Effect of temperature on the shoot growth of Sargassum muticum under laboratory culture conditions

抄録

We tested the effects of temperature on the growth of cultured Sargassum muticum during the shoot growth stage, during which main branches are produced instead of cauline leaves. Combinations of five temperature conditions (16, 20, 24, 28 and 30℃) with two irradiance levels (saturated and unsaturated levels for growth, i.e., 130 and 20 μmol m^-2s^-1, respectively) were set to examine whether the growth response to temperature was differed under different levels of irradiance. Under conditions of saturated irradiance, the elongation of the main branch was most rapid at 16 and 20 ℃, but when growth was expressed as weight, there was no significant difference among 16-28 ℃. Under higher temperatures (24 and 28 ℃), leaf formation on branches contributed increases in weight instead of main branch elongation. Under conditions of unsaturated irradiance, growth based on weight was negative at 28 and 30 ℃ due to the loss of leaves, but the main branches remained intact and alive. This was unlike a previously reported case of S. horneri, in which S. horneri died at these high temperatures when the irradiance was insufficient. This tolerance to higher temperatures even under insufficient irradiance is advantageous in establishing communities in enclosed coastal areas of the Seto Inland Sea, where temperature and turbidity of seawater are high during summer.