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Progress and challenges in exploring aquatic microbial communities using non-targeted metabolomics

Advances in bioanalytical technologies are constantly expanding our insights into complex ecosystems. Here, we highlight strategies and applications that make use of non-targeted metabolomics methods in aquatic chemical ecology research and discuss opportunities and remaining challenges of mass spectrometry-based methods to broaden our understanding of environmental systems.

The mechanism effects of root exudate on microbial community of rhizosphere soil of tree, shrub, and grass in forest ecosystem under N deposition

Forests are composed of various plant species, and rhizosphere soil microbes are driven by root exudates. However, the interplay between root exudates, microbial communities in the rhizosphere soil of canopy trees, understory shrubs, grasses, and their responses to nitrogen (N) deposition remains unclear. Pinus tabulaeformis, Rosa xanthina, and Carex lancifolia were used to investigate root exudates, rhizosphere soil microbial communities, and their responses to N application in forest ecosystem. Root exudate abundances of P. tabulaeformis were significantly higher than that of R. xanthina and C. lancifolia, with carbohydrates dominating P. tabulaeformis and R. xanthina root exudates, fatty acids prevailing in C. lancifolia root exudates. Following N application, root exudate abundances of P. tabulaeformis and R. xanthina initially increased before decreasing, whereas those of C. lancifolia decreased. Microbial number of rhizosphere soil of C. lancifolia was higher than that of P. tabulaeformis and R. xanthina, but there was insignificant variation of rhizosphere soil microbial diversity among plant species. N application exerted promotional and inhibitory impacts on bacterial and fungal numbers, respectively, while bacterial and fungal diversities were increased by N application. Overall, N application had negative effects on root exudates of P. tabulaeformis, inhibiting rhizosphere soil microbial populations. N application suppressed rhizosphere soil microbial populations by increasing root exudates of R. xanthina. Conversely, N application elevated nutrient content in the rhizosphere soil of C. lancifolia, reducing root exudates and minimally promoting microbial populations. This study highlights the importance of understory vegetation in shaping soil microbial communities within forests under N deposition.

High intensity perturbations induce an abrupt shift in soil microbial state

Soil microbial communities play a pivotal role in regulating ecosystem functioning. But they are increasingly being shaped by human-induced environmental change, including intense “pulse” perturbations, such as droughts, which are predicted to increase in frequency and intensity with climate change. While it is known that soil microbial communities are sensitive to such perturbations and that effects can be long-lasting, it remains untested whether there is a threshold in the intensity and frequency of perturbations that can trigger abrupt and persistent transitions in the taxonomic and functional characteristics of soil microbial communities. Here we demonstrate experimentally that intense pulses of drought equivalent to a 30-year drought event (<15% WHC) induce a major shift in the soil microbial community characterised by significantly altered bacterial and fungal community structures of reduced complexity and functionality. Moreover, the characteristics of this transformed microbial community persisted after returning soil to its previous moisture status. As a result, we found that drought had a strong legacy effect on bacterial community function, inducing an enhanced growth rate following subsequent drought. Abrupt transitions are widely documented in aquatic and terrestrial plant communities in response to human-induced perturbations. Our findings demonstrate that such transitions also occur in soil microbial communities in response to high intensity pulse perturbations, with potentially deleterious consequences for soil health.

Extreme drought-heatwave events threaten the biodiversity and stability of aquatic plankton communities in the Yangtze River ecosystems

Rivers are crucial to biogeochemical cycles, connecting terrestrial, oceanic, and atmospheric systems. However, their ecosystems are increasingly threatened by extreme weather events. Here we used the environmental DNA approach to assess the impact of extreme drought-heatwave events on the aquatic plankton communities of the Yangtze River. We showed that an extreme drought-heatwave event reduced the α diversity of communities, increased their β diversity, and simultaneously simplified and destabilized community network structure. This event also shifted the dominant algae taxa from Bacillariophyta to Cyanobacteria, accompanied by increases in organic carbon and labile organic carbon contents. Globally, temperature rises during this extreme drought-heatwave event are more pronounced in high-latitude regions, likely amplifying impacts on river ecosystem biodiversity and stability. Our findings highlight the vulnerability of river ecosystems to extreme events and underscore the need to mitigate climate change’s effects on river ecosystems.

Microbial phosphorus recycling in soil by intra- and extracellular mechanisms

Rising global stoichiometric imbalance between increasing nitrogen (N) availability and depleting phosphorus (P) resources increases the importance of soil microbial P recycling. The contribution of extra- versus intracellular P (re-)cycling depending on ecosystem nutrient status is vastly unclear, making soil microorganisms a blind spot in our understanding of ecosystem responses to increasing P deficiency. We quantified P incorporation into microbial DNA and phospholipids by 33P labeling under contrasting conditions: low/high P soil × low/high carbon (C)NP application. By combining 33P and 14C labeling with tracing of microbial community biomarkers and functional genes, we disengaged the role of DNA and phospholipids in soil P cycling. Microorganisms in low P soil preferentially allocated P to phospholipids with an acceleration of phospholipids metabolism driven by C addition, which was strongly related to high abundances of microbial community members (e.g. some G-) with a fast phospholipids turnover. In high P soil, however, more P was allocated to DNA with a microbial functional shift towards DNA synthesis to support a replicative growth when sufficient C was supplied, which was coupled with a strong enrichment of fungal copiotrophs and microbial genes coding DNA primase. Consequently, adaptation to low P availability accelerated microbial intracellular P recycling through reutilization of the P stored in phospholipids. However, microorganisms under high P availability commonly adopted extracellular P recycling with release and reuse of DNA P by microbial death-growth dynamics. These results advance our understanding on microbial adaptation to P deficiency in soil by regulating component-specific P pathways and reflect the specific functions of phospholipids and DNA for P recycling.

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