Journal
AQUATIC BOTANY
Volume 92, Issue 2, Pages 119-128Publisher
ELSEVIER
DOI: 10.1016/j.aquabot.2009.10.017
Keywords
Light-adapted; Macrocystis pyrifera; Photo acclimation; Photosynthesis; Photosystem II; Pulse-amplitude modulated fluorescence (PAM); Shade-adapted
Categories
Funding
- California Sea Grant [R/CZ 201]
- Korean Government (MOEHRD) [KRF2005-070-C00143]
- Korea Institute of Marine Science & Technology Promotion (KIMST) [20088140, 20090267] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Pulse-amplitude modulated (PAM) fluorometry allows instantaneous estimates of photosynthetic rates, but may well produce variable measurements of photosynthetic activity depending on time of day, recent light history, internal fluctuations, and environmental variability. To investigate this, we compare estimates of diurnal variability in relative photosynthetic performance for the giant kelp, Macrocystis pyrifera (L.) C. Agardh, obtained from PAM fluorometry at three depths during 3 days characterized by different light conditions, and for two different blade ages. Sampling in the mid morning, late morning, early afternoon and late afternoon, we examined diurnal changes in relative photosynthetic performance in meristematic tissue and older blades occurring near the bottom, in the mid water, and at the water surface. Measures of maximum relative electron transport rates (rETR(max)) minimum saturating irradiance (E-k), photosynthetic efficiency (alpha) and maximum quantum yield (F-v/F-m) show that giant kelp blades in the mid water and near the bottom exhibit little to no photosynthetic changes during the day. Near the surface, however, blades exhibit photosynthetic characteristics similar to light-adapted species in that they begin the day acclimated to low light, acclimate to increasing irradiance during the day, and end the day acclimated to low light. Consequently, while estimates of rETR(max) were highest during the midday for all sample depths and days, they were also always highest near the surface for both old blades (112.16 +/- 8.7, 98.6 +/- 14.7, 70.16 +/- 5.7) and meristematic tissue (109.0 +/- 9.0, 86.9 +/- 1.9, 59.2 +/- 11.6, surface, mid water and bottom, respectively). Similar patterns were observed for E-k for both old blades (169.2 +/- 5.4, 88.0 +/- 11.2, 83.8 +/- 5.2) and meristematic tissue (138.4 +/- 11.5, 96.6 +/- 4.69, 68.4 +/- 10.6). In contrast, estimates of F-v/F-m were lowest near the surface during the midday for both old blades (0.6 +/- 0.02, 0.73 +/- 0.69, 0.75 +/- 0.01) and meristematic tissue (0.58 +/- 0.02, 0.69 +/- 0.05, 0.74 +/- 0.01, surface, mid water and bottom, respectively). These patterns coincided with similar patterns in ambient light, which was most variable and reached its greatest values near the surface during the midday. (C) 2009 Elsevier B.V. All rights reserved.
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