Methane Emission and Acetate-dependent Methanogenesis in Rice-based Cropping Systems with Urea Addition
Guangbin Zhang, Xiaoli Zhu, Wanyu Shen, Yang Ji, Hua Xu and Jing Ma
Published: November 11, 2021.
Abstract
Urea application is a fundamental practice to increase rice grain yields, but it also plays a significant role in CH4 emission from rice paddy fields. To quantify the effect on CH4 emission, we measured soil dissolved organic carbon (DOC) content, CH4 production potentials of paddy soil and rice roots, CH4 concentration in soil pore water, and their corresponding stable carbon isotopes (δ13C) under four urea application rates (0, 120, 240 and 300 kg N ha-1) in 2010–2015 based on incubation, pot and field experiments. In addition, the abundance of methanogenic archaea in paddy soils was quantified by quantitative PCR targeting mcrA genes. Field and pot experiments show that urea addition decreased seasonal CH4 emissions by 20–35% and enhanced δ13C-values of emitted CH4 by 3‰ on average. The decreased CH4 production potentials in paddy soil and on rice roots (by 16–30%) were found to be the major reason for the reduction of CH4 emission with urea addition. In contrast, applying urea increased the content of soil DOC and the abundance of methanogenic mcrA genes. The contribution of acetoclastic methanogenesis was also increased by urea addition both in the soil (by 10–12%) and on the roots (by 5%), which might have positive effects on the δ13C-values of emitted CH4 and porewater CH4. The findings demonstrate that the decrease of CH4 emission was attributed to CH4 production reduced with urea addition, and the promotion of acetate-dependent methanogenesis was possibly ascribed to related methanogenic substrates and archaea increased.
Keywords: N addition; CH4 production; Stable carbon isotopes; Methanogenic archaea; Methanogenic pathway; Rice-based cropping system