Phosphate Uptake by Microbial Assemblages: Model Requirements and Evaluation of Experimental Methods

Abstract

AbstractA “compound” Michaelis‐Menten model provides a conceptual framework for analyzing substrate‐dependent phosphate (P) uptake by natural microbial assemblages. Phosphate uptake can be separated into three substrate domains: a region near ambient P concentrations, an intermediate region, and a high‐substrate region representing substrate saturation of microbial uptake sites. Simulated P uptake for hypothetical microbial communities, ranging from non‐phosphorus‐limited to multiple‐nutrient‐limited communities, shows that (i) commonly used “high‐level” P addition schemes will underestimate community uptake rates near natural ambient P concentrations in phosphorus‐stressed systems by at least an order of magnitude, and (ii) deviations from the simple Michaelis‐Menten model may be widespread in nature, particularly in highly phosphorus‐stressed or multiple‐nutrient‐limited systems. A P uptake experiment on a natural microbial assemblage from a phosphorus‐limited oligotrophic lake illustrates application of the compound model and statistical procedures for analyzing data. An empirical procedure, based on the concept of substrate‐dependent continuity in P uptake, is proposed to determine if P addition schemes are adequate to estimate uptake constants near ambient lakewater P concentrations.