The influence of ozone pollution on CO 2 , CH 4 , and N 2 O emissions from a Chinese subtropical rice–wheat rotation system under free-air O 3 exposure T.J. Kou a, *, X.H. Cheng a , J.G. Zhu b , Z.B. Xie b a College of Agriculture, Henan University of Science and Technology, Luoyang 471003, PR China b State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China ARTICLE INFO Article history: Received 10 November 2014 Received in revised form 23 February 2015 Accepted 26 February 2015 Available online 3 March 2015 Keywords: Ozone exposure Greenhouse gas Global warming potential Rice–wheat rotation system Global climate change ABSTRACT A better understanding of the effects of ozone (O 3 ) on greenhouse gas (GHG) emissions in rotational rice (Oryza sativa L.)–wheat (Triticum aestivum L.) systems is essential for reducing potential GHG emissions in agroecosystems due to the projected increase in O 3 concentrations. Rice and wheat were rotationally grown in a free-air O 3 enrichment platform, and crop production and N 2 O, CH 4 , and CO 2 emissions from the soils were investigated as well as the global warming potential (GWP) of the GHGs. Exposure to elevated O 3 (50% greater than ambient O 3 ) slightly reduced the total biomass of wheat and significantly decreased that of rice, significantly decreased the root to total biomass ratio of wheat and slightly increased that of rice. Elevated O 3 significantly increased the CO 2 emission but did not influence the CH 4 and N 2 O emissions in the rice–soil system; however, elevated O 3 did not influence the CO 2 emission, significantly increased the CH 4 emission, and significantly reduced N 2 O emissions in the root-free soil during the rice season. Elevated O 3 increased the CO 2 emission and decreased the CH 4 and N 2 O emissions in the wheat–soil system and root-free soil during the wheat season, although the decrease in N 2 O emission in the wheat–soil system was not significant. The effects of elevated O 3 on GHGs emissions and biomass accumulation were related to crop species, plant coverage, and GHG type. Elevated O 3 significantly increased the GWP in the rice–soil system and the GWP per unit of rice yield; however, it did not change the GWP in the wheat–soil system or in the root-free soil during the wheat–rice growing period, nor did it change the GWP per unit of wheat yield. Considering the decreases in wheat and rice dry matter, reducing CO 2 emissions and planting O 3 -tolerant crop cultivars during future elevated O 3 scenarios, especially during the rice-growing season, should be a primary focus of the research aimed at reducing the GWP and increasing the soil C and N sequestration of rotational rice–wheat cropping systems. ã 2015 Elsevier B.V. All rights reserved. 1. Introduction Ozone (O 3 ) is a highly reactive and oxidative pollutant. Anthropogenic activity has increased the concentration of tropospheric O 3 (Vingarzan, 2004). Tropospheric O 3 has strongly increased in East Asia since the 1990s (Schnadt Poberaj et al., 2009; IPCC, 2013) and is still rising (Stevenson et al., 2013). The Yangtze River Delta of China, one of the most important rice–wheat production regions, is under an increasingly serious threat of O 3 pollution (Shao et al., 2006). As levels of tropospheric O 3 > 40 ppb would cause visible leaf injury, plant damage, and a reduction in crop and forest productions (Sitch et al., 2007; Zhang et al., 2010), the effect of elevated tropospheric O 3 on terrestrial ecosystems is a concern to global scientists and the public (Ashmore, 2005; Fiscus et al., 2005; Fuhrer, 2009). Many O 3 exposure experiments (using closed chambers, open-top chambers, or free-air O 3 enrichment systems (O 3 FACE)) have elucidated the responses of various ecosystems to elevated O 3 (Manning, 2005; Wang et al., 2007; Kou et al., 2014). Elevated O 3 has been demonstrated to decrease net photosyn- thesis (Nie et al., 1993) via oxidative damage to cell membranes and chloroplasts (Karberg et al., 2005) and consequently reduces dry matter accumulation (Nouch et al.,1991; Kobayashi and Okada, 1995; Maggs and Ashmore, 1998; Feng et al., 2008; Shi et al., 2009) and alters its allocation belowground (Fiscus et al., 2005; McCrady and Andersen, 2000; Kanerva et al., 2006; Jones et al., 2009; * Corresponding author. Fax: +86 379 64282340. E-mail address: tjkou@aliyun.com (T.J. Kou). http://dx.doi.org/10.1016/j.agee.2015.02.013 0167-8809/ ã 2015 Elsevier B.V. All rights reserved. Agriculture, Ecosystems and Environment 204 (2015) 72–81 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee