Seasonal Changes in Photosynthetic Energy Utilization in a Desert Shrub (Artemisia ordosica Krasch.) during Its Different Phenophases

Cai Ren,Charles Bourque,Xin Jia,Tianshan Zha,Yun Tian,Jingyong Ma,Yajuan Wu,Yujie Bai,Wei Feng

doi:10.3390/f9040176

Abstract

Our understanding of the mechanisms of plant response to environment fluctuations during plants’ phenological phases (phenophases) remains incomplete. Continuous chlorophyll fluorescence (ChlF) measurements were acquired from the field to quantify the responses in a desert shrub species (i.e., Artemesia ordosica Krasch. (A. ordosica)) to environmental factors by assessing variation in several ChlF-linked parameters and to understand plant acclimation to environmental stresses. Maximal quantum yield of PSII photochemistry (Fv/Fm) was shown to be reduced by environmental stressors and to be positively correlated to air temperature (Ta) during the early and late plant-growing stages, indicating a low temperature-induced inhibition during the leaf expansion and coloration phases. Effective quantum yield of PSII photochemistry (ΦPSII) was negatively correlated to incident photosynthetically active radiation (PAR) irrespective of phenophase, suggesting excessive radiation-induced inhibition at all phenophases. The main mechanism for acclimating to environmental stress was the regulatory thermal dissipation (ΦNPQ) and the long-term regulation of relative changes in Chl a to Chl b. The relative changes in photosynthetic energy utilization and dissipation in energy partitioning meant A. ordosica could acclimatize dynamically to environmental changes. This mechanism may enable plants in arid and semi-arid environments to acclimatize to increasingly extreme environmental conditions under future projected climate change.

Highlights

Photosynthesis is a fundamental mechanism in plant metabolism that converts light energy into biochemical energy [1]
Our results show that ΦPSII decreased with increasing daily mean photosynthetically active radiation (PAR) during the three phenophases (Figure 4b), indicating that the reduction in photochemical efficiency was driven by excessive solar radiation during the growing season
Inhibition happened throughout the growing season, being largely induced by cold air temperature (Ta ) during the leaf-expanding and coloring phases and PAR in all phenophases

Summary

Introduction

Photosynthesis is a fundamental mechanism in plant metabolism that converts light energy into biochemical energy [1]. A vast number of studies have shown that the activity of PSII and its associated light harvesting proteins gradually declined during the entire time of exposure to high illumination and that non-photochemical quenching (NPQ) increased in response to excessive radiation energy [11,12,13]. Such inhibition of photosynthesis can arise from exposure to high light in the absence of other stresses, and from too much light in the presence of other stresses that limit photosynthesis and plant growth [14]. When facing low temperature stress, plants showed a sustained NPQ and improved photo-protection, which is associated with the reorganization of the light harvesting complex into aggregates [18,19]

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