Energy-efficient and environmentally friendly production of starch-rich duckweed biomass using nitrogen-limited cultivation

Abstract

Here, we combined the aquatic cultivation of the energy crop duckweed and nitrogen limitation to quickly produce starch-rich biomass. Under N limitation, duckweed can quickly accumulate starch at up to 52.37 ± 0.57% (dry weight). In the process, nitrogen use efficiency (NUE) reached 61.3 ± 1.8 kg biomass kg−1 N, exceeding that of most cereals. In this paper, we elucidated for the first time the mechanism of the high NUE of duckweed under N limitation. First, duckweed possesses higher N transport ability than most cereals and trees and can efficiently accumulate abundant N in vivo under N-sufficient condition. In addition, under N limitation, the stable expression and activity of key enzymes related to both carbon fixation and N assimilation ensured normal biomass accumulation. Furthermore, the efficient ubiquitin-proteasome system (UPS) and autophagy activated the endogenous N remobilization and recycling. Combined with the sharp increase in the expression and activity of duckweed glutamine synthase (GS), duckweed can efficiently redistribute and reuse the endogenous N to support its growth and starch accumulation. Especially, sewage was used to duckweed pre-cultivation in pilot-scale experiment, the approach can simultaneously achieve starch production and wastewater treatment. In a word, this paper provides an environmentally friendly, cost-effective and promising technology for starch production.