Time-Resolved Investigation of the Priming Effect of Biodegradable Plastics on Soil Organic Matter Using Radiocarbon Analysis

Time-Resolved Investigation of the Priming Effect of Biodegradable Plastics on Soil Organic Matter Using Radiocarbon Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Time-Resolved Investigation of the Priming Effect of Biodegradable Plastics on Soil Organic Matter Using Radiocarbon Analysis Sungbin Ju, Lam Tan Hao, Semin Kim, Minkyung Lee, Hyo Jeong Kim, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9383674/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract As biodegradable plastics become more commonly integrated to the modern economy, soil contamination by biodegradable microplastics (MPs) has raised concerns owing to their potential to alter soil organic matter (SOM), an important carbon reservoir, through priming effects. Priming effects refer to the acceleration (positive) or suppression (negative) of SOM decomposition following external carbon input. Previous studies have relied on carbon-13 isotope analysis, which lacks the resolution required for precise carbon tracing, to study the priming effects of biodegradable MPs. Herein, we present a robust approach combining accelerator mass spectrometry-based radiocarbon (carbon-14) analysis with a closed-jar incubation system to quantify the priming effects of two fossil-based biodegradable MPs, poly(ε-caprolactone) (PCL) and poly(butylene adipate--terephthalate) (PBAT). This method enables high-resolution time-resolved partitioning of biogenic and fossil-derived carbons. Both biodegradable MPs show a net negative priming effect (up to − 35.4 µg C g soil for PCL and − 9.6 µg C g soil for PBAT) over a 50-d incubation period, with transient positive priming observed at certain time points. This study provides a robust approach for accurate assessment of plastic–SOM interactions and offers an important analytical framework to devise end-of-life management strategies for biodegradable plastics in agroecosystems. priming effect biodegradable plastic soil carbon-14 soil organic matter acceleration mass spectrometry Figures Figure 1 Figure 2 Figure 3 Figure 4 Synopsis This study employs radiocarbon analysis using accelerator mass spectrometry to investigate the priming effect of biodegradable microplastics on soil organic matter, highlighting the need for their management strategies in agroecosystems. Introduction The Earth’s carbon cycle has been increasingly disrupted by human activities since industrialization. In particular, fossil fuel combustion and land use changes (such as deforestation and agricultural practices) annually emit over 13 Gt of carbon dioxide (CO 2 ) into the atmosphere, significantly contributing to global warming. 1 , 2 As an important terrestrial carbon reservoir, soil stores approximately 2344 Gt of carbon but is susceptible to anthropogenic disturbances (Fig. 1 A). 3 – 6 The loss of soil carbon can accelerate atmospheric CO 2 accumulation and intensify climate change. 7 , 8 A key anthropogenic influence on soil carbon dynamics is the introduction of external carbon inputs through a process known as the priming effect, in which foreign organic matter alters the decomposition rate of native soil organic matter (SOM). 9 – 11 Positive priming accelerates SOM decomposition, releasing additional CO 2 into the atmosphere and intensifying global warming, whereas negative priming slows SOM breakdown, enhancing carbon retention in soil, and supporting soil biota and ecosystem functions. 12 – 14 Plastic pollution in soil has become one of the most pervasive environmental challenges. A major concern is the accumulation of microplastics (MPs; 0.1–5,000 µm) and nanoplastics (NPs; 1–100 nm), where concentrations can reach up to 2830 particles kg − 1 soil. 15 – 18 These particles represent a growing persistent carbon input that not only alters soil physical structure but also influences SOM dynamics through priming effects. 19 – 21 To address plastic pollution, bioplastics have been developed. Together with conventional plastics, these materials are classified according to feedstock origin (bio-based vs. fossil-based) and biodegradability into four types. 22 Type 1 comprises bio-based biodegradable plastics, such as polylactide (PLA), polyhydroxyalkanoate (PHA), and starch-based plastics. Type 2 includes fossil-based biodegradable plastics, represented by poly(butylene adipate- co -terephthalate) (PBAT), poly(ε-caprolactone) (PCL), and poly(butylene succinate) (PBS). Type 3 refers to bio-based nonbiodegradable plastics, including bio-poly(ethylene terephthalate) (bio-PET), bio-polyethylene (bio-PE), bio-polypropylene (bio-PP), and isosorbide-based polymers. Type 4 consists of conventional fossil-based, nonbiodegradable plastics, such as polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polystyrene (PS). Under this classification, biodegradable plastics correspond to Types 1 and 2, whereas bioplastics encompass Types 1–3. Biodegradable plastics are designed to be broken down by microorganisms into water and CO 2 (under aerobic conditions) or CH 4 (under anaerobic conditions). Their environmental effects have recently become controversial, as once introduced to soil, biodegradable plastics fragment into MPs and NPs (during the early stages of biodegradation) that can persist temporarily before complete mineralization. 