Rapid microbial phosphorus immobilization dominates gross phosphorus fluxes in a grassland soil with low inorganic phosphorus availability |
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| Institution: | 1. Institute of Agricultural Sciences, ETH Zurich, Eschikon 33, CH-8315 Lindau, Switzerland;2. School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Waite Campus, Urrbrae, SA 5064, Australia;3. Agroscope, Institute for Sustainability Sciences (ISS); Reckenholzstrasse 191, 8046 Zürich, Switzerland;1. ETH Zurich, Institute of Agricultural Sciences, Lindau, Switzerland;2. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia;3. Universidad de la Amazonia, Florencia, Colombia;1. The James Hutton Institute, Aberdeen AB15 8QH, UK;2. The James Hutton Institute, Dundee DD2 5DA, UK;3. Rothamsted Research North Wyke, Okehampton, Devon EX20 2SB, UK;4. College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK;5. CSIRO Plant Industry, Black Mountain, Canberra ACT 2601, Australia;6. Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln 7647, Canterbury, New Zealand;7. Lancaster Environment Centre, Lancaster University, LA1 4YQ, UK;8. Institute of Bio and Geosciences, Agrosphere, Forschungszentrum Jülich IBG-3, 52428 Jülich, Germany;1. School of Environmental Sciences, University of Guelph, Guelph, ON N1G 2W1, Canada;2. School of Environmental Sciences, University of Guelph Ridgetown Campus, Ridgetown, ON N0P 2C0, Canada |
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| Abstract: | Gross phosphorus (P) fluxes measured in isotopic dilution studies with 33P labeled soils include the biological processes of microbial P immobilization, remineralization of immobilized P and mineralization of non-microbial soil organic P. In this approach, isotopic dilution due to physicochemical processes is taken into account. Our objectives were to assess the effect of inorganic P availability on gross P mineralization and immobilization in soil under permanent grassland, and to relate these fluxes to soil respiration, phosphatase activity and substrate availability as assessed by an enzyme addition method. We used soils from an 18-year-old grassland fertilization experiment near Zurich, Switzerland, that were collected in two treatments which differed only in the amount of mineral P applied (0 and 17 kg P ha−1 yr−1 in NK and NPK, respectively). Water-extractable phosphate was low (0.1 and 0.4 mg P kg−1 soil in NK and NPK, while hexanol-labile (microbial) P was high (36 and 54 mg P kg−1 soil in NK and NPK). Extremely fast microbial P uptake under P-limited conditions in NK necessitated the use of a microbial inhibitor when determining isotopic dilution due to physicochemical processes. At the higher inorganic P availability in NPK, however, isotopic exchange parameters were similar in the presence and absence of a microbial inhibitor. Phosphatase activity was higher in NK than in NPK, while soil respiration, water-extractable organic P and its enzyme-labile fraction were not affected by P status. Together, the results showed that inorganic P availability primarily affected microbial P immobilization which was the main component of gross P fluxes in both treatments. Gross P mineralization rates (8.2 and 3.1 mg P kg−1 d−1 for NK and NPK) during the first week were higher than reported in other studies on arable and forest soils and at least equal to isotopically exchangeable P due to physicochemical processes, confirming the importance of microbial processes in grassland soils. |
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