Soil biota account for ~25% of global biodiversity and underpins a wide range of ecosystem services. Here defined as soil-dwelling bacteria, archaea, fungi, protists, animals, and viruses, soil biota have often been overlooked and generalised in biodiversity surveys and studies of ecosystem service provision. However, studying the response of the whole community is highly likely to obscure important biodiversity trends in the constituent fractions of soil biota. The aims of this thesis were to determine how belowground biodiversity and community structure are related to land use and soil physicochemical properties at the national-scale and investigate shifts of organisms with important functional roles. Also, the fate of soil communities and impacts on nutrient cycling under long-term carbon deprivation at the plot-level were investigated. To address the first aspect of the thesis, biological (invertebrate specimens and environmental DNA sequences) and environmental (soil and environmental properties) data were collected as part of the Glastir Monitoring & Evaluation Programme, an assessment of the impacts of the Glastir agri-environment scheme on soils across Wales, UK. Using this data, I showed that diversity and abundance of mesofauna, and richness of soil animals generally, from metabarcoding analyses, but supported by traditional taxonomy are reduced in arable land. I suggest therefore that mesofauna could be valuable biological indicators, due to the congruence between results obtained from morphological and molecular analyses. Metabarcoding data also revealed a trend of declining richness from high-productivity arable sites to low-productivity upland habitats shared by bacteria, fungi, and protists. Archaea showed an opposing trend. All groups were strongly influenced by pH and carbon-to-nitrogen ratio. A comparison of primer choice for fungi (ITS1 vs. 18S) revealed biases stemming from primer and database choice that influenced functional diversity but not the overarching trend in fungal richness in response to land use. Using 18S primers detected Glomeromycetes and other groups that greatly influenced functional diversity across land uses. All of these investigations determined soil type was a poor predictor of soil biota metrics. The distribution of sulphate-reducing bacteria (SRB) was also investigated. I found that richness of these bacteria was relatively constant across land uses. Concurrent analysis of common generalist anaerobic taxa followed the overarching trend across land use productivity mentioned previously. There was a shift in proportional abundance of SRB to generalist anaerobes along the productivity gradient, indicating that competitive forces may be at play, like niche separation. The results of a long-term carbon-deprivation experiment comprise the final chapter of this thesis. I found that following ten years of suspension of carbon inputs, richness of all soil microbes and viruses declined along with a range of measures of soil chemical and physical quality. Functional genes shifted to anaerobic and recalcitrant energy sources. The work has provided diverse, essential information on patterns of soil biota and the physicochemical and land use factors governing the distributions of the many fractions of soil biodiversity. The thesis is important in understanding the natural history of Welsh and temperate soil biota in general. It also provides an important framework for future analyses and projections of the response of soil biota, associated function and ecosystem services in the context of predicted environmental change.