Lemna minor and Spriodela polyrhiza are two species of duckweed, small fast-growing, floating aquatic plants. Our previous studies showed that Lemna biomass had high energy content, but suffered from pests during long-term outdoor cultivation. Current research compares the growth rate and energy content of two duckweed species, Lemna minor (native to Oklahoma) and Spirodela polyrhiza (a larger, non-native species). Outdoor cultures (90 L in quarter-strength Hoagland’s basal salts medium, with approximately 20 ft2 surface area) were inoculated with similar masses of rapidly growing Lemna or Spirodela. Biomass was harvested at one to two week intervals from half of the surface by skimming plants from the surface with a metal strainer. Pools were allowed to regrow to cover the surface, and harvested again. Fresh and dry weights were recorded. Biomass was dried at 60 °C and pulverized. Percent total carbon and nitrogen values were determined at an agricultural analysis lab. Energy content (kJ/g) was determined using oxygen bomb calorimetry, with powdered samples contained in gelatin capsules. Spirodela grew significantly faster than Lemna based on fresh and dry weight measurements. Energy contents are being determined for samples of the two species grown under identical conditions. Preliminary energy content data indicate that the dried Spirodela biomass has a higher energy (kJ/g) compared to Lemna grown under identical conditions, but more analysis is needed. The energy content of dried samples of both species appeared to increase at later harvest times, as the nutrients in the pools were depleted. Both species could be potential biofuel crops in Oklahoma, or used as animal feeds, while removing agricultural pollutants from water sources.

Comparison of growth and energy content of Spriodela polyrhiza and Lemna minor, two potential biofuel sources

255th National Meeting (2018)

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