Alterations in leaf photosynthetic electron transport in Welsh onion (Allium fistulosum L.) under different light intensity and soil water conditions

Abstract Background: Welsh onions are often affected by stressful environments, such as high light and drought, during summer cultivation, which hinders their growth. To date, few studies have focused on leaf photosynthesis of Welsh onions during summer. We used carbon dioxide assimilation and OJIP transient and MR curves to analyze the photosynthetic characteristics of Welsh onions. Results: The results showed that strong light and drought could lead to a decrease in leaf pigment content. Simple high light stress caused a decrease in the net photosynthetic rate through stomatal limitation, while the simple drought treatment and the two stress factors combined caused a nonstomatal limitation. PSII energy distribution indicated that strong light and drought stress reduced the photochemical quantum efficiency of PSII. OJIP curve analysis showed that FO and FJ were increased, Fm was decreased, and a distinct K-phase was induced. In addition, OJIP parameters, including RC/CSO, TRO/ABS, ETO/TRO, and PIABS, were significantly reduced. MR analysis showed that strong light and drought stress blocked MR transients, leading to a gradual decrease in VPSI and VPSII-PSI. Conclusions: In general, the photosynthesis of Welsh onion was inhibited by high light and drought, which destroyed the receptor and donor side of PSII and reduced the electron transport capacity of PSII and PSI.