Abstract
In an open field trial on two agricultural soils in NW Italy, the impact of two seed-applied biostimulants on the rhizosphere bacterial community of young maize plants was evaluated. The 16S rDNA profiling was carried out on control and treated plant rhizosphere samples collected at the 4-leaf stage and on bulk soil. In both soils, the rhizospheres were significantly enriched in Proteobacteria, Actinobacteria, and Bacteriodetes, while the abundances of Acidobacteria, Cloroflexi and Gemmatimonadetes decreased compared with bulk soil. Among the culturable bacteria genera that showed an increase by both biostimulants, most are known to be beneficial for nutrient uptake, such as Opitutus, Chryseolinea, Terrimonas, Rhodovastum, Cohnella, Pseudoduganella and the species Anaeromyxobacter dehalogenans; others are known to be involved in root growth, such as Niastella, Labrys, Chloroflexia and Thermomonas; or in plant defence, such as Ohtaekwangia, Quadrisphaera, Turneriella, and Actinoallomurus. Both biostimulants were also found to stimulate gen. Nannocystis, a potential biocompetitive agent against aflatoxigenic Aspergillus moulds. Under controlled conditions, both biostimulants enhanced the shoot and root biomass at the 4–5 leaf stage. We conclude that the biostimulants do not decrease the biodiversity of the microbial community rhizosphere of young maize plants, but stimulate rare bacterial taxa, some involved in plant growth and pathogen resistance, a result that may have implications in improving crop management.
Highlights
Plant biostimulants have been defined as “material containing substance(s) and/or microorganisms whose function is to stimulate natural processes, to enhance/benefit nutrient uptake, nutrient efficiency, to increase tolerance to abiotic stresses and crop quality when applied to plants or to the rhizosphere” [1]
Biostimulants based on the mixtures of plant growth promoting bacteria and arbuscular mycorrhizae fungi might represent an interesting tool for increasing crop tolerance to alkalinity and salinity and for helping plants withstand soil pathogen stress
Agricultural biostimulants, which may be formulated from different compounds, substances and microorganisms, are applied to achieve improved crop vigour, yield, quality, and tolerance to abiotic stresses [6,28]
Summary
Plant biostimulants have been defined as “material containing substance(s) and/or microorganisms whose function is to stimulate natural processes, to enhance/benefit nutrient uptake, nutrient efficiency, to increase tolerance to abiotic stresses and crop quality when applied to plants or to the rhizosphere” [1]. Many biostimulants contain simple and complex carbohydrates that, when applied to plants, improve the efficiency of plant metabolism by directly acting as a source of energy for rhizosphere microbial populations or by acting as signal molecules to activate defence reactions [2]. Biostimulant formulations without microorganisms have the potential to enhance the endogenous rhizosphere microbial community, selecting beneficial bacteria as PGPR, with positive effects on plant growth. The authors showed a greater soil microbial activity with faster plant establishment on degraded soils due to biostimulant application
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