The use of Microalgae as Plant Biostimulant for Sustainable Agriculture
Thadomal Shahani Engineering College
Plant biostimulants (PBSs) are picking up popularity among scientists because of the need to fulfil global food requirements of the ever-increasing population. PBSs are organic substances that improve crop quality by increasing the crops’ nutrient uptake, yield, resistance to environmental stresses and also the overall quality of produce. They are considered as extra additives, which help the plants when used in small, predetermined doses. They are different from fertilizers and plant nutrients in the sense that they promote plant growth without adding any nutritional benefits to the soil or plants.
PBSs are being looked upon by the scientific community and from a commercial point of view as a potential aid to optimize crop productivity and abiotic stress tolerance without being harmful to the environment. Plant stimulants have been known to enhance the physiological activities of plants like better protection against photodamage, better fruiting and longer shelf-life of the produce. Natural biostimulants have an added advantage that they are sustainable in the longer run because of their renewability. As of now, they encompass a wide variety of organic components (humic acids, protein hydrolysates, and seaweed extracts) and microbial organisms (mycorrhizal fungi and N-fixing bacteria).
In any experimentation process, standardization of raw material is very important for reproducibility of results. The difficult part about using naturally grown products, like seaweed, is that it makes standardization difficult.
Seaweeds have different physiological properties depending upon their source, age, etc. and this translated to the extracts as well, leading to variations in composition. This makes growing and processing biostimulants correctly, a compulsory step in the process. Low cost and large scale production is desirable for commercial supply of PBSs. Microalgae, which include a wide range of phototrophic and unicellular organisms, have proven to be a promising choice for this process.
Experimentation over the last few years have shown that microalgal extracts tested on plants have demonstrated stimulation of germination, seedling growth, shoot and root biomass in a large number of crops like lettuce, tomato and pepper. These extracts are made up of bioactive compounds derived from the microalgae. They can be added to the soil in a number of ways like adding algal dry biomass or suspended liquid culture to the soil, etc. The modulation and manipulation of microbial communities present in the phyllosphere and rhizosphere of the plant system is one of the main ways how PBSs work. They are known to secrete substances into the soil, which attracts beneficial microbes, that in turn helps in increasing the solubilisation, mineralization, and bioavailability of macro and micronutrients for the crop.
Thus, microalgae have great potential to serve as good quality biostimulants. They can be grown using wastewater and in both freshwater and marine environments. Isochrysis spp., Chaetoceros spp., Chlorella spp., Arthrospira spp. and Dunaliella spp. are among the most commercially cultivated microalgae species. They are being used mainly in the organic farming sectors, where growers avoid using synthetic and chemical fertilizers. However, they are yet to be explored to their full potential. More and more measures need to be taken to bring the laboratory experiments onto fields. More efforts to identify the various effects these stimulants have on plants have to be made by extensive research and experimental analysis. This can really go a long way in the setting-up of standardized protocol for the application of PBSs to crop plants globally.