Nutrient Limitation and the Stoichiometry of Nutrient Uptake in a Tropical Rain Forest Stream

Flavia Tromboni, Steven A. Thomas, Björn Gücker, Vinicius Neres-Lima, Christine Lourenço-Amorim, Timothy P. Moulton, Eduardo F. Silva-Junior, Rafael Feijó-Lima, Iola G. Boëchat, Eugenia Zandonà

Research output: Contribution to journalArticlepeer-review

Abstract

Nutrient limitation assessment is important to understand stream ecosystem functioning. Aquatic primary producers are often limited by nitrogen, phosphorus, or both, as assessed by nutrient diffusing substrata (NDS), a common method for assessing nutrient limitation in streams. But little is known regarding how this method relates to patterns of nutrient uptake at the whole-stream scale. We combined two techniques to examine nutrient limitation in a tropical stream. First, we conducted two NDS experiments using ammonium, nitrate, and phosphate alone and combined, to determine nutrient limitation at substrata scale over several weeks. Second, we conducted whole-stream nutrient addition experiments over the course of a year, using nutrients alone and in combination, to test theoretical predictions about uptake characteristics of limiting and nonlimiting nutrients. NDS results consistently indicated N limitation. Ambient uptake length (SW-amb) suggested either P limitation (shorter SW-amb for P than N) or colimitation (similar SW-amb for both nutrients). The relationship between N uptake and concentration when added alone or with P suggested P limitation, colimitation, or neither, depending on the date. We speculate that the different conclusions arise from differences in the spatial and temporal scale assessed by these techniques and the microbial processes involved, and the potential for physical processes influencing whole-stream uptake estimates. We conclude that nutrient limitation is not as categorical as NDS results often imply, rather habitat, resource, and biotic diversity result in nutrient uptake rates that do not necessarily conform to predictions drawn from fine scale, process-specific bioassays such as chlorophyll-a accrual on NDS.

Original languageEnglish (US)
Pages (from-to)2154-2167
Number of pages14
JournalJournal of Geophysical Research G: Biogeosciences
Volume123
Issue number7
DOIs
StatePublished - Jul 2018

Keywords

  • autotrophic
  • heterotrophic
  • nutrient diffusing substrata
  • nutrient spiraling
  • periphyton
  • TASCC

ASJC Scopus subject areas

  • Soil Science
  • Forestry
  • Water Science and Technology
  • Palaeontology
  • Atmospheric Science
  • Aquatic Science
  • Ecology

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