Data for: Coupled anaerobic methane oxidation and metal reduction in soil under elevated CO2
Data files
May 15, 2023 version files 1.97 MB
Abstract
Continued current emissions of carbon dioxide (CO2) and methane (CH4) by human activities will increase global atmospheric CO2 and CH4 concentrations and surface temperature significantly. Fields of paddy rice, the most important form of anthropogenic wetlands, account for about 9% of anthropogenic sources of CH4. Elevated atmospheric CO2 may enhance CH4 production in rice paddies, potentially reinforcing the increase in atmospheric CH4. However, what is not known is whether and how elevated CO2 influences CH4 consumption under anoxic soil conditions in rice paddies, as the net emission of CH4 is a balance of methanogenesis and methanotrophy. In this study, we used a long-term free-air CO2 enrichment experiment to examine the impact of elevated CO2 on the transformation of CH4 in a paddy rice agroecosystem. We demonstrate that elevated CO2 substantially increased anaerobic oxidation of methane (AOM) coupled to manganese and/or iron oxides reduction in the calcareous paddy soil. We further show that elevated CO2 may stimulate the growth and metabolism of Candidatus Methanoperedens nitroreducens, which is actively involved in catalyzing AOM when coupled to metal reduction, mainly through enhancing the availability of soil CH4. These findings suggest that a thorough evaluation of climate-carbon cycle feedbacks may need to consider the coupling of methane and metal cycles in natural and agricultural wetlands under future climate change scenarios.
Methods
File 1 and File 5: We incubated the soils from the two paddy systems to examine whether anaerobic oxidation of methane could be coupled to the reduction of nitrate (NO3-), manganese (Mn(IV)), iron (Fe(III)) or sulfate (SO42-) in soils (exp. 1). Soil slurries were anaerobically incubated following a completely randomized design (CRD), in which two main factors were 13CH4 (no 13CH4 addition vs +13CH4) and e-acceptor (no e-acceptor addition, +NO3-, +Mn(IV), +Fe(III), and +SO42-). Each treatment replicated 3 times. We measured 13CH4 consumption, 13CO2 production and Mn2+/Fe2+ production after incubation.
File 2: We incubated the soils from the rice FACE system to investigate the influence of eCO2 on the coupling of anaerobic oxidation of methane to metal reduction. Soil slurries were incubated following a split-plot experiment with factorial structure, and whole-plots were organized as a RCBD (3 blocks). The CO2 treatment (aCO2 vs eCO2) was considered the whole-plot factor, while the two nested treatments 13CH4 addition (no 13CH4 addition and +13CH4) and e-acceptor identity (no e-acceptor addition, +Mn(IV) and +Fe(III)) constituted a 2×3 factorial structure. Each treatment replicated 3 times (exp. 2). We measured 13CH4 consumption and Mn2+/Fe2+ production after incubation. Also, We carried out a field study to examine the influence of eCO2 on the anaerobic transformation of 13CH4 in the paddy system. The experiment was a split-plot design with whole-plots arranged in a RCBD (3 blocks). The CO2 treatment (aCO2 vs eCO2) was the whole-plot treatment, whereas the e-acceptor identity (no e-acceptor addition, +Mn(IV) and +Fe(III)) was considered the split-plot factor. There were 3 replicates per treatment (exp. 3). We measured 13CH4 production and 13CO2 production after incubation.
File 3: We performed qPCR tests using a specific primer set targeting the mcrA gene of Ca. M. nitroreducens to quantify the role of Ca. M. nitroreducens in mediating anaerobic oxidation of methane coupled to metal reduction in soils. We measured the absolute abundance of Ca. M. nitroreducens by qPCR.
File 4: We used metagenomic sequencing to analyze microbial functional genes involved in CH4 cycling in the field to explore the possible biological mechanisms underlying the eCO2 effect on the transformation of CH4. Genomic DNA, for soil metagenomic sequencing, was extracted from 5 g aliquots of field soils sampled at the heading stage of rice plants from aCO2 and eCO2 plots in 2015 using PowerSoil® kits, and was then sequenced on the Illumina HiSeq 2500 platform. We analyzed the functional genes using KEGG database.
File 6: We carried out a field study to examine the potential of denitrification in the paddy system. We measured in-situ 30N2 and 29N2 production following the addition of 15NO3- after one day incubation in the field. Values are means (n = 3) ± SEM.
File 7: We conducted a sterilization test to determine the involvement of soil microbes in the coupling of anaerobic oxidation of methane to metal reduction. Soil slurries were incubated following a CRD, in which two factors were the sterilization treatment (non-sterilized and sterilized) and the e-acceptor identity (no e-acceptor addition, +Mn(IV) and +Fe(III)). There were 3 replicates per treatment. We measured 13CO2 production after incubation. We also sequenced the 16S rRNA genes of genomic DNA in the calcareous soil sampled from exp. 1.
File 8: We conducted an incubation using the calcareous soil to investigate the influence of CO2 on the coupling of anaerobic oxidation of methane to iron reduction. Soil slurries were incubated following the additions of CH4, CH4+Fe(III), CH4+CO2 or +CH4+Fe(III)+CO2. There were 3 replicates per treatment. We measured CH4 consumption after incubation.