Microbial community structure, function, and assembly in Texas prairie soils : insights from a preindustrial-to-future CO2 enrichment gradient.

Abstract

Anthropogenic activities have escalated recent increases in atmospheric CO2 concentration and significantly contributed to global climate change since the industrial revolution. Direct and indirect effects of atmospheric CO2 enrichment on terrestrial ecosystems have primarily focused on aboveground vegetation. Although soil microbial communities play a crucial role in nutrient cycling processes, we lack a comprehensive understanding of their sensitivity, resistance, or resilience to atmospheric CO2 enrichment across divergent ecosystems. Furthermore, most long-term CO2 enrichment studies only include elevated versus ambient CO2 concentrations and rarely consider more than one soil type or plant species. My dissertation research focuses on how microbial community structure, function, and assembly processes are affected by a decade-long preindustrial-to-future CO2 enrichment gradient (250-500 ppm) in Texas Prairie soils. First, I investigated bacterial community response to an ongoing CO2 enrichment gradient in silty clay, clay and sandy loam soils with mixed C3/C4 vegetation. The findings suggest that long-term edaphic properties (soil texture/nutrient content) and soil moisture rather than CO2 gradient had a pronounced effect on global community structure. However, the results also illustrated soil-specific variation in community structure. For example, silty clay communities were better structured along the CO2 gradient. Second, I assessed the effects of CO2 enrichment gradient and its legacy on the structure and functional potential of switchgrass silty clay and clay soil communities by employing shotgun metagenome sequencing approach. Switchgrass soil microbiomes were resistant to long-term CO2 enrichment gradient and exhibited minimal shifts in functional gene abundance linked to carbohydrate degradation, nitrogen cycling and phosphate metabolism. Finally, I examined bacterial community response to an ongoing CO2 treatment in 2015 and their recovery after the cessation of CO2 application in two subsequent years (2016/2017). Here, I primarily focused on overall community stability, assembly processes and cooccurrence patterns. The results from ecological null models indicate that stochastic processes dominated community assembly, but the relative influence of selection-based processes markedly varied among soil and plant categories. Nonetheless, highly interconnected cooccurrence networks revealed stable and distinct interactions among taxa across CO2 treatment years. Taken together, these findings provide novel insights into soil microbiome stability and resilience under climate change.