Carbon sharing through physiological integration in the threatened seagrass Halophila Johnsonii
Carbon sharing among ramets of the clonal marine angiosperm Halophila johnsonii Eiseman was investigated in plants collected from Biscayne Bay, Florida, USA, and cultured in a seawater-supplied greenhouse facility in Wilmington, North Carolina. different ramets along four-ramet segments (genets) were shaded for 3 d. At the end of the shading period, neighboring ramets were supplied with Nah14CO3 (5μCi) to determine rates of carbon fixation and patterns of carbon allocation. The direction and degree of carbon support among ramets were determined by employing whole-plant autoradiography and scintillation spectrophotometry. genets with shaded ramets were not statistically different in terms of carbon uptake per gram dry weight than genets with un-shaded ramets, suggesting that genet carbon uptake is unaffected by shading. Autoradiograms indicated a trend towards H. johnsonii allocating more carbon to younger parts of the genet. however, scintillation analysis showed no significant directionality in photosynthate allocation to ramets with respect to age or shading. photosynthate was allocated to ramets proportional to their proximity to the source ramets rather than because of the condition of the neighboring ramets. The fast turnover and short lived deterministic leaves of H. johnsonii suggest that no advantage may be gained by selectively supporting ramets based on condition or age. The physiological strategy we describe indicates that H. johnsonii does not support stressed ramets along its genet. Along with this species' low capacity for storage, our data suggest that vegetative growth over large unsuitable patches may be unlikely and that H. johnsonii's ability to recover from widespread habitat loss may be limited.
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Document Type: Research Article
Publication date: 2007-07-01
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