Carsten Simon

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Simon

First Name

Carsten

ORCID

0000-0003-3882-3013

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Publications 1 - 4 of 4

Stability and carbon uptake of the soil microbial community is determined by differences between rhizosphere and bulk soil
Lange, Markus; Azizi-Rad, Mina; Dittmann, Georg; et al. (2024)
Soil Biology and Biochemistry
The interactions between plants and soil microorganisms are fundamental for ecosystem functioning. However, it remains unclear if seasonality of plant growth impacts plant-microbial interactions, such as by inducing shifts in the microbial community composition, their biomass, or changes in the microbial uptake of plant-derived carbon. Here, we investigated the stability of the microbial community and their net assimilation of plant-derived carbon over an entire growing season. Using a C3–C4 vegetation change experiment, and taking advantage of a natural 13C label, we measured the plant-derived carbon in lipid biomarkers of soil microorganisms in rhizosphere and bulk soil in two soils with contrasting textures. We found that temporal stability was higher in bacterial than in fungal biomass, whereas the spatial stability of the fungal biomass was higher than that of bacterial biomass. Moreover, symbiotic AM fungi tended to be more stable in the uptake of plant-derived carbon than bacteria and saprophytic fungi. While soil texture did influence microbial community composition as expected, it had no effect on the microbial plant carbon assimilation and the differences between rhizosphere and bulk soil. In addition, the putative differences in carbon utilization between microbial groups, with the exception of AM fungi, were generally smaller than expected, reflecting opportunistic utilization of energy sources. Our results suggest that microbial uptake of plant carbon is primarily limited by plant carbon allocation rather than by environmental factors such as soil texture and seasonality. This indicates that the ongoing carbon assimilation during the growing season is supported by a functional redundancy within the microbial community, which, in turn, helps sustain ecosystem functioning.
Molecular links between whitesand ecosystems and blackwater formation in the Rio Negro watershed
Simon, Carsten; Pimentel, Tiago P.; Monteiro, M.T.F.; et al. (2021)
Geochimica et Cosmochimica Acta
Tropical rivers such as the Rio Negro constitute a major portion of the global aquatic flux of dissolved organic carbon (DOC) entering the ocean, but the exact amount, source contributions and fate of terrestrial DOC remain unknown. We investigated the role of valley and upland whitesand ecosystems (WSEs) and terra firme plateaus in forming blackwater tributaries in the Rio Negro basin to develop novel constraints for the terrestrial export of carbon. 5709 molecular markers from ground- and surface waters of two contrasting valley and upland sites feeding Rio Negro tributaries were identified by ultrahigh resolution mass spectrometry (FT-MS), analyzed by multivariate statistics and compared to known Rio Negro markers. In a Principal Coordinates Analysis, valley and upland DOC molecular composition differed by 78% from plateau DOC, which was characterized by reworked, aliphatic and unsaturated N- and S-containing molecules, while valley and upland DOC contained mainly condensed aromatics, aromatics and oxidized unsaturated structures. Valley and upland samples differed by 10% in molecular DOC composition and by their isotopic content (14C of SPE-DOC, 18O and 2H of water) which indicated differences in hydrology and C turnover. Against expectation, markers of widespread whitesand valleys did not emerge as a major source of Rio Negro markers, but specific upland markers did. Pubchem suggested chromene and benzofuran structures as promising candidates for further study. Our findings indicate that the export of molecular markers diverges from expected transport-limited DOC behavior, and thereby opens new avenues for source annotation beyond DOC quantity. Terrestrial DOC from upland whitesand areas is a major source of specific blackwater molecules missing in the regional ecosystem C balance, whereas C export from the whitesand valleys and especially from terra firme plateaus represents mainly recycled and transformed carbon not directly affecting the ecosystem C balance and possibly, the watersheds downstream molecular signature. Our study highlights the potential of high-resolution techniques to constrain carbon balances of ecosystems and landscapes by novel molecular markers. A comparison with other terrestrial DOM datasets indicated molecular similarities with temperate acidic soils and tropical rivers that warrant further analysis of common DOM markers. Implications, limitations, and future challenges are discussed in the light of potential applications of diagnostic molecular links for DOC source annotation and estimation of terrestrial DOM export in the land-to-ocean continuum.
Mass Difference Matching Unfolds Hidden Molecular Structures of Dissolved Organic Matter
Simon, Carsten; Dührkop, Kai; Petras, Daniel; et al. (2022)
Environmental Science & Technology
Ultrahigh-resolution Fourier transform mass spectrometry (FTMS) has revealed unprecedented details of natural complex mixtures such as dissolved organic matter (DOM) on a molecular formula level, but we lack approaches to access the underlying structural complexity. We here explore the hypothesis that every DOM precursor ion is potentially linked with all emerging product ions in FTMS2 experiments. The resulting mass difference (delta m) matrix is deconvoluted to isolate individual precursor ion delta m profiles and matched with structural information, which was derived from 42 delta m features from 14 in-house reference compounds and a global set of 11 477 delta m features with assigned structure specificities, using a dataset of similar to 18 000 unique structures. We show that delta m matching is highly sensitive in predicting potential precursor ion identities in terms of molecular and structural composition. Additionally, the approach identified unresolved precursor ions and missing elements in molecular formula annotation (P, Cl, F). Our study provides first results on how delta m matching refines structural annotations in van Krevelen space but simultaneously demonstrates the wide overlap between potential structural classes. We show that this effect is likely driven by chemodiversity and offers an explanation for the observed ubiquitous presence of molecules in the center of the van Krevelen space. Our promising first results suggest that delta m matching can both unfold the structural information encrypted in DOM and assess the quality of FTMS-derived molecular formulas of complex mixtures in general.
Photochemical Chain Scissions Enhance Polyethylene Glycol Biodegradability: from Probabilistic Modeling to Experimental Demonstration
Kleemann, Kevin; Jaggi, Madalina; Bernasconi, Stefano M.; et al. (2025)
Environmental Science & Technology
Polyethylene glycols (PEGs), a major class of water-soluble polymers (WSPs), are widely used in diverse applications, from which PEGs may be released into the environment. This work investigates the effect of PEG reaction with photochemically produced hydroxyl radicals (•OH), an important environmental oxidant, on the molecular weight (MW) distribution of PEGs and their subsequent biodegradation in soil and sediment. Monte Carlo simulations demonstrated a pronounced decrease in the PEG MW after only a few •OH-reaction-induced chain scissions on initial PEG molecules. The simulation results were validated by experimentally reacting 13C-labeled PEGs ( 𝑀¯n = 6380 ± 400 Da) with photochemically produced •OH to three extents and by analyzing the formed low MW PEG reaction products. Incubation of unreacted and •OH-reacted PEGs in both a sediment and a soil over 150 days demonstrated increasing rates and extents of PEG biodegradation into 13CO2 with increasing •OH-reaction extent and thus increasing amounts of low MW PEG products. This work underscores the importance of considering WSP MW distributions and dynamics caused by biotic or abiotic chain scission reactions when advancing a detailed understanding of WSP fate and biodegradability in natural and engineered receiving environments.

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