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Regulation of growth in laminaria digitata use of in vivo nitrate reductase activities as an indicator of nitrogen limitation in field populations of laminaria spp


Marine Biology (Berlin) 84(2): 207-217
Regulation of growth in laminaria digitata use of in vivo nitrate reductase activities as an indicator of nitrogen limitation in field populations of laminaria spp
The seasonal variation in growth rate of a population of Laminaria digitata (Huds). Lamour growing at Arbroath, Scotland [UK] was studied between Aug. 1981 and Sept. 1982, and was found to follow the biphasic annual cycle typical of this genus. Growth rates were maximum (0.3 cm cm-1 mo.-1) in early June and minimum (0.05 cm cm-1 mo.-1) between Sept. and Jan. An analysis of the relationship between the seasonal changes in environmental factors (inorganic N concentrations, irradiance and temperature) with those of growth rate and the accumulation or mobilization of cellular reserves of carbohydrates and NO3-, indicated that growth was N-limited between June and Oct. and light-limited (with a possible co-involvement of temperature) for the remainder of the year. These conclusions were supported by the seasonal changes in the ratio of actual:potential in-vivo nitrate reductase activities in L. digitata, thus confirming the suitabiity of this technique for monitoring the occurrence of N limitation in Laminaria spp. The seasonal changes in blade nitrate reductase activities closely followed those of growth rate, with maximum activities [0.3 .mu.mol NO3- reduced g-1 (wet wt) h-1] being present in late May and minimum levels [0.01 .mu.mol NO3- reduced g-1 (wet wt) h-1] occurring between Nov. and March. The correlation observed between nitrate reductase activities and growth rate is consistent with the ability of Laminaria spp. to store excess inorganic N, available during winter and early spring, as NO3-, and with the requirement to conserve enzyme protein during the summer period of N limitation.


Accession: 006288300



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