| Lagerstroemia indica ’Zi Jing Ling’ is an excellent new variety of Lagerstroemia indica belonging to Lythraceae.With unique flower color,long flowering period and beautiful tree posture,it is a garden tree with high ornamental value in summer.Currently,there are few studies on the fertilization techniques for L.indica container seedlings,and a scientific fertilization formula system has yet to be established,limiting its large-scale production and application.In this study,we used two-year-old L.indica container seedlings as the material and adopted the "3414" fertilization test design to study the effects of different fertilization treatments on the growth,flowering and physiological characteristics of L.indica container seedlings.A comprehensive analysis was conducted to determine the optimal fertilization formula,providing theoretical and technical references for the efficient cultivation of high-quality L.indica seedlings.The research results were as follows:(1)The effects of different fertilization treatments on the growth indexes of L.indica were different.The total plant height growth,the total ground diameter growth,the total crown growth,above-ground biomass,below-ground biomass,total biomass,leaf area,total root length,total root surface area,total root volume,and root tip number were all best under the T6(N2P2K2)treatment,with increases of 69.04%,111.97%,24.16%,67.03%,143.48%,89.08%,155.71%44.55%,48.83%,114.34%,and 81.75%,respectively,compared with the no-fertilization treatment(T1),with significant differences(P<0.05).The total root length and root tip number under the T11(N3P2K2)treatment were both lower than those under the no-fertilization treatment(T1),with no significant differences(P>0.05).(2)Different fertilization treatments had different effects on the flowering indexes of L.indica.The number of inflorescences per plant,the number of flowers per inflorescence,the length of the inflorescence,the width of the inflorescence,the flower diameter,and the flowering period all reached their maximum values under the T6(N2P2K2)treatment,with increases of 200.04%,109.09%,92.31%,66.23%,20.01%,and 33 days,respectively,compared with the no-fertilization treatment(T1),with significant differences.The width of the inflorescence under the T2(N0P2K2)treatment,the flower diameter under the T4(N2P0K2)treatment,and the flowering period under the T11(N3P2K2)treatment were all shorter,with no significant differences compared with the no-fertilization treatment(T1).(3)Different fertilization treatments promoted the photosynthesis of L.indica to varying degrees.The net photosynthetic rate,intercellular CO2 concentration,stomatal conductance,transpiration rate,and SPAD value all reached their maximum values under the T6(N2P2K2)treatment,with increases of 65.90%,26.92%,60.09%,102.13%,and 56.17%,respectively,compared with the no-fertilization treatment(T1),with significant differences.The net photosynthetic rate and stomatal conductance under the T10(N2P2K3),T11(N3P2K2),and T14(N2P1K1)treatments were smaller,with no significant differences compared with the no-fertilization treatment(T1).(4)Different fertilization treatments had different effects on the nutrient and endogenous hormone contents of L.indica.The soluble sugar content,soluble protein content,IAA content,and ZR content under the T6(N2P2K2)treatment were the highest,with increases of 30.96%,37.02%,59.43%,and 71.25%,respectively,compared with the no-fertilization treatment(T1),with significant differences.The GA3 content under the T3(N1P2K2)treatment was the highest,with an increase of 51.16%compared with the no-fertilization treatment(T1),with a significant difference.The soluble sugar content under the T11(N3P2K2)treatment was significantly lower than that under the no-fertilization treatment(T1),and the ABA content under all fertilization treatments was significantly lower than that under the no-fertilization treatment(T1).(5)Different fertilization treatments promoted the increase of nutrient content of L.indica leaves and substrate.Total nitrogen,total phosphorus and total potassium of leaves and substrate reached maximum values in T11(N3P2K2),T7(N2P3K2)and T10(N2P2K3)treatments,respectively,all of which were significantly different from the no-fertilization treatment(T1).Comprehensive analysis showed that the total nitrogen,phosphorus,and potassium content in leaves increased with the application levels of nitrogen,phosphorus,and potassium fertilizers,and the total nitrogen,phosphorus,and potassium content in the substrate showed the similar trend.(6)Correlation analysis showed that the leaf ABA content was negatively correlated with all indicators,and growth indicators were significantly or extremely significantly positively correlated with most flowering,physiological,and leaf nutrient indicators.In the fuzzy comprehensive evaluation of membership function,the membership mean of the T6(N2P2K2)treatment was the highest,and the membership mean of the no-fertilization treatment(T1)was the lowest.Fertilizer effect models were fitted with N,P and K fertilizer application rates with total plant height growth and the number of flowers per inflorescence,respectively.The optimized fertilizer application scheme for total plant height growth and the number of flowers per inflorescence was obtained after optimizing the fertilizer effect model by frequency analysis,respectively.With the intersection method used,the results were N:10.95～17.37 g·plant-1,P2O5:5.89～9.37 g·plant-1,K2O:7.01～10.25 g·plant-1.In summary,the T6(N2P2K2)treatment was the best fertilization formula in this study,which can significantly promote the photosynthesis and synthesis and accumulation of nutrients in L.indica,thus promoting seedlings growth and flowering.However,it was not possible to make recommendations based on a single fertilization combination to suit local conditions.In actual production,the optimized fertilization scheme(N:10.95～17.37 g·plant-1,P2O5:5.89～9.37 g·plant-1,K2O:7.01～10.25 g·plant-1)can be selected according to the actual conditions. |
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