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Photosynthetic indexes of Cassia bakeriana, Syzygium hainanense, Ilex rotunda and Phoebe sheareri seedlings were determined under simulated low temperature stress using artificial climate chambers. The results showed that with increasing low temperature time, the net of photosynthetic rate (P_n), stomatal conductance (G_s) transpiration rate (T_r) and stomatal limitation (L_s) of seedlings of the four tree species decreased; intercellular CO₂ concentration (C_i) of C. bakeriana fluctuated and then increased, S. hainanense continuously increased, I. rotunda and P. sheareri decreased followed by an increase. Two days after low-temperature release, P_n, T_r, G_s and L_s of seedlings of the four species increased. C_i of C. bakeriana, S. hainanense, and P. sheareri increased, whereas I. rotunda decreased. The photosynthetic indexes of seedlings of the four tree species was evaluated using principal component analysis, indicating that cold-resistance ability decreased in the order of C. bakeriana>P. sheareri>I. rotunda>S. hainanense

Density effect on physiological characteristics in Michelia chapensis seedlings was studied using potted method. The seedlings were planted with four different densities: 1, 2, 4 and 8 seedlings of each plant bag (density I, II, III and density IV). The physiological characteristics of the seedlings under different densities were determined. Results showed that density effect on contents of chlorophyll and proline was not obvious. Soluble sugar content of 1 seedling bag^-1 was significantly greater than that of other density seedlings. With increasing density, soluble protein content increased firstly and then decreased, whereas the superoxide dismutase (SOD) activity and the malondialdehyde (MDA) content increased.