Abstract: One-year old Fraxinus mandshurica seedlings were sand-cultured and subjected to different light intensity (2 levels) and N supply (4 levels) to examine their photosynthetic rate and chlorophyll fluorescence response to environmental change. The results showed that comparing with full light, shading decreased the maximum photosynthesis rate (A_max), light compensation point (LCP) and photochemical quenching coefficient (qP) obviously, while increased the apparent quantum yield (AQY), maximum fluorescence (F_m) and maximal photochemical efficiency (F_v/F_m) markedly. The total chlorophyll, chlorophyll a and carotenoid contents and chlorophyll a/b per unit area of leaf were lower under shading. At two light levels, the F_m,F_v/F_m,φ_PSⅡand qP increased with increasing N supply (P<0.05), and φ_PSⅡ increased more quickly at lower N levels than at higher N levels. Light intensity and N supply had a significant interaction on the F_m,φ_PSⅡ, F_v/F_m,qN and qP （P<0.01）.One-year old Fraxinus mandshurica seedlings were sand-cultured and subjected to different light intensity (2 levels) and N supply (4 levels) to examine their photosynthetic rate and chlorophyll fluorescence response to environmental change. The results showed that comparing with full light, shading decreased the maximum photosynthesis rate (A_max), light compensation point (LCP) and photochemical quenching coefficient (qP) obviously, while increased the apparent quantum yield (AQY), maximum fluorescence (F_m) and maximal photochemical efficiency (F_v/F_m) markedly. The total chlorophyll, chlorophyll a and carotenoid contents and chlorophyll a/b per unit area of leaf were lower under shading. At two light levels, the F_m,F_v/F_m,φ_PSⅡand qP increased with increasing N supply (P<0.05), and φ_PSⅡ increased more quickly at lower N levels than at higher N levels. Light intensity and N supply had a significant interaction on the F_m,φ_PSⅡ, F_v/F_m,qN and qP （P<0.01）.

Key words: Wheat, Leaf layer, Leaf water content, Plant water content, Reflectance spectra, Spectral index