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Title:Soil phosphatase activity: sources of variability and relationships with phosphorus fractions
Author(s):Nakayama, Yuhei
Advisor(s):Margenot, Andrew J
Contributor(s):Mulvaney, Richard L; Bollero, Germán A; Wade, Jordon
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
enzyme assay
soil phosphorus fractionation
Abstract:Soil phosphorus (P) is hypothesized to exist in pools varying in availability given that its availability is controlled by interacting soil geochemical and biological processes. Soil P pools have been widely characterized by sequentially extracting P from soils with increasing strength of extractants to obtain P fractions. Although the characterized distribution of P across these pools can help inform the ability of the soils to supply available P through P cycling, soil P availability ultimately depends on the processes that govern the rate of movement of P between these pools. One such process is mineralization, responsible for the transformation of organic P (Po) into inorganic P (Pi) and catalyzed by phosphatase enzymes produced by soil organisms. This M.S. thesis addresses phosphomonoesterase (PME), a phosphatase that catalyzes the terminal step of Po mineralization. The rate of catalysis by soil PME, often referred to as activity, has been measured widely. However, soil PME activity assay faces challenges in the interpretation of obtained data due to incomplete methodological standardization and uncertainties in the degree to which PME activity reflects soil P availability. Nevertheless, soil PME activity has been illustrated to be sensitive to various environmental changes and thus offers potential as a biogeochemical tool to assess ability of soils to supply available P. The overall objective of this M.S. thesis was to evaluate soil PME activity as a tool to assess soil P mineralization capacity. The first chapter investigated how methodological inconsistencies influence measured PME activity by quantifying variabilities in measured PME activity due to soil sampling timing, within-plot sampling location, and sample processing and storage. PME activity was measured at co-located cropland and grassland on a Mollisol and at co-located tilled and no-till croplands on an Andisol. The second chapter tested hypothesized relationships of PME activity with P fractions using a dataset compiled from published and unpublished studies. The study evaluated the sensitivity of PME activity to P fractions hypothesized to be involved in mineralization. Evaluation of sources of variabilities showed the soil PME activity to be subject to site and land management specific variabilities from sampling and sample storage. When contributions of spatiotemporal variability and variability from choice of sample storage were compared, storage choice was generally a minor source of variability. Although the compiled PME activities used in the second chapter were obtained using various methods of soil sampling and storage, the dataset supported the hypothesized relationships of PME activity associating positively with Po and negatively with Pi. In addition, the evaluation of relationships among P fractions revealed that the groupings of P fractions were generally consistent with the hypothesized differentiation of extracted P based on the form (Pi vs. Po) and availability. The second chapter also identified the indirect influence of soil weathering on the relationships among P fractions and PME activity. Overall, the work demonstrates that although PME activity measurement is subject to various sources of variability, PME activity can be concurrently evaluated with P fractions to better explain P availability by estimating not only the distribution of P across pools but also the processes that govern exchange of P between pools.
Issue Date:2020-12-04
Rights Information:Copyright 2020 Yuhei Nakayama
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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