Effects of Nitrogen Form and Concentration on Growth and Chlorophyll Fluorescence Parameters of Banana Seedlings Before and After Foc TR4 Infection

Banana Fusarium wilt represents a considerable threat to the sustainable development of the global banana industry. Nonetheless, the regulatory mechanisms through which different nitrogen forms (nitrate, ammonium) and concentrations (low, normal) affect the growth and photosynthetic functions of banana seedlings following Foc TR4 infection are not yet fully elucidated. This study employed these nitrogen treatments to assess seedling growth indicators, chlorophyll fluorescence parameters, and light response curves both prior to and following Foc TR4 infection. The findings indicated that, before infection, ammonium nitrogen significantly enhanced root growth and increased leaf relative chlorophyll content (SPAD) and non-photochemical quenching (NPQ) values, whereas low-nitrogen conditions promoted biomass allocation to roots but inhibited maximum photochemical quantum yield of photosystem II (Fv/Fm). Post-infection, critical photosynthetic parameters such as SPAD value and Fv/Fm were significantly elevated in the nitrate nitrogen treatment compared to the ammonium nitrogen treatment, with the normal-nitrogen treatment yielding the most favorable results. Furthermore, Foc TR4 infection significantly reduced the leaf electron transport rate (ETR) across all treatments. In summary, nitrogen is integral to the modulation of seedling growth and stress resistance, primarily through its regulation of leaf photosynthetic apparatus efficiency, photoprotection mechanisms, and biomass allocation. These findings offer significant insights for formulating nitrogen management strategies aimed at the sustainable prevention and control of banana Fusarium wilt.