Large‐scale variability and interactions among phytoplankton, bacterioplankton, and phosphorus

The literature suggests two models describing the relationship between phyto‐ and bacterioplankton abundance in freshwater: that total P abundance determines algal abundance, which in turn determines bacterial abundance, or that algae and bacteria compete for P. In four data sets investigating the variability of algae, bacteria, and P among lakes, bacterial abundance was more closely related to P concentration than to chlorophyll. Bacterial abundance was strongly related to the residuals of the Chl‐P relationship, explaining 18–65% of the residual variance. The partial correlation is positive, however, indicating that algal‐bacterial competition for P does not determine algal or bacterial abundance. The data are most consistent with an alternative model postulating that P directly influences both algal and bacterial abundance, that algae and bacteria directly influence each other’s abundance, and that a third factor (temperature or perhaps bacterivore abundance) also influences both algal and bacterial abundance in the same manner.