Light Energy Partitioning and Photoprotection in an Exotic Species (Salix Psammophila) Grown in a Semi-Arid Area of Northwestern China

Yini Han,Yujie Bai,Yajuan Wu,Xin Jia,Charles Bourque,Juying Wu,Tianshan Zha,Yun Tian,Mingyan Zhang,Jingyong Ma

doi:10.3390/f9060341

Yini Han, Yujie Bai + Show 8 more

Open Access

https://doi.org/10.3390/f9060341

Copy DOI

Abstract

Thermal dissipation of excess excitation energy is an important photoprotective mechanism that plants have evolved to cope with surplus illumination. However, light-energy-partitioning dynamics in an exotic sand-dune willow (Salix psammophila) commonly used in restoring and/or stabilizing sand lands in northwestern China is largely unknown. In this study, chlorophyll fluorescence (ChlF) of photosystem II (PSII) was continuously monitored in situ in Salix psammophila to investigate plant acclimation processes driven by excessive solar radiation and extreme air temperatures (Ta). As part of a heat-regulation mechanism, energy partitioning is shown to vary with prevailing environmental conditions. In this investigation, energy absorbed during periods of moderate photosynthetically active radiation (PAR < 1200 μmoL·m−2·s−1) was largely allocated towards photochemistry (ΦPSII) with nominal amounts to thermal dissipation through reversible thermal dissipation (ΦNPQr). In extremely high solar radiation (PAR > 1500 μmoL·m−2·s−1) or in a cold temperature (Ta < 0 °C), more energy was dissipated by way of non-regulated thermal energy (Φf,D) and sustained thermal dissipation (ΦNPQs), leading to non-reversible photoinhibition or photodamage. This was mainly as a result of the low utilization and high absorption of light energy by PSII under cold conditions and physiologically-induced vulnerability. It was concluded that Salix psammophila had a clear tolerance to high temperatures and moderate solar radiation, but tended to be more vulnerable to high solar radiation and cold temperature. Based on species sensitivity to extreme environmental conditions, practical application and extension of Salix psammophila for land-restoration purposes should be approached cautiously, especially in high-latitude or high-altitude desert ecosystems commonly affected by events of high solar radiation and cold temperature.

Highlights

Chlorophyll fluorescence (ChlF) has been one of the most dependable and preferred methods of determining physiological responses in plants growing in stressed environments [1,2]
The objective of this study was to: (i) examine the diurnal and seasonal dynamics of energy partitioning in environmentally-stressed plants through continuous measurement of ΦPSII, Φf,D, and ΦNPQ, as key functional indicators of plant response; and (ii) explore species-specific acclimation strategies to anomalous temperatures and solar radiation intensities
There were periods of intense solar radiation and high temperature differences between daytime and nighttime periods (Figure 1), which are typical in semi-arid areas of northwestern China

Summary

Introduction

Chlorophyll fluorescence (ChlF) has been one of the most dependable and preferred methods of determining physiological responses in plants growing in stressed environments [1,2]. Pulse-amplitude modulated (PAM) fluorescence provides a rapid and non-intrusive means of estimating ChlF-associated parameters in investigating vegetation response to stressful conditions [3,4,5,6]. The non-photochemical quenching coefficient (NPQ) of excess light energy within the light-harvesting antennae of PSII (LHCII) is believed to be the most effective. As a ratio of regulated and non-regulated heat dissipation, the increase in NPQ indicates elevated photoprotection in response to excessive sunlight [12,13]. Even though the majority of excess light energy is safely dissipated through the NPQ pathway, photoinhibition is still inevitable, leading to photodamage as a result of the overproduction of reactive oxygen species (ROS) [14,15]

Objectives

Methods

Results

Discussion

Conclusion