Forest mesophication alters soil fungal community structure and depletes genomic decay traits

<title>Abstract</title> <p>The widespread and sustained removal of fire from forests in eastern North America has led to ongoing changes in tree species composition, shifting dominance by pyrophytic species such as pine and oaks to more mesophytic species such as maples and cherries. While this shift, also known as mesophication, generally corresponds with a major shift in dominant tree mycorrhizal type, soil abiotic conditions, and nutrient availability, its effect of soil fungal community structure and associated functional traits is largely unknown. Using a space-for-time substitution approach, we sampled soils in a newly established ForestGEO plot in Minnesota, USA, to compare the soil fungal communities in three forest types (pine, oak, and maple-oak) representing different stages of mesophication. In each forest type, we quantified fungal community structure and soil organic matter (SOM) decay potential using high throughput sequencing, quantitative PCR, and metagenomics. We found that although total soil fungal community abundance did not vary across the three forest types, fungal richness and community composition shifted significantly across the mesophication gradient in a guild-specific manner. These structural shifts corresponded with changes in richness and composition of fungal metagenomic decay traits (carbohydrate-active enzyme genes, i.e. CAZymes). Specifically, less acidic soils and more mesophytic host tree abundances had lower SOM decay potential, both of which align with biotic and abiotic trends of mesophication. We conclude that mesophication is likely to significantly alter soil fungal community structure and functioning, with important consequences on soil carbon cycling.</p>