Abstract
Agriculture is undergoing important changes in order to meet sustainable soil management with respect to biodiversity (namely agroecology). Within this context, alternative solutions to mineral fertilizers such as agricultural biostimulants are thus promoted and being developed. The mechanisms by which some soil biostimulants sustain soil biological functioning and indirectly increase crop yields are still unknown. Our goal in the present study was to demonstrate if and to what extent the application of a soil biostimulant affects the soil heterotrophic microbial communities that are involved in organic matter decomposition and carbon mineralization. We hypothesized that the addition of a biostimulant results in changes in the composition and in the biomass of soil microbial communities. This in turn increases the mineralization of the organic matter derived from crop residues. We performed soil microcosm experiments with the addition of crop residues and a biostimulant, and we monitored the organic carbon (orgC) mineralization and the microbial biomass, along with the microbial community composition by sequencing 16S rRNA gene and ITS amplicons. The addition of a soil biostimulant caused a pH neutralizing effect and simultaneous enhancement of the orgC mineralization of crop residues (+ 400 μg orgC g-1 dry soil) and microbial biomass (+ 60 μg orgC g-1 dry soil) that were linked to changes in the soil microbial communities. Our findings suggest that the soil carbon mineralization enhancement in the presence of the biostimulant was supported by the specific recruitment of soil bacteria and fungi. Whereas archaea remained stable, several operational taxonomic units (OTUs) of indigenous soil bacteria and fungi were enriched and affiliated with known microbial decomposers such as Cytophagaceae, Phaselicystis sp., Verrucomicrobia, Pseudomonas sp., Ramicandelaber sp., and Mortierella sp., resulting in lower soil microbial richness and diversity.
Highlights
With the ecological transition, agricultural practices attempt to reduce their dependence on chemicals and to sustain natural resources while producing healthy food
In the soil with straw (SS) treatment, we observed a significant increase in emitted CO2 compared to the control soil (CS) treatment indicating that the straw, as an added organic substrate, was metabolized by heterotrophic microorganisms
The increased emission of CO2 observed in the SS compared to the CS treatments (+1390 μg of C-CO2) (Kruskal-Wallis, H = 7.2, P = 0.027) corresponded to 69.5% of the organic carbon (orgC) potentially derived from the inoculated straw
Summary
With the ecological transition, agricultural practices attempt to reduce their dependence on chemicals and to sustain natural resources while producing healthy food. Microorganisms are involved in various biogeochemical cycles and contribute to soil fertility [3,4], providing mineral nutrients to crops through the mineralization of soil organic matter (SOM) [5]. Because this ecosystem service of SOM mineralization relies mainly on bacteria, fungi and archaea [6], changes in either their diversity, abundance or activity may significantly impact the subsequent supply of nutrients to plants. The manipulation of soil microbiota has emerged as a new practice in agriculture with respect to the ecological transition that promote sustainable soils. The use of agricultural biostimulants (BS) that are intended to stimulate and regulate soil microorganisms could be promoted as an alternative solution to the use of mineral fertilizers, which are more expensive [7,8,9]
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