Suttle, C.A., W.P. Cochlan and J.G. Stockner. 1991. Size-dependent ammonium and phosphate uptake, and N:P supply ratios in an oligotrophic lake. Canadian Journal of Fisheries and Aquatic Sciences 48:1226-1234.

One arm of oligotrophic Sproat Lake was fertilized with weekly additions of inorganic phosphorus and nitrogen (N:P = 50:1, by atoms). There was a lag of greater than 1 mo before changes in N:P supply ratio were reflected by "relative uptake rates" (RURs) of saturating ammonium and phosphate additions. This supports previous findings that RUR is a sensitive indicator of changes in N:P supply ratio, but suggests that changes in RUR are mediated by changes in composition rather than physiological state of the plankton community. The < 3 µm fraction showed a greater demand for phosphate than ammonium compared with larger cells (> 3 µm), as indicated by maximum uptake rates for the two nutrients.