Variability of microbial taxonomic and functional diversities across management boundaries in a boreal podzol

Abstract

Land capability classification describes boreal podzols as soils with severe to moderately severe limitations that restrict the capability of the land to produce crops. Nevertheless, they are used for crop production and it is predicted that more boreal podzols will be converted from forestry use to agricultural uses. This usually requires intensive conservation and fertility improvement practices aimed at correcting the excessively low pH and improving soil carbon parameters. Under such management, it is expected that the biotic parameters and drivers of soil fertility would be drastically affected. It is hypothesized that mass and energy fluxes across the edge of a cropped field, between natural and managed conditions of soil, will alter the diversity of microbial populations and their fertility relevant functions. To verify this, I surveyed a cropped field and its immediate surrounding areas, located within a Boreal Forest Ecosystem in Western Newfoundland. The surrounding areas, outside the four field edges covered four distinct non-cropped conditions, i.e. forested, wetland, grassland and grassed farm road border. Bacterial taxonomic diversity was assessed via a 16S rRNA obtained through an Illumina MiSeq PE 250bp amplicon sequencing of the V4 hypervariable region. Fungal taxonomic diversity was assessed on an ITS dataset obtained through an Illumina MiSeq PE 250bp amplicon sequencing of the ITS1-2 region. A predictive functional profiling of the bacterial community, based on the 16S rRNA results (PICRUSt) was then carried out. Results are contextualized by standard abiotic soil parameters and compared to potential nitrogen mineralization rates along a management intensity gradient, i.e. a gradient crossing from natural to cropped conditions. Both surface and subsurface layers were considered. Standard and exploratory statistics were carried out and included an analysis of ecological indicators for population diversity. Statistical analysis was carried out separately on soil physicochemical properties, microbial taxonomic diversity, and microbial functional diversity. Correlational analyses between microbial diversity and physicochemical properties and were carried out separately. It was found that, while the natural conditions tested had distinct diversities, the results became increasingly similar towards the field centre, away from the natural edge. Thus, land management affects the taxonomic and functional diversity of microorganisms and also found that the shift in taxonomic and functional diversity is directly related to the distance from the natural areas.