Lime amendment to chronically acidified forest soils results in shifts in prokaryotic communities

ABSTRACT A consequence of past acid rain events has been chronic acidification of Nova Scotian forests, leading to a loss of essential nutrients and subsequent decreases in forest productivity and biodiversity. Liming—supplementing forests with crushed limestone—can restore essential nutrients to acidified soils and increase the pH of soils and the carbon capture by forests through the promotion of tree growth. Liming treatments are often assessed through tree growth measurements, although little is known about how microorganisms respond to these changes in pH and nutrient availability. Understanding the impacts of liming on microbial communities will help determine whether liming is a good remediation strategy for Nova Scotia. A pilot study evaluating liming in acidified forests in Nova Scotia began in 2017. Microbiome analysis (prokaryotic 16S and fungal ITS2 rRNA gene amplicon sequencing) of three different horizons (depths; upper forest floor, lower forest floor, and upper B horizon) of soil in a softwood forest area showed significant differences between lime-treated and control soils for the prokaryotic but not fungal communities, particularly in the uppermost soil horizon. Several genera from the Alphaproteobacteria class were significantly higher in abundance in treated than control soils, whereas genera from the Acidobacteriia (previously Acidobacteriae) class were significantly lower in abundance in treated versus control soils. Soil chemistry analysis of the same three horizons showed a significant increase in base cations and pH of the uppermost soil horizon in control versus treatment sites. IMPORTANCE Forests are increasingly being managed with an emphasis on understanding how forests function. Lime amendments are used to promote forest health and increase resilience to climate change. To date, only a handful of studies have analyzed the effects of liming on microbial communities in forest soils. Our study combines soil chemistry with prokaryotic and fungal communities of limed and control soils. Shifts in microbial composition that are coincident with liming may provide early indications of the effectiveness of liming and provide insight into the roles of microbes in forest health.