2007 Volume 55 Issue 4 Pages 587-597
Hatchery-raised young sporophytes of the kelp Laminaria japonica from the coast of Osatsube, Hokkaido, were cultivated in Matsushima Bay from November 2000 to July 2001. The seasonal gross photosynthetic rate, uptake rates of NH4-N, NO3-N and PO4-P, and the carbon and nitrogen contents were examined. High photosynthetic rates were found in the middle part with maximum blade width, in contrast to low rates in the meristem. The photosynthetic rate remained stable from January to June even though the temperature ranged from 7.3 to 17.7°C, suggesting that the photosynthetic activity was adjusted to seawater temperature. Uptake of NO3-N occurred mainly in the meristem, whereas NH4-N and PO4-P uptake also occurred in other blade parts. The uptake rates of NH4-N and PO4-P increased with ambient nutrient concentrations up to 800 and 160μg/l, respectively, whereas the uptake rate of NO3-N remained stable or decreased when ambient nutrient concentration exceeded 400μg/l. Carbon and nitrogen were transported to, and stored in, the meristem, although some was consumed for growth. The erosion of the apical tissues was initiated from December and the total erosion length reached 196 cm during the cultivation period. There may be a mechanism that recycles nitrogen for sorus formation and storage for plants that persist for a second year.
