Abstract
Plant biostimulants (PBs) attract interest in modern agriculture as a tool to enhance crop performance, resilience to environmental stress, and nutrient use efficiency. PBs encompass diverse organic and inorganic substances (humic acids and protein hydrolysates) as well as prokaryotes (e.g., plant growth promoting bacteria) and eukaryotes such as mycorrhiza and macroalgae (seaweed). Microalgae, which comprise eukaryotic and prokaryotic cyanobacteria (blue-green algae), are attracting growing interest from scientists, extension specialists, private industry and plant growers because of their versatile nature: simple unicellular structure, high photosynthetic efficiency, ability for heterotrophic growth, adaptability to domestic and industrial wastewater, amenability to metabolic engineering, and possibility to yield valuable co-products. On the other hand, large-scale biomass production and harvesting still represent a bottleneck for some applications. Although it is long known that microalgae produce several complex macromolecules that are active on higher plants, their targeted applications in crop science is still in its infancy. This paper presents an overview of the main extraction methods from microalgae, their bioactive compounds, and application methods in agriculture. Mechanisms of biostimulation that influence plant performance, physiology, resilience to abiotic stress as well as the plant microbiome are also outlined. Considering current state-of-the-art, perspectives for future research on microalgae-based biostimulants are discussed, ranging from the development of crop-tailored, highly effective products to their application for increasing sustainability in agriculture.
Highlights
MICROALGAE AS A RENEWABLE SOURCE OF PLANT BIOSTIMULANTSGlobal demographic pressure on agricultural production calls for novel and sustainable approaches toward satisfying the ever-growing demand for plant biomass destined for human food, animal feed, and energy production
Reviewed by: Spyridon Alexandros Petropoulos, University of Thessaly, Greece Andrea Ertani, Università degli Studi di Padova, Italy
Specialty section: This article was submitted to Crop and Product Physiology, a section of the journal Frontiers in Plant Science
Summary
Global demographic pressure on agricultural production calls for novel and sustainable approaches toward satisfying the ever-growing demand for plant biomass destined for human food, animal feed, and energy production. Reduction of growing area and protection against potential contamination can be obtained in closed-ponds, referred to as photobioreactors This type of cultivation method is often used for the production of high added-value molecules, such as pharmaceutical compounds. Microalgae have the potential to reduce the negative discharges to the environment by, for instance, re-using nutrients and products and valorizing waste from different sources, including those related to agriculture This mini-review presents the various methods of production of microalgal extracts, their biologically active compounds and application methods in agriculture. The choice of extraction method used to obtain biologically active compounds from the microalgal biomass is mainly dictated by the type of raw material and by the target molecule(s) (Michalak and Chojnacka, 2014). The foliar application method appeared to be the most effective if applied under high relative humidity conditions and when leaf stomata are open, in order to increase the permeability and uptake of the product
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