Ulvan crude extract's chemical and biophysical profile and its effect as a biostimulant on Arabidopsis thaliana

Seaweed-derived extracts hold the promise of providing novel biostimulants to sustainably increase crop yields. The objective of this work was to determine whether ulvan crude extract could be used as a biostimulant for terrestrial plants. Herein we show that the crude extract of ulvan, extracted from cultivated Ulva sp., promotes growth of Arabidopsis thaliana. Ulvan's stimulative effect is both dose- and light intensity-dependent. We tested the effects of supplementation of 6 crude ulvan extract concentrations in the 0.01mg/ml - 1.43mg/ml range on A. thaliana growth for 3 weeks after sowing on agar plates under 90μmol m^-2 sec^-1 and 320μmol m^-2 sec^-1 light intensities. The addition of 0.07mg/ml ulvan extract to plant growth media for 3 weeks under 320μmol m^-2 sec^-1 light intensity led to an increase of 174% in root length, 83% in root dry weight, 54% in shoot dry weight, and 62% of total plant dry weight compared to untreated controls. The addition of 0.07mg/ml ulvan extract to plant growth media for 3 weeks in 90μmol m^-2 sec^-1 led to an increase of 120% in root length; no effect was observed on the total plant, shoot, or root weights compared to untreated controls. These results have applicative importance, as the use of biostimulants, such as ulvan, could potentially reduce the use of harmful agrochemicals, thus mitigating their negative environmental impacts, while increasing crop yield and contributing to global food security.