| Summary: | 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
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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. === Irving K. Barber School of Arts and Sciences (Okanagan) === Biology, Department of (Okanagan) === Graduate
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