Diurnal Variations in Physiological Characteristics, Photoassimilates, and Total Ascorbate in Early and Late Sown Indian Wheat Cultivars under Exposure to Elevated Ozone

Durgesh Singh Yadav,Shashi Bhushan Agrawal,Madhoolika Agrawal,Bhavna Jaiswal

doi:10.3390/atmos12121568

Abstract

Rising tropospheric ozone (O3) in the atmosphere is detrimental to crop’s productivity and is one of the reasons for a warmer climate. The present study describes diurnal changes in gaseous exchange, chlorophyll fluorescence, ascorbic acid, and photoassimilate parameters in flag leaves of four Indian wheat (Triticum aestivum L.) cultivars (two early sown and two late sown cultivars) under ambient and elevated O3 treatments, using the open-top chambers (OTCs). Results showed that the diurnal pattern of photosynthetic rate (Ps), sucrose, and ascorbic acid content varied according to changes in photosynthetically active radiation (PAR) and O3 concentrations during the daytime and were maximum between 10:00 to 12:00. The present study suggested that elevated O3 caused more negative effects on photosystem II in early sown compared to late sown cultivars. The greater loss of photosynthesis led to lower production of photoassimilates in early sown cultivars, which utilized more assimilates in ascorbic acid formation for detoxification of ROS formed due to elevated O3. This work will also help to identify the robustness of physiological machinery in different wheat cultivars under elevated levels of O3, and may be used for selection of suitable cultivars during future breeding programs.

Highlights

O3 and elevated O3 treatments, while storage of photoassimilates was more active during the afternoon period
Rising photosynthetically active radiation (PAR) intensity from 10:00 am to 12:00 p.m. stimulated the production of photoassimilates and ascorbic acid content in all the test cultivars
The present study suggested that elevated O3 concentration caused more negative effects on photosystem II in early sown compared to late sown cultivars

Summary

Introduction

Predicting the exact concentration of ambient ozone (O3 ) in the future is critical as the concentration of O3 varies diurnally, seasonally, and spatially [1,2,3,4]. Many researchers have developed exposure regimes where ambient O3 concentration reaches its highest level diurnally in mid- to late-afternoon [6]. The concentration of tropospheric O3 is increasing rapidly in the Asian countries since 1990 due to rising O3 precursors [3,7]. As tropospheric O3 is a greenhouse gas and long-range transboundary air pollutant, the rising trend of O3 concentration is impacting climate, human health and vegetation [3,7]. Many studies have estimated wheat yield losses under future climate and air pollution scenarios [8,9,10,11]. Diurnal changes in O3 concentration may modify the response pattern of the plants

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