Temporal discontinuity of nutrient limitation in plankton communities
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- Davies, JM., Nowlin, W.H., Matthews, B. et al. Aquat. Sci. (2010) 72: 393. doi:10.1007/s00027-010-0143-x
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Ideas on how various measures of nutrient limitation relate to plankton biomass and species composition are re-examined. While long-term and multi-lake studies typically focus on determining overall biomass, seasonal studies are more focused toward understanding species composition. We use physiological assays to assess short-term nutrient deficiency of nitrogen and phosphorus in two moderately fertile lakes. While biomass in the lakes was considered to ultimately be limited by total phosphorus, nutrient assays were variable in time. Nutrient ratios (TN:TP, PN:PP, PC:PP and PC:PN) did not predict short-term deficiencies, notably that nitrogen deficiency occurred in these phosphorus-limited lakes. In one of our study lakes, there was a relaxation of phosphorus deficiency despite phosphate concentrations occurring below traditional detection limits. Following this period, there was an autumn bloom of Aphanizomenon flos-aquae. This relationship corresponds with other studies that have found A. flos-aquae to be a poor competitor for phosphorus. In contrast, phosphorus deficiency remained high prior to the autumn diatom bloom in our other study lake. Deficiency measures remain an excellent means of assessing physiological status of plankton communities and provide greater insight into species compositional changes, especially when other potential indicators like dissolved nutrient concentrations are inconclusive. Regardless of the nutrient limitation indicator used for a given study, it is critical to consider the appropriate scale of the measure.