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Bacteria and fungi are core microorganisms in diverse ecosystems, and their cross‐kingdom interactions are considered key determinants of microbiome structure and ecosystem functioning. However, how bacterial‐fungal interactions mediate soil organic carbon (SOC) dynamics remains largely unexplored in the context of artificial forest ecosystems.Here, we characterised soil bacterial and fungal communities in four successive planting of Eucalyptus and compared them to a neighbouring evergreen broadleaf forest. Carbon (C) mineralisation combined with five C‐degrading enzymatic activities was investigated to determine the effects of successive planting of Eucalyptus on SOC dynamics.Our results indicated that successive planting of Eucalyptus significantly altered the diversity and structure of soil bacterial and fungal communities and increased the negative bacterial‐fungal associations. The bacterial diversity significantly decreased in all Eucalyptus plantations compared to the evergreen forest, while the fungal diversity showed the opposite trend. The ratio of negative bacterial‐fungal associations increased with successive planting of Eucalyptus due to the decrease in SOC, ammonia nitrogen (NH4+‐N), nitrate nitrogen (NO3−‐N) and available phosphorus (AP). Structural equation modelling indicated that the potential cross‐kingdom competition, based on the ratio of negative bacterial‐fungal correlations, was significantly negatively associated with the diversity of total bacteria and keystone bacteria, thereby increasing C‐degrading enzymatic activities and C mineralisation.Synthesis and applications: Our results highlight the regulatory role of the negative bacterial‐fungal association in enhancing the correlation between bacterial diversity and C mineralisation. This suggests that promoting short‐term successive planting in the management of Eucalyptus plantations can mitigate the impact of this association on SOC decomposition. Taken together, our study advances the understanding of bacterial‐fungal negative associations to mediate carbon mineralisation in Eucalyptus plantations, giving us a new insight into SOC cycling dynamics in artificial forests. [ABSTRACT FROM AUTHOR]

Terrestrial plants can affect the growth and health of adjacent plants via interspecific interaction. Here, we studied the mechanism by which plant root exudates affect the recruitment of the rhizosphere microbiome in adjacent plants—with implications for plant protection—using a tomato (Solanum lycopersicum)–potatoonion (Allium cepa var. agrogatum) intercropping system. First, we showed that the intercropping system results in a disease-suppressive rhizosphere microbiome that protects tomato plants against Verticillium wilt disease caused by the soilborne pathogen Verticillium dahliae. Second, 16S rRNA gene sequencing revealed that intercropping with potatoonion altered the composition of the tomato rhizosphere microbiome by promoting the colonization of specific Bacillus sp. This taxon was isolated and shown to inhibit V. dahliae growth and induce systemic resistance in tomato plants. Third, a belowground segregation experiment found that root exudates mediated the interspecific interaction between potatoonion and tomato. Moreover, experiments using split-root tomato plants found that root exudates from potatoonion, especially taxifolin—a flavonoid compound—stimulate tomato plants to recruit plant-beneficial bacteria, such as Bacillus sp. Lastly, ultra-high-pressure liquid chromatography–mass spectrometry analysis found that taxifolin alters tomato root exudate chemistry; thus, this compound acts indirectly in modulating root colonization by Bacillus sp. Our results revealed that this intercropping system can improve tomato plant fitness by changing rhizosphere microbiome recruitment via the use of signaling chemicals released by root exudates of potatoonion. This study revealed a novel mechanism by which interspecific plant interaction modulates the establishment of a disease-suppressive microbiome, thus opening up new avenues of research for precision plant microbiome manipulations. Intercropping with potatoonions can enhance tomato resistance to Verticillium wilt disease by changing rhizosphere microbiome recruitment via root-exudate-mediated belowground interspecific plant interaction. Experiments suggest that root exudates from potatoonions, especially taxifolin—a flavonoid compound—alter tomato root exudate chemistry and recruit plant-beneficial bacteria, such as Bacillus sp. [ABSTRACT FROM AUTHOR]

Soil bacterial communities play fundamental roles in ecosystem functioning and often display a skewed distribution of abundant and rare taxa. So far, relatively little is known about the biogeographical patterns and mechanisms structuring the assembly of abundant and rare biospheres of soil bacterial communities. Here, we studied the geographical distribution of different bacterial sub‐communities by examining the relative influence of environmental selection and dispersal limitation on taxa distributions in paddy soils across East Asia. Our results indicated that the geographical patterns of four different bacterial sub‐communities consistently displayed significant distance–decay relationships (DDRs). In addition, we found niche breadth and dispersal rates to significantly explain differences in community assembly of abundant and rare taxa, directly affecting the strength of DDRs. While conditionally rare and abundant taxa displayed the strongest DDR due to higher environmental filtering and dispersal limitation, moderate taxa sub‐communities had the weakest DDR due to greater environmental tolerance and dispersal rate. Random forest models indicated that soil pH (9.13%–49.78%) and average annual air temperature (16.59%–46.49%) were the most important predictors of the variation in the bacterial community. This study advances our understanding of the intrinsic links between fundamental ecological processes and microbial biogeographical patterns in paddy soils. [ABSTRACT FROM AUTHOR]

