max),with root mean square error(RMSE)and mean absolute error(MAE)values closest to zero.The T3 treatment exhibited the highest light saturation point(LSP),reaching 1 884.874 2 μmol·m-2·s-1,and the largest Pnmax at 16.686 8 μmol·m-2·s-1.With increasing fertilization levels,key photosynthetic parameters such as initial quantum efficiency(α),Pn max,LSP,and Rd increased progressively,while LCP decreased.These results suggest that increased fertilization would enhance light use efficiency and reveal the response mecha-nism of M.Jinxiu photosynthetic parameters to fertilization,providing theoretical support for under-standing its ecological adaptability.[Conclusion]Based on the fitting performance of the four light re-sponse models,the modified rectangular hyperbola model demonstrated the best overall fit.Among the fertilization treatments,T3-consisting of 1.33 kg of Shilomei macronutrient water-soluble fertilizer and 5.34 kg of organic water-soluble fertilizer for root protection,root development,and fruit expansion re-sulted in superior photosynthetic parameters compared with other treatments,indicating that it would be a relatively optimal fertilization scheme.However,the results suggest that this treatment still would fall short of meeting the optimal nutritional requirements of M.Jinxiu.Therefore,future studies should re-fine the fertilization gradient to further assess its impact on plant physiological growth.