Abstract: The effects of different seawater iron concentrations \[23 (natural seawater, control), 100, 300, 500, 700, and 900 μg·L^-1\] on relative growth rate, phycobiliprotein content, peroxidase activity, and nitrogenase activity of Plocamium telfairiae were examined at 20 ℃ under controlled laboratory conditions to determine the suitability of seawater iron concentration for P. telfairiae during a period of 30 days. The results showed that the greatest relative growth rate (RGR) attained was 1.14 %·d^-1 under the 100 μg·L^-1 treatment, which was significantly higher (P<0.01) than those attained under other treatments. RGR of P. telfairiae ranged from 0.26 %·d^-1 at 900 μg·L^-1 to 0.34 %·d^-1 at 500 μg·L^-1 with an average of 0.30 %·d^-1, which showed no significant difference compared with that attained in control treatment (P>0.05). The contents of three phycobiliproteins exhibited a similar variation pattern, increasing significantly with the seawater iron concentration increasing from 23 to 100 μg·L^-1 and decreasing gradually with the seawater iron concentration increasing from 100 to 900 μg·L^-1. The greatest peroxidase activity was 14.5 U·mg^-1 in the 100 μg·L^-1 treatment, which was significantly higher than those attained in the other treatments (P<0.05). However, no marked difference was found in nitrogenase activity among different seawater iron concentration treatments (P>0.05). Suitability analysis suggested that growth of P. telfairiae was significantly promoted by seawater iron concentration of 100 μg·L^-1 as compared to the higher iron enrichment in seawater (300-900 μg·L^-1).

Key words: maize, soybean, intercropping, plant density, yield, economic output value.