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Somatic, respiratory, and photosynthetic responses of the seagrass Halodule wrightii to light reduction in Tampa Bay, Florida including a whole plant carbon budget
Neely, M.B. (2000). Somatic, respiratory, and photosynthetic responses of the seagrass Halodule wrightii to light reduction in Tampa Bay, Florida including a whole plant carbon budget, in: Bortone, S.A. (Ed.) Seagrasses: monitoring, ecology, physiology, and management. pp. 33-48
In: Bortone, S.A. (Ed.) (2000). Seagrasses: monitoring, ecology, physiology, and management. CRC Marine Science Series, 16. CRC Press: Boca Raton. ISBN 0-8493-2045-3. 318 pp., more
In: Kennish, M.J.; Lutz, P.L. (Ed.) CRC Marine Science Series., more

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    VLIZ: Botany [8753]

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    Marine

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  • Neely, M.B.

Abstract
    Treatment plots (1.5 m2) within a shallow, monospecific seagrass bed of Halodule wrightii (Aschers.) located off Mullet Key (Fort DeSoto Park), Pinellas County, Florida, were subjected to in situ light reductions of 43, 60, and 86% from September 1994 to early March 1995 and compared with control plots for changes in morphology and photosynthesis vs. irradiance (PE) response. Winter die-back caused a 50% reduction in biomass and shoot density in control plots between September and February/March. A further reduction in total and non-photosynthetic biomass of 50% compared to control occurred as a result of treatment effect regardless of the amount of light reduction. However, reduction in photosynthetic biomass was related to the amount of light reduction (r2 = 0.89). There was an inverse relationship between light reduction and shoot number (r2 = 0.98). Leaves on shoots within the 43% light reduction plots were longer than leaves on shoots in either control or other light reduction treatment plots after the second month of the experiment. This is probably a morphological response to light reduction, as reported for other species. Respiration and PE responses (alpha, PMAX, IC, and IK) and leaf chlorophyll content in H. wrightii were variabIe and did not exhibit trends related to light reduction. The ICPLANT values ranged from 30 to 100 µEm-2s-l, and averaged 39 to 62 µEm-2s-l. This corresponds to approximately 4.5-7% of surface irradiance (SI) in September and February/March, respectively, in Tampa Bay. Carbon budget calculations, using the HSAT model and accounting for water column attenuation and shade in the treatments, indicate net areal productivity by H. wrightii in control plots was 0.25 g C m-2d-l, and in 43% light reduction plots was 0.025 g C m-2d-l, in September. Other light reduction treatments were at a carbon deficit in September, and all treatments and controls were at a carbon deficit in February/March. These deficits explain the loss of biomass as a result of winter die-back and with a > 60% reduction in light. The discrepancy between the morphological changes that occurred in H. wrightii as a result of a 43% light reduction and a calculated positive carbon budget suggest that other somces of light attenuation (epiphytes, surface scattering, etc.) must be accounted for, or it may reflect carbon budget precision or assumptions.

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