Arrow bamboo (Pseudosasa japonica), planted in the state-owned protective coastal sandy forest of horsetail tree (Casuarina equisetifolia) in Chishan, Dongshan, Fujian Province, China, was investigated to analyze the morphological characteristics of aboveground components and root systems. The study also examined biomass accumulation, non-structural carbohydrates, antioxidant enzymes, and malondialdehyde levels in arrow bamboo leaves under three forest canopy conditions: large gaps, medium gaps, and forest understory. The results show that each forest canopy environment led to significant differences (P < 0.05) in specific morphological characteristics of arrow bamboo, including plant height, basal diameter, under-branch height, total root length, surface area, and volume. Leaf and branch biomass of arrow bamboo in the forest understory was significantly higher than in large- and medium-gap environments (P < 0.05). Conversely, culm, stem, root biomass, and total biomass were significantly greater in the large-gap compared to the medium-gap and understory environments (P < 0.05). Soluble sugar and starch levels in arrow bamboo leaves were significantly higher in the forest understory compared to the large- and medium-gap environments (P < 0.05). Superoxide dismutase, peroxidase, and catalase activities in arrow bamboo leaves were significantly higher in the medium-gap compared to the large-gap (P < 0.05). Conversely, the malondialdehyde concentration in arrow bamboo leaves exhibited an opposite trend. It was conclusion that the leaf physiological responses of arrow bamboo. enhances its adaptability to coastal sandy land by modulating morphological characteristics, biomass allocation, and regulating leaf antioxidant enzyme activity.