Biostimulant action of Lithothamnium sp. promoting growth, yield, and biochemical and chemical changes on onion

The development of new natural biostimulant sources for a sustainable agriculture is a strategic issue aiming to improve the healthy food production. In this sense, the goal was to identify the biostimulant action of the calcareous alga Lithothamnium sp. (Rhodophyta) on onion in two experiments, (i) in pots and (ii) at field under organic system, both in factorial scheme with two onion cultivars and foliar sprays with micronized Lithothamnium sp. at concentration of 1.5 and 3.0 g L−1. The plant growth promotion and commercial yield improvement of two onion cultivars were achieved and related to changes on amino acid metabolism and source-to-sink flow stimuli. Better nutrient acquisition also was achieved related to the stimuli to thin roots growth, with N, Mg, Mn, Zn, and Cu content in bulbs improved at 3.0 g L−1, while 1.5 g L−1 allowed highest Ca, Mg, Mn, and Zn content in bulbs. Thus, the results presents Lithothamnium sp. as novel biostimulant source to grow onion, which effects related to the presence of bioactive humic acid that calcareous algae release by micronization.