Does soil phosphomonoesterase activity reflect phosphorus pools estimated by Hedley phosphorus fractionation?

Understanding soil phosphorus (P) availability can benefit from characterizing P pools and processes governing P distribution among such pools. Hedley P fractionation has been widely used to characterize P pools, whereas soil phosphomonoesterase (PME) activity assays have been used to assess potential rates of organic P (P_o) mineralization to available inorganic P (P_i). We evaluated 1) the extent to which P fractions are consistent with the theorized P pools and 2) relationships of PME activity with P fractions using observations compiled across diverse (agro)ecosystems. We hypothesized that P fractions are differentiated based on the form (i.e. organic and inorganic) and availability of P pools they estimate. Given that P_i is product and P_o is substrate for PME, we further hypothesized that PME activity associates negatively with P_i fractions representing available P pool and positively with P_o fractions. Factor analysis grouped measured P fractions into three pools: non-occluded P_i, soil organic P, and secondary P_i. These groupings generally supported the differentiation of P fractions by form (P_i vs P_o) and availability of P pools they are commonly used to estimate but were also sensitive to the degree of soil weathering. Structural equation modeling supported biochemical mechanisms of product inhibition and substrate induction of PME activity and also identified an influence of weathering degree on relationships of specific measured P fractions with PME activity. This work demonstrates that evaluating PME activity in conjunction with P fractions can be a useful framework to better understand soil P cycling. Incorporating additional variables—such as P_o fractionated physically or enzymatically, and phosphodiesterase activity—into the current statistical framework may further improve understanding of how soil P cycling determines P availability.