Plants with arbuscular mycorrhizal fungi efficiently acquire nitrogen from substrate additions by shaping the decomposer community composition and their net plant carbon demand

Aims: We investigated the role of plants and their plant-derived carbon in shaping the microbial community that decomposes substrates and traced the return of nutrients from decomposition back to plant shoots in order to understand the importance of plants for ecosystem element cycling. Methods: We performed a greenhouse experiment having plant communities with and without arbuscular mycorrhizal fungi (AMF) and ingrowth cores that held different 15N labeled substrates. We determined the microbial community structure using molecular sequencing and the net assimilation of plant carbon into soil microorganisms using a 13CO2 pulse and 13C measurements of microbial biomarkers. We determined the return of nitrogen back to the shoots using the 15N signal, which was provided from the decomposition of the substrate added to the ingrowth cores. Results: We observed that the microbial community composition in the ingrowth cores and their net 13C assimilation depended on the presence of AMF and the added substrate. Both plant communities had similar 15N uptake into their shoots, but the net N uptake cost was significantly lower in presence of AMF. In the presence of AMF also lower net N uptake cost was observed for the decomposition of plant-derived and microorganism-derived substrates compared to inorganic nitrogen suggesting that AMF actively controls the decomposer comunity and their carbon demand. Conclusion: Our results identify for the first time a functional overlap of soil microorganisms as identical substrate is decomposed by different microorganisms suggesting functional redundancy of microbial communities. In consequence a better understanding of ecosystem element cycling can only be achieved when the whole plant-microorganism-organic matter-soil continuum is investigated

Soil fungal : Bacterial ratios are linked to altered carbon cycling

Acknowledgments We thank Steffen Ruehlow, Agnes Fastnacht, Karl Kuebler, Iris Kuhlmann, Heike Geilmann, and Petra Linke for technical support in establishing the experiment and with stable isotope analyses. We also thank Markus Lange, Daniel Read, and Hyun Gweon for helpful discussions. Funding AM has received funding from Max Planck Society and the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 655240. AM has also received a career orientation grant from the Jena School for Microbial Communication (JSMC) that funded the laboratory visits. DFG SFB Aquadiva funded part of this work.Peer reviewedPublisher PD

Storage of carbon reserves in spruce trees is prioritized over growth in the face of carbon limitation

Climate change is expected to pose a global threat to forest health by intensifying extreme events like drought and insect attacks. Carbon allocation is a fundamental process that determines the adaptive responses of long-lived late-maturing organisms like trees to such stresses. However, our mechanistic understanding of how trees coordinate and set allocation priorities among different sinks (e.g., growth and storage) under severe source limitation remains limited. Using flux measurements, isotopic tracing, targeted metabolomics, and transcriptomics, we investigated how limitation of source supply influences sink activity, particularly growth and carbon storage, and their relative regulation in Norway spruce (Picea abies) clones. During photosynthetic deprivation, absolute rates of respiration, growth, and allocation to storage all decline. When trees approach neutral carbon balance, i.e., daytime net carbon gain equals nighttime carbon loss, genes encoding major enzymes of metabolic pathways remain relatively unaffected. However, under negative carbon balance, photosynthesis and growth are down-regulated while sucrose and starch biosynthesis pathways are up-regulated, indicating that trees prioritize carbon allocation to storage over growth. Moreover, trees under negative carbon balance actively increase the turnover rate of starch, lipids, and amino acids, most likely to support respiration and mitigate stress. Our study provides molecular evidence that trees faced with severe photosynthetic limitation strategically regulate storage allocation and consumption at the expense of growth. Understanding such allocation strategies is crucial for predicting how trees may respond to extreme events involving steep declines in photosynthesis, like severe drought, or defoliation by heat waves, late frost, or insect attack.DATA AVAILABITY : All study data are included in the article and/or supporting information. Transcriptome data have been deposited in the NCBI database under BioProject accession no. PRJNA751264.Max Planck Society.https://www.pnas.orghj2022BiochemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant Patholog

