Starch Accumulation in Duckweed for Bioethanol Production

Abstract

In an effort to explore novel starch sources for fuel ethanol production, Spirodela polyrrhiza, a local duckweed strain in North Carolina, was studied at different growing conditions including temperature, nutrient level, and daily light integral (DLI) for starch accumulation. The results show that lower temperatures, nutrient starvation, and higher DLIs favor starch accumulation. At a DLI of 1.75 mol m-2 d-1 and an ammonium (NH4-N) concentration of 20 mg L-1, simply reducing the growing temperature from 20°C to 5°C caused an increase of duckweed starch content by 67.5% within four days. In transferring duckweed into well water, the highest starch content of 26.6% was achieved after four days at the combination of the lowest temperature of 5°C and the highest DLI of 2.33 mol m-2 d-1, which was three times as high as the starch content of untreated duckweed. During nutrient starvation, the protein content of duckweed decreased due to the rise in the proportion of starch in the duckweed biomass. The protein reduction could also be the result of the limited availability of nitrogen in the medium for protein synthesis.