Ammonium and nitrate distinctly regulate photosynthetic and growth performance, eliciting antagonistic responses in yellow passion fruit plants

Ammonium (NH4+) and nitrate (NO3−) are the primary sources of nitrogen (N) taken up by plants. Plant species differentially respond to both N sources, and the optimal N concentration and ideal NH4+/NO3− proportions for each crop are essential to plant performance. These informations are absent especially for fruit species grown in tropical climates. Our investigative study aimed to explored the physiological and growth performance of yellow passion fruit plants under three nitrogen (N) concentrations (2.5, 10, 20 mmol L−1) in three NH4+/NO3− proportions (0/100, 50/50, 100/0). After 47 days of cultivation, NH4+ and NO3−contents, gas exchanges, photosynthetic pigments, chlorophyll a fluorescence, growth and dry biomass were examined. Total NO3− content was found to be 2.5-fold higher than the NH4+ content in plant tissues. Plants exposed to concentrations of 10 and 20 mmol L−1 in the 100/0 NH4+/NO3− proportions exhibited excess free energy in photosystem II and non-photochemical quenching, resulting in reduced gas exchange and symptoms of toxicity in yellow passion fruit plants. Multivariate analysis showed that groups 1 and 3, consisting of 20 mmol L−1 N in the 0/100 ratio and 10 and 20 mmol L−1 in the 50/50 NH4+/NO3−proportions, reduce the degradation of photosynthetic pigments. The plant group maintained the electron transport in photosystems, supported gas exchange and favored the accumulation of dry biomass, thus promoting the growth of both the shoot and the roots of yellow passion fruit plants. Our results show that there are different responses to the supply of both nitrogen sources, providing strategies for growing yellow passion fruit in the early growth stage.