Long-term CO2 injection and its impact on near-surface soil microbiology.

Impacts of long-term CO2 exposure on environmental processes and microbial populations of near-surface soils are poorly understood. This near-surface long-term CO2 injection study demonstrated that soil microbiology and geochemistry is influenced more by seasonal parameters than elevated CO2 Soil samples were taken during a 3-year field experiment including sampling campaigns before, during and after 24 months of continuous CO2 injection. CO2 concentrations within CO2-injected plots increased up to 23% during the injection period. No CO2 impacts on geochemistry were detected over time. In addition, CO2-exposed samples did not show significant changes in microbial CO2 and CH4 turnover rates compared to reference samples. Likewise, no significant CO2-induced variations were detected for the abundance of Bacteria, Archaea (16S rDNA) and gene copy numbers of the mcrA gene, Crenarchaeota and amoA gene. The majority (75%-95%) of the bacterial sequences were assigned to five phyla: Firmicutes, Proteobacteria, Actinobacteria, Acidobacteria and Bacteroidetes The majority of the archaeal sequences (85%-100%) were assigned to the thaumarchaeotal cluster I.1b (soil group). Univariate and multivariate statistical as well as principal component analyses showed no significant CO2-induced variation. Instead, seasonal impacts especially temperature and precipitation were detected.

Differential response of archaeal and bacterial communities to nitrogen inputs and pH changes in upland pasture rhizosphere soil.

Grassland management regimens influence the structure of archaeal communities in upland pasture soils, which appear to be dominated by as yet uncultivated non-thermophilic Crenarchaeota. In an attempt to determine which grassland management factors select for particular crenarchaeal community structures, soil microcosm experiments were performed examining the effect of increased pH, application of inorganic fertilizer (ammonium nitrate) and sheep urine deposition on both archaeal and bacterial communities in unmanaged grassland soil. As grassland management typically increases pH, a further experiment examined the effect of a reduction in pH, to that typical of unimproved grassland soils, on archaeal and bacterial communities. The RT-PCR amplification of 16S rRNA followed by denaturing gradient gel electrophoresis analysis demonstrated a distinct and reproducible effect on bacterial communities after incubation for 28 or 30 days. In contrast, none of the treatments had a significant effect on the structure of the crenarchaeal community, indicating that these factors are not major drivers of crenarchaeal community structures in grassland soils.