THE ROLE OF PHYTOPLANKTON SIZE ON PHOTOCHEMICAL RECOVERY DURING THE SOUTHERN OCEAN IRON EXPERIMENT 1

• Published in: Journal of Phycology
• Main Authors: Peloquin, Jill A., Smith, Walker O.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2006
• Subjects: Southern Ocean
• Online Access: http://dx.doi.org/10.1111/j.1529-8817.2006.00266.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1529-8817.2006.00266.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1529-8817.2006.00266.x

Phytoplankton primary productivity in the Southern Ocean is controlled by complex interactions among iron, light, and grazing. This project interfaced with the Southern Ocean iron experiment (SOFeX) that created two iron‐enriched patches north and south of the Polar Front each with distinct silicic acid concentrations. We used pulse amplitude modulated fluorometry and measured the recovery of the maximum quantum yield of photochemistry ( F v / F m ) for three size fractions (whole, <5, <20 μm) and light adapted quantum yield (Δ F / F ′ m ) for single phytoplankton cells. The rates of recovery from iron stress were found to be unrelated to average cell size for both size‐fractioned and single‐celled measurements. The smallest cells appeared to exhibit more severe iron stress at the onset of the experiment than the larger taxa. The largest response detected in regression parameters was that of the pennate diatoms, which took only ∼3.4 days to reach the maximum quantum yield, whereas the centric diatom Asteromphalus sp. reached maximum Δ F / F ′ m after ∼10.4 days. The north patch measurements showed a different response; the smallest cells never reached maximum Δ F / F ′ m , whereas the size fraction containing the largest cells did. Single‐celled measurements made nearly 30 days after the initial iron enrichment suggested that diatoms were experiencing either silicic acid or iron limitation, whereas measurements of Phaeocystis sp. did not. These data represent the first study of in situ recovery rates of PSII for groups of diatoms, and may help elucidate the mechanisms of species change in response to environmental perturbation.