Responses Of The Red Algae Gracilaria Lemaneiformis To Changes Of Solar Radiation And Nitrate Concentration

Macroalgae compose the important parts of primary production near the sea, and the photosynthesis and growth of which are affected by many kinds of environmental factors. Gracilaria lemaneiformis Bory as a commercial alga, is farmed in the south of China with greater scale. Although many studies have been done on the biological characteristics, little is known about the responses of thalli to southern solar radiation. The characteristics of photobiology and bio-ecology were studied, and the main results are as follows:The growth of Gracilaria lemaneiformis was usually inhibited by nitrate. After 16 days of continuous incubation in the natural seawater, the fresh weight was 1.1 higher than initial values under P treatment; but only 0.6 under full solar radiation (PAR+UVR), which indicated the inhibitory effect of UVR. The relative growth rate were 4.3 and 2.7 % respectively with the two treatments (P and PAB). The content of UVAC was also low with 34.5 and 42.1μg·g^-1 (F.W.) under P and PAB treatments when thalli were incubated in natural seawater.After 16 days of incubation, the fresh weight of thalli grown in enriched seawater (SW+300, SW+600) were 6.6, 3.8 and 9.6, 6.0 higher than initial ones under P and PAB treatments, and the RGR were 11.4, 8.9%·d^-1 and 14.1, 10.0%·d^-1. UVAC content was 47.2μg·g^-1 (F.W.) under P treatment and 54.2μg·g^-1 (F.W.) under PAB when thalli were cultured in SW+300; for SW+600, the content of UVAC were 65.7μg·g^-1 (F.W.) and 70.3μg·g^-1 (F.W.) under P and PAB treatments, respectively. The photosynthetic activity was also improved under the enriched seawater, the maximum of which were 0.8-1.0 and 0.9-1.1 higher than initial ones under P and PAB treatments, respectively. The negative relationship between content of UVAC and inhibitory rate induced by UVR, indicated the protection of UVAC against UVR.The content of UVAC changed normally when thlli were treated with P and PAB in turn, and decreased under P inside but increased under PAB outside, And was about 17% higher when thalli were treated with P outside compared with that treated with P inside; but was about 16% lower than that treated with PAB outside, indicating that the increase of PAR and the existence of UVR could induce the synthesis of UVAC.