Potassium deficiency impairs photosynthetic induction via disrupted electron transport and photochemistry in Phaseolus vulgaris

Our previous study revealed that potassium (K) deficiency depressed carbon assimilation during photosynthetic induction in <i>Phaseolus vulgaris</i>. Building on this work, the current study presents a re-analysis of previously collected gas exchange and fluorescence measurements to further explore the contribution of electron transport and its components in regulating carbon assimilation under K deficiency, specifically examining electron transport rate (<i>J</i>), the fraction of open PSII reaction centers (q_L), and non-photochemical quenching (NPQ). Our re-analysis revealed that plants supplied with deficient potassium demonstrated pronounced delay in electron transport activation, with c.430 s to achieve steady-state conditions compared to potassium sufficient plants (c. 215 s), which the delay was primarily attributed to slower q_L increment and the sustained NPQ elevation. Normal K supplied plants maintained higher q_L and <i>J</i> values throughout the induction, while NPQ levels eventually converged between treatments. Increased q_L led to higher photosynthesis, highlighting q_L as a key limiting factor in early photosynthesis induction. Taken together, under potassium deficiency, the delayed activation of electron transport reduces photosynthetic rates during induction, suggesting that improving q_L could enhance photosynthesis under K-deficient conditions.