What Limits Dryland Ecosystems? Patterns of Soil Fertility and Resource Limitation in the Chihuahuan Desert

Human activities are substantially altering global resource cycles with widespread implications for biogeochemistry and ecosystem functioning globally. Drylands, regions where precipitation is outweighed by water losses, are especially sensitive to these large shifts in resource cycles due to their inherently low and variable resource availability. In these regions, resource availability and biological activity are often concentrated around plants – or fertile islands – and predominantly driven by pulses of water. However, our knowledge of the processes influencing biological productivity in drylands – patterns of soil fertility and resource limitation – remains lacking, and their unique biogeochemical and biological processes create difficulties in predicting dryland responses to global change. To improve our understanding of ecological function and biogeochemistry in drylands, I determine how patterns of soil fertility change across multiple spatial scales in the Chihuahuan Desert (Chapter 2), examine how soil nutrient pools change in response to changing resource availability (Chapter 3), investigate signatures of resource limitation in the microbial community and whether resource limitation constrains microbial function in this system (Chapter 4), and explore how the plant community responses to resource addition treatments (Chapter 5). This dissertation presents evidence of the inherent complexity of the biogeochemistry and ecology of these unique systems, demonstrating the urgent need to improve our understanding of the relationship between drylands and global biogeochemical cycles.