Regulation solution of water-fertilizer coupling for comprehensive growth of Pinus massoniana seedlings based on multi-level fuzzy evaluation and genetic algorithm

[Objective]This study aims to explore the comprehensive regulatory of water-fertilizer coupling on the growth and development of Pinus massoniana seedlings,to understand how multiple factors of water and fertilizer affect the growth of seedlings and to quantify the water-fertilizer combination conducive to seedling comprehensive growth and the combined water-fertilizer application for the coordinated development of the environment and seedling quality.[Method]The experiment was carried out based orthogonal design of volumes water content(W1:100%θ,W0.5:85%θ,W-0.5:65%θ,W-1:45%θ;θ:maximum volumetric water content),substrate available nitrogen(N1:840,N0.5:420,N0:210,N-0.5:105),phosphorus(P1:128,P0.5:64,P0:32,P-0.5:16),and potassium(K1:936,K0.5:468,K0:234,K-0.5:117,mg/kg·substrate).In addition,two control groups with sufficient water(W0.5)no fertilization(N-1P-1K-1)and mild water deficit(W0,75%θ)moderate fertilization(N0P0K0)were set.The multilevel fuzzy comprehensive evaluation(MFCE)model was used to comprehensively evaluate the four factors and 12 sub-factors for characterization of P.massoniana and the nondominated sorting genetic algorithm(NSGA-III)was utilized for multiple objective function optimization to achieve coordinated development of seedlings and reduce environmental pollution.[Result]The highest values of height,stem diameter,first-order literal root number,photosynthetic rate,absorption of nitrogen and phosphorus,seedling quality indicators were observed under the W85%θN420P128K234 treatment,while the root tip number,transpiration rate,Chls,potassium absorption were highest on the W65%θN210P128K468 combination.The W85%θN420P128K234 combination is most conducive to the comprehensive growth of the seedlings,followed by W65%θN210P128K468,which are 1.401 to 141.413 times and 1.284 to 129.630 times higher than other water-fertilizer combinations,respectively.In terms of single-factor effects,the comprehensive growth index(CGI)of the seedlings followed a linear pattern with P and a downward-opening parabola with W,N,and K,peaking at 128(P,1),235.725(N,0.06),254.78 mg/kg·dry substrate(K,0.04),85%θ(W,0.5).W?N and W-K had negative interaction effects on the growth of seedlings,while P-W,P-K,and N-K had the opposite effects.In terms of multi-factor coupling effects,adjusting the input of other elements had no positive impact on seedling growth,as long as the substrate P≤32 mg/kg·substrate.Whereas P was 128 mg/kg·dry substrate,the negative effects caused by low water could not be alleviated,even if moderate N and K levels were maintained if only W was below 45%θ.Redundancy analysis and partial least squares path modeling revealed that W and P had a direct and significant positive effect on the growth of seedlings,while N and K had a negative effect.85-91.06%θ(W),65.95-134.27(N),128(P),and 215.87-234 mg/kg·dry substrate(K)were observed as combinations conducive to the growth of seedlings based on the MFCE model.W of 90.712%θ combined with the N,P,and K of 57.39,88.397,and 123.084 mg/kg·dry substrate could obtain the coordinated development of environmental and seedling growth by NSGA-III.[Conclusion]P is the key driving factor affecting the CGI of P.massoniana seedlings.Maintaining adequate moisture,appropriately reducing N and K applications,and increasing P fertilizer can help improve the quality of nursery stock and reduce environmental pollution.The test results have important guiding significance for water and fertilizer management in the growth process of P.massoniana seedlings.