Balancing biomass and starch accumulation in duckweed: Unraveling the regulation mechanism of nutrient concentration via transcriptomics

Duckweed has rapid growth, high starch content, and is easily regulated, making it a novel starch resource. Nutrient restriction accelerates starch accumulation in duckweed. However, the impact of changes in the nutrient concentration regulatory mechanism underlying starch accumulation remains unclear. This study optimized the nutrient concentration and analyzed key parameters of Spirodela polyrhiza ZH0196 starch accumulation, including starch content, photosynthetic pigments, and soluble sugars, to clarify the role of nutrient concentration. It also conducted an investigation and identification of key enzyme activities and key metabolic pathways involved in starch accumulation. Results showed that Spirodela polyrhiza ZH0196 growth and starch accumulation responded differently to initial nutrient levels. The 0 % nutrient group had the highest AGPase enzyme activity (12.42 ± 1.58 U/mg protein) among all groups (1.8–8.5 U/mg protein), but its final starch output was lower than that of the 40 % group. As Spirodela polyrhiza ZH0196 grew and nutrient concentration declined, photosynthetic pigments and biomass decreased, while starch-synthetic enzyme activity increased, leading to starch accumulation. These processes are closely associated with photosynthetic metabolism. Analysis of differentially expressed genes revealed a downregulation in biological processes related to ATP and NADPH generation, while genes involved in starch-sucrose metabolism and glycolysis were upregulated. Overall, these findings demonstrate that Spirodela polyrhiza ZH0196 exhibits notable advantages under lower (40 %) nutrient concentrations by reducing biomass production and enhancing starch accumulation. This study provides a theoretical basis for regulating starch biosynthesis in duckweed and offers a potential technical strategy for sustainable duckweed cultivation as bioenergy. • 40 % nutrient concentration gradient balanced the biomass of duckweed and the accumulation of starch. • 40 % nutrient concentration gradient promotes the starch synthesis pathway. • 40 % nutrient concentration gradient regulates the light and system and the sugar metabolism pathways.