Early detection and recovery assessment of water deficit in strawberry using leaf position-specific chlorophyll fluorescence responses

초록

Water deficit substantially constrains strawberry (Fragaria & times; ananassa) productivity, yet the differential photosynthetic sensitivity across leaf developmental stages remains poorly characterized. This study investigated water deficit-induced impairment of photosystem II (PSII) in two contrasting leaf positions using chlorophyll a fluorescence transient (OJIP) analysis and JIP-test parameters, supplemented by machine learning classification and SHapley Additive exPlanations (SHAP) feature attribution. Plants were subjected to mild and severe water deficit for six days, followed by a recovery experiment to assess the reversibility of the detected responses. In the first fully expanded leaf (L1), limitation progressed sequentially from I-step perturbation and reduced electron transport efficiency toward J-step involvement, K-band development, and extensive OJIP collapse under severe stress. The performance index (PIabs) declined irreversibly from Day 3, with structural collapse by Day 6. The third fully expanded leaf (L3) exhibited simultaneous J- and I-phase engagement from early water deficit, with preserved reaction center integrity. PIabs became irreversible only from Day 4, while structural parameters remained reversible throughout. Among four classifiers, the multilayer perceptron (MLP) achieved the highest accuracy (0.932 at 4 days after treatment in the younger leaf). SHAP analysis identified REo/CSm and Vk/Vi as the influential predictors for the L1 and L3, respectively, consistent with their contrasting OJIP kinetic dynamics. These results support a leaf-position-specific, time-resolved fluorescence framework for early, non-destructive water deficit detection that may help inform irrigation management in strawberry cultivation.

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