Table 1.
Tradeoffs and co-limitation scenarios for iron-nitrogen, manganese, copper, and light interactions.
| Resource | Description of interaction | Type of interaction/s with iron | Trade offs | Adaptations to low [Fe] | Co-limitation scenarios |
|---|---|---|---|---|---|
| Nitrogen | Photochemically produced reductive energy (NADPH) requires Fe based electron carriers. Fe dependent enzymes: Nitrate and nitrite reductases (NO3) Nitrogenase (N2) |
Biochemical dependence | Ambient Fe concentrations constrain biogeographic distribution of diazotrophic/non-diazotrophic phytoplankton in accordance with their partitioning strategy. | Temporal partitioning of N2 fixations allows for smaller cells and Fe recycling. | While iron limitation lowers the efficiency of NO3 uptake, nitrogen demands of Fe-limited cells can still be fully met. Nitrogen fixation may be Fe limited. |
| Manganese | Mn-SOD may replace Fe-SOD Transporter promiscuity – Mn may enter cell via specific Fe transporters. | Substitution Indirect |
Mn-SOD compensates for decreased levels of Fe-SOD under limitation. | Mn concentrations in most natural waters are above limiting levels (see Brand et al., 1983 and Hecky and Kilham, 1988). | |
| Copper | Plastocyanin is a Cu based electron carrier which may substitute for the Fe containing cytochrome c6. Cu dependent high affinity Fe transporters. |
Substitution Biochemical dependence | Fe demands decreased but greater Cu demands of open ocean diatoms leave them more prone to Cu limitation. | Plastocyanin is constitutively expressed in open ocean diatoms in lieu of cytochrome c6. | Ambient Cu concentrations are mostly sufficient (see Peers et al., 2005 and Peers and Price, 2006). |
| Light | Iron is essential to photosynthesis, the greatest cellular Fe sink. | Biochemical dependence | Species with lowered PSI:PSII and Cytochrome b6f:PSII ratios have lower Fe demands but smaller dynamic range for handling fluctuating light intensities. | Open ocean strains have less PSI and Cytochrome b6f. Southern Ocean diatoms increase PSU size rather than number, increasing light capture without inflating Fe costs. |
Low iron waters at high latitudes. |