Implication of O2 dynamics for both N2O and CH4 emissions from soil during biological soil disinfestation

Soil O2 dynamics have significant influences on greenhouse gas emissions during soil management practice. In this study, we deployed O2-specific planar optodes to visualize spatiotemporal distribution of O2 in soils treated with biological soil disinfestation (BSD). This study aimed to reveal the role of anoxia development on emissions of N2O and CH4 from soil amended with crop residues during BSD period. The incorporation of crop residues includes wheat straw only, wheat straw with biochar and early straw incorporation. The anoxia in soil developed very fast within 3 days, while the O2 in headspace decreased much slower and it became anaerobic after 5 days, which was significantly affected by straw and biochar additions. The N2O emissions were positively correlated with soil hypoxic fraction. The CH4 emissions were not significant until the anoxia dominated in both soil and headspace. The co-application of biochar with straw delayed the anoxia development and extended the hypoxic area in soil, resulting in lower emissions of N2O and CH4. Those results highlight that the soil O2 dynamic was the key variable triggering the N2O and CH4 productions. Therefore, detailed information of soil O2 availability could be highly beneficial for optimizing the strategies of organic amendments incorporation in the BSD technique.

Clostridium fungisolvens sp. nov., a new β-1,3-glucan-decomposing bacterium isolated from anoxic soil subjected to biological soil disinfestation

Biological soil disinfestation (BSD) or reductive soil disinfestation (RSD) is a bioremediation method used to suppress or eliminate soil-borne plant pathogens by stimulating activities of indigenous anaerobic bacteria of the soil. An anaerobic bacterial strain (TW1T) was isolated from an anoxic soil sample subjected to the BSD treatment and comprehensively characterized. Cells of the strain were Gram-stain-positive, slightly curved and motile rods producing terminal spores. The strain was aerotolerant. Strain TW1T was saccharolytic and produced acetate, butyrate, H2 and CO2 as fermentation end products. Strain TW1T decomposed β-1,3-glucan (curdlan and laminarin) and degraded mycelial cells of an ascomycete Fusarium plant pathogen. Major cellular fatty acids of strain TW1T were C14 : 0, C14 : 0 dimethylacetal (DMA), C16 : 0 aldehyde and C16 : 0 DMA. Strain TW1T made a group on the phylogenetic tree constructed based on 16S rRNA gene sequences with species such as Clostridium fallax (96.3 %) and Clostridium polyendosporum (96.0 %). Whole genome analysis of strain TW1T showed that the total length of the genome was 5.28 Mb with the DNA G+C content of 31.3 mol%. The average nucleotide identity (ANIb) between strain TW1T and C. fallax was 71.2 %. Presence of the genes encoding laminarinase or GH16 β-glucosidase was confirmed from the genome analysis of strain TW1T. Based on the genomic, phylogenetic and phenotypic properties obtained, we propose strain TW1T should be assigned in the genus Clostridium in the family Clostridiaceae as Clostridium fungisolvens sp. nov. The type strain TW1T (=NBRC 112097T=DSM 110791T).