Chitosan reduces naturally occurring plant pathogenic fungi and increases nematophagous fungus Purpureocillium under field soil conditions

Chitosan reduced soil pH, conductivity (CE) and cation exchange capacity (CEC) in pots when applied at field capacity. However, chitosan did not affect these soil physicochemical properties, when applied monthly to agricultural fields. Chitosan did not affect field respiration. Increases in field soil respiration found in chitosan plots, especially in spring-midsummer, were not significant. Although, no differences in soil mineral nitrogen were found, chitosan influenced field soil microbiota. Metabarcoding showed chitosan significantly modifies fungal genera composition of ecologically managed field soil. On the contrary, chitosan caused no significant differences in bacterial taxa composition of field soil. Chitosan coacervates increase naturally occurring nematophagous fungus Purpureocillium in soil respect to chitosan solution treated soil and untreated controls. Besides chitosan reduces inoculum of plant pathogenic fungi Alternaria and Fusarium in field soil. Soil microbial co-occurrence network analysis clustering coefficient (CC) for ITS+V1-V2 regions show that the nematophagous fungus Pochonia promoted network clustering into modules. In addition, CC in ITS+V3-V4 regions show that the nematode trapping-fungus Orbilia and bacteria belonging to Acidimicrobiales and Cytophagales also significantly contributed to microbial network clustering in field soil. Our results show that chitosan coacervates increase soil nematophagous microbiota and that both nematode egg-parasites and trapping-fungi help to structure soil microbiota.