23 Unlike their nonbiodegradable counterparts that are inert, biodegradable MPs and NPs can act as carbon sources accessible to microorganisms. 24 As soil microorganisms generally prefer labile organic matter, low concentrations of easily metabolizable substrates (such as glucose) added to soil generally suppress SOM breakdown (negative priming). 9 , 25 – 27 By contrast, higher concentrations stimulate microbial activity, triggering nutrient mining, in which microorganisms decompose SOM to access other nutrients such as nitrogen or phosphorus (positive priming). 28 , 29 Similarly, biodegradable MPs and their decomposition products may induce priming effects, thereby influencing soil carbon cycling and ecosystem processes. Understanding the priming effects of biodegradable MPs is therefore essential for improving the end-of-life management strategies for biodegradable plastics in agroecosystems. As these materials become increasingly prevalent in the modern economy, research on their soil–carbon interactions has intensified over the past few years.. Elucidating the priming effect of plastics on SOM requires identifying the source of CO 2 evolved after MP addition (i.e., whether CO 2 originates from plastics or SOM decomposition) and comparing SOM-derived CO 2 with that from unamended soil. Stable isotope (carbon-13, 13 C) analysis via isotope-ratio mass spectrometry (IRMS) has been commonly used for this purpose. 30 This technique relies on differences in the natural abundance of 13 C (expressed as δ 13 C: 13 C/ 12 C atomic ratio), which varies between bioplastics and soil. Fossil-based plastics typically exhibit δ 13 C values between − 36 and − 24‰, while bio-based plastics derived from C4 plants such as maize range from − 14 to − 10‰. Soil δ 13 C values usually reflect the vegetation type, ranging from − 35 to − 25‰ for C3 plants, and − 14 to − 10‰ for C4 plants. 31 Most studies investigating priming effects of biodegradable plastics, such as PLA, 32–34 (PHA), 33 PBS, 35 and (PBAT), 33 have relied on this 13 C isotope approach. Although their reported priming effects vary (depending on substrates and soil biotic/abiotic factors), the method itself has a critical limitation. The resolution of 13 C analysis becomes inadequate when the δ 13 C ranges of the input plastic and soil overlap, such as fossil-derived plastics in C3-vegetated soils or C4 plant-derived bioplastics in C4-vegetated soils. The complexity further increases with blends of fossil- and bio-based plastics in soil influenced by mixed vegetation types, making CO 2 source attribution and priming effect interpretation highly uncertain. To address this issue, carbon isotope-labeled substrates have been used to create distinct isotopic profiles with that of soil for improving CO 2 tracing. 27 , 36 However, isotope labeling is technically demanding and may lead to biased positive priming, as many catabolytic microorganisms preferentially metabolize lighter isotopes ( 12 C), leading to underrepresentation of the heavy carbon isotopes in decomposition products. 14 , 37 Therefore, approaches based on natural isotope abundance remain more reliable for accurately assessing the priming effects of plastics in soils. A higher-resolution alternative for tracing CO 2 sources is radiocarbon analysis based on the natural abundance of carbon-14 ( 14 C). 14 C is a radioactive isotope continuously produced in the atmosphere with a half-life ( t 1/2 ) of approximately 5700 ± 30 y. 38 Living organisms maintain equilibrium with atmospheric 14 C (δ 14 C: 14 C/ 12 C ~ 1–1.5× 10 –12 ), but this exchange stops after death, and the decay of 14 C over time renders fossil-derived carbon as 14 C-free. 39 , 40 The clear distinction in δ 14 C between biogenic and fossil carbon, combined with the high sensitivity of radiocarbon analysis, allows unambiguous source distinction, even when their δ 13 C signatures overlap. 41 Despite these advantages, 14 C analysis has not yet been applied to study the priming effects of biodegradable plastics on SOM. Radiocarbon measurements are typically performed by liquid scintillation counting (LSC) or accelerator mass spectrometry (AMS) (Figure S1 ). LSC detects 14 C by measuring light pulses generated from beta emissions during radioactive decay that interact with a liquid scintillator. This method offers low instrumentation costs but is limited by its low sensitivity and precision. 