Responses of Growth and Root Vitality of Fokienia hodginsii Seedling to the Neighbor Competition in Different Heterogeneous Nutrient Environments

Fokienia hodginsii is characterized by shallow and developed lateral roots with no obvious taproot. It can be used as a pioneer tree species for opening up barren land and as a mixed species for creating plantation forests. During the growth process of F. hodginsii seedlings, they are often exposed to heterogeneous nutrient environments and competition for nutrients, water, and space from neighboring plants, which have significant impacts on the growth of F. hodginsii. These impacts are most directly reflected in the root vitality of F. hodginsii, whose physiological changes embody the plant's adaptability to different heterogeneous nutrient environments and neighbor competition. Herein, high-quality one-year-old F. hodginsii seedlings were subjected to three planting patterns to simulate different competition patterns. The three planting patterns were also exposed to three heterogeneous nutrient environments and a homogeneous nutrient environment (control) to determine the differences in the F. hodginsii seedling growth and root vitality under different heterogeneous nutrient environments and planting patterns. The F. hodginsii seedling height, ground diameter (root neck diameter), and root biomass under the heterospecific neighbor condition were significantly higher than under the single-plant condition. Across heterogeneous nutrient environments, the average seedling height in the N heterogeneous environments was higher than in the P and K heterogeneous environments. The root biomass in the P heterogeneous environment was slightly higher than in the N heterogeneous environment and significantly higher than in the homogeneous and the K heterogeneous environments. Moreover, the average F. hodginsii seedling root vitality under the heterospecific neighbor was the highest, and the root vitality in the N heterogeneous environment was the highest under each planting pattern. The F. hodginsii root catalase (CAT) and peroxidase (POD) activities under the competition patterns were significantly higher than under the single-plant condition. Additionally, the superoxide dismutase (SOD) activity under single-plant was higher than under the competition patterns. At the same time, the F. hodginsii root malondialdehyde (MDA) content was the highest under the conspecific neighbor. Relative to the homogeneous environment, the root CAT, SOD, and POD activities were increased in the N and P heterogeneous environments. The CAT, SOD, and POD activities were highest in the P heterogeneous environment, while the K heterogeneous environment had the highest average MDA content. From the results of principal component analysis, when F. hodginsii seedlings were in N and P heterogeneous nutrient environments and heterospecific neighbor, their growth, root biomass accumulation, and root activity indexes reached better levels.