Abstract: Different levels (0, 90, 180, and 270 g per tree) of compound fertilizer containing 15% N, 15%P₂O₅, and 15%K₂Owere applied to young Eucalyptus grandis to study the diurnal variations of its leaf stomatal conductance (G_s), intercellular CO₂ concentration (C_i), net photosynthesis rate (P_n), transpiration rate (T_r), water use efficiency (WUE), and vapor pressure deficiton leaf surface (V_pdl) as well as the variation of leaf chlorophyll content, aimed to approach the relationships of E. grandis photosynthesis with fertilization and environmental factors. In all treatments, the diurnal variation of P_n presented a single-peak curve, with the peak at 14:00 and not showing midday depression. TheG_s,T_r, and V_pdlshowed the similar trend with P_n, while theC_ihad a minimum value at 14:00. The WUE demonstrated a double-peak curve, with the first and second peak occurred at 10:00 and 14:00, respectively. Comparing with the control, the mean values of G_s,P_n,T_r,WUE, and chlorophyll a, chlorophyll b, and total chlorophyll contents under fertilization increased by 4.6%-15.9%, 7.8%-21.8%, 4.8%-11.6%, 3.2%-8.8%, 15.5%-62.0%, 14.5%-44.5% and 15.3%-57.1%, respectively, and the increment increased with fertilization level. By contrast, the mean values of C_i and V_pdl decreased by 14.5%-44.5% and 15.3%-57.1%, respectively, and the decrement increased with fertilization level. The G_s, P_n, and T_r were significantly correlated with air temperature, relative humidity (RH), and photosynthetic active radiation (PAR), and also, the G_s was significantly correlated with P_n and T_r. It was suggested that fertilization could promote E. grandis growth and enhance its WUE and biological carbon sequestration, and air temperature, RH, PAR, and G_s were the main factors causing the diurnal variations of photosynthesis and transpiration of E. grandis.

Key words: Eucalyptus grandis, photosynthesis, transpiration, water use efficiency, diurnal variation, pollen limitation, experimental level, pollen quality, resource reallocation, Sagittaria trifolia.