Graduate Thesis Or Dissertation

Seasonality as a driving factor of decomposition pathways in both meadows and forests : an exploration across a gradient of climate in Oregon

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  • Soil food webs process the majority of terrestrial carbon, and influence overall ecosystem function. A primary distinction among soil food webs is based on fungal versus bacterial pathways of decomposition; these lead to fundamentally different soil function, and are expected to differ in dominance between meadows and forests. This assumption is the basis of ecological hypotheses, yet conclusive studies to test this assumption are lacking. To examine climatic factors which might relate to this property of soil food webs, I selected six sites along an Oregon (USA) transect of climate and productivity with paired forests and meadows. I compared biomass of active and total fungi and bacteria in meadows and forests throughout the year. Ratios of total fungal to total bacterial biomass are higher in forests than in meadows (p = 0.01), but also vary strongly by season ( p < 0.001). Ratios of active fungal to bacterial biomass do not differ significantly between forests and meadows, but instead vary primarily by season (p = 0.007). This apparent seasonal difference is enhanced by the summer dry season, where fungi predominate in both forests and meadows along the transect. In conclusion, although total microbial biomass type differs between forests and meadows, there is a seasonal shift in active microbial biomass which dictates flow of nutrients via active decomposition in both forests and meadows. These systems are therefore dynamic, and decomposition pathways are determined by season as well as by ecosystem type.
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