Physiological Effects Of Nutrient And Incubation Density On Gracilaria Lemaneiformis

Gracilaria lemaneiformis (Rhodophyta) is an important cultivated species in China. It is not only an economic red alga, but also a primary producer in costal ecosystem. The photosynthesis and other physiological traits of the alga are affected by nutrients, cultivated densities and other various kinds of environmental factors. Studies of the physiological effects of nutrients and cultivated densities on Gracilaria lemaneiformis can lay down a certain theory foundation for further understanding the purification function on eutrophication of the sea water and for guiding the mass culture of the alga. Therefore, priority in this paper was given to analysis some main physiological effects of nutrients and incubation densities on the alga, including growth, photosynthesis and purification capability. Studies were carried out on the (1) effects of nitrogen and phosphate on the physiological traits of Gracilaria lemaneiformis;(2) effects of incubation densities on the physiological traits of Gracilaria lemaneiformis;(3) effects of different nutrients and incubation densities on the physiological traits of Gracilaria lemaneiformis. The main results were listed as follows:Growth, photosynthetic rates and pigment contents of Gracilaria lemaneiformis were enhanced with the low N and high P treatment, high N and low P treatment, and high N and high P treatment, compared to low N and low P treatment. The ability of photosynthetic utilization of HCO3-was also increased at the above three nutrients conditions. The light saturated maximum photosynthetic rate (Pmax), apparent photosynthetic efficiency (a) and pigment contents were highest at high N and low P treatment among the four treatments. The highest relative growth rate (RGR), yield, carbon-saturated photosynthetic rate (Vmax) and apparent half saturation constant (Km) were observed at high N and high P treatment. Photochemical efficiency of Gracilaria lemaneiformis was stimulated with low N and high P treatment, but was inhibited at high N treatments (either high N and low P treatment or high N and high P treatment) compared with low N and low P treatment.The growth and pigment contents of Gracilaria lemaneiformis were decreased with increased density (from0.25g FW L"1to2.0g FW L-1). Growth rate and pigment contents were reduced at high incubation density of2.0FW L-1. Yield, photosynthesis and nutrient assimilation efficiency were enhanced by middle and high incubation density (1.0g FW L-1and2.0g FW L-1), compared to low incubation density of0.25g FW L-1. The greatest value of yield, Pmax, α and nutrient assimilation efficiency were obtained at the density of2.0g FW L"1. There was density-dependent effect on nutrient assimilation of Gracilaria lemaneiformis.Two nutrients levels (filtered natural seawater and nutrient enriched seawater) and three incubation densities (0.25,1.0and2.0g FW L-1) exerted complicated influence on the photosynthesis and other physiological traits. The physiological traits of Gracilaria lemaneiformis grown at nutrient enriched seawater was enhanced, with the highest yield, photosynthetic rates, nutrient assimilation ability and pigment contents at high incubation density of2.0g FW L-1. The NR activity was significantly greater at nutrient enriched seawater and low incubation density of0.25g FW L-1than other culture conditions. The RGR of Gracilaria lemaneiformis was not remarkably affected by nutrients and densities, with a slightly greater value at filtered natural seawater and low incubation density of0.25g FW L-1. The density dependent effect on nutrient assimilation efficiency of Gracilaria lemaneiformis was not obvious, which could be the result of various abilities of nutrient assimilation to different nutrients levels (filtered natural seawater and nutrient enriched seawater).In conclusion, nutrient and density have significant effects on the growth, photosynthesis and nutrient purification traits of Gracilaria lemaneiformis, which were also related to experimental conditions, including irradiances and temperatures. It is essential to further study the nutrient purification capability and optimum nutrient concentration and density for the growth and photosynthesis traits of Gracilaria lemaneiformis grown at natural environment.