Effects of soil improvement treatments on bacterial community structure and soil processes in an upland grassland soil

Abstract

Temporal temperature gradient electrophoresis (TTGE) analysis of 16S rRNA gene fragments amplified with primers selective for eubacteria and beta-proteobacterial ammonia-oxidising bacteria (AOB) was used to analyse changes in bacterial and AOB community profiles of an upland pasture following soil improvement treatments (addition of sewage sludge and/or lime). Community structure was compared with changes in activity assessed by laboratory measurements of basal respiration and ammonia oxidation potentials, and with measurements of treatment- and time-related changes in soil characteristics. The predominant bacterial populations had a high degree of similarity under all treatment regimens, which was most pronounced early in the growing season. Most of the differences that occurred between soil samples with time could be accounted for by spatial and temporal variation; however, analysis of variance and cluster analysis of similarities between 16S rDNA TTGE profiles indicated that soil improvement treatments exerted some effect on community structure. Lime application had the greatest influence. The impact of soil improvement treatments on autotrophic ammonia oxidation was significant and sustained, especially in soils which had received sewage sludge and lime treatments in combination. However, despite obvious changes in soil characteristics, e.g. pH and soil nitrogen, increasing heterogeneity in the AOB community structure over time obscured the treatment effects observed at the beginning of the experiment. Nevertheless, time series analysis of AOB TTGE profiles indicated that the AOB community in improved soils was more dynamic than in control soils where populations were found to be relatively stable. These observations suggest that the AOB populations exhibited a degree of functional redundancy.

Nitrogen and phosphorus enrichment alter the composition of ammonia-oxidizing bacteria in salt marsh sediments

“…Composition was highly variable over seasons and years, and compositional changes in response to the nutrient treatments were minor in comparison. High temporal variability in AOB communities (both abundance and composition) has been observed in both soils and the water column (Gray et al, 2003;O'Mullan and Ward, 2005) and in estuarine sediments (Bernhard et al, 2007;Ando et al, 2009;Fortunato et al, 2009). Given the importance of temperature on the spatial variability of AOB in soils (Fierer et al, 2009), we speculate that temperature could be one important factor contributing to this temporal variability.…”

“…Once they accounted for this variability statistically, however, they could detect a correlation between contaminant concentrations and bacterial composition. Similarly, Gray et al (2003) determined that soil amendments had a minor effect on eubacterial (and AOB) composition relative to natural, temporal and spatial variability.…”

Effect of nitrogen fertilizer on nitrogen pools and soil communities under grazed pastures

“…The mechanism is unknown but both are direct effects of fertilizer itself, and changes in the plant community and litter associated with fertilizers could be involved (Donnison et al 2000;Manning et al 2006). Fungal DNA profiles can also undergo a reduction in diversity in response to fertilizer (Allison et al 2007), but others found that the bacterial communities (but not fungi) can be altered by high rates of fertilizer (Gray et al 2003;Kennedy et al 2004Kennedy et al , 2005.…”

Effect of Nutrient Periodicity on Microbial Community Dynamics

“…Thus, although different phylotypes arose in different replicates, their performances in these systems were similar enough to result in communities whose functions were indistinguishable from each other. This implies a substantial degree of functional redundancy in these microbial communities, as has been found in a variety of natural and engineered microbial ecosystems (2,10,22,38,45). One rationale for the emphasis on analysis of microbial community composition in microbial ecology has been that determining composition is key to understanding community functionality.…”