, Volume 363, Issue 1, pp 1–12

Interactions of top-down and bottom-up control in planktonic nitrogen cycling


  • Patricia M. Glibert
    • Horn Point Environmental Laboratory, Center for Environmental and Estuarine StudiesUniversity of Maryland

DOI: 10.1023/A:1003125805822

Cite this article as:
Glibert, P.M. Hydrobiologia (1997) 363: 1. doi:10.1023/A:1003125805822


Although our understanding of the complexity of theplankton and microbial food webs has increasedsubstantially over the past decade or two, there hasbeen little appreciation to date of the interactionsbetween top-down (grazing) control and bottom-up(nutrient supply) control on the structure andnutrient cycling processes within these webs. Thequality of nutrient supply, both in terms of therelative proportion of inorganic: organic nitrogen,as well as the relative proportion of inorganicnitrogen substrates has a direct impact on rates ofnitrogen uptake, and ultimately on the relativecomposition of phytoplankton and bacteria. At thesame time, grazing by microzooplankton andmacrozooplankton also influences both thecomposition of the food web and the rate of supplyof nitrogen. The impact of macrozooplankton onrates of nitrogen cycling in a microbial communityis complex: macrozooplankton release NH4+,urea, and amino acids by direct excretion and by’sloppy feeding‘, but they also control both therates of nitrogen regeneration and uptake within thecommunity by grazing the microzooplankton, theprimary regenerators of NH4+, and thephytoplankton, the primary consumers of nitrogen. Thus, grazing and nitrogen recycling are intricatelyconnected: the presence of large zoooplanktonsimultaneously provides top-down control of biomassand bottom-up nutrient supply. These relationshipsvary depending on the scale of interest, and haveimportant consequences for how we measure and modeltotal nitrogen cycling in a natural food web.

top-down controlbottom-upcontrolNH4+regenerationnutrientlimitationtrophodynamics
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© Kluwer Academic Publishers 1998