Abstract: In the natural environment, the photosynthetic rate were studied and the relationships between the photosynthetic capacity and N content in the leaf were analyzed in 6 main secondary forest-forming species of Heilongjiang Province (Quercus mongolica, Betula platyphylla, Populus davidiana, Fraxinus mandshurica, Juglans mandshurica, phellodendron amurense). The results showed that the seasonal changes of the photosynthetic capacity were obvious while the photosynthetic rate potential in the 6 species were different. In growing period, the photosynthetic capacity of Juglans mandshurica was the greatest, annual average photosynthetic capacity of Betula platyphylla was the greatest, and the photosynthetic potential of Quercus mongolica was the greatest. Significant linear relationship (r=0.97) between the photosynthetic capacity and leaf nitrogen content was observed in Quercus mongolica, while conic relationships(r=0.61,r=0.51) between the photosynthetic capacity and leaf nitrogen were observed in Fraxinus mandshurica and Betula platyphylla.

Key words: photosynthetic ccapacity, photosynthetic potential, leaf nitrogen content, seasonal changes