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, more
|  |
| Keywords |
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]
AW, West Atlantic [Marine Regions]
Marine/Coastal |
| Author keywords |
glutamine synthetase; glutamine transferase; Gulf of Mexico; N-15;nitrate reductase; seagrass |
| Authors | | 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. |
|
