Phosphorus and light colimit periphyton growth at subsaturating irradiances

Walter R. Hill, Shari E. Fanta

Research output: Contribution to journalArticlepeer-review


1. This study investigated the combined effects of light and phosphorus on the growth and phosphorus content of periphyton. To investigate the potential for colimitation of algal growth by these two resources, diatom-dominated periphyton communities in large flow-through laboratory streams were exposed under controlled conditions to simultaneous gradients of light and phosphorus. 2. Periphyton growth rate was predictably light-limited by the subsaturating irradiances (12-88 μmol photons m -2 s -1) used in this experiment. However, phosphorus concentration also limited growth rate: growth increased hyperbolically with increasing soluble reactive phosphorus (SRP), reaching a threshold of growth saturation between 22 and 82 μg L -1. 3. Periphyton phosphorus content was strongly and nonlinearly related with SRP, reaching a maximum at 82 μg L -1 SRP. Contrary to the Light : Nutrient Hypothesis, periphyton phosphorus content did not decrease with increasing light, even at the lowest concentrations of SRP. Periphyton phosphorus was highly correlated with periphyton growth rate (Spearman's ρ = 0.63, P < 0.005). 4. Multiple regression analysis reinforced evidence of simultaneous light and phosphorus limitation. Both light and periphyton phosphorus content were significant variables in multiple regressions with growth parameters as dependent variables. Light alone accounted for 67% of the variance in periphyton biomass, and the addition of periphyton phosphorus as an additional independent variable increased the total amount of variance explained to 81%. 5. Our results did not support the hypothesis that extra phosphorus is required for photoacclimation to low light levels. Rather, the effect of additional phosphorus may have been to accommodate increased requirements for P-rich ribosomal RNA when growth was stimulated by increased light. The potential colimitation of periphyton growth by phosphorus and light at subsaturating irradiances has important implications in both theoretical and applied aquatic ecology.

Original languageEnglish (US)
Pages (from-to)215-225
Number of pages11
JournalFreshwater Biology
Issue number2
StatePublished - Feb 2008


  • INHS
  • Stoichiometry
  • Colimitation
  • Light
  • Benthic algae
  • Phosphorus

ASJC Scopus subject areas

  • Aquatic Science


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