Comparing stoichiometric measures of microbial limitation in wetlands of contrasting vegetation and nutrient status

Microbial stoichiometries are commonly used to assess nutrients [carbon (C), nitrogen (N), and phosphorus (P)] status and infer limitation in ecosystems, yet their consistency across environments remains largely unexamined. In this study, we compared microbial nutrient and enzymatic stoichiometries and enzymatic vector analysis across two well-characterized constructed wetland systems differing in dominant vegetation [emergent aquatic vegetation (EAV) vs submerged aquatic vegetation (SAV)] and associated nutrient gradients in the water column (high total P at inflow to low total P at outflow along the transect). Microbial nutrient stoichiometries suggested N and P co-limitation, but enzyme activity stoichiometries indicated either N or C and N co-limitation. Thus, enzymatic stoichiometries did not necessarily follow the microbial nutrient stoichiometries. In contrast, enzyme activity-based vector analysis indicated nutrient limitation patterns associated with difference between the two wetland systems and transect locations. The EAV dominated flow-ways were associated with C and N co-limitation, whereas SAV dominated flow-ways showed greater evidence of P limitation. Additionally, vector analysis demonstrated that inflows in EAV were more C and N limited than outflows, while outflows in both EAV and SAV showed greater P limitation compared to other locations. These findings were supported by a linear discriminatory analysis of total organic, mineral, labile, and dissolved nutrient stoichiometries, which further confirmed the observed nutrient limitation patterns. Overall, vector analysis provided more consistent assessment of nutrient limitation across these contrasting wetlands than microbial biomass or enzyme activity ratios, suggesting its potential as a useful tool for guiding management decision for enhanced wetland function.