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Soil nutrient status and fungal community structure of high and low phosphatase microsites in a mixed Douglas-­fir paper birch stand Godin, Aaron Michael


Phosphorus (P) plays an important role in driving primary production in terrestrial ecosystems. However, the majority of P in soil is covalently bound to complex organic compounds and is largely inaccessible to plants. Soil fungi facilitate the release of mineral P from organic forms, through the release of extracellular phosphatase enzymes. To date, very little work has been done to identify fungal communities physically located with phosphatase activity in situ in the field. In the current study, I examined soil nutrient status and fungal communities associated with high and low phosphatase areas. I used an enzyme imprinting method to detect mmscale phosphatase activity from soil profiles in a mixed Douglas fir and paper birch stand in British Columbia. Small (0.05 g) soil samples were removed from areas of high and low phosphatase activity at five root windows. Total extractable P (p=0.95), inorganic phosphate (p=0.87), and soluble organic P (p=0.20) were not different between areas of high and low phosphatase activity across all windows, suggesting that P availability alone was not important in driving phosphatase activity. However, percent total carbon (p=0.05) and percent total nitrogen (p=0.05) were higher in microsites with high phosphatase activity. This implies that higher levels of carbon and nitrogen, especially relative to P, stimulated phosphatase activity. Additions of carbon (C) and nitrogen (N) to randomly-selected microsites, to test this hypothesis, were inconclusive. I used pyrosequencing to characterize fungal communities from microsites differing in phosphatase activity. When examined as assemblages of operational taxonomic units (OTUs), fungal communities were not different (Bray Curtis, p=0.53; Jaccard p=0.52) between areas of high and low phosphatase activity iii across all windows, though communities did differ among the five windows (Bray Curtis, p<0.01; Jaccard p<0.01). Furthermore, the number of sequences as OTUs grouped by trophic status differed between microsites in some windows. Specifically, the ratio of saprotrophic (SAP) to ectomycorrhizal (EM) fungi was higher in high than low phosphatase sites in windows with low EM fungal richness. The results of these experiments contribute to our understanding of fine-scale controls of P cycling in forest soils, as well as the relative importance of various spatial scales in structuring soil fungal communities.

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