Sustainable agriculture practices involve the application of environment-friendly plant growth promoters and additives that do not negatively impact the health of the ecosystem. Stringent regulatory frameworks restricting the use of synthetic agrochemicals and the increase in demand for organically grown crops have paved the way for the development of novel bio-based plant growth promoters. In this context, microalgae biomass and derived agrochemicals offer novel sources of plant growth promotors that enhance crop productivity and impart disease resistance. These beneficial effects could be attributed to the presence of wide range of biomolecules such as soluble amino acid (AA), micronutrients, polysaccharides, phytohormones and other signaling molecules in microalgae biomass. In addition, their phototrophic nature, high photosynthetic efficiency, and wide environmental adaptability make them an attractive source of biostimulants, biofertilizers and biopesticides. The present review aims to describe the various plant growth promoting metabolites produced by microalgae and their effects on plant growth and productivity. Further, the effects elicited by microalgae biostimulants with respect to different modes of applications such as seed treatments, foliar spray and soil/root drenching is reviewed in detail. In addition, the ability of microalgae metabolites to impart tolerance against various abiotic and biotic stressors along with the mechanism of action is discussed in this paper. Although the use of microalgae based biofertilizers and biostimulants is gaining popularity, the high nutrient and water requirements and energy intensive downstream processes makes microalgae based technology commercially unsustainable. Addressing this challenge, we propose a circular economy model of microalgae mediated bioremediation coupled with biorefinery approaches of generating high value metabolites along with biofertilizer applications. We discuss and review new trends in enhancing the sustainability of microalgae biomass production by co-cultivation of algae with hydroponics and utilization of agriculture effluents.

The present study was aimed at developing Arthrospira platensis (Spirulina) fortified traditional foods of the Indian subcontinent, namely sattu (multigrain beverage mix) and chikki (peanut bar) and evaluating their ability to promote recovery from protein and iron deficiency anaemia (IDA) using albino Wistar rats. Addition of Spirulina (at 4% w/w Spirulina inclusion levels) enriched the protein content by 20.33% in sattu and 15.65% in chikki while the iron content was enhanced by 45% in sattu and 29.6% in chikki. In addition, the total carotenoid and polyphenol content and antioxidant capacity of the food products improved after Spirulina incorporation. Supplementation of 100 g of Spirulina fortified food products meets more than 50% of recommended dietary allowances (RDA) of protein, dietary fiber, iron and zinc for the age group 3 to 10 years of children. Spirulina contributed between 11% and 22% of RDA for protein and iron, respectively; however it contributed very negligibly to RDA of dietary fibre with respect to the nutrient requirements for the target age group. Supplementation of Spirulina fortified foods individually promoted bodyweight gain in malnourished rats and restored haemoglobin, serum protein, albumin, serum iron, and hepcidin levels and reduced the iron binding capacity indicating recovery from IDA. Spirulina supplementation ameliorated malnutrition induced oxidative stress in the liver, spleen and kidneys by reducing the lipid peroxidation and enhancing superoxide dismutase and glutathione activities. Histopathological analysis revealed that supplementation of Spirulina fortified foods reversed pathological changes such as fatty changes in the liver cells, thinning of cardiac muscle fibers and degeneration of intestinal villi. Fe–protein deficiency significantly altered the gut microflora by reducing the abundance of beneficial microbes. However, supplementation of Spirulina fortified foods improved the levels of beneficial gut microbes such as Lactobacillus reuteri and Akkermansia muciniphila while reducing the abundance of Helicobacteraceae, Enterobacteria and Clostridia. In summary, supplementation of Spirulina fortified foods promoted recovery from protein and iron deficiency indicating the bioavailability of nutrients (iron and protein) from Spirulina at par with casein and ferrous ascorbate.

Four edible flowers commonly consumed in the Western Himalayan region, namely, Bauhinia variegata (Kachnar), Tropaeolum majus (Nasturtium), Matricaria chamomilla (Chamomile), and Tagetes erecta (Marigold), were characterized for their nutritional and phytochemical composition. Through the UHPLC-QTOF-IMS-based metabolomics approach, 131 compounds were tentatively identified consisting of phenolic acids, flavonoid glycosides, terpenoids, amino acids, and fatty acid derivatives. Kaempferol and quercetin glycosides for Kachnar, apigenin glycosides and caffeoylquinic acid derivatives for Chamomile, patulin and quercetin derivatives for Marigold, cyanidin and delphinidin glycosides for Nasturtium were the predicted marker metabolites identified through non-targeted metabolomics. Kachnar and Chamomile scored best in terms of macronutrients and essential micronutrients, respectively. Nasturtium contained high concentrations of α-linolenic acid, anthocyanins, and lutein. Kachnar contained the highest total phenolic acids (63.36 ± 0.38 mg GAE g^-1), while Marigold contained the highest total flavonoids (118.90 ± 1.30 mg QUE g^-1). Marigolds possessed excellent free radical scavenging and metal chelation activities. Chamomile exhibited strong α-glucosidase inhibition activity, followed by Nasturtium. The in vitro gastrointestinal digestibility of flower extracts indicated that the bioaccessibility of phenolic acids was higher than that of flavonoids. Polyphenols from Nasturtium and Chamomile showed the highest bioaccessibility. The study is an attempt to characterize traditionally consumed edible flowers and promote their wider utilization in gastronomy and nutraceuticals.