SummaryIt is well established that resource quantity and elemental stoichiometry play major roles in shaping below and aboveground plant biodiversity, but their importance for shaping microbial diversity in soil remains unclear. Here, we used statistical modeling on a regional database covering 179 locations and six ecosystem types across Scotland to evaluate the roles of total carbon (C), nitrogen (N) and phosphorus (P) availabilities and ratios, together with land use, climate and biotic and abiotic factors, in determining regional scale patterns of soil bacterial diversity. We found that bacterial diversity and composition were primarily driven by variation in soil resource stoichiometry (total C:N:P ratios), itself linked to different land uses, and secondarily driven by other important biodiversity drivers such as climate, soil spatial heterogeneity, soil pH, root influence (plant-soil microbe interactions) and microbial biomass (soil microbe-microbe interactions). In aggregate, these findings provide evidence that nutrient stoichiometry is a strong predictor of bacterial diversity and composition at a regional scale.

Loss of microbial diversity is considered a major threat because of its importance for ecosystem functions, but there is a lack of conclusive evidence that diversity itself is reduced under anthropogenic stress, and about the consequences of diversity loss. Heavy metals are one of the largest, widespread pollutant types globally, and these represent a significant environmental stressor for terrestrial microbial communities. Using combined metagenomics and functional assays, we show that the compositional and functional response of microbial communities to long-term heavy metal stress results in a significant loss of diversity. Our results indicate that even at a moderate loss of diversity, some key specialized functions (carried out by specific groups) may be compromised. Together with previous work, our data suggest disproportionate impact of contamination on microbes that carry out specialized, but essential, ecosystem functions. Based on these findings, we propose a conceptual framework to explicitly consider diversity of functions and microbial functional groups to test the relationship between biodiversity and soil functions.

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Aims:  To evaluate: (i) the impact of air‐drying on bacterial, archaeal and fungal soil DNA profiles and (ii) the potential use of multiplex‐terminal restriction fragment length polymorphism (M‐TRFLP) as a tool for forensic comparison of soil. Methods and Results:  An M‐TRFLP approach was used to profile bacterial, archaeal and fungal DNA profiles from five different soil sites. Air‐drying soil significantly reduced the quantity of DNA but the number of operational taxanomic units (OTU) was unaffected. The impact of air‐drying on soil DNA profiles was dependent on soil site and microbial primers. Fungal profiles were altered the least by air‐drying. For prokaryotic profiles, air‐drying altered the relative similarity/dissimilarity between soil sites. The M‐TRFLP approach was more discriminatory compared with soil colour and single‐taxa profiling, but did not significantly improve resolution between two similar soils. Conclusions:  Of those tested, soil fungi were potentially the more robust target for application to soil forensic studies as they were altered less by air‐drying and provided clear discrimination of soils from different sites. The M‐TRFLP method demonstrated potential to achieve greater resolution, discriminating the soil sites based on both bacterial and fungal components. Significance and Impact of the Study:  Soil DNA profiling has potential as a forensic tool, but sample condition and the appropriate selection of microbial target taxa must be considered.