Neale, P. J. Smithsonian Environmental Research Center, firstname.lastname@example.org
, . J. ,
THE DYNAMICS OF PHOTOSYNTHETIC RESPONSE TO UV EXPOSURE: INHIBITION, RECOVERY AND ACCLIMATION
Three elements required to model UV effects in the planktonic environment are quantitative descriptions of the underwater irradiance field, spectral variation in sensitivity (biological weighting function) and the time-dependence of the response. Time-course observations at different exposure levels show whether responses are cumulative and reversible, and guide the modeling of responses as exposure varies during vertical mixing. Time variation in photosynthesis during UV exposure has been measured using 14C assimilation and Pulse Amplitude Modulated (PAM) fluorescence for phytoplankton assemblages in tropical, temperate and polar environments. Deeply-mixed assemblages in the Southern Ocean had limited capacity to counteract UV exposure and photosynthesis exhibited a simple exponential fall-off. Coastal Antarctic and temperate estuarine assemblages had significant constitutive ability to repair ongoing damage by UV as evidenced by a steady-state photosynthetic rate during constant exposure. Photosynthesis by nutrient-sufficient tropical assemblages was initially sensitive to UV but rebounded after 30 min suggesting rapid acclimation. The time course of recovery also varied between assemblages. These results can all be viewed in the general context of the balance between UV damage and repair processes. However, changes in the balance lead to very different models for relating response to exposure, even within Antarctic waters.
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