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Microbiome-based solutions are regarded key for sustainable agroecosystems. However, it is unclear how agricultural practices affect the rhizosphere microbiome, plant–microorganism interactions and crop performance under field conditions. Therefore, we installed root observation windows in a winter wheat field cultivated either under long-term mouldboard plough (MP) or cultivator tillage (CT). Each tillage practice was also compared at two nitrogen (N) fertilization intensities, intensive (recommended N-supply with pesticides/growth regulators) or extensive (reduced N-supply, no fungicides/growth regulators). Shoot biomass, root exudates and rhizosphere metabolites, physiological stress indicators, and gene expression were analyzed together with the rhizosphere microbiome (bacterial/archaeal 16S rRNA gene, fungal ITS amplicon, and shotgun metagenome sequencing) shortly before flowering. Compared to MP, the rhizosphere of CT winter wheat contained more primary and secondary metabolites, especially benzoxazinoid derivatives. Potential copiotrophic and plant-beneficial taxa (e.g. Bacillus, Devosia, and Trichoderma) as well as functional genes (e.g. siderophore production, trehalose synthase, and ACC deaminase) were enriched in the CT rhizosphere, suggesting that tillage affected belowground plant–microorganism interactions. In addition, physiological stress markers were suppressed in CT winter wheat compared to MP. In summary, tillage practice was a major driver of crop performance, root deposits, and rhizosphere microbiome interactions, while the N-fertilization intensity was also relevant, but less important., Microbiome-based solutions are regarded key for sustainable agroecosystems. However, it is unclear how agricultural practices affect the rhizosphere microbiome, plant–microorganism interactions and crop performance under field conditions. Therefore, we installed root observation windows in a winter wheat field cultivated either under long-term mouldboard plough (MP) or cultivator tillage (CT). Each tillage practice was also compared at two nitrogen (N) fertilization intensities, intensive (recommended N-supply with pesticides/growth regulators) or extensive (reduced N-supply, no fungicides/growth regulators). Shoot biomass, root exudates and rhizosphere metabolites, physiological stress indicators, and gene expression were analyzed together with the rhizosphere microbiome (bacterial/archaeal 16S rRNA gene, fungal ITS amplicon, and shotgun metagenome sequencing) shortly before flowering. Compared to MP, the rhizosphere of CT winter wheat contained more primary and secondary metabolites, especially benzoxazinoid derivatives. Potential copiotrophic and plant-beneficial taxa (e.g. Bacillus, Devosia, and Trichoderma) as well as functional genes (e.g. siderophore production, trehalose synthase, and ACC deaminase) were enriched in the CT rhizosphere, suggesting that tillage affected belowground plant–microorganism interactions. In addition, physiological stress markers were suppressed in CT winter wheat compared to MP. In summary, tillage practice was a major driver of crop performance, root deposits, and rhizosphere microbiome interactions, while the N-fertilization intensity was also relevant, but less important.

The long-term effects of agricultural management such as different fertilization strategies on soil microbiota and soil suppressiveness against plant pathogens are crucial. Therefore, the suppressiveness of soils differing in fertilization history was assessed using two Rhizoctonia solani isolates and their respective host plants (lettuce, sugar beet) in pot experiments. Further, the effects of fertilization history and the pathogen R. solani AG1-IB on the bulk soil, root-associated soil and rhizosphere microbiota of lettuce were analyzed based on amplicon sequencing of the 16S rRNA gene and ITS2 region. Organic fertilization history supported the spread of the soil-borne pathogens compared to long-term mineral fertilization. The fertilization strategy affected bacterial and fungal community composition in the root-associated soil and rhizosphere, respectively, but only the fungal community shifted in response to the inoculated pathogen. The potential plant-beneficial genus Talaromyces was enriched in the rhizosphere by organic fertilization and presence of the pathogen. Moreover, increased expression levels of defense-related genes in shoots of lettuce were observed in the soil with organic fertilization history, both in the absence and presence of the pathogen. This may reflect the enrichment of potential plant-beneficial microorganisms in the rhizosphere, but also pathogen infestation. However, enhanced defense responses resulted in retarded plant growth in the presence of R. solani (plant growth/defense tradeoff).

