Rising atmospheric CO2 concentration affects terrestrial ecosystem carbon cycle and storage, plant productivity and nutrient dynamics. While vegetation response to experimentally-manipulated CO2 enrichment have been well reported, the influence of elevated CO2 on soil microbial communities remains largely elusive due to the complexity of plant-soil-microbe interactions. Furthermore, the study of complex spatial and temporal dynamics of soil microbial communities in most field CO2 enrichment studies is usually limited to few levels of CO2 treatment and a single soil type. Lysimeter CO2 gradient (LYCOG) facility located in the USDA site at Temple, TX represents preindustrial-to-future CO2 levels (250 - 520 ppm) spanning three Texas Prairie soils (Houston, Austin and Bastsil series) with a wide range of texture, nutrient and hydrological properties. The objective of this study was to investigate the effects of (1) CO2 gradient, (2) three soil types, and (3) seasonal variation on soil bacterial and archaeal community structure in a mixed C3/C4 grassland. To accomplish this goal, we analyzed soil microbial communities by 16s rRNA gene amplicon sequencing using Illumina’s MiSeq platform and processed the sequences through QIIME pipeline.
Alpha diversity (OTU richness and Shannon index) was positively correlated to increasing CO2 concentrations. Initial increase in OTU richness and Shannon index along the CO2 gradient could be mediated by increasing availability of labile carbon at higher CO2 concentrations. NMDS ordinations showed distinct clusters of microbial communities based on soil type. Thus, our results demonstrate that soil type is a strong driver of community structure. Furthermore, temporal variation due to plant carbon inputs in the beginning, middle and end of growing season seemed to influence the community structure. This study provides insights into the historical trajectory of microbial community response to a CO2 gradient and the interactive effects with other factors such as soil type and seasonal dynamics.