The Ecological Effects of Nitrogen Enrichment in Aridlands

Anthropogenic nitrogen (N) deposition is one of the most prominent factors driving global change. Across the globe, N deposition has driven major changes in terrestrial ecosystems, such as declines in plant biodiversity, enhanced exotic plant growth, and changes to biogeochemical processes involved in carbon and nutrient cycling. While noteworthy effort has been put forth to investigate the effects of N deposition on terrestrial ecosystems, a disproportionate number of N addition studies have been conducted in temperate mesic systems. Thus, we lack a holistic and mechanistic understanding of how N deposition impact aridland ecosystems. Additionally, our predictions of the effects of anthropogenic N deposition in more remote aridlands receiving elevated but low N deposition are constrained due to the relatively high abundance of aridland N addition studies adding N at high rates. To improve our understanding and predictive ability of the effects of N deposition in aridlands, here I1. review the literature examining the effects of N inputs on aridlands from microbial to ecosystem scales (Chapter 2),2. examine how multiple resources may limit soil microbial processes in a semi-arid northern Chihuauhan Desert grassland ecosystem (Chapter 3),3. assess the effects of simulated N deposition on plant communities, ecosystem properties, and biogeochemical processes in three semi-arid northern Chihuauhan Desert grassland sites (Chapter 4), and lastly, 4. investigate how invasive exotic grass (Eragrostis lehmanniana) management (i.e., removal) and N inputs may interact to affect ecosystem structure and function, as well as exotic grass management in a semi-arid northern Chihuahuan Desert grassland dominated by E. lehmanniana (Chapter 5). Overall, this dissertation adds to the growing evidence revealing the complex nature of N deposition effects in aridland ecosystems, including context dependencies linked to water availability, multiple resource limitations, and experimental N dose