Response of photosynthetic and stoichiometric characteristics of female and male leaves of Fraxinus mandshurica to exogenous hormones

Objective This paper aims to assess the effects of exogenous hormone addition on the photosynthesis and stoichiometry of male and female Fraxinus mandshurica leaves, elucidate differential responses to different hormone ratio combinations between male and female Fraxinus mandshurica, and provide a basis for precision breeding of Fraxinus mandshurica.

Method The experiment utilized a two-factor, four-level fractional factorial experimental design, with mature female and male F. mandshurica trees from artificial forests as the test subjects. Gibberellin (GA₃) and cytokinin (6-BA) hormone treatments were administered separately to female and male trees through stem drip method. The photosynthetic parameters, leaf area, chlorophyll content (SPAD), leaf carbon (C), nitrogen (N) content, and C/N ratio of female and male trees were measured.

Result (1) The optimal hormone treatment for female trees was A₂B₁ (GA₃ 60 mg/L, 6-BA 30 mg/L), which significantly increased leaf C content, and had the highest leaf N content and C/N ratio, as well as significantly increased leaf area and SPAD value (P < 0.05), achieving the highest net photosynthetic rate. (2) The optimal hormone treatment for male trees was A₃B₂ (GA₃ 90 mg/L, 6-BA 60 mg/L), which achieved the highest leaf C and N content, the second highest C/N ratio, significantly increased leaf area and SPAD value (P < 0.05), and the highest net photosynthetic rate. (3) Overall, the photosynthetic and stoichiometric indicators of female trees were higher than those of male trees after hormone treatment.

Conclusion Female F. mandshurica trees have optimal photosynthetic functionality with GA₃ 60 mg/L and 6-BA 30 mg/L treatment, while male trees show optimal photosynthetic functionality with GA₃ 90 mg/L and 6-BA 60 mg/L treatment. Leaf carbon (C) and nitrogen (N) content are significantly increased under these treatments. The photosynthetic and stoichiometric characteristics of female and male Fraxinus mandshurica leaves show significant differential responses to the type and ratio of exogenous hormones.