Abstract/Summary

Soil extracellular enzymes released by microorganisms break down organic matter and are crucial in regulating C, N and P cycling. Soil pH is known to influence enzyme activity, and is also a strong driver of microbial community composition; but little is known about how alterations in soil pH affect enzymatic activity and how this is mediated by microbial communities. To assess long term enzymatic adaptation to soil pH, we conducted enzyme assays at buffered pH levels (2.5 to 10, 0.5 interval) on two historically managed soils maintained at either pH 5 or 7 from the Rothamsted’s Park Grass Long-term experiment ). The pH optima for a range of enzymes was found to differ between the two soils, the direction of the shift being toward the source soil pH, indicating the production of pH adapted isoenzymes by the soil microbial community. Soil bacterial and fungal communities determined by amplicon sequencing were found to be clearly distinct between pH 5 and soil pH 7 soils, possibly explaining differences in enzymatic responses. Furthermore, β-glucosidase sequences extracted from metagenomes revealed an increased abundance of Acidobacteria in the pH 5 soils, and increased abundance of Actinobacteria in pH 7 soils; these taxonomic shifts were more pronounced for enzymatic sequences when compared with a number of housekeeping gene sequences. Particularly for the Acidobacteria, this indicates that broad taxonomic groups at phylum level may possess enzymatic adaptations which underpin competitiveness in different pH soils. More generally our findings have implications for modelling the efficiency of different microbial enzymatic processes under changing environmental conditions; and future work is required to identify trade-offs with pH adaptations, which could result in different activity responses to other environmental perturbations.