They show that short photoperiod during autumn induces zeaxanthin-independent mechanisms for non-photochemical quenching. This change remains undetected by a widely used vegetation index, PRI, which is used in remote sensing to assess physiological performance and phenology in plants. As a result of these zeaxanthin-independent quenching mechanisms they observed a discrepancy in the relationship between PRI and photosynthesis, which can cause an overestimation of photosynthesis, if assessed by PRI and remote sensing approaches alone.