Effect of light intensity, septage nitrogen, and salinity on the productivity and protein content of duckweed
1993
Minh, Van Phan
Study was undertaken in outdoor conditions to determine the effect of natural light intensity, septage-nitrogen loading rate, and salinity on the productivity and protein content of duckweed, Lemna aequinoctialis. The highest productivity of duckweed was only observed in full sunlight when most days had a maximum light intensity below 100,000 lux, the lowest with 25 % ambient light, 4.4 g dry weight/square m/day and 1 g dry weight/square m/day, respectively. These corresponded to 1.5 g and 0.3 g true protein/square m/day, respectively. The optimal range of septage-nitrogen loading rate varied from 5 mg to 15 mg N/l, depending on the level of ambient light of 25, 50 and 100 %. The nitrogen loading rate interacted with light intensity only when light intensity was optimal (below 100,000 lux) for duckweed growth (P0.001), indicating that light intensity is the predominant factor in this interaction. In constrast, there was an interaction between nitrogen loading rate and light intensity on the total nitrogen content of duckweed as it varied in all conditions of light intensity and nitrogen loading rate studied (P0.001). Duckweed showed a significantly higher productivity at a salinity of 3 ppt than in freshwater or at 6 ppt (P0.05), suggesting a high mineral requirement of duckweed. There was no interaction between salinity and nitrogen loading rate on either the productivity or total nitrogen content of duckweed. The highest productivity of duckweed at 3 ppt was 2.7 g dry weight/square m/day whereas it was only 1.9 g dry weight/square m/day in fresh water.
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