Sulfur supply and ammonium toxicity affect photosynthesis and plant nutrition in Tanzania guinea grass
摘要
Ammonium (NH4+) toxicity is a significant challenge for the growth and productivity of Tanzania guinea grass (Megathyrsus maximus Jacq.), yet the interaction between NH4+ and sulfur (S) applications remains poorly understood. In this study, we explore how varying S concentrations can alleviate the negative impacts of excessive NH4+ on plant performance, with a particular focus on photosynthesis and nutrient uptake. A greenhouse experiment was conducted with three NH4+ proportions (30%, 50%, and 70%) and three S rates (0.1, 2.0, and 4.0 mmol L–1) in nutrient solution. NH4+ toxicity significantly impaired photosynthetic activity, with plants receiving higher NH4+ proportions exhibiting reduced number of tillers, number of leaves, and biomass. Nevertheless, S supplementation improved photosynthesis, chlorophyll concentration, and promoted S uptake, especially under high NH4+ toxicity. Interestingly, no significant interaction between S and NH4+ effects was observed for plant growth, but S played a key role in supporting chlorophyll fluorescence, especially restoring non-photochemical quenching. These findings contribute to understanding the importance of S supply in enhancing the resilience of Tanzania guinea grass to nutrient imbalances, particularly in environments where ammonium toxicity is a concern.