Abstract: We investigated leaf morphology, diurnal variation of photosynthesis, and chlorophyll content of Schima superba along different positions of canopy (top, middle and bottom layers) to determine its eco-physiological response to spatial variation. The results showed that specific leaf area of S. superba from the top layer was significantly lower than that from the middle and bottom layers. Leaf length and maximum width were significantly different among the three layers (P<0.01), being bottom layer > middle layer > top layer. Compared with the middle and bottom layers, photosynthetically active radiation was the highest at the top canopy. Leaves from the top layer had significantly higher net photosynthesis rate (P_n), stomatal conductance (g_s), carboxylation efficiency (V_c), transpiration rate (T_r) and stomatal limitation (L_s) than that from either the middle or bottom layer. Conversely, leaves from the bottom layer had the highest intercellular CO₂ concentration (C_i). Photosynthetically active radiation from each layer had a significant positive correlation with P_n, g_s, V_c, T_r and L_s, and was negatively correlated with C_i. The highest contents of chlorophyll a+b (Chl-a+b) and carotenoid (Car) of leaves were found from the middle and bottom layers, while the top layers had much higher chlorophyll a/b (Chl-a/b). The results indicated that illumination was the primary driver of variation in leaf morphological and physiological characteristics of S. superba along the vertical space of canopy.

Key words: combined exposure, oxidative stress, PPCPs, neurotoxicity, digestive toxicity.