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Sustainable transformation of agricultural plant production requires the reduction of nitrogen (N) fertilizer application. Such a reduced N fertilizer application may impede crop production due to an altered symbiosis of crops and their rhizosphere microbiome, since reduced N input may affect the competition and synergisms with the plant. The assessment of such changes in the crop microbiome functionalities at spatial scales relevant for agricultural management remains challenging. We investigated in a field plot experiment how and if the N cycling guilds of the rhizosphere of globally relevant cereal crops - winter barley, wheat and rye - are influenced by reduced N fertilization. Crop productivity was assessed by remote sensing of the shoot biomass. Microbial N cycling guilds were investigated by metagenomics targeting diazotrophs, nitrifiers, denitrifiers and the dissimilatory nitrate to ammonium reducing guild (DNRA). The functional composition of microbial N cycling guilds was explained by crop productivity parameters and soil pH, and diverged substantially between the crop species. The responses of individual microbial N cycling guild abundances to shoot dry weight and rhizosphere nitrate content was modulated by the N fertilization treatments and the crop species, which was identified based on regression analyses. Thus, characteristic shifts in the microbial N cycling guild acquisition associated with the crop host species were resolved. Particularly, the rhizosphere of rye was enriched with potentially N-preserving microbial guilds - diazotrophs and the DNRA guild - when no fertilizer was applied. We speculate that the acquisition of microbial N cycling guilds was the result of plant species-specific acquisition strategies. Thus, the investigated cereal crop holobionts have likely different symbiotic strategies that make them differently resilient against reduced N fertilizer inputs. Furthermore, we demonstrated that these belowground patterns of N cycling guilds from the rhizosphere microbiome are linked to remotely sensed aboveground plant productivity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Seed inoculation with beneficial microorganisms has gained importance as it has been proven to show biostimulant activity in plants, especially in terms of abiotic/biotic stress tolerance and plant growth promotion, representing a sustainable way to ensure yield stability under low input sustainable agriculture. Nevertheless, limited knowledge is available concerning the molecular and physiological processes underlying the root-inoculant symbiosis or plant response at the root system level. Our work aimed to integrate the interrelationship between agronomic traits, rhizosphere microbial population and metabolic processes in roots, following seed treatment with either arbuscular mycorrhizal fungi (AMF) or Plant Growth-Promoting Rhizobacteria (PGPR). To this aim, maize was grown under open field conditions with either optimal or reduced nitrogen availability. Both seed treatments increased nitrogen uptake efficiency under reduced nitrogen supply revealed some microbial community changes among treatments at root microbiome level and limited yield increases, while significant changes could be observed at metabolome level. Amino acid, lipid, flavone, lignan, and phenylpropanoid concentrations were mostly modulated. Integrative analysis of multi-omics datasets (Multiple Co-Inertia Analysis) highlighted a strong correlation between the metagenomics and the untargeted metabolomics datasets, suggesting a coordinate modulation of root physiological traits., (© 2022 The Authors. Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Water deficit is one of the most important climate events that has strong effect on agricultural ecosystem functionality comprising soil microbial communities and their functions. Arbuscular mycorrhizal fungi (AMF) are widely known for their roles in combating drought, including facilitation of drought-tolerant bacteria. However, differences in cultivar/variety affinity for mycorrhization have never been considered as influencing factors. In the present study, we evaluated the influence of mycorrhizal affinity of two durum wheat (T. turgidum subsp. Durum (Desf.)) varieties, Iride and Ramirez (high and low, respectively) on root and soil bacteriomes under well-watered and drought conditions. We used the 16S metagenomics approach (amplicon sequencing) to assess the bacterial communities of root and soil samples. The suppression effect of drought was evident across a wide range of bacterial taxa, including drought-tolerant taxa, especially in the non-inoculated plants. Nevertheless, the protective effect of AMF was also shown, especially in the Iride variety (high AMF colonization affinity) in both compartments (root and soil), as the relative abundance of drought-depleted taxa, such as Planctomycetes, Bacteroidetes and Verrucomicrobia, was either similar under well-watered and water deficit conditions or increased under water deficit conditions. Moreover, drought reduced the network complexity of root and soil bacteria, especially in Ramirez variety which has a lower AMF colonization affinity. Together, our results suggest that not only AMF colonization, but also host plant colonization affinity is one of the regulating factors in alleviating drought-induced changes in wheat plants by altering plant-fungal-bacterial interactions. • Wheat varieties Iride and Ramirez have high and low mycorrhizal affinities, respectively. • Influence of mycorrhizal affinity of both varieties on root and soil bacteriomes under well-watered and drought conditions was analyzed. • Drought reduced the network complexity of root and soil bacteria, especially in Ramirez variety. • Higher colonization affinity of Iride resulted in a higher bacterial resilience to drought stress. • Host plant mycorrhizal affinity is one of the key factors in alleviating drought-induced changes. [ABSTRACT FROM AUTHOR]