An overview of biostimulant activity and plant responses under abiotic and biotic stress conditions

Currently, extreme weather events caused by climate change, such as heat waves, drought, frost, and heavy precipitation, have become a threat to agriculture by detrimentally affecting plant productivity and quality. The overuse of synthetic fertilizers is another major concern damaging the soil quality and water and air quality. In this regard, biostimulants could be a promising and potent solution to address these environmental concerns and meet the need for developing sustainable and green modern agriculture. Biostimulants that are primarily composed of natural substances and/or microorganisms can be broadly divided into non-microbial and microbial categories. In this review, the applications of the main types of biostimulants to plant growth and development are discussed, and the possible associated mechanisms of action are described as well. Furthermore, the current status and challenges relating to commercialization and large-scale implementation under changing climate conditions are covered. Overall, this review article could offer insights and knowledge of biostimulants' uses in agriculture for both academia and industrial sectors.