Storage and abiotic regulation of investment in vegetative vs. sexual reproduction in the clonal kelp, Laminaria sinclairii

Laboratory temperature and nutrient manipulation experiments demonstrated that investment in sexual and vegetative reproduction in the clonal kelp Laminaria sinclairii are regulated by different abiotic factors. Sorus production (sexual investment) and blade growth were significantly higher at 12°C compared to 17°C, regardless of nutrient concentration. Net carbon storage and depletion in rhizomes were observed in the low and high temperature treatments, respectively under low nutrients (2µM NO₃), while no trend was apparent at higher nutrient levels (12µM NO₃). Blade growth of plants in the field substantiated these results and was also negatively correlated with seawater temperature. On the other hand, rhizome elongation (investment in vegetative reproduction) in laboratory manipulations, was significantly higher at high nutrient concentrations, irrespective of temperature. This increase in rhizome growth was concurrent with an increase in rhizome percent tissue nitrogen observed at higher nutrient levels. Light level manipulation revealed no relationship between light availability and the growth response variables (sexual or vegetative reproductive output); equal investment was observed even in near darkness. However, a significant positive relationship was observed between light level and percent tissue carbon and nitrogen of rhizomes after the experiment, suggesting that the rhizome served as a storage organ of carbon and nitrogen, which allowed more regular growth when nutrients and productivity were limited. These results suggest that physiologically, Laminaria sinclairii is similar to aclonal kelps and that its rhizome functions similar to the stipes of other kelps with respect to carbon and nitrogen storage