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

Abstract

Welsh onions (Allium fistulosum L.) are often affected by stressful environments, such as high light and drought, during summer cultivation, which hinders their growth. We used CO₂ assimilation, OJIP transient and MR curves to analyse the photosynthetic characteristics of Welsh onion. The results showed that single high light stress caused a decrease in the net photosynthesis rate through stomatal limitation, while the single drought treatment and the combined stress induced nonstomatal limitation. F_O and F_J increased, F_m decreased, and a distinct K-phase was induced. High light and drought stress blocked MR transients, leading to a gradual decrease in V_PSI and V_PSII-PSI . In general, photosynthesis of Welsh onion was inhibited by high light and drought, which destroyed the receptor and donor side of PSII and reduced electron transport capacity of PSII and PSI.

Keywords: Drought; Welsh onion; high light; photoinhibition; photosystem.