Soils with high salinity are often also affected by waterlogging with hypoxic conditions in the root zone, which severely reduces plant growth and crop yield. The combination of salinity and hypoxia generates an intense stress for the plant: On the one hand, hypoxic conditions at the root level cause a severe energy deficit due to the inhibition of oxidative phosphorylation, on the other hand, energy-consuming tolerance mechanisms have to be maintained to cope with salt stress. To better understand the tolerance mechanisms to combined saline and hypoxic conditions, the metabolic and physiological adaptation capacity of the model halophyte Suaeda maritima, typically found in flooded saline soils, and the closely related sugar beet (Beta vulgaris L.) were analysed. Salt tolerant plants are characterised by their ability to tolerate high Na+ and Cl- concentrations without being damaged by ion toxicity. The basis of this tolerance is primarily osmotic adaptation, the compartmentalisation of ions in cell organelles and the ability to replace K+ with Na+ in important cellular processes. Li+ has similar physico-chemical properties to Na+ and K+, but forms complexes with organic and inorganic anions more readily than other alkali metals. Therefore, Li+ can displace metals during the uptake and translocation by the plant and at enzymatic binding sites, which impairs enzyme activity and can lead to toxic effects. The effects of different cations with similar physicochemical properties on their accumulation pattern at high and low osmolarity were investigated to determine whether Li+ toxicity could be mitigated by competitive uptake of K+ and Na+. Hydroponic culture experiments with increasing salt concentration demonstrated the ability of S. maritima and B. vulgaris to tolerate high salt concentrations by maintaining ion homeostasis and high tissue tolerance to Na+ accumulation. An increased Na+/K+ ratio under hypoxic conditions indicates that an energy shortage caused by oxy, Dieser Arbeit befasst sich mit den metabolische und physiologische Anpassungsfähigkeit des Modellhalophyten Suaeda maritima, der typischerweise in überfluteten salzhaltigen Böden vorkommt, und der eng verwandten Zuckerrübe (Beta vulgaris). Salztolerante Pflanzen zeichnen sich durch ihre Fähigkeit aus, hohe Na+ und Cl- Konzentrationen zu tolerieren, ohne durch Ionentoxizität geschädigt zu werden. Die Grundlage dieser Toleranz ist in erster Linie die osmotische Anpassung, die Kompartimentierung von Ionen in Zellorganellen und die Fähigkeit K+ durch Na+ bei wichtigen zellulären Vorgängen zu ersetzen. Li+ hat ähnliche physikalisch-chemische Eigenschaften wie Na+ und K+, reagiert aber leichter als andere Alkalimetalle mit organischen und anorganischen Anionen. Daher kann Li+ andere Metalle bei der Aufnahme und Verlagerung in die Pflanze und an enzymatischen Bindungsstellen verdrängen, was die Enzymaktivität beeinträchtigt und toxisch wirken kann. In einer weiteren Studie wurden die Auswirkungen verschiedener Kationen mit ähnlichen physikalisch-chemischen Eigenschaften auf ihr Akkumulationsmuster bei hoher und niedriger Osmolarität untersucht, um festzustellen, ob die Toxizität von Li+ durch die konkurrierende Aufnahme von K+ und Na+ abgeschwächt werden kann. Experimente in Hydrokulturen mit steigender Salzkonzentration zeigten die Fähigkeit von S. maritima und B. vulgaris, hohe Salzkonzentrationen zu tolerieren, indem sie die Ionenhomöostase aufrechterhalten und eine hohe Gewebetoleranz gegenüber Na+-Akkumulation aufweisen. Ein erhöhtes Na+/K+-Verhältnis unter hypoxischen Bedingungen deutet darauf hin, dass der durch die Reduzierung des Sauerstoffs in der Wurzel verursachte Energiemangel den Na+ Ausschluss und die K+ Aufnahme beeinträchtigt, wodurch das ionische Ungleichgewicht unter hypoxischen Bedingungen verstärkt wird. Das Stoffwechselprofil zeigte eine gewebespezifische Reaktion auf Salinität und Hypoxie: In den Wurzeln wird der Stoffwechsel hauptsächlich von Hypoxi