From Roots to Microbes: Ecosystem Responses to Invasion and Climate Variability in Arid Landscapes

Abstract

Arid ecosystems are increasingly vulnerable to global change, facing simultaneous pressures from rising temperatures and species invasions. These stressors alter the structure and function of plant and microbial communities with cascading effects on ecosystem stability. This thesis explores how plant metabolite traits and microbial processes mediate arid ecosystem responses to environmental disturbance using high-resolution metabolomic tools. In Chapter 1, we apply matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) coupled to a Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) to visualize spatial metabolite patterns in roots of the invasive grass Lehmann’s lovegrass and the native Arizona cottontop. Results reveal enhanced nitrogen allocation and reduced defensive metabolites in Lehmann’s, suggesting a growth strategy that may support its invasiveness. In Chapter 2, we investigate how short-term temperature shifts impact microbial function and soil organic matter (SOM) composition in arid soils from Yuma, Arizona. Using Electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI FTICR-MS) by direct injection and 16S rRNA sequencing, we show that microbial community composition remained stable across temperatures while functional traits shifted over time. Warmer conditions accelerated carbon and nitrogen turnover, followed by compositional shifts toward more chemically recalcitrant SOM. Together, these findings highlight the adaptive capacity of plants and microbes to environmental variability and demonstrate the power of metabolomic approaches in uncovering molecular mechanisms of ecosystem resilience. This work provides insights into the biochemical and microbial responses that shape arid ecosystem trajectories under global change, with implications for restoration and long-term sustainability.