Rhizosphere microbial communities adapt their structural and functional compositions to water scarcity and have the potential to substantially mitigate drought stress of crops. To unlock this potential, it is crucial to understand community responses to drought in the complex interplay between soil properties, agricultural management and crop species. Two winter wheat cultivars, demanding and non-demanding, were exposed to drought stress in loamy Chernozem and sandy Luvisol soils under conventional or organic farming management. Structural and functional adaptations of the rhizosphere bacteria were assessed by 16S amplicon sequencing, the predicted abundance of drought-related functional genes in the bacterial community based on 16S amplicon sequences (Tax4Fun) and the activity potentials of extracellular enzymes involved in the carbon cycle. Bacterial community composition was strongly driven by drought and soil type. Under drought conditions, Gram-positive phyla became relatively more abundant, but either less or more diverse in Luvisol and Chernozem soil respectively. Enzyme activities and functional gene abundances related to carbon degradation were increased under drought in the rhizosphere of the demanding wheat cultivar in organic farming. We demonstrate that soil type, farming system and wheat cultivar each constitute important factors during the structural and/or functional adaptation of rhizobacterial communities in response to drought.

Climate and agricultural practice interact to influence both crop production and soil microbes in agroecosystems. Here, we carried out a unique experiment in Central Germany to simultaneously investigate the effects of climates (ambient climate vs. future climate expected in 50-70 years), agricultural practices (conventional vs. organic farming), and their interaction on arbuscular mycorrhizal fungi (AMF) inside wheat (Triticum aestivum L.) roots. AMF communities were characterized using Illumina sequencing of 18S rRNA gene amplicons. We showed that climatic conditions and agricultural practices significantly altered total AMF community composition. Conventional farming significantly affected the AMF community and caused a decline in AMF richness. Factors shaping AMF community composition and richness at family level differed greatly among Glomeraceae, Gigasporaceae and Diversisporaceae. An interactive impact of climate and agricultural practices was detected in the community composition of Diversisporaceae. Organic farming mitigated the negative effect of future climate and promoted total AMF and Gigasporaceae richness. AMF richness was significantly linked with nutrient content of wheat grains under both agricultural practices.

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Climate change models predict more frequent and prolonged drought events in Central Europe, which will exert extraordinary pressure on agroecosystems. One of the consequences is drought-related nutrient limitations for crops negatively affecting agricultural productivity. These effects can be mitigated by beneficial plant growth promoting rhizobacteria. In this study, we investigated the potential of cultivable bacterial species for phosphate solubilization in the rhizosphere of winter wheat at two relevant growth stages-stem elongation and grain filling stages. Rhizosphere samples were collected in the Global Change Experimental Facility in Central Germany, which comprises plots with conventional and organic farming systems under ambient and future climate. Phosphate-solubilizing bacteria were selectively isolated on Pikovskaya medium, phylogenetically classified by 16S rRNA sequencing, and tested for in vitro mineral phosphate solubilization and drought tolerance using plate assays. The culture isolates were dominated by members of the genera Phyllobacterium, Pseudomonas and Streptomyces. Cultivation-derived species richness and abundance of dominant taxa, especially within the genera Phyllobacterium and Pseudomonas, as well as composition of Pseudomonas species were affected by wheat growth stage. Pseudomonas was found to be more abundant at stem elongation than at grain filling, while for Phyllobacterium the opposite pattern was observed. The abundance of Streptomyces isolates remained stable throughout the studied growth stages. The temporal shifts in the cultivable fraction of the community along with considerable P solubilization potentials of Phyllobacterium and Pseudomonas species suggest functional redundancy between and among genera at different wheat growth stages. Phosphate-solubilizing Phyllobacterium species were assigned to Phyllobacterium

Land use is a key factor driving changes in soil carbon (C) cycle and contents worldwide. The priming effect (PE)—CO2 emissions from changed soil organic matter decomposition in response to fresh C inputs—is one of the most unpredictable phenomena associated with C cycling and related nutrient mobilization. Yet, we know very little about the influence of land use on soil PE across contrasting environments. Here, we conducted a continental‐scale study to (i) determine the PE induced by 13C‐glucose additions to 126 cropland and seminatural (forests and grasslands) soils from 22 European countries; (ii) compare PE magnitude in soils under various crop types (i.e., cereals, nonpermanent industrial crops, and orchards); and (iii) model the environmental factors influencing PE. On average, PEs were negative in seminatural (with values ranging between −60 and 26 µg C g−1 soil after 35 days of incubation; median = −11) and cropland (from −55 to 27 µC g−1 soil; median = −4.3) soils, meaning that microbial communities preferentially switched from soil organic C decomposition to glucose mineralization. PE was significantly less negative in croplands compared with seminatural ecosystems and not influenced by the crop type. PE was driven by soil basal respiration (reflecting microbial activity), microbial biomass C, and soil organic C, which were all higher in seminatural ecosystems compared with croplands. This cross European experimental and modeling study elucidated that PE intensity is dependent on land use and allowed to clarify the factors regulating this important C cycling process.