About this Research Topic
Modern agriculture needs to review and broaden its practices and business models, by integrating opportunities coming from different adjacent sectors and value chains, including the bio-based industry, in a fully circular economy strategy. Searching for new tools and technologies to increase crop productivity under optimal and sub-optimal conditions and to improve resources use efficiency is crucial to ensure food security while preserving soil quality, microbial biodiversity, and providing business opportunities for farmers. Biostimulants based on microorganisms or organic substances obtained from renewable materials represent a sustainable, efficient technology or complement to synthetic counterparts, to improve nutrient use efficiency and secure crop yield stability. Under the new European Union Regulation 2019/1009, plant biostimulants were defined based on four agricultural functional claims as follows: Plant biostimulants are products that stimulate plant nutrition processes independently of the product's nutrient content with the sole aim of improving one or more of the following characteristics of the plant and/or the plant rhizosphere: 1) nutrient use efficiency, 2) tolerance resistance to (a)biotic stress, 3) quality characteristics or 4) availability of confined nutrients in the soil or rhizosphere’. Many diverse natural substances and chemical derivatives of natural or synthetic compounds, as well as beneficial microorganisms, are cataloged as plant biostimulants including i) humic substances, ii) plant or animal-based protein hydrolysates, iii) macro and micro-algal extracts, iv) silicon, v) arbuscular mycorrhizal fungi (AMF) and vi) plant growth-promoting rhizobacteria (PGPR) belonging to the Azotobacter, Azospirillum and Rhizobium genera.
Microbial and non-microbial plant biostimulants are usually used for open field and greenhouse crops. The biostimulants market is increasing year by year; with the market of biostimulant, active ingredients (amino acids, seaweed extracts, humic substances, and selected microorganisms or their metabolites) is estimated to account for 2.6 billion dollars in 2019 and is projected to reach almost $US 5 billion by 2025. Moreover, in the last 10 years (2010-2020) more than 1,000 scientific papers on ‘plant biostimulants’ were published and a bigger number of articles are available on the Scopus database using related words/terms (i.e., humic substances, seaweed extracts, microalgae, silicon, AMF or PGPR and microbial metabolites). Despite the huge scientific and commercial interest in microbial and non-microbial plant biostimulants, the detailed molecular, cellular, and physiological mechanisms underlying plant-biostimulant interactions under different environments and management strategies remain largely unknown. Therefore, there is an urgent need among the scientific community and commercial enterprises to better elucidate the causal/functional mechanisms of biostimulants, their potential side-effects on the environment, and their effect on the incidence or prevalence of plant or human pathogens. The elucidation of mechanisms from plant biostimulants will permit the development of a second generation of biostimulants where synergistic and complementary mechanisms can be functionally designed.
This Research Topic welcome Original Research, Review*, Policy and Practice Reviews, Methods, Opinion and Perspectives dissecting the agricultural functions and action mechanisms of plant biostimulants under optimal and adverse environmental situations (e.g., salinity, drought, thermal stress, suboptimal pH values, heavy metals, nutrient stress) or in optimum growing conditions. This compilation of hypothesis-driven studies on the physiological mechanisms of plant biostimulants will foster discussions within this new field, promote collaborations, and provide important information needed for downstream translational research, including designing and formulating biostimulants.
*Please note: If you intend to submit a Review Article you are highly encouraged to submit an abstract, highlighting the area of focus, and a suggested table of contents.
Please note: descriptive studies that report responses of growth, yield, or quality to biostimulant treatments will not be considered if they do not progress physiological understanding of these responses.
Keywords: humic substances, protein hydrolysates, silicon, arbuscular mycorrhiza, plant growth promoting rhizobacteria, macroalgae, microalgae, abiotic stresses, nutrient use efficiency, physiological mechanisms, plant-microbiome
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