Effects of foliar fertilizer with different nitrogen forms on photosynthetic physiological characteristics of Camellia oleifera Abel spring shoot

【Objective】To study effects of treatments of foliar fertilizer with different nitrogen forms on Camellia oleifera Abel spring shoot's leaf photosynthesis,and to provide reference for the planting,management and operation of C. oleifera Abel forest.【Method】Cenruan No. 3 C. oleifera Abel was used as the test material,and four treatments of foliar fertilizers with different nitrogen forms,namely N1-N4 treatments were set. Urea(amide nitrogen),ammonium sulfate and potassium nitrate at 1:1(ammonium nitrate nitrogen),ammonium sulfate(ammonium nitrogen),potassium nitrate(nitrate nitrogen) were added,in which pure nitrogen content was consistent with the proportion of medium and trace elements and growth substances,and the treatment with only medium and trace elements and growth substances was used as the control(CK). The photosynthetic parameters and photosynthetic pigment content in C. oleifera Abel leaves were determined and four models,such as rectangular hyperbolic model,were used to fit the photosynthetic-light response curves of different treatments to evaluate the fertilizer efficiency of foliar fertilizer with different nitrogen forms.【Result】Under 1000 μmol/(m² ·s) light intensity,all treatments increased the net photosynthetic rate(P_n),transpiration rate(T_r),stomatal conductance of leaves(G_s),and decreased the intercellular CO₂ concentration(C_i). The values of P_n,G_s and T_r of ammonium nitrogen and nitrate nitrogen treatment(N2) fertilization were significantly higher than those of other treatments(P<0.05,the same below),while the C_i of the treatment was significantly lower than that of other treatments.According to light response curve,as light intensity grew,treatments of foliar fertilizer with different nitrogen forms could make G_s,T_r and P_n increase but C_i decrease;in mixed ammonium nitrogen and nitrate nitrogen fertilization treatment,G_s,T_r and P_n increased faster while C_i decreased faster. According to light response curve fitting and comparison,the best model was the modified rectangular hyperbola model that helped reach the conclusions: treatments of foliar fertilizer with different nitrogen forms could increase apparent quantum efficiency(α) and maximum net photosynthetic rate(P_n-max) of leaves and reduce light compensation point(LCP) value,in which mixed ammonium nitrogen and nitrate nitrogen fertilization treatment had the maximum increase of α and P_n-max,0.072 and 8.5473 μmol/(m² ·s) respectively. At the same time,it decreased light compensation point(LCP) value and mixed ammonium nitrogen and nitrate nitrogen fertilization treatment had the minimum LCP value;spraying foliar fertilizer containing nitrogen increased foliar photosynthetic pigment content whose highest value was witnessed in mixed ammonium nitrogen and nitrate nitrogen fertilization treatment.【Conclusion】Foliar fertilizers with different nitrogen forms are beneficial to improve the photosynthesis of C. oleifera Abel spring shoot leaves,and the best effect comes from foliar fertilizer mixed with ammonium nitrogen and nitrate nitrogen.