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Effects of simulated herbivory on nitrogen enzyme levels, assimilation and allocation in Thalassia testudinum
Valentine, J.F.; Blythe, E.F.; Madhavan, S.; Sherman, T.D. (2004). Effects of simulated herbivory on nitrogen enzyme levels, assimilation and allocation in Thalassia testudinum. Aquat. Bot. 79(3): 235-255. https://dx.doi.org/10.1016/j.aquabot.2004.04.001
In: Aquatic Botany. Elsevier Science: Tokyo; Oxford; New York; London; Amsterdam. ISSN 0304-3770; e-ISSN 1879-1522
Peer reviewed article  
Beschikbaar in  Auteurs 
Trefwoorden
    AW, West Atlantic
    Flora > Weeds > Marine organisms > Seaweeds > Sea grass
    Glutamine synthetase
    Gulf of Mexico
    Hydrographic features > Gulfs > Western central atlantic > Gulf of mexico
    Peptides > Proteins > Enzymes > Oxidoreductases > Nitrate reductase
    Thalassia testudinum K.D.Koenig, 1805 [WoRMS]
    West Atlantic [Marine Regions]
    Marien/Kust
Author keywords
    glutamine synthetase; glutamine transferase; Gulf of Mexico; N-15;nitrate reductase; seagrass
Auteurs  Top 
  • Valentine, J.F.
  • Blythe, E.F.
  • Madhavan, S.
  • Sherman, T.D.
Abstract
    Recent estimates suggest that turtlegrass (Thalassia testudinum) can persist while being heavily grazed by smaller herbivores (e.g., sea urchins and bucktooth parrotfish) in many areas of the western North Atlantic. Based on studies conducted in terrestrial and aquatic ecosystems, we hypothesized that seagrasses compensate for grazer-induced losses of aboveground production by (1) increasing the uptake of growth-limiting nitrogen from the surrounding environment and (2) translocating this newly acquired nitrogen to grazed tissues. We tested our hypotheses by comparing the activity levels of nitrogen metabolizing enzymes (nitrate reductase (NR) and glutamine synthetase (GS/T)) and the distance of nitrogen translocation, in the roots and leaves of mechanically damaged and undamaged plants. These experiments were repeated along a seasonal productivity gradient (in mid summer, early fall, and late fall). Significantly greater enzyme activity (GS/T) was measured in the roots of clipped plants in all months. NR and GS/T activity was also significantly higher in partially clipped leaves than in unclipped outer leaves in two of three months. The degree of leaf damage had no impact on the enzyme activity of inner (i.e., younger) leaves. Nitrogen-15, as either ammonium or nitrate, was translocated up to 50 cm away from the application point within 48 h. Defoliation, however, did not lead to increased 15N accumulation in clipped segments, suggesting that turtlegrass does not preferentially translocate nitrogen toward grazed areas.
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