DNA-based stable isotope probing identifies formate-metabolizing methanogenic archaea in paddy soil

Study of Archaeal Diversity in the Arctic Meltwater Lake Region

Two typical lakes formed from meltwater in the Ny-Ålesund area were taken as the study subjects in 2018. To investigate the archaeal community compositions of the two lakes, 16S rRNA genes from soil samples from the intertidal and subtidal zones of the two lakes were sequenced with high throughput. At the phylum level, the intertidal zone was dominated by Crenarchaeota and the subtidal zone was dominated by Halobacter; at the genus level, the intertidal zone was dominated by Nitrososphaeraceae_unclassified and Candidatus_Nitrocosmicus, while the subtidal zone was dominated by Methanoregula. The soil physicochemical factors pH, moisture content (MC), total organic carbon (TOC), total organic nitrogen (TON), nitrite nitrogen (NO₂^--N), and nitrate nitrogen (NO₃^--N) were significantly different in the intertidal and subtidal zones of the lake. By redundancy analysis, the results indicated that NH₄⁺-N, SiO₃^2--Si, MC, NO₃^--N, and NO₂^--N have had highly significant effects on the archaeal diversity and distribution. A weighted gene co-expression network analysis (WGCNA) was used to search for hub archaea associated with physicochemical factors. The results suggested that these physicochemical factors play important roles in the diversity and structure of the archaeal community at different sites by altering the abundance of certain hub archaea. In addition, Woesearchaeales was found to be the hub archaea genus at every site.

Effects of Water and Fertilizer Management Practices on Methane Emissions from Paddy Soils: Synthesis and Perspective

Water and fertilizer management practices are considered to have great influence on soil methane (CH₄) emissions from paddy fields. However, few studies have conducted a quantitative analysis of the effects of these management practices. Here, we selected 156 observations of water management from 34 articles and 288 observations of fertilizer management from 37 articles and conducted a global meta-analysis of the effects of water and fertilizer management practices on soil CH₄ emissions in paddy fields. In general, compared with traditional irrigation (long-term flooding irrigation), water-saving irrigation significantly decreased soil CH₄ emissions but increased rice yield. Among the different practices, intermittent irrigation had the fewest reductions in CH₄ emissions but the greatest increase in rice yield. In addition, fertilization management practices such as manure, mixed fertilizer (mixture), and straw significantly enhanced CH₄ emissions. Rice yields were increased under fertilization with a mixture, traditional fertilizer, and controlled release fertilizer. Our results highlight that suitable agricultural water and fertilizer management practices are needed to effectively reduce CH₄ emissions while maintaining rice yields. We also put forward some prospects for mitigating soil CH₄ emissions from paddy fields in the context of global warming in the future.

Microbial community structure and co-occurrence are essential for methanogenesis and its contribution to phenanthrene degradation in paddy soil

Although polycyclic aromatic hydrocarbons (PAHs) degradation under methanogenesis is an ideal approach to remediating PAH-polluted soil, the contribution of methanogenesis to soil PAH elimination and the relationships between microbial ecological characteristics and PAH degradation during this process remain unclear. Here, we conducted a short-term (60 days) incubation using a paddy soil amended with phenanthrene and examined the effects of a specific methanogenic inhibitor (2-bromoethanesulfonate, BES) on this process. As treatment assessments, the methane production activity (MPA), phenanthrene degradation rate (PDR), and microbial ecological characteristics were determined. The results indicated that BES significantly inhibited both soil MPA and PDR, and we detected a positive relationship between MPA and PDR. Furthermore, BES significantly altered the soil microbial community structure, and it was the microbial community structure but not α-diversity was significantly correlated with soil MPA and PDR. BES decentralized the co-occurrence of bacterial genera but intensified the co-occurrence of methanogens. Moreover, certain bacterial taxa, including Bacteroidetes-vadinHA17, Gemmatimonas, and Sporomusaceae, were responsible for the MPA and PDR in this paddy soil. Collectively, these findings confirm the role of methanogenesis in PAH elimination from paddy soil, and reveal the importance of microbial co-occurrence characteristics in the determination of soil MPA and pollutant metabolism.