Winter leaf reddening and photoprotection accessed by vegetation indices and its influence on canopy light-use efficiency of a Japanese cypress (Chamaecyparis obtusa) forest

Abstract

Japanese cypress (Chamaecyparis obtusa Sieb. et Zucc.) is an evergreen conifer native to Japan and widely distributed in East Asia. Evergreen forests in temperate regions are usually exposed to high solar radiation and low temperatures during winter, a combination of stresses that can negatively impact leaf photosynthetic capacity. In response to excessive light energy stress under cold temperatures, Japanese cypress canopies exhibit a reversible color change associated with several photoprotective mechanisms known as “winter leaf reddening.” Here, several vegetation indices (VIs), including the photochemical reflectance index (PRI), rhodoxanthin index (RI), chlorophyll/carotenoid ratio index (CCI), triangular PRI index (tri-PRI), and red-green vegetation index (RGVI) were utilized to track the influence of winter leaf reddening and photoprotection on canopy-scale light-use efficiency (LUE) determined by the eddy covariance technique. Seasonal changes in VIs, environmental factors, and LUE in Japanese cypress canopies between 2017 and 2021 indicated that VIs could detect the phenology and LUE changes during winter leaf reddening. Our results suggest that winter leaf reddening occurrence is driven by prolonged low temperatures, and accompanied by dynamic xanthophyll cycle suppression, rhodoxanthin accumulation, and LUE reduction. Once stressful conditions are released, rhodoxanthin quickly decomposes and the remaining xanthophyll pigment may lead the canopy reddish-brown to persist longer. The integration of remote sensing and eddy covariance methods facilitates the validation of traditional results observed at the leaf scale within the context of the canopy scale, offering insights into how vegetation adjusts photosynthesis in response to environment stress.