Objective  Coastal protection forests serve as vital green ecological barriers safeguarding the ecological security of coastal regions. However, they are prone to the formation of forest gaps due to disturbances such as strong winds. Light intensity is one of the most critical environmental factors within forest gaps and plays a vital role in the natural seedling regeneration. This study aims to clarify the effects of different light intensities on the growth and gas exchange characteristics of seedlings of L. compactum, a representative tree species in coastal protection forests.

Methods One-year-old L. compactum seedlings were used as experimental materials. Different light intensity environments were set up using black shading nets: high light intensity (30% shading rate), medium light intensity (60% shading rate) and low light intensity (90% shading rate), so as to simulate the light intensity environments in forest gaps of different sizes, seedling growth, leaf morphology and gas exchange parameters were measured.

Results Light intensity had significant effects on the growth and leaf gas exchange of L. compactum seedlings. The ground diameter, net photosynthetic rate and water use efficiency of the seedlings all increased significantly with the increase of light intensity, whereas the leaf morphological index significantly decreased, and the leaf width showed a significant increasing trend. Although the leaf morphological index was the highest under the medium light intensity treatment, the net photosynthetic rate was significantly lower than that under the high light intensity group; under the low light intensity condition, the seedling growth and gas exchange capacity were both significantly inhibited. Correlation analysis showed that medium light intensity is conducive to the synergy of physiological and ecological indices, while the trade-offs among indices under high light intensity may be more obvious.

Conclusion The high light intensity environment is beneficial to the growth of L. compactum seedlings and the improvement of their net photosynthetic rate. Measures such as reducing shading can be taken to provide a strong light environment for the naturally regenerated seedlings of L. compactum in gaps, thereby promoting community establishment. These findings provide a scientific basis for the regulation of natural gap regeneration and species allocation of coastal protection forests in Zhejiang Province.