N-damo, an opportunity to reduce methane emissions?

Nitrate-dependent anaerobic methane oxidation (N-DAMO) as a bioremediation strategy for waters affected by agricultural runoff

Agricultural drainage ditches are subjected to high anthropogenic nitrogen input, leading to eutrophication and greenhouse gas emissions. Nitrate-dependent anaerobic methane oxidation (N-DAMO) could be a promising remediation strategy to remove methane (CH4) and nitrate (NO3-) simultaneously. Therefore, we aimed to evaluate the potential of N-DAMO to remove excess NO3- and decrease CH4 release from agricultural drainage ditches. Microcosm experiments were conducted using sediment and surface water collected from three different sites: a sandy-clay ditch (SCD), a freshwater-fed peatland ditch (FPD), and a brackish peatland ditch (BPD). The microcosms were inoculated with an N-DAMO enrichment culture dominated by Candidatus Methanoperedens and Candidatus Methylomirabilis and supplemented with 13CH4 and 15NO3-. A significant decrease in CH4 and NO3- concentration was only observed in the BPD sediment. In freshwater sediments (FPD and SCD), the effect of N-DAMO inoculation on CH4 and NO3- removal was negligible, likely because N-DAMO microorganisms were outcompeted by heterotrophic denitrifiers consuming NO3- much faster. Overall, our results suggest that bioaugmentation with N-DAMO might be a potential strategy for decreasing NO3- concentrations and CH4 emission in brackish ecosystems with increasing agricultural activities where the native microbial community is incapable of efficient denitrification.

Periphytic biofilms function as a double-edged sword influencing nitrogen cycling in paddy fields

It remains unclear whether periphytic biofilms are beneficial to N cycling in paddy fields. Here, based on a national-scale field investigation covering 220 rice fields in China, the N accumulation potential of periphytic biofilms was found to decrease from 8.8 ± 2.4 to 4.5 ± 0.7 g/kg and 3.1 ± 0.6 g/kg with increasing habitat latitude and longitude, respectively. The difference in abundant and rare subcommunities likely accounts for their geo-difference in N accumulation potential. The N cycling pathways involved in periphytic biofilms inferred that soil N and N₂ were two potential sources for N accumulation in periphytic biofilms. Meanwhile, some of the accumulated N may be lost via N₂ , N₂ O, NO, or NH₃ outputs. Superficially, periphytic biofilms are double-edged swords to N cycling by increasing soil N through biological N fixation but accelerating greenhouse gas emissions. Essentially, augmented periphytic biofilms increased change of TN (ΔTN) content in paddy soil from -231.9 to 31.9 mg/kg, indicating that periphytic biofilms overall benefit N content enhancement in paddy fields. This study highlights the contribution of periphytic biofilms to N cycling in rice fields, thus, drawing attention to their effect on rice production and environmental security.