Phosphate Uptake by Microbial Assemblages: Model Requirements and Evaluation of Experimental Methods
- Stephen J. Tarapchak * and
- Lynn R. Herche
A “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.
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