Monitoring and analysis of the structure, function and biodiversity of soils


Soil health and function is key to general ecosystem health and human society, yet soils are under ever-increasing pressure from anthropogenic activities. The complexity of the soil system, with physical, chemical and biological factors interacting, make it difficult to understand what underpins soil health. The technical capabilities within soil science are greater than ever before, generating vast amounts of data. Despite this, identifying the key properties and interactions that influence soil health at policy-relevant scales remains an ongoing challenge. Evaluating current soil health and predicting future responses to global change therefore requires soil information at national levels as well as experimental analyses. The objectives of this thesis were (i) to evaluate the state of soils in Wales in regard to their physicochemical properties and biological communities, (ii) to establish the relative roles of physicochemical and biological factors in determining soil biodiversity, (iii) to explore the associations between soil physical properties and biological communities across Wales, and (iv) to evaluate the impact of climate change on soil microbial communities and function. This thesis combined soil physicochemical and microbial community characterisation through DNA sequencing results from a national scale field survey of the Welsh landscape and a long term climate change experiment in order to identify key dynamics and better predict responses to future change. Results from the national scale field survey indicated that soil pH and carbon drive many of the gradients in soil physicochemical and biological properties across Wales, with limited impact of land use. The Welsh soil landscape was largely split into two groupings: that of the near-neutral soils underlying improved and neutral grasslands, and that of the acidic soils that underlie bogs, heathlands and acidic grasslands. Soil microbial diversity was positively driven by soil pH, with soil textural heterogeneity increasing bacterial diversity once the increase with pH and decrease with carbon was accounted for. Soil physical properties were both influencing biological communities and being influenced by them, as shown by soil surface water repellency being associated with plant and microbial community composition. Plant and soil microbial diversity were positively correlated but this was driven entirely by changes in soil pH. However, the composition of above and belowground communities showed associations even after accounting for environmental gradients. In the long term field experiment, soil bacterial and fungal communities responded to experimental drought and warming, yet at a Welsh landscape scale microbial communities were largely unresponsive to climatic variables. Plant communities were an important link between climate and land use drivers and soil biological and functional responses. The combination of soil physicochemical, microbial and aboveground information throughout this thesis provides new understanding of the complex interactions and feedbacks that underpin soil health and function. Consideration of these dynamics is key to evaluating and monitoring soil health and resilience to future change.