Do nitrogen fertilizers stimulate or inhibit methane emissions from rice fields?

Abstract

In rice cultivation, there are controversial reports on net impacts of nitrogen (N) fertilizers on methane (CH ) emissions. Nitrogen fertilizers increase crop growth as well as alter CH producing (Methanogens) and consuming (Methanotrophs) microbes, and thereby produce complex effects on CH emissions. Objectives of this study were to determine net impact of N fertilizers on CH emissions and to identify their underlying mechanisms in the rice soils. Database was obtained from 33 published papers that contained CH emissions observations from N fertilizer (28-406 kg N ha ) treatment and its control. Results have indicated that N fertilizers increased CH emissions in 98 of 155 data pairs in rice soils. Response of CH emissions per kg N fertilizer was significantly (P < 0.05) greater at < 140 kg N ha than > 140 kg N ha indicating that substrate switch from CH to ammonia by Methanotrophs may not be a dominant mechanism for increased CH emissions. On the contrary, decreased CH emission in intermittent drainage by N fertilizers has suggested the stimulation of Methanotrophs in rice soils. Effects of N fertilizer stimulated Methanotrophs in reducing CH emissions were modified by the continuous flood irrigation due to limitation of oxygen to Methanotrophs. Greater response of CH emissions per kg N fertilizer in urea than ammonia sulfate probably indicated the interference of sulfate in the CH production process. Overall, response of CH emissions to N fertilizers was correlated with N-induced crop yield (r = +0.39; P< 0.01), probably due to increased carbon substrates for Methanogens. Using CH emission observations, this meta-analysis has identified dominant microbial processes that control net effects of N fertilizers on CH emissions in rice soils. Finally, we have provided a conceptual model that included microbial processes and controlling factors to predict effects of N fertilizers on CH emissions in rice soils.

Competitive interactions between methane- and ammonia-oxidizing bacteria modulate carbon and nitrogen cycling in paddy soil

“…Physiologically, the enzymatic similarity of ammonia oxidizers and MOB may result in ammonia oxidation by MOB (Bodelier and Frenzel, 1999), leading to reduced availability of ammonia for ammonia oxidizers. However, previous studies showed that MOB had lower affinity for ammonia than for CH 4 (Banger et al, 2012;Bedard and Knowles, 1989;Yang et al, 2011). Moreover, it has been proposed that ammonia oxidation by MOB occurred only when the ratio of ammonia to CH 4 is higher than 30 in soils (Banger et al, 2012;Bodelier and Laanbroek, 2004;Yang et al, 2011).…”

“…The tight coupling between nitrogen fertilization and methane emission from rice paddy ecosystems in combination with the significant contribution of these systems to the global methane emission, 15 to 25 % (Bodelier, 2011), has evoked numerous studies focusing on this topic. Recent meta-analysis indicates that the increasing rice biomass by nitrogen fertilization may result in the elevated supply of readily available carbon in support of methanogenesis, stimulating methane emission in paddy fields (Banger et al, 2012). However, opposed to this is a strong body of evidence demonstrating stimulation of methane oxidation by ammonium-based fertilizers in rice 3354 Y. Zheng et al: Interactions between soil methane and ammonia oxidizers soil, leading to reduced methane flux (Bodelier et al, 2000b).…”

Global warming potential and greenhouse gas intensity in rice agriculture driven by high yields and nitrogen use efficiency

“…The total N 2 O emissions decreased by 7-38 and 26-42 % in the rice and wheat seasons, respectively, when the conventional N management (300 kg N ha −1 for rice and 180 kg N ha −1 per crop for wheat) changed to optimum N management (225-270 kg N ha −1 for rice and 135-162 kg N ha −1 per crop for wheat). It is likely that more N 2 O was emitted (Mosier et al, 2006) as a result of the additional N made available to the soil microbes through N fertilizer application, which also probably contributed to increased CH 4 emissions (Banger et al, 2013). Strategies that can reduce N fertilization rates without influencing crop yields can inevitably lower GHG emissions (Mosier et al, 2006).…”

Stimulation of long-term ammonium nitrogen deposition on methanogenesis by Methanocellaceae in a coastal wetland

“…According to the genome sequence of Methanocellaceae (Erkel et al, 2006), a unique set of genes encoding antioxidant enzymes and oxygen-insensitive fermentation enzymes were found, which probably improved their ability to adapt to alternate dry/wet conditions. Although nitrate nitrogen may compete for electrons, which was crucial for methane production (Lai et al, 2016;Zhu et al, 2016), stimulation of plant growth by nitrate based fertilizers can enhance methane production by increased organic carbon availability for fermenting microbes delivering methanogenic substrates (Banger et al, 2012). Thus, the effects of nitrate nitrogen on methane emission were complicated.…”