Contribution of pathogenic fungi to NO emissions increases temporally in intensively managed strawberry cropping soil.

Intensively managed agriculture land is a significant contributor to nitrous oxide (NO) emissions, which adds to global warming and the depletion of the ozone layer. Recent studies have suggested that fungal dominant NO production may be promoted by pathogenic fungi under high nitrogen fertilization and continuous cropping. Here, we measured the contribution of fungal communities to NO production under intensively managed strawberry fields of three continuous cropping years (1, 5, and 10 years) and compared this adjacent bare soil. Higher NO emission was observed from the 10-year field, of which fungi and prokaryotes accounted for 79.7% and 21.3%, respectively. Fungal population density in the 10-year field soil (4.25 × 10 colony forming units per g (CFU/g) of air-dried soil) was greater than the other cropping years. Illumina MiSeq sequencing of the nirK gene showed that long-term continuous cropping decreased the diversity of the fungal denitrifier community, but increased the abundance of Fusarium oxysporum. Additionally, F. oxysporum produced large amounts of NO in culture and in sterile 10-year field soil. A systemic infection displayed by bioassay strawberry plants after inoculation demonstrated that F. oxysporum was a pathogenic fungus. Together, results suggest that long-term intensively managed monocropping significantly influenced the denitrifying fungal community and increased their biomass, which increased fungal contribution to NO emissions and specifically by pathogenic fungi. KEY POINTS: • Distinguishing the role of fungi in long-term continuous cropping field. • Identifying the abundant fungal species with denitrifying ability.