Biostimulants for Resilient Agriculture-Improving Plant Tolerance to Abiotic Stress: A Concise Review

The FAO estimates a 34% increase in the world population by 2050. As a result, the productivity of important staple crops needs to be boosted by ca. 43%. Against the mosaic of global climate change and shifting arable land ranges, plant and soil sciences play a primordial role in finding solutions to the internationally shared challenges of ensuring sustainable agricultural and biomass production. However, to effectively meet these challenges and demands, knowledge obtained from essential plant and soil sciences must be connected to innovative applications in agriculture and plant cultivation. Particularly with the increase and severity of abiotic stresses such as drought, salinity, soil organic matter, nutrient poverty, heavy metals, extreme temperatures, and floods. Hence, sustainable biological practices such as biostimulants that boost plant yield, quality or even novel functionality, and tolerance to abiotic stresses should be exploited to improve agricultural production. Thus, the biostimulants segment is very promising with a growth rate of over 12%. This effervescence explains the growing interest of scientists and industrialists to find new sources of plant biostimulants targeting specific agronomic needs. This review focuses on (i) the impact of abiotic stresses on crop growth and tolerance and their response mechanisms, (ii) the main categories of biostimulants (compost, humic substances, protein hydrolysate, seaweed extract, chitosan, inorganic compounds, and microorganisms (i.e. endophytes, AMF, and PGPR)), (iii) the application methods and mode/mechanisms action of biostimulants, (iv) mechanisms of plant tolerance by microbes in interaction with organic and inorganic fertilizers, and (v) the main constraints noted limiting the use of biostimulants.