Abstract: Red pine (Pinus resinosa) is one of the most important tree species for timber plantation in North America, and preliminary success has been achieved in its introduction to the mountainous area of Northeast China since 2004. In order to expand its growth area in other parts of Northeast China, a pot experiment was conducted to study the adaptability of this tree species to varying soil acidity. P. resinosa seedlings were grown in soils with different acidity (pH=4.5, 5.5, 6.5, 7.5, and 8.0) to test the responses of their photosynthesis and chlorophyll fluorescence parameters to soil pH levels, and the appropriate soil acidity was evaluated. Dramatic responses in chlorophyll a and b contents, P_n, and chlorophyll fluorescence parameters (F_o,F_m,F_v,F_v/F_m, and Φ_PSⅡ) were detected under different soil acidity (P<0.05), with the highest chlorophyll content and P_n under soil pH 5.5, and significantly lower chlorophyll content and P_n under soil pH 7.5 and 8.0. The chlorophyll content and P_n were 41% and 50%, and 61% and 88% higher under soil pH 5.5 than under soil pH 7.5 and 8.0. The seedlings had a significant photosynthetic inhibition under soil pH 7.5 and 8.0, but the highest F_v/F_m and Φ_PSⅡ under soil pH 5.5. Comparing with those under soil pH 7.5 and 8.0, the F_v/F_m and Φ_PSⅡ under soil pH 5.5 were 8% and 12%, and 22% and 35% higher, respectively. It was suggested that soil pH 5.5 was most appropriate for P. resinosa growth.

Key words: Pinus resinosa, soil acidity, net photosynthesis, chlorophyll fluorescence, adap-tability, Odontothrips loti, alfalfa, insect resistance, phenols, lignin.