Browsing by Author "Marhan, Sven"

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    Hydrolyzable microplastics in soil : low biodegradation but formation of a specific microbial habitat?
    (2022) Schöpfer, Lion; Schnepf, Uwe; Marhan, Sven; Brümmer, Franz; Kandeler, Ellen; Pagel, Holger
    Microplastics (MP, plastic particles between 0.1 and 5000 μm) contaminate agricultural soils through the application of organic fertilizers, sewage sludge, and plastic mulch. MP surfaces and the MP-soil interface provide specific habitats for soil microorganisms - the plastisphere. Microorganisms in the plastisphere may benefit from utilizing MP as a carbon (C) source. Hydrolyzable MP with ester bonds are susceptible to enzymatic depolymerization by hydrolysis. In a microcosm experiment, we investigated MP biodegradation of small and large (< 0.5 mm and 0.5-2 mm respectively), hydrolyzable (a poly(lactic acid)/poly(butylene co-adipate terephthalate) blend, PLA/PBAT) and non-hydrolyzable (low-density polyethylene, LDPE) polymers, and the effects of these MP on microorganisms in dry and wet MP-amended soil. MP affected neither abundance and composition of the main soil microbial groups (fungi, Gram-negative, and Gram-positive bacteria), specific activities of ß-glucosidase, ß-xylosidase, lipase, and phenoloxidase, nor respiration in MP-amended soil. Only large PLA/PBAT particles in dry soil were significantly mineralized (15.4% of initial PLA/PBAT-C after 230 days). PLA/PBAT mineralization coincided with enhanced lipase and ß-glucosidase activities on the surfaces of individual PLA/PBAT particles extracted from the soil after incubation (compared to LDPE and non-incubated PLA/PBAT particles). We detected cracks on the surfaces of PLA/PBAT particles using scanning electron microscopy, indicating initiation of MP biodegradation, presumably due to depolymerization by lipases. Results suggest that the PLA/PBAT plastisphere is a polymer-specific habitat for lipase-producing soil microorganisms. Our study demonstrates that analyzing biogeochemical interactions within polymer-specific plastispheres is essential to assess MP fate and their impacts on microbially driven soil processes.
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    Microplastics persist in an arable soil but do not affect soil microbial biomass, enzyme activities, and crop yield
    (2022) Schöpfer, Lion; Möller, Julia N.; Steiner, Thomas; Schnepf, Uwe; Marhan, Sven; Resch, Julia; Bayha, Ansilla; Löder, Martin G. J.; Freitag, Ruth; Brümmer, Franz; Laforsch, Christian; Streck, Thilo; Forberger, Jens; Kranert, Martin; Kandeler, Ellen; Pagel, Holger
    Microplastics (MP, plastic particles <5 mm) are ubiquitous in arable soils due to significant inputs via organic fertilizers, sewage sludges, and plastic mulches. However, knowledge of typical MP loadings, their fate, and ecological impacts on arable soils is limited. We studied (1) MP background concentrations, (2) the fate of added conventional and biodegradable MP, and (3) effects of MP in combination with organic fertilizers on microbial abundance and activity associated with carbon (C) cycling, and crop yields in an arable soil. On a conventionally managed soil (Luvisol, silt loam), we arranged plots in a randomized complete block design with the following MP treatments (none, low‐density polyethylene [LDPE], a blend of poly(lactic acid) and poly(butylene adipate‐co‐terephthalate) [PLA/PBAT]) and organic fertilizers (none, compost, digestate). We added 20 kg MP ha-1 and 10 t organic fertilizers ha-1. We measured concentrations of MP in the soil, microbiological indicators of C cycling (microbial biomass and enzyme activities), and crop yields over 1.5 years. Background concentration of MP in the top 10 cm was 296 ± 110 (mean ± standard error) particles <0.5 mm per kg soil, with polypropylene, polystyrene, and polyethylene as the main polymers. Added LDPE and PLA/PBAT particles showed no changes in number and particle size over time. MP did not affect the soil microbiological indicators of C cycling or crop yields. Numerous MP occur in arable soils, suggesting diffuse MP entry into soils. In addition to conventional MP, biodegradable MP may persist under field conditions. However, MP at current concentrations are not expected to affect C turnover and crop yield.