Salt Stress Reduced the Seedling Growth of Two Larch Species Under Elevated Ozone

Tetsuto Sugai,Fuyuki Satoh,Takayoshi Koike,Laiye Qu,Wang Yannan,Toshihiro Watanabe

doi:10.3389/ffgc.2019.00053

Abstract

The effect of elevated ozone (O3) and soil salinization with alkaline salts in northeastern (NE) China is a serious concern in the success of the national replanting project. As the areas planted exceed 4 million hectares in China, we must consider the future afforestation after thinning and harvest at some parts of them. Here, we investigated the effects of O3 and salt stress on seedlings of Dahurian larch (Larix gmelinii var. japonica; DL) and Japanese larch (L. kaempferi; JL). The two species of seedlings were exposed to elevated O3 [approximately 70 nmol mol-1] and ambient control [approximately 40 nmol mol-1] for one growing season in an open top chamber (OTC) system that simulated the salinity in NE China [alkaline salt, NaHCO3 : NaCl = 9:1, 20mM Na+]. The seedlings under salt free treatment received tap water. Effects of O3 on the growth of both larches were not significant, although the LMA of JL was reduced more than that of DL seedlings. Further, the combined effects of O3 and salt stress were not significant. This may be attributable to the stronger effects of salt stresses on both larch seedlings. Salt stress decreased the total dry mass in both larch species by more than 10%. DL seedlings showed specific salt tolerance in absorption of some mineral nutrients. Although salt stress reduced Ca and Mg content in needles, we found the degree of reduction was lower in DL than JL, with specific salt tolerance of mineral homeostasis in DL seedlings. Our results indicated that DL seedlings may be future candidate afforestation species even in saline soil and O3 levels less than 70 nmol mol-1.

Highlights

Ground-level ozone (O3) is the most harmful air pollutant to forest ecosystems on both local and global scales (Paoletti et al, 2007, 2010; Matyssek et al, 2012; Sicard and Dalstein-Richier, 2015; Sicard et al, 2016)
The mean value of total dry mass and total leaf area index (TLA) at elevated O3 (eO3) were ∼23 and 34% higher than at the ambient O3 condition, respectively
Needle Na contents were significantly increased under salt stresses in both larches

Summary

Introduction

Ground-level ozone (O3) is the most harmful air pollutant to forest ecosystems on both local and global scales (Paoletti et al, 2007, 2010; Matyssek et al, 2012; Sicard and Dalstein-Richier, 2015; Sicard et al, 2016). Accelerates leaf senescence, changes carbon allocation to roots, and induces nutritional imbalances in leaves (Matyssek et al, 2012; Agathokleous et al, 2015; Shi et al, 2017). In China, the annual daily maximum O3 concentration in some regions often reaches 60 nmol mol−1 (Gaudel et al, 2018). The current eO3 level is high enough to suppress tree growth and degrade ecosystem health (Chen et al, 2015; Feng et al, 2015). The conservation of forests in China is an issue of increasing interest in regions that face multiple environmental stresses, such as eO3, nitrogen deposition, and drought (Reilly et al, 2007; Fang et al, 2014; Hu et al, 2015; Yuan et al, 2016)

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