Iron-mediated change in phytoplankton photosynthetic competence during SOIREE

• Main Authors: Philip Boyd, Edward Abraham, P. W. Boyd, E. R. Abraham
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2001
• Subjects: Pacific; Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.23.5067; http://www.mcs.vuw.ac.nz/~abraham/Publications/SOIREE_FvFm.pdf

Active fluorescence (Fast Repetiton Rate Fluorometry, FRRF) was used to follow the photosynthetic response of the phytoplankton community during the Southern Ocean Iron RElease Experiment (SOIREE). This in situ iron enrichment was conducted in the polar waters of the Australasian-Pacific sector of the Southern Ocean in February 1999. Iron fertilisation of these High Nitrate Low Chlorophyll (HNLC) waters resulted in an increase in the photosynthetic competence (Fv/Fm) of the resident cells from around 0.20 to greater than 0.60 (i.e. close to the theoretical maximum) by days 10/11 of the experiment. Although a significant iron-mediated response in Fv/Fm was detected as early as 24 h after the initial enrichment, the increase in Fv/Fm to double ambient levels took 6 days. This response was five-fold slower that observed in iron enrichments (in situ and in vitro) in the HNLC waters of the sub-polar and Equatorial Pacific. During SOIREE, the photosynthetic competence of the resident phytoplankton in iron-enriched waters increased at dissolved iron levels above 0.2 nM, suggesting that iron limitation was alleviated at this concentration. Increases in Fv/Fm of cells within three algal size classes suggested that all taxa displayed a photosynthetic response to iron enrichment. Other physiological proxies of algal iron stress (such as flavodoxin expression) exhibited different trends than Fv/Fm during the time-course of SOIREE, the relationship between Fv/Fm, algal growth rate and such proxies in Southern Ocean waters is discussed.