Abstract: In order to understand the light requirement and adaptability of Juglans mandshurica seedlings, two-year-old J. mandshurica seedlings were grown under four light regimes (100%, 60%, 30%, and 15% of natural irradiance). After 1-year adaptation, the seasonal variations of the seedlings photosynthetic variables were measured by a Li-6400 portable photosynthesis system. The J. mandshurica seedlings were insensitive to the changes of light environment in spring, but their maximum net photosynthetic rate, maximum carboxylation rate, and maximum electron transport rate increased significantly with increasing light intensity in summer and autumn (P<0.05). The light saturation point declined with decreasing light intensity (P<0.05), but the apparent quantum yield, dark respiration rate, and light compensation point under different light environments had no significant changes. The relative growth rate under 100% and 60% of natural irradiance had no significant difference (P>0.05), but declined significantly in the order of 60%> 30％> 15% of natural irradiance (P<0.05). These results indicated that J. mandshurica seedlings had the maximum relative growth rate under 100% and 60% of natural irradiances, and could tolerate 15%-30% of natural irradiance by reducing light saturation point and carbon accumulation, exhibiting strong adaptability and plasticity to light environment.

Key words: Juglans mandshurica, light adaptation, seasonal dynamics, plasticity, secondary forest, oriented object, multi-resolution segmentation, vegetation classification, vegetation index.