Environmental conditions dictate the long-term photosynthetic and developmental response of lettuce to cold plasma priming

Cold plasma (CP) seed treatment is a promising non-chemical priming technique, yet its long-term physiological effects remain poorly understood and highly context-dependent. This study evaluated CP treatment (50-150 W) on lettuce seeds grown under controlled phytotron and semi-controlled greenhouse conditions. Germination kinetics, flowering dynamics, shoot biomass, chlorophyll fluorescence (OJIP), and leaf reflectance indices were assessed. CP consistently accelerated germination compared with the untreated control, with only minor differences among plasma power levels. Under stable phytotron conditions, higher plasma power (100-150 W) delayed flowering, increased biomass, and maintained PSII performance, consistent with prolonged vegetative growth. In contrast, greenhouse-grown plants exhibited a distinct physiological response characterised by transient alterations in chlorophyll fluorescence, earlier flowering at the highest plasma power, and no significant biomass increase. Overall, the findings demonstrate that the long-term effects of cold plasma priming depend strongly on post-treatment environmental conditions, highlighting environmental stability as a key determinant of its agronomic potential.