Differential Responses in Non-structural Carbohydrates of Machilus ichangensis Rehd. et Wils. and Taxus wallichiana Zucc. Var. chinensis (Pilg.) Florin Seedlings to Elevated Ozone

Jixin Cao,He Shang,Hao Yu,Zhan Chen

doi:10.3390/f8090323

Jixin Cao, He Shang + Show 2 more

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https://doi.org/10.3390/f8090323

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Abstract

Tropospheric ozone (O3) enrichment could change the carbon (C) metabolism and decrease the C stock for tree species. To assess the differences in response of non-structural carbohydrates (NSCs) between Machilus ichangensis Rehd. et Wils. (M. ichangensis) and Taxus wallichiana Zucc. var. chinensis (Pilg.) Florin (T. wallichiana) with elevated O3, one-year-old container seedlings of the two species were grown with ambient air (AA), 100 ppb (elevated O3 treatment 1, E1-O3), and 150 ppb (elevated O3 treatment 2, E2-O3) treatments using open top chambers. During the experiment, net photosynthetic rate (Pn) of M. ichangensis and T. wallichiana were examined once each month from April to October. At the end of experiment, plants were harvested to examine the NSC concentrations and tissue C stocks. Results suggest elevated O3 significantly decreased Pn and total C stock for both M. ichangensis and T. wallichiana, while it also significantly decreased the NSC concentrations in the foliage of the two species, and the roots of T. wallichiana. However, the concentrations of NSCs and their components in other tissues did not change obviously. Significant increases in the ratio of soluble sugars to starch were observed in the foliage of M. ichangensis and the roots of T. wallichiana. For M. ichangensis, Pn was significantly and positively correlated with NSCs and their components only in foliage. In contrast, NSCs in both foliage and roots were significantly and positively correlated with Pn for T. wallichiana. Based on the results for Pn, total C stock, and NSC concentrations, M. ichangensis appeared more sensitive to elevated O3 than T. wallichiana. It is suggested that the strategies of C allocation in the two species are different with elevated O3.

Highlights

In many parts of the world tropospheric ozone (O3 ), which is harmful to human health and plant growth, is one of the most important secondary air pollutants [1,2]
M. ichangensis with elevated O3, which is consistent with the results described by Riikonen et al [38]
Chen et al [17] found that the foliar soluble sugars concentration in Phoebe bournei (Hemsl.) Yang and Pinus massoniana Lamb did not respond clearly to O3 stress; other studies reported that elevated O3 obviously enhanced the soluble sugars of foliage in other tree species [40,41]

Summary

Introduction

In many parts of the world tropospheric ozone (O3 ), which is harmful to human health and plant growth, is one of the most important secondary air pollutants [1,2]. The background levels of tropospheric O3 concentration in the Northern Hemisphere have increased by around 2–4.5 times since the pre-industrial age [3], and the peak value frequently exceeds 100 ppb (or about 200 μg m−3 ). Tropospheric O3 concentrations over 40 ppb are known to damage forest trees and agricultural crops [7]. Forests 2017, 8, 323 that has been accompanied by increasing concentrations of atmospheric pollutants [8,9]. In most parts of China, mean daily 8 h (9:00–17:00) O3 concentrations over 50–60 ppb have been documented [10]

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