In contrast with other studies on brown algae, inclusive of C. implexa (e.g., Larned 1998, Schaffelke and Klumpp 1998a,b, Schaffelke 1999), nutrient enrichment appeared to play no role in the elevated growth rates. This disparity may be due to the different experimental designs used: in previous studies nutrients were added as pulses and the experimental period was considerably shorter, whereas learn more in the present study, press nutrient treatments were
applied over 1 month. The mean growth rates of C. implexa under enriched November-PI scenarios over nonenriched treatments are slightly but not significantly elevated. This difference in growth rate between enriched- and ambient-PI scenarios is surpassed by the stimulation of growth observed in November-PI scenarios compared with all other scenarios. Potentially, PI3K Inhibitor Library it is the interaction between light, temperature and SW pCO2 that is driving the response, with light levels 20% greater in November than those observed in August, but the photosynthetic apparatus seemingly only able to
take advantage of the greater light availability when temperature and pCO2 are both relatively low. At present, C. implexa cover at the study site is highest in the month of December (Rogers 1997), but the present data also suggest that the late spring period is not necessarily also the period of greater growth under present-day conditions. The importance of the timing of the experiment as well as the applied scenario conditions is reflected in all productivity measurements (dark-adapted Fv/Fm, Pnmax and Rdark). The dark-adapted Fv/Fm showed a similar trend as the growth data, due to its tendency to be elevated in the November-PI scenario and relatively low in the August-A1FI scenario. The opposing patterns observed for dark-adapted Fv/Fm and O2 flux (Pnmax and Pgross, Pgross
not shown) are unexpected. In the short term, dark-adapted Fv/Fm is typically reduced following closure of reaction centers Adenosine triphosphate (RC) and under conditions that lead to an imbalance between light harvested and photochemical quenching capability (Genty et al. 1989). Frequently, the response to such conditions is to increase nonphotochemical quenching (NPQ); rerouting captured light energy to heat prior to its activation of the RC and hence O2 evolution (Müller et al. 2001). Both the closure of RCs and the activation of NPQ should reduce O2 evolution, that is, Fv/Fm and O2 evolution should work in concert. Decoupling of dark-adapted Fv/Fm and O2 flux responses has previously been observed for Palmaria palmata, in this case constant O2 flux gave way to decreased O2 flux only when Fv was reduced by 40% (Hanelt and Nultsch 1995).