Characterization of soil bacterial profiles in extremely acidic forest soils

Soil bacterial communities respond to their biotic and abiotic environment. Two key drivers, soil biochemical properties and forest type, are known to correlate with the composition of specific communities. The humus-type concept captures these drivers along a gradient of soil nutrient availability, quality, and pH. For example, deciduous forests (mull-like soils) often have nutrient-rich and alkaline soils compared with coniferous forests (mor-like soils). While climate change might favor deciduous forests over coniferous forests in temperate regions and further acidification of soils is expected, essential ecosystem services such as nutrient cycling and carbon storage might be threatened. Our study aims at 1) characterizing soil bacterial community characteristics under coniferous and deciduous stands in an acidic-stress environment and 2) exploring the effect of extreme acidification on soil bacterial community profiles. We collected 147 soil samples in two European temperate forests in The Netherlands and in Germany, measured their biochemical properties, and used in-depth next-generation sequencing to produce bacterial profiles. We found distinct bacterial profiles between forest types, with mull-like soils having a higher bacterial richness and diversity. In addition, extreme acidification of soils emphasized a bacterial diversity loss and a shift in community composition associated with changes in the soil functional profile. Our study is the first to demonstrate strong changes along an extremely acidic soil pH gradient. The results of this study not only highlight the relevance of metabarcoding for biodiversity assessment and monitoring but also provide a baseline for soil microbial functions at large spatial scales.