Abstract
The worldwide use of plant biostimulants (PBs) represents an environmentally friendly tool to increase crop yield and productivity. PBs include different substances, compounds, and growth-promoting microorganism formulations, such as those derived from arbuscular mycorrhizal fungi (AMF) or seaweed extracts (SEs), which are used to regulate or enhance physiological processes in plants. This study analyzed the physiological, ecological, and biochemical implications of the addition of two PBs, AMF or SE (both alone and in combination), on tomato plants (Solanum lycopersicum L. cv. “Rio Fuego”). The physiological responses evaluated were related to plant growth and photosynthetic performance. The ecological benefits were assessed based on the success of AMF colonization, flowering, resistance capacity, nonphotochemical quenching (NPQ), and polyphenol content. Biochemical effects were evaluated via protein, lipid, carbohydrate, nitrogen, and phosphorous content. Each PB was found to benefit tomato plants in a different but complementary manner. AMF resulted in an energetically expensive (high ETRMAX but low growth) but protective (high NPQ and polyphenol content) response. AMF + nutritive solution (NS) induced early floration but resulted in low protein, carbohydrate, and lipid content. Both AMF and AMF + NS favored foliar instead of root development. In contrast, SE and SE + NS favored protein content and root development and did not promote flowering. However, the combination of both PBs (AMF + SE) resulted in an additive effect, reflected in an increase in both foliar and root growth as well as protein and carbohydrate content. Moreover, a synergistic effect was also found, which was expressed in accelerated flowering and AMF colonization. We present evidence of benefits to plant performance (additive and synergistic) due to the interactive effects between microbial (AMF) and nonmicrobial (SEs) PBs and propose that the complementary modes of action of both PBs may be responsible for the observed positive effects due to the new and emerging properties of their components instead of exclusively being the result of known constituents. These results will be an important contribution to biostimulant research and to the development of a second generation of PBs in which combined and complementary mechanisms may be functionally designed.
Highlights
The current challenges associated with horticultural production are growing due to the ever-increasing worldwide demand for efficient, environmentally friendly, and sustainable food production
The treatments consisted of (1) plants grown without any Plant biostimulant” (PB) and only irrigated with Rorison nutritive solution (NS); (2) plants treated with a microbial-based biostimulant containing Rhizophagus intraradices, a type of arbuscular mycorrhizal fungi (AMF); (3) plants treated with a microbial-based biostimulant containing AMF and irrigated with the NS (AMF + NS); (4) plants treated with a nonmicrobialbased biostimulant from a Padina gymnospora extract (SE); (5) plants treated with a nonmicrobial-based biostimulant from seaweed extracts (SEs) and irrigated with the NS (SE + NS); and (6) plants grown with both PBs and irrigated with the NS (AMF + SE + NS)
The findings of this study have identified patterns in complex data and elucidated the inherent activity and synergy of potential microbial and nonmicrobial PBs that may be used in commercial agriculture
Summary
The current challenges associated with horticultural production are growing due to the ever-increasing worldwide demand for efficient, environmentally friendly, and sustainable food production. PBs were defined therein as highly heterogeneous materials that could be classified into eight categories: humic substances, complex organic materials, beneficial chemical elements, inorganic salts, seaweed extracts (SEs), chitin and chitosan derivates, antitranspirants, and free amino acids and Ncontaining substances This PB classification did not include any microbial biostimulants. The new proposed definition of a PB is “a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds” (Yakhin et al, 2017) This particular conceptualization of PBs, in addition to allowing for a better understanding of their physiological and biochemical modes of action, has contributed to the development of PB science, industry, and legislation. Despite the notable progress in PB science in recent years, there are still many questions that remain open as well as many challenges and opportunities to identify patterns in complex data and elucidate the inherent activity and potential synergistic effects of the combination of microbial and nonmicrobial PBs for agricultural purposes (Rouphael and Colla, 2018)
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