Mechanistic Modeling Reveals Adaptive Photosynthetic Strategies of Pontederia crassipes: Implications for Aquatic Plant Physiology and Invasion Dynamics

The invasive aquatic macrophyte <i>Pontederia crassipes</i> (water hyacinth) exhibits exceptional adaptability across a wide range of light environments, yet the mechanistic basis of its photosynthetic plasticity under both high- and low-light stress remains poorly resolved. This study integrated chlorophyll fluorescence and gas-exchange analyses to evaluate three photosynthetic models-rectangular hyperbola (RH), non-rectangular hyperbola (NRH), and the Ye mechanistic model-in capturing light-response dynamics in <i>P. crassipes</i>. The Ye model provided superior accuracy (<i>R</i>² > 0.996) in simulating the net photosynthetic rate (<i>P</i>_n) and electron transport rate (<i>J</i>), outperforming empirical models that overestimated <i>P</i>_nmax by 36-46% and <i>J</i>_max by 1.5-24.7% and failed to predict saturation light intensity. Mechanistic analysis revealed that <i>P. crassipes</i> maintains high photosynthetic efficiency in low light (<i>LUE</i>_max = 0.030 mol mol^-1 at 200 µmol photons m^-2 s^-1) and robust photoprotection under strong light (<i>NPQ</i>_max = 1.375, PSII efficiency decline), supported by a large photosynthetic pigment pool (9.46 × 10¹⁶ molecules m^-2) and high eigen-absorption cross-section (1.91 × 10^-21 m²). Unlike terrestrial plants, its floating leaves experience enhanced irradiance due to water-surface reflection and are decoupled from water limitation via submerged root uptake, enabling flexible stomatal and energy regulation. Distinct thresholds for carboxylation efficiency (<i>CE</i>_max = 0.085 mol m^-2 s^-1) and water-use efficiency (<i>WUE</i>_i-max = 45.91 μmol mol^-1 and <i>WUE</i>_inst = 1.96 μmol mmol^-1) highlighted its flexible energy management strategies. These results establish the Ye model as a reliable tool for characterizing aquatic photosynthesis and reveal how <i>P. crassipes</i> balances light harvesting and dissipation to thrive in fluctuating environments. These resulting insights have implications for both understanding invasiveness and managing eutrophic aquatic systems.