Objective Acid-aluminum stress is an important abiotic stress factor limiting plant growth, which seriously restricts the productivity of acid soil forests in southern China. In order to explore the growth variation law under acid aluminum environment of Pinus massoniana seedlings, sselect aluminum-tolerant families and sensitive families adapted to aluminum stress, and provide basis for genetic improvement of Pinus massoniana under aluminum stress.

Method The seedlings of 55 second-generation superior families (201 - 255) were used to study the growth and root morphological changes under 0, 0.1, 0.3, 0.6, 1.2 and 2.4 mmol·L⁻¹ aluminum concentration in acidic environment by sand culture of P. massoniana. The aluminum tolerance characteristics were graded by principal component analysis and cluster analysis. The excellent aluminum tolerance, the superior families of the seedlings were sselected and identified.

Results There were significant differences in seedling height, ground diameter, height-diameter ratio, biomass (aboveground biomass, root biomass, total biomass, root-shoot ratio), root morphology (total root length, root surface area, root volume) between families and aluminum concentration treatments (p <0.05). The ground diameter, seedling height, biomass and root morphological indexes increased first and then decreased with the increase of aluminum concentration of the seedlings, which was the highest at 0.6 mmol·L ⁻¹ aluminum concentration, significantly higher than that of 0 and 2.4 mmol·L⁻¹ treatment. There were no significant differences with 0.3 mmol·L⁻¹ treatment. The coefficient of variation of root biomass and root morphology was large, with an average of 30.79%. Using the above 10 indicators to calculate the comprehensive evaluation value (CEV) and analyze for systematic clustering of aluminum resistance characteristics among families, 3 families with strong aluminum resistance (accounting for 5.45%) and 11 families with moderate aluminum resistance (accounting for 20%) were selected. 37 families (67.28%) with general aluminum tolerance, and 4 families (7.27%) with aluminum sensitivity were evaluated.

Conclusion Suitable aluminum concentration can promote the growth, especially at the concentration of 0.3-0.6 mmol·L⁻¹ aluminum. Selecting aluminum-tolerant and sensitive families is of great significance for the improvement of aluminum tolerance of P. massoniana.