Abstract
Acute salt shock can perturb photosynthetic function before severe visual injury becomes pronounced, creating a short interval in which early photochemical responses can be resolved. This study compared preventive and concurrent foliar application of LEAFENERGY® (LE), a proprietary commercial biostimulant whose active components are described by the manufacturer as naturally derived rare fatty acids produced from plant oils, in Welsh onion (Allium fistulosum L.) seedlings subjected to a single-step 200 mmol L−1 NaCl shock. Four treatments were established with 10 independent plant/vessel biological replicates per treatment: normal nutrient solution (CK), 200 mmol L−1 NaCl (SALT), 1% (v/v) LE applied 24 h before NaCl (T1), and 1% (v/v) LE applied concurrently with NaCl (T2). Fast chlorophyll fluorescence was repeatedly measured on the same plants at −1, 2, 4, 8, 23, 28, and 47 h. Repeated measurements were analyzed using generalized estimating equations (GEEs), with pre-specified contrasts adjusted by the Holm procedure. Significant treatment × time interactions were detected for Fv/Fm, PIABS, and the principal JIP-test parameters. At 4 h, PIABS declined to approximately 0.58-fold of baseline in SALT but remained at 0.95- and 0.91-fold in T1 and T2, respectively. Both LE treatments significantly moderated salt-shock-induced increases in VJ and M0 and decreases in ψ0 and φE0; T1 also significantly reduced ABS/RC and DI0/RC. No robust T1–T2 difference remained after multiplicity correction. At 47 h, neither LE treatment significantly restored leaf relative water content relative to SALT. Thus, under this single-run controlled acute-shock experiment, preventive and concurrent LE application transiently attenuated several components of the early PSII disturbance, particularly at 4 h. These findings do not demonstrate sustained salinity acclimation or long-term salt tolerance; longer-term, dose–response, timing, and production-scale studies are required before agronomic recommendations can be made.