Abstract: This study focused on the effects of magnesium (Mg²⁺) on growth, photosynthetic characteristics and chlorophyll fluorescence parameters of Tung tree leaves under sandy culture conditions. The results showed that the optimal concentrations of Mg²⁺ for Tung tree growth and photosynthesis were 2-4 mmol·L^-1. Under low Mg concentration (Mg²⁺ <2 mmol·L^-1), the growth of Tung tree was inhibited. This low level of Mg²⁺ resulted in significant decreases of leaf chlorophyll content, RuBP carboxylase and PEPC activities, net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), stomatal limitation value (L_s), water use efficiency (WUE), maximum photochemical efficiency (F_v/F_m), Φ_PSII,F_v/F_o and q_P, but increases of intercellular CO₂ concentration (C_i), F_o and NPQ. Under high Mg stress (Mg²⁺ >4 mmol·L^-1), the growth of Tung tree was also inhibited. The chlorophyll content, RuBP carboxylase activity, P_n, G_s, F_v/F_m, F_v/F_o and q_P were reduced (P<0.05). With the increasing Mg supply, the growth, chlorophyll content, RuBP carboxylase and PEPC activities, P_n and Φ_PSII all exhibited a trend of increasing initially and decreasing later. The decrease of net photosynthetic rate in Tung tree seedlings under Mgdeficient stress was probably due to nonstomatal factors.

Key words: hydrological connectivity, flow length, scenario simulation, vegetation pattern, riparian buffer zone