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Riverine islands are widespread alluvium wetlands developed in large rivers, and bacterial communities are crucial to their ecological function, yet their assembly processes are rarely addressed. The ecosystem services provided by the middle and the lower Yangtze are primarily threatened by pollution discharge from agricultural land use, and resource overutilization (e.g., embankments), respectively. Here, we assessed bacterial community assembly processes and their drivers within riverine islands in the middle Yangtze River (MR islands) and those in the lower reach (LR islands). A significant distance–decay relationship was observed, although the turnover rate was lower than that of the terrestrial ecosystem with less connectivity. Deterministic and stochastic processes jointly shaped community patterns, and the influence of stochastic increased from 26% in MR islands to 59% for those in LR islands. Meanwhile, the bacterial community in MR islands was controlled more by inorganic nitrogen availability, whereas those in LR islands were governed by pH and EC, although those factors explained a limited fraction of variation in the bacterial community. Potential indicator taxa (affiliated with Nocardioides and Lysobacter ) characterized the waterway transport pollution. Overall, our study demonstrated that bacterial community dissimilarity and the importance of dispersal limitation increased concurrently along the flow direction, while distinct local factors further determined bacterial community compositions by selecting habitat-specificity taxa and particularly metabolism function. These findings enhanced our understanding of the mechanisms driving changes in bacterial communities of riverine islands subject to increased anthropogenic impacts. IMPORTANCE Rivers are among the most threatened ecosystems globally and face multiple stressors related to human activity. However, linkages between microbial diversity patterns and assembly processes in rivers remain unclear, especially in riverine islands developed in large rivers. Our findings reveal that distinct factors result in divergent bacterial community compositions and functional profiles in the riverine islands in the middle Yangtze and those in the lower Yangtze, with substantial differentiation in deterministic and stochastic processes that jointly contribute to bacterial community assemblages. Additionally, keystone species may play important metabolic roles in coping with human-related disturbances. This study provides an improved understanding of relationships between microbial diversity patterns and ecosystem functions under environmental changes in large river ecosystems.
Riverine islands are widespread alluvium wetlands developed in large rivers, and bacterial communities are crucial to their ecological function, yet their assembly processes are rarely addressed. The ecosystem services provided by the middle and the lower Yangtze are primarily threatened by pollution discharge from agricultural land use, and resource overutilization (e.g., embankments), respectively. Here, we assessed bacterial community assembly processes and their drivers within riverine islands in the middle Yangtze River (MR islands) and those in the lower reach (LR islands). A significant distance–decay relationship was observed, although the turnover rate was lower than that of the terrestrial ecosystem with less connectivity. Deterministic and stochastic processes jointly shaped community patterns, and the influence of stochastic increased from 26% in MR islands to 59% for those in LR islands. Meanwhile, the bacterial community in MR islands was controlled more by inorganic nitrogen availability, whereas those in LR islands were governed by pH and EC, although those factors explained a limited fraction of variation in the bacterial community. Potential indicator taxa (affiliated with Nocardioides and Lysobacter ) characterized the waterway transport pollution. Overall, our study demonstrated that bacterial community dissimilarity and the importance of dispersal limitation increased concurrently along the flow direction, while distinct local factors further determined bacterial community compositions by selecting habitat-specificity taxa and particularly metabolism function. These findings enhanced our understanding of the mechanisms driving changes in bacterial communities of riverine islands subject to increased anthropogenic impacts. IMPORTANCE Rivers are among the most threatened ecosystems globally and face multiple stressors related to human activity. However, linkages between microbial diversity patterns and assembly processes in rivers remain unclear, especially in riverine islands developed in large rivers. Our findings reveal that distinct factors result in divergent bacterial community compositions and functional profiles in the riverine islands in the middle Yangtze and those in the lower Yangtze, with substantial differentiation in deterministic and stochastic processes that jointly contribute to bacterial community assemblages. Additionally, keystone species may play important metabolic roles in coping with human-related disturbances. This study provides an improved understanding of relationships between microbial diversity patterns and ecosystem functions under environmental changes in large river ecosystems.
Background Excessive fertilization and tillage erosion pose threats to food security and crop yields. A transition towards more sustainable agricultural practices may be advanced by harnessing ecosystem services provided by plant microbiomes. However, targeting microbiota at the agroecosystem scale necessitates bridging the gap to micro-scale structures of microbiomes. We hypothesized, that relevant changes of microbial N cycle guilds in the rhizosphere of rye align with a soil catena determined by tillage erosion. Aboveground patterns of crop biomass along such a catena persist in hummocky landscapes and are of practical relevance to farmers. Results The rhizosphere of the topsoil at four typical soils in an arable field grown with rye within the Quillow catchment (NE Germany) was sampled. The soils represent a complete tillage erosion gradient from an extremely eroded Calcaric Regosol over a strongly eroded Nudiargic Luvisol to a non-eroded Calcic Luvisol and colluvial Gleyic-Colluvic Regosols. Gene abundances characteristic of microbial N cycle guilds were analysed using shotgun metagenomic sequencing. Distinct growth of rye plants along the catena was correlated with the nitrogen cycle functions of the rhizosphere microbiome based on multivariate analyses. Gene ratios describing differential denitrification potential of the microbiome differed significantly between soils. The norBC gene abundance was most strongly coupled to plant productivity, which is likely due to its involvement into multiple plant microbiome interactions besides denitrification. Genes associated with DNRA and diazotrophy prevailed at eroded soils. The eroded sites showed the lowest plant productivity and soil mineral N availability. Additionally, N limitation at the eroded sites was implied by the lowered gdh to glnA ratio and its association to plant productivity compared to the depositional site. Conclusions Thus, gradients in legacy of agricultural management such as tillage erosion capture substantial changes in rhizosphere microbiome functionality. These specific microbiome assembly patterns are a function of above ground in field-plant productivity patterns accessible by remote sensing. Thus, the interrelation of in-field crop biomass patterns and the rhizosphere microbiome opens up the opportunity to assess distribution patterns of plant microbiota functional distribution at scales relevant to agricultural production and agroecosystems functioning.
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