Characteristics of chlorophyll fluorescence in the light‐adapted state as indicators of plant leaf relative water content

Premise Chlorophyll fluorescence (ChlF) in the light‐adapted state is a convenient indicator of plant water status but is heavily reliant on nonphotochemical quenching (NPQ). The usefulness of ChlF as an indicator can be enhanced by reducing NPQ effects. Methods ChlF and relative water content (RWC) were measured from leaves of Arabidopsis thaliana and Spinacia oleracea while the leaf samples progressively lost water. ChlF characteristics were then reformulated and tested as indicators of RWC via regression analysis. Results We demonstrate that measured NPQ varies and is by itself not a consistent indicator of RWC of plant leaves. Using NPQ as a scaler in ChlF‐based photochemical efficiency measures resulted in two NPQ‐adjusted ChlF characteristics as indicators of RWC: photosystem II photochemical quenching (PSII PQ) and an NPQ‐scaled PSII photochemical efficiency (Y(II) ′ ) measure. The results were experimentally demonstrated in A. thaliana , then validated in A. thaliana with varied illumination intensities, and finally validated in another plant ( S. oleracea ). Further analysis revealed a linear correlation between steady‐state ChlF ( F s ) and maximum fluorescence ( F m ′ ) across different RWCs and a time constant to account for the NPQ effect. Discussion This research shows that ChlF characteristics are affected by NPQ during water loss and that adjusting PSII efficiency measures based on NPQ provides enhanced effectiveness in indicating plant water status.