Contrasting dynamics of soil fungal functional groups in the plant rhizosphere

Background and aims: Soil microbiomes, critical for plant productivity and ecosystem functioning, mediate essential functions such as pathogenesis, mutualism, and decomposition through different fungal functional groups. Yet, our understanding of the dynamics of co-existing soil fungal functional groups in the plant rhizosphere remains limited. Methods: By leveraging a 'natural' experiment in urban farming with fields of different ages and multiple plant genotypes, we tracked the relative abundance, richness, and microbial networks of plant pathogens, mycorrhizal fungi, and saprotrophic fungi across fields over two years. Results: We observed an increase in the relative abundance of plant pathogens in older fields relative to younger fields, supporting the prediction of pathogen accumulation over time. In contrast, there was a decrease in the relative abundance of mycorrhizal fungi in older fields. Unlike plant pathogens and mycorrhizal fungi, the relative abundance of saprotrophic fungi remained similar among fields. While the richness of plant pathogens and saprotrophic fungi were similar across fields, the community structure of both groups differed between younger and older fields. For mycorrhizal fungi, the richness declined in older fields and over the two years. These dynamics led to distinct microbial networks, with decreased network links for mycorrhizal fungi and increased links for saprotrophic fungi in older fields, whereas the links for plant pathogens remained similar across fields. Conclusion: Our study reveals contrasting dynamics of essential soil fungal functional groups in the plant rhizosphere, and provides a predictive insight into the potential shifts in soil function and their impact on plant productivity.