Rice plants reduce methane emissions in high-emitting paddies.

Masato Oda,Nguyen Huu Chiem

doi:10.12688/f1000research.15859.3

Masato Oda, Nguyen Huu Chiem

Open Access

https://doi.org/10.12688/f1000research.15859.3

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Abstract

Background: Rice is understood to enhance methane emissions from paddy fields in IPCC guidelines. However, rice actually has two opposite functions related to methane: i) emission enhancement, such as by providing emission pathways (aerenchyma) and methanogenetic substrates; and ii) emission suppression by providing oxygen pathways, which suppress methanogenesis or enhance methane oxidation. The overall role of rice is thus determined by the balance between its enhancing and suppressing functions. Although previous studies have suggested that rice enhances total methane emissions, we aimed to demonstrate in high-emitting paddy fields that the overall methane emission is decreased by rice plants. Methods:We compared methane emissions with and without rice plants in triple cropping rice paddy fields in the Mekong Delta, Vietnam. The gas samples are collected using chamber method and ware analyzed by gas chromatography. Results:We found that rice, in fact, suppressed overall methane emissions in high-emitting paddies. The emission reductions increased with the growth of rice to the maximum tillering stage, then decreased after the heading stage, and finally recovered. Discussion: Our result indicates that the overall methane emission is larger than that of rice planted area. In addition, although many studies in standard-emitting paddies have found that the contribution of soil organic matter to methanogenesis is small, prior studies in high-emitting paddies suggest that methanogenesis depended mainly on soil organic matter accumulated from past crops. The higher the methane emission level, the lower the contribution of the rice-derived substrate; conversely, the higher the contribution of the rice providing oxygen. Finally, rice plants reduce methane emissions in high-emitting paddies. Conclusion: The present study demonstrates that during the growing season, rice is suppressing methane emissions in high-emitting paddies. This means the significance of using the rice variety which has high suppressing performance in high-emitting paddies.

Highlights

The role of rice in methane (CH4) emissions changes according to emission levels
These findings suggest that total CH4 emissions are reduced by oxidation or methanogenesis inhibition associated with growing the rice plant
To our knowledge, most studies of CH emissions in paddy fields have been conducted in fields with low overall emission levels

Summary

Introduction

The role of rice in methane (CH4) emissions changes according to emission levels. Because, rice performs three key functions related to CH emissions: i) providing a CH pathway through a well-developed system of intercellular air spaces (aerenchyma), ii) providing a substrate for methanogenesis, and iii) oxidizing CH4 in rhizosphere by supporting O2 countertransport through aerenchyma system[1,2,3,4,5,6]. To the best of our knowledge, rice enhances overall CH4 emissions from paddy fields. Previous studies have mostly disregarded a potential impact of overall emission levels on the role of rice in enhancing or suppressing CH4 emissions. We changed the last part as follows: “; the higher the contribution of the rice providing oxygen. Rice plants reduce methane emissions in high-emitting paddies.” 5. Previous studies have suggested that rice enhances total methane emissions, we aimed to demonstrate in high-emitting paddy fields that the overall methane emission is decreased by rice plants. Results: We found that rice, suppressed overall methane emissions in high-emitting paddies. Rice plants reduce methane emissions in high-emitting version 3 (revision)

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Conclusion