42 – 44 In contrast, AMS provides exceptionally high sensitivity and accuracy by ionizing the sample, accelerating and separating the ions, and directly counting individual 14 C atoms, thereby enabling the detection of minute 14 C concentrations. AMS is therefore better suited for resolving small changes in CO 2 sources, but it has not been applied to investigate the priming effects of biodegradable plastics on SOM. Herein, we investigated the priming effects of fossil-based biodegradable MPs (Type 2) on SOM using AMS-based radiocarbon analysis. The fossil δ 14 C signature of MPs (~ 0) allows for a clear distinction from the biogenic δ 14 C of SOM (~ 1.2 × 10 − 12 ), enabling precise source partitioning of evolved CO 2 from MP degradation and SOM mineralization. To achieve time-resolved sampling, we employed a modified ASTM D5988 biodegradation test protocol 45 to capture CO 2 in sealed incubation jars using an alkaline solution and replacing the absorbent at defined intervals, The captured CO 2 was precipitated as barium carbonate (BaCO 3 ), graphitized, and analyzed by AMS. This setup not only accurately traces CO 2 sources but also captures short-term variations in priming effect dynamics. Our study offers a robust framework for understanding the effects of biodegradable MPs on soil carbon and helps devise strategies for managing biodegradable plastics in terrestrial environments. Results and Discussion Biodegradation and CO 2 Partitioning The biodegradation of fossil-based MPs was conducted following ASTM D5988 (Figure S1 ). Treatments included soil only (negative controls) and soil amended with biodegradable poly(ε-caprolactone) (PCL) and poly(butylene adipate- co -terephthalate) (PBAT) MPs. Polystyrene (PS) MPs were used as a nonbiodegradable control. Key physicochemical properties of the soil are summarized in Table S1 (initial organic matter content of 17.63 wt%, an average moisture content of 28%, and a C/N ratio of 12.5). Soil microbial activity was first activated by adding 1 wt% glucose 46–50 and preincubating for about three weeks at 50°C until the CO 2 released from SOM stabilized. After the preconditioning phase, MPs (< 125 µm; Figure S2) were added at 0.2 g MP 100 g − 1 soil. This level exceeds the typical field concentrations (~ 4.5 mg MP kg − 1 soil), 17 and was intentionally chosen to simulate an extreme contamination scenario and ensure sufficient CO 2 evolution for quantifying priming effects within a practical lab time scale. CO 2 sampling was done daily during the first week and then twice weekly thereafter to assess the initial and longer-term priming effects, respectively. Released CO 2 captured and precipitated as BaCO 3 was quantified to assess the biodegradation progress of the MPs. Soil amended with PCL and PBAT consistently released more cumulative CO 2 than the unamended control soil, indicating active microbial degradation (Figure S3). PCL-amended soil released 7.49 mmol more CO 2 than the control by day 7 ( p 0.05). In comparison, PBAT-amended soil produced 3.3 mmol more CO 2 than the control by day 7 ( p 0.05). PCL degraded faster than PBAT, likely due to its lower melting point (~ 55–60°C) and simpler chemical structure, facilitating enhanced microbial accessibility. 51 In contrast, the PS-amended soil released 16 mmol less cumulative CO 2 than the untreated soil ( p > 0.05) (Figure S5). Subsequently, we calculated the first derivatives of the cumulative CO 2 release to evaluate the biodegradation dynamics and select suitable time points for AMS analysis (Figure S4). In the PCL treatment, a sharp peak (~ 4.4 mmol d − 1 ) was observed within the first 5 d, followed by a steady decline until day 9, indicating rapid initial mineralization by soil microorganisms. In contrast, PBAT showed a sustained CO 2 release rate over 50 d, with notable peaks at days 3 (~ 2.6 mmol d − 1 ) and 24 (~ 1.6 mmol d − 1 ). Based on these trends, BaCO 3 sampling for AMS analysis was conducted on days 3, 5, and 9 for PCL and on days 2, 3, and 24 for PBAT. Additionally, samples were collected on day 2 for PCL and day 1 for PBAT post-MP addition to capture the early priming effects, which are typically the most pronounced immediately following external carbon input. 