Differentiated Mechanisms of Biochar Mitigating Straw-Induced Greenhouse Gas Emissions in Two Contrasting Paddy Soils

Abstract

Straw returns to the soil is an effective way to improve soil organic carbon and reduce air pollution by straw burning, but this may increase CH4 and N2O emissions risks in paddy soils. Biochar has been used as a soil amendment to improve soil fertility and mitigate CH4 and N2O emissions. However, little is known about their interactive effect on CH4 and N2O emissions and the underlying microbial mechanisms. In this study, a 2-year pot experiment was conducted on two paddy soil types (an acidic Utisol, TY, and an alkaline Inceptisol, BH) to evaluate the influence of straw and biochar applications on CH4 and N2O emissions, and on related microbial functional genes. Results showed that straw addition markedly increased the cumulative CH4 emissions in both soils by 4.7- to 9.1-fold and 23.8- to 72.4-fold at low (S1) and high (S2) straw input rate, respectively, and significantly increased mcrA gene abundance. Biochar amendment under the high straw input (BS2) significantly decreased CH4 emissions by more than 50% in both soils, and increased both mcrA gene and pmoA gene abundances, with greatly enhanced pmoA gene and a decreased mcrA/pmoA gene ratio. Moreover, methanotrophs community changed distinctly in response to straw and biochar amendment in the alkaline BH soil, but showed slight change in the acidic TY soil. Straw had little effect on N2O emissions at low input rate (S1) but significantly increased N2O emissions at the high input rate (S2). Biochar amendment showed inconsistent effect on N2O emissions, with a decreasing trend in the BH soil but an increasing trend in the TY soil in which high ammonia existed. Correspondingly, increased nirS and nosZ gene abundances and obvious community changes in nosZ gene containing denitrifiers in response to biochar amendment were observed in the BH soil but not in the TY soil. Overall, our results suggested that biochar amendment could markedly mitigate the CH4 and N2O emissions risks under a straw return practice via regulating functional microbes and soil physicochemical properties, while the performance of this practice will vary depending on soil parent material characteristics.

Greater promotion of DNRA rates and nrfA gene transcriptional activity by straw incorporation in alkaline than in acidic paddy soils

“…Soil properties in 2016 have been presented in our previous work (Table S1) (Wang et al, 2018b), and the results of 2017 were similar to that of 2016. In 2017, soil pH ranged between 8.4 to 8.6 in the BH soil (Inceptisol) with no significant difference among the treatments, while pH in the TY soil was significantly increased by 0.8-1.0 unit after one-year rice plantation, compared with the newly flooded N0 treatment (pH at 6.4) in 2017 (Table 1).…”

“…In addition, we found that nrfA gene abundance significantly decreased over time in 2016, indicating a declined effect from straw incorporation. Considering the facts that rice straw amendment could effectively improve DNRA while high N input had reverse effect on DNRA as observed in this study and above mentioned studies, together with our previous finding that straw amendment had potential risk in enhancing N 2 O emission in the same soils (Wang et al, 2018b), we recommended that simultaneous application of both nitrogen fertilizers and rice straws should be avoided in paddy rice fields.…”

“…A two-year outdoor pot experiment was set up in 2016 as previously described (Wang et al, 2018b), including three treatments: (1) no rice straw addition (S0), (2) 0.33% (w:w) straw addition (S1) and (3) 0.66% (w:w) straw addition (S2). Briefly, three replicate pots were included for each treatment and each pot contained 10 kg of soils (dry weight).…”

Sustainable management of paddy crop residues: effects on methanotrophs diversity and value for soil health restoration

“…The FTIR results of RHB indicated that the presence of the carboxyl group (COOH), OH −, and NH 2 (Singh & Gautam, 2017) could be beneficial to enhance soil elemental status (Ding et al, 2016) compared to inorganic fertilizer. The biochars derived from CRs contain elemental nutrient contents useful for paddy plants and provides shelter for micro‐flora (Wang et al, 2018; Warnock et al, 2010). The porous quality, larger internal surface area, ability to adsorb soluble organic matter and inorganic nutrients (Singh et al, 2018) of RHB could be a potential soil amendment for paddy agriculture.…”

Effect of straw incorporation and nitrification inhibitor on nitrous oxide emission in various cropland soils and its microbial mechanism

“…In all, 1,296 gas samples were collected and measured. Calculation of N2O flux was performed via a linear regression model (Wang et al, 2018b),…”