Synergic combination of calcareous algae and cyanobacteria stimulate metabolic alterations improving plant growth and yield

Abstract

The use of natural bioactive sources to promote plant growth and crop yield gains, such as those obtained from algae, are in evidence as a sustainable agriculture practice. In this sense, recently the calcareous alga Lithothamnium sp. had its bioactive plant growth promoting effect related to the presence of high degree of humification humic acid with pronounced auxin-like effects, while the cyanobacterium Arthrospira platensis (Spirulina plantensis) has the plant growth promoting effect attributed to a pool of bioactive molecules, such as the free L-amino acids and polyamines. To explore the effect of algae sources combinations as plant biostimulants, the aim of this work was to evaluate the effects of foliar application of micronized Lithothamnium (Lm) associated with A. platensis (Ap) dried biomass in onion (Allium cepa) metabolism, growth and yield. For that, adopting an step by step approach three experiments were conducted: (i) foliar application to onion plants grown in pots in greenhouse comparing algae sources alone and combined, (ii) foliar application to onion plants in the field under organic system testing algae sources combinations (first season), and (iii) foliar application in the field comparing doses and frequencies of selected combinations (second season). The association of algae sources promoted growth and biochemical changes, thus pigment contents, total sugars, amino acids and nitrate reductase enzyme activity were improved, increasing the onion yield by two seasons in a nature friendly way.