27 The AMS data were first used to partition CO 2 emissions into SOM- and plastic-originated fractions based on the δ 14 C and percent modern carbon (pMC) values, using oxalic acid as the reference standard (Table S2). The δ 14 C value of the soil used was ~ 1.2× 10 –12 , corresponding to 99 ± 0.35 pMC, which is close to the modern atmospheric level (~ 100 pMC). In contrast, added MPs showed < 0.1 pMC, consistent with their fossil origin (Table S3). Because of the substantial time and cost required for radiocarbon sample pretreatment and AMS, measurements were not feasible for all samples across all collection time points over the 50-d incubation period. To estimate carbon source contribution throughout the entire PCL and PBAT biodegradation period, we applied Gaussian process regression (GPR) to the pMC data from representatively sampled time points to interpolate the CO 2 partitioning results for unsampled time points (Fig. 2 ). This approach balanced analytical rigor with practical feasibility over extended timeframes. The results revealed that biogenic carbon remained the dominant source of daily CO 2 release and confirmed that PCL degraded more rapidly than PBAT. Priming Effect Quantification Based on CO 2 fractionation data, the priming effects of fossil-derived biodegradable MPs were calculated as the difference in SOM-derived CO 2 production between MP-amended and unamended soils (Fig. 3 ), reported in µg C g − 1 soil. Following the addition of biodegradable MPs, an initial negative priming effect was observed, with 35.4 µg C g − 1 soil for PCL (day 2) and 7.2 µg C g − 1 soil for PBAT (day 1) (absolute values). Throughout the incubation period, priming effects remained predominantly negative, except for brief positive responses, on day 5 for PCL and day 2 for PBAT. For PCL, the positive priming effect was weaker than its initial negative response. Toward the end of the incubation, strong negative priming effects for both MPs reemerged, with 26.6 µg C g − 1 soil for PCL (day 9) and 9.6 µg C g − 1 soil for PBAT (day 24) (absolute values). In contrast, PS exhibited consistent negative priming (21.6 µg C g − 1 at day 2, 32.58 µg C g − 1 at day 9) throughout the incubation period (Figure S6). Because PS is not biodegradable, all CO 2 released in PS-amended soil originated solely from SOM, allowing direct calculation of priming effects without AMS-based carbon partitioning.. The magnitude and mechanisms of the priming effect depended on the type of MP. Among the biodegradable MPs, PCL induced a stronger and more immediate negative priming effect than PBAT, likely due to its higher biodegradability (Fig. 3 A). 34 , 52 – 54 Its simple molecular structure and low melting point ( T m ~55–60°C) facilitated rapid chain scission and hydrolysis, generating degradation intermediates readily assimilated by soil microorganisms. This preferential utilization of PCL-derived carbon reduces microbial reliance on SOM, thereby enhancing the negative priming effect. The intermittent shifts between positive and negative priming observed during the incubation can be attributed to microbial substrate switching, as microorganisms alternated between the SOM and MP-derived carbon depending on nutrient availability. 55 – 57 This was indirectly supported by changes in biodegradation kinetics for both PCL and PBAT. Following the brief positive priming (day 5 for PCL and day 2 for PBAT), the relative contribution of biogenic carbon from SOM increased compared with fossil-derived carbon from MPs, as indicated by the GPR-based partitioning (Fig. 2 ). This shift suggests a temporary reduction in plastic degradation as microorganisms increasingly utilized SOM. Because the tested MPs lack nitrogen, the temporary positive priming effects likely resulted from microbial mining of SOM to acquire nitrogen. 58 As the degradation progressed and labile MP-derived compounds accumulated, they increasingly served as carbon sources and reinforced the negative priming effect. In contrast, PS induced a net negative priming effect through a different mechanism (Fig. 3 B). As a non-biodegradable MP, PS acted as a nutrient adsorber or chelator, reducing nutrient bioavailability without providing assimilable carbon. 59 This suppressed microbial growth and activity, resulting in a negative priming effect throughout the incubation (Fig. 3 B). 59 – 61 Further evidence of priming effect dynamics and nutrient mining was provided by SOM analysis (Table S1 ). Comparison between the pre- and post-incubation samples revealed a decrease in SOM (%C from 17.6% to 17.1%) in the control and PCL-amended soil samples, indicating microbial mineralization of organic matter. In contrast, PBAT- and PS-amended soil samples exhibited an apparent increase in the SOM content (%C from 17.6% to 17.8%), likely attributed to residual PBAT and non-degraded PS MPs remaining in the soil contributing to the measured organic fraction Furthermore, an increase in the C/N ratio (from 12.5 to 13.6–15.8) in the MP-amended soil supports the nitrogen mining by soil microorganisms in response to MP addition. Technological Advances in Investigating the Priming Effects of Biodegradable MPs on SOM Recent studies have increasingly investigated the ecological impacts of biodegradable MPs, particularly their priming effects on SOM, with most relying on 13 C analysis to distinguish carbon sources between biodegradable plastics and soil. 33 – 35 , 55 , 56 , 62 However, as