Microorganisms play essential roles in soil ecosystem functioning and maintenance, but methods are currently lacking for quantitative assessments of the mechanisms underlying microbial diversity patterns observed across disparate systems and scales. Here we established a quantitative model to incorporate pH into metabolic theory to capture and explain some of the unexplained variation in the relationship between temperature and soil bacterial diversity. We then tested and validated our newly developed models across multiple scales of ecological organization. At the species level, we modeled the diversification rate of the model bacterium Pseudomonas fluorescens evolving under laboratory media gradients varying in temperature and pH. At the community level, we modeled patterns of bacterial communities in paddy soils across a continental scale, which included natural gradients of pH and temperature. Last, we further extended our model at a global scale by integrating a meta-analysis comprising 870 soils collected worldwide from a wide range of ecosystems. Our results were robust in consistently predicting the distributional patterns of bacterial diversity across soil temperature and pH gradients--with model variation explaining from 7 to 66% of the variation in bacterial diversity, depending on the scale and system complexity. Together, our study represents a nexus point for the integration of soil bacterial diversity and quantitative models with the potential to be used at distinct spatiotemporal scales. By mechanistically representing pH into metabolic theory, our study enhances our capacity to explain and predict the patterns of bacterial diversity and functioning under current or future climate change scenarios. [ABSTRACT FROM AUTHOR]

Sorghum is a major staple crop in sub-Saharan Africa with yields severely impacted by biotic and abiotic factors. Here, we analysed the taxonomic diversity and biogeographical distribution of bacterial taxa of 48 agricultural fields along a transect of approximately 2000 km across the Ethiopian sorghum belt, the centre of origin of sorghum. The ultimate goal is to identify—yet-unexplored—beneficial plant–microbe associations. Based on bulk soil bacterial communities and DArT-SNP analyses of 59 sorghum accessions, we selected three microbiologically distinct field soils and 12 sorghum genotypes, including commercial varieties, wild relatives, and farmer-preferred landraces. The results showed a core rhizosphere microbiome of 2125 amplicon sequence variants (ASVs), belonging to eight bacterial families consistently found across the three soil types and the 12 sorghum genotypes. Integration of the rhizosphere bacterial community analysis with DArT-SNP sorghum genotyping revealed the association of differentially abundant ASVs with sorghum genotypic traits, including the distinct recruitment of Pseudomonadaceae by the stay-green, drought-tolerant, and wild sorghum genotypes. Collectively, these results provide new insights into the core and accessory bacterial taxa in the sorghum rhizosphere in the centre of origin, setting a baseline for targeted isolation and functional characterization of putative beneficial rhizobacteria. [ABSTRACT FROM AUTHOR]

Beneficial host-associated bacteria can assist plant protection against pathogens. In particular, specific microbes are able to induce plant systemic resistance. However, it remains largely elusive which specific microbial taxa and functions trigger plant immune responses associated with disease suppression. Here, we experimentally studied this by setting up two independent microcosm experiments that differed in the time at which plants were exposed to the pathogen and the soil legacy (i.e., soils with historically suppressive or conducive). Overall, we found soil legacy effects to have a major influence on disease suppression irrespective of the time prior to pathogen exposure. Rhizosphere bacterial communities of tomato plants were significantly different between the two soils, with potential beneficial strains occurring at higher relative abundances in the suppressive soil. Root transcriptome analysis revealed the soil legacy to induce differences in gene expression, most importantly, genes involved in the pathway of phenylpropanoid biosynthesis. Last, we found genes in the phenylpropanoid biosynthesis pathway to correlate with specific microbial taxa, including Gp6, Actinomarinicola, Niastella, Phaeodactylibacter, Longimicrobium, Bythopirellula, Brevundimonas, Ferruginivarius, Kushneria, Methylomarinovum, Pseudolabrys, Sphingobium, Sphingomonas, and Alterococcus. Taken together, our study points to the potential regulation of plant systemic resistance by specific microbial taxa, and the importance of soil legacy on disease incidence and eliciting plant-defense mechanisms. [ABSTRACT FROM AUTHOR]

Plant roots are colonized by a multitude of microbial taxa that dynamically influence plant health. Plant-microbe interactions at the root-soil interface occur at the micro-scale and are affected by variation in root phenotypes. Different root phenotypes can have distinct impacts on physical and chemical gradients at the root-soil interface, leading to heterogeneous microhabitats for microbial colonization. Microbes that influence plant physiology will establish across these heterogeneous microhabitats, and, therefore, exploiting variation in root phenotypes can allow for targeted manipulation of plant-associated microbes. In this mini-review, we discuss how changes in root anatomy and architecture can influence resource availability and the spatial configuration of microbial microhabitats. We then propose research priorities that integrate root phenotypes and microbial microhabitats for advancing the manipulation of root-associated microbiomes. We foresee the yet-unexplored potential to harness diverse root phenotypes as a new level of precision in microbiome management in plant-root systems. [ABSTRACT FROM AUTHOR]