Empirical evidence challenges the effectiveness of the enzymatic stoichiometry of glucosidase and phosphatase as an indicator of microbial C vs P limitation.

ABSTRACT

The ratio of ß-1,4-glucosidase (BG) to acid/alkaline phosphomonoesterase (AP) (BGAP) is commonly employed as an indicator to assess the relative microbial limitations of carbon (C) and phosphorus (P), whereby a higher BGAP ratio suggests stronger C limitations. This approach is based on the assumption that BG and AP can represent enzymes targeting C and P, respectively. Nevertheless, it is crucial to recognize that microbial C and P acquisition involves the participation of other enzymes alongside BG and AP, and thus, the capacity of BG and AP to accurately and comprehensively represent the entire spectrum of C and P acquisition is questionable. Here, analyzing previously published data, I present a piece of empirical evidence that challenges the suitability of the BGAP ratio as an accurate indicator of microbial limitations concerning C vs P. P fertilization decreased BGAP in up to 27 % out of the total 109 observations, which represents a clear contradiction, as this outcome is interpreted by the enzymatic stoichiometry approach as indicating an intensified P limitation arising from P fertilization. Furthermore, the effect of P fertilization on the BGAP ratio did not show significant differences between experimental sites characterized by higher BGAP ratios (indicative of lesser P limitation) and those with lower BGAP ratios (indicative of greater P limitation). Consequently, I conclude that the BGAP ratio inadequately reflects microbial C vs P limitations.