Growth strategies and phenotypic plasticity of improved Chinese fir families across soil types.

To enhance phenotypic plasticity, it is vital to maximize the genetic growth potential of trees and understand their adaptive responses to environmental conditions. Tree species adapt to dynamic environmental conditions by leveraging the interactions among the environment, genotype, and genotype-by-environment. A total of 25 improved varieties of Chinese fir were transplanted and developed through multi-generational breeding into four types of artificial forest soils. Through a quantitative analysis of genotypic, soil environmental conditions, and genotype-by-environment interaction effects on variations in growth, biomass, and root functional traits, the key drivers of phenotypic plasticity were identified. The results indicate that soil environmental conditions and genotype-by-environment interactions are the primary factors influencing trait variation, explaining 55.89% to 93.94% of the observed variation, while the family effect is relatively minor. Notably, pronounced phenotypic plasticity drives divergent selection in both aboveground and belowground growth strategies. Critical traits influencing root dry weight include root average diameter, total root volume, and root-to-shoot ratio. Although root dry weight does not directly affect plant height, it has a substantial impact on aboveground dry weight. These findings highlight that the changes in the aboveground and belowground growth strategies of Chinese fir during the seedling stage are closely linked to the plasticity of root functional traits. For multi-generational genetically improved varieties, this study examined how the integration of genetic effects, soil environmental conditions, and genotype-by-environment interactions in the selection of aboveground growth and root functional traits influences the mechanisms driving biomass accumulation. The results provide actionable insights for selecting soil-specific families in subtropical plantations.