Spatial variability linking carbon resource heterogeneity and microorganisms; causes and consequences

Abstract: Organic carbon and bacteria have a high variability at different scales in the soil, and organic carbon may be a limiting factor for growth of soil bacteria. Thus, it can be expected that these co-vary at different scales in the soil. In this thesis, I have studied the spatial interaction between soil bacteria and natural and contaminant (polycyclic aromatic hydrocarbon, PAH) organic carbon. The overall objective was to suggest reasons why there is an absence or presence of co-variation between them. The spatial patterns of PAHs at a creosote contaminated site were clearly related to their water solubility. The microbial community fingerprint (PLFA analysis) co-varied with PAH concentrations while microbial community diversity was positively correlated to PAH concentrations. Taken together it was demonstrated that a diverse gram-negative bacterial community with a patchy spatial distribution similar to the PAH spatial distribution dominated the creosote contaminated site. Catabolic genes for PAH degradation in bacteria had a more even distribution across the site although hotspots and/or cold spots of PAH concentrations and catabolic genes often coincided.Bacterial biomass and soil respiration was spatially autocorrelated and positively dependent on PAH concentrations. PAH biodegradation lacked a spatial pattern and was uncoupled from most microbial and abiotic soil properties. The results indicated that creosote rather than PAHs was a major carbon source for the microbial community and that PAH biodegradation was controlled by a multitude of soil properties simultaneously, each with its own spatial pattern.In soil peat cores, pore water flow rate had a significant non-linear effect on respiration and methane production while the amount and type of dissolved organic carbon (DOC) remained unimportant for respiration. In contrast, in carbon limited river water, both the quality and quantity of DOC had a clear effect on respiration and bacterial growth efficiency.The main factor determining microbial biomass, community composition, and activity were both the amount and the type of organic carbon regardless of any toxic effects of the carbon.