Cultivar-specific drought responses in pineapple revealed by concurrent changes in PSII and PSI energy partitioning

Pineapple (Ananas comosus (L.) Merr.), a typical Crassulacean acid metabolism (CAM) crop, exhibits remarkable drought tolerance; however, the concurrent responses of photosystem II (PSII) and photosystem I (PSI) under drought stress remain unclear. In this study, three pineapple cultivars ('MD-2', 'Tainong21', and 'Paris') were subjected to progressive drought stress (mild, moderate, and severe) followed by rewatering, PSII energy allocation and PSI limitation responses was evaluated using Dual-PAM chlorophyll fluorescence measurements. Drought stress significantly altered photosynthetic energy partitioning among cultivars, as reflected by consistent changes in ETR(II), NPQ, and Y(NO) across drought stages. Under mild drought, 'Tainong21' showed an early reduction in ETR(II) accompanied by relatively elevated NPQ, whereas 'Paris' exhibited a comparatively conservative response by reducing photochemical activity under moderate drought. In contrast, 'MD-2' maintained relatively higher ETR(II) together with stable NPQ throughout drought progression and showed the strongest recovery after rewatering. Across cultivars, severe drought was associated with decreased NPQ and increased Y(NO). PSI-related parameters showed comparatively smaller variation, with stable Y(ND) but increased Y(NA) under severe drought. Linear mixed-effects model analysis further indicated that the estimated cyclic electron flow (CEF), used as a proxy, exhibited a significant cultivar × drought interaction under high light conditions. Most fluorescence parameters partially recovered after rehydration, suggesting that the observed limitations were largely reversible at the functional level. Overall, these results demonstrate cultivar-specific photosystem response patterns under drought and provide a physiological basis for fluorescence-based phenotyping and drought-tolerance screening in CAM crops.