Photoprotection mechanism of temperate Japanese cypress canopy in response to excessive light stress in winter
Abstract
Evergreen cypress canopy in temperate regions often changes color from green to red before or during winter and persists until the following spring. This phenomenon is known as "winter leaf reddening", which may be a photoprotection strategy for plant leaves to deal with excess light energy in winter and early spring. A non-chemical quenching mechanism - the xanthophyll cycle (VAZ cycle) and a physical protection mechanism - accumulation of red pigment (e. g. rhodoxanthin) in gymnosperms can protect photosynthetic apparatus from damage caused by excessive light energy. However, the combined effect of these two mechanisms on canopy photosynthesis under excess light stress conditions in winter has not been further investigated. This study aimed to determine the following: (1) Dynamic change patterns of the VAZ cycle and rhodoxanthin accumulation under the winter leaf reddening phenomenon; (2) The specific excess light stress conditions that triggered this phenomenon; and (3) Whether rhodoxanthin and the VAZ cycle play a cooperative role in regulating canopy low light use efficiency (LUE) and gross primary production (GPP) under low winter temperature conditions.
These two mechanisms were monitored by a spectroradiometer and calculated as vegetation indices after spectral reflectance analysis in this study. The rhodoxanthin index (RI) and photochemical reflectance index (PRI) was used to track rhodoxanthin variation patterns and the VAZ cycle dynamic, respectively. A digital camera-equipped automated system was used to monitor canopy color changes and express leaf redness as the red-green vegetation index (RGVI). The eddy covariance method was used to measure the canopy CO2 flux, which can be used to calculate GPP and LUE. Micrometeorological data were also monitored. This study showed that RI and PRI were at their highest and lowest levels during winter leaf reddening, respectively, along with lower levels of Ta, PAR, GPP, and LUE. Winter leaf reddening is a common phenomenon that occurs due to the photoprotection function. Winter leaf reddening may be more accurately reflected by RI than other indices due to changes in canopy GPP and LUE. Rhodoxanthin accumulation may be more directly responsible for winter leaf reddening.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.B45L1879C
- Keywords:
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- winter leaf reddening;
- Japanese cypress;
- photochemical reflectance index (PRI);
- Red index (RI);
- Red-Green vegetation index (RGVI);
- phenological analysis;
- digital camera;
- light-use efficiency (LUE);
- gross primary production (GPP)