Photosynthetic maximum quantum yield increases are an essential component of the Southern Ocean phytoplankton response to iron

Publication Type  Journal Article
Year of Publication  2008
Authors  Hiscock, M. R.; Lance, V. P.; Apprill, A. M.; Bidigare, R. R.; Johnson, Z. I.; Mitchell, B. G.; Smith, W. O.; Barber, R. T.
Journal Title  Proceedings of the National Academy of Sciences of the United States of America
Volume  105
Issue  12
Pages  4775-4780
Journal Date  Mar 25
ISBN Number  0027-8424
Accession Number  ISI:000254772700044
Key Words  climate change; iron fertilization; primary production; high-latitude photophysiology; photochemical efficiency; equatorial pacific-ocean; primary productivity; enrichment experiment; atlantic sector; light; fertilization; size; models; color; water

It is well established that an increase in iron supply causes an increase in total oceanic primary production in many regions, but the physiological mechanism driving the observed increases has not been clearly identified. The Southern Ocean iron enrichment experiment, an iron fertilization experiment in the waters closest to Antarctica, resulted in a 9-fold increase in chlorophyll (Chl) concentration and a 5-fold increase in integrated primary production. Upon iron addition, the maximum quantum yield of photosynthesis (phi(m)) rapidly doubled, from 0.011 to 0.025 mol C.mol quanta(-1). Paradoxically, this increase in light-limited productivity was not accompanied by a significant increase in light-saturated productivity (P-max(b)). P-max(b) maximum Chl normalized productivity, was 1.34 mg Chl(-1).h(-1) outside and 1.49 mg Chl(-1)-h(-1) inside the iron-enriched patch. The importance of phi(m) as compared with P-max(b) in controlling the biological response to iron addition has vast implications for understanding the ecological response to iron. We show that an iron-driven increase in phi(m) is the proximate physiological mechanism affected by iron addition and can account for most of the increases in primary production. The relative importance of phi(m) over P-max(b) in this iron-fertilized bloom highlights the limitations of often-used primary productivity algorithms that are driven by estimates of P-max(b) but largely ignore variability in phi(m) and light-limited productivity. To use primary productivity models that include variability in iron supply in prediction or forecasting, the variability of light-limited productivity must be resolved.


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URL  <Go to ISI>://000254772700044
DOI  DOI 10.1073/pnas.0705006105