Land use driven change in soil pH affects microbial carbon cycling processes

Soil microorganisms act as gatekeepers for soil–atmosphere carbon exchange by balancing the accumulation and release of soil organic matter. However, poor understanding of the mechanisms responsible hinders the development of effective land management strategies to enhance soil carbon storage. Here we empirically test the link between microbial ecophysiological traits and topsoil carbon content across geographically distributed soils and land use contrasts. We discovered distinct pH controls on microbial mechanisms of carbon accumulation. Land use intensification in low-pH soils that increased the pH above a threshold (~6.2) leads to carbon loss through increased decomposition, following alleviation of acid retardation of microbial growth. However, loss of carbon with intensification in near-neutral pH soils was linked to decreased microbial biomass and reduced growth efficiency that was, in turn, related to trade-offs with stress alleviation and resource acquisition. Thus, less-intensive management practices in near-neutral pH soils have more potential for carbon storage through increased microbial growth efficiency, whereas in acidic soils, microbial growth is a bigger constraint on decomposition rates

Effect of plant inputs and nutrient acquisition strategies on soil microbial community

Plant associated soil microbial communities play a critical role in productivity of Earth's ecosystems as they ensure cycling of key elements. Specifically, plant biodiversity losses alters soil microbial communities and can have significant consequences for plant resistance to biotic and abiotic stress. Across a biodiversity gradient this thesis found that bacterial communities are uncoupled from plant diversity. However, specific groups of bacteria respond to changes in plant diversity. Plant and soil factors clearly favoured different bacterial groups and notably on the lines of their growth strategies, with plants selecting fast growing species and negatively influencing groups that are antagonistic and slow growing. Furthermore, plant diversity not only altered fungal diversity but demonstrated specific effects on fungal guilds. Due to the highlighted importance of fungal association a pot experiment controlling for AMF association was also carried out to observe effects of the fungal association on decomposition of stoichiometrically similar organic matter types and examine carbon-nitrogen trade between plant and associated microbial community. Arbuscular mycorrhizal Fungi (AMF) associated plants allocated more carbon to their roots but due to assistance of AMF incurred a lower cost of nutrient acquisition. Additionally, distinct microbial communities were fostered in presence of symbiotic fungal associations possibly explaining the amount of carbon used for exchange of nutrients from decomposing organic matter. In conclusion, the data compiled in this thesis shows plant diversity and their microbial association related traits are important modifiers of soil microbial communities. In summary, in a multispecies environment microbial associations are a fundamental part of efficient nutrient acquisition from decomposing organic matter in soil

Selective Imaging of Quorum Sensing Receptors in Bacteria Using Fluorescent Au Nanocluster Probes Surface Functionalized with Signal Molecules

Fluorescent ultrasmall gold clusters decorated with bacterial quorum sensing signal molecules, acyl homoserine lactone, are synthesized. These fluorescent probes are found to have emission in the near-infrared spectral region advantageous for bioimaging. Imaging studies using different strains of bacteria with and without acyl homoserine lactone receptors with the aid of confocal microscopy have shown that the probe interacts preferentially with cells possessing these receptors. This indicates that, with appropriate surface functionalization, the Au clusters can be used for receptor specific detection with enhanced selectivity

Secretor Status Is Strongly Associated with Microbial Alterations Observed during Pregnancy

<div><p>During pregnancy there are significant changes in gut microbiota composition and activity. The impact of secretor status as determined by genotyping <i>FUT2</i> (fucosyltransferase 2) gene was taken as one of the confounding factors associated with faecal microbiota changes during pregnancy. In this prospective study, we followed women during pregnancy (total = 123 of which secretors = 108, non-secretors = 15) and characterised their gut microbiota by quantitative polymerase chain reaction (qPCR), Fluorescence In situ Hybridisation (FISH), Denaturing Gradient Gel Electrophoresis (DGGE) and pyrosequencing. qPCR revealed that <i>C</i>. <i>coccoides group</i> counts decreased significantly in non-secretors in comparison to secretors (p = 0.02). Similar tendency was found by FISH analysis in <i>Clostridium histolyticum</i> and <i>Lactobacillus-Enterococcus</i> groups between the secretor and the non-secretor pregnant women. DGGE analysis showed significant decrease in richness of <i>Clostridium</i> sp. between secretor and non-secretor mothers during pregnancy. Pyrosequencing based analysis at phyla level showed that there is greater increase in Actinobacteria in secretors in comparison to non-secretors, whereas Proteobacteria showed more increase in non-secretors. Change in relative abundance of <i>Clostridiaceae</i> family from first to third trimester were significantly associated with secretor status of pregnant women (p = 0.05). Polyphasic approach for microbiota analysis points out that the host secretor status (FUT2 genotype) affects the gut microbiota during pregnancy. This may lead to altered infant gut microbiota colonization.</p></div