Dynamics of Foliar Responses to O3 Stress as a Function of Phytotoxic O3 Dose in Hybrid Poplar.

Benjamin Turc,Marcus Schaub,Yves Jolivet,Anthony Gandin,Pierre Vollenweider,Didier Le Thiec,Mireille Cabané

doi:10.3389/fpls.2021.679852

Abstract

With background concentrations having reached phytotoxic levels during the last century, tropospheric ozone (O3) has become a key climate change agent, counteracting carbon sequestration by forest ecosystems. One of the main knowledge gaps for implementing the recent O3 flux-based critical levels (CLs) concerns the assessment of effective O3 dose leading to adverse effects in plants. In this study, we investigate the dynamics of physiological, structural, and morphological responses induced by two levels of O3 exposure (80 and 100 ppb) in the foliage of hybrid poplar, as a function of phytotoxic O3 dose (POD0) and foliar developmental stage. After a latency period driven by foliar ontological development, the gas exchanges and chlorophyll content decreased with higher POD0 monotonically. Hypersensitive response-like lesions appeared early during exposure and showed sigmoidal-like dynamics, varying according to leaf age. At current POD1_SPEC CL, notwithstanding the aforementioned reactions and initial visible injury to foliage, the treated poplars had still not shown any growth or biomass reduction. Hence, this study demonstrates the development of a complex syndrome of early reactions below the flux-based CL, with response dynamics closely determined by the foliar ontological stage and environmental conditions. General agreement with patterns observed in the field appears indicative of early O3 impacts on processes relevant, e.g., biodiversity ecosystem services before those of economic significance – i.e., wood production, as targeted by flux-based CL.

Highlights

The ground-level concentrations of ozone (O3) have increased during the past century (Maas and Grennfelt, 2016), and are predicted to remain stable or increase during the 21st century (Revell et al, 2015; Fu and Tian, 2019)
reactive oxygen species (ROS) can act as elicitors of programed cell death (PCD) reminiscent of plant responses during defensive plant/pathogen interactions which are subsequently designated as hypersensitive responselike (HR-like; Vollenweider et al, 2002; Bhattacharjee, 2005; Günthardt-Goerg and Vollenweider, 2007; Moura et al, 2018)
The physiological and structural responses detected during 30 days of O3 exposure developed mostly before and in some cases at the same time as the initial visible injury and first treatment, sampled at the same leaf position and the end of treatment

Summary

Introduction

The ground-level concentrations of ozone (O3) have increased during the past century (Maas and Grennfelt, 2016), and are predicted to remain stable or increase during the 21st century (Revell et al, 2015; Fu and Tian, 2019). The characteristic symptoms include marked degenerative injuries in chloroplasts, in apparent relation to an increase in the constitutive ROS load resulting from the daily photosynthetic activity. As a consequence, these latter organelles are sensitive to O3 stress (Joo et al, 2005; Kangasjarvi et al, 2005). The dynamics of responses to O3 stress as a function of environmental conditions needs further research

Methods

Results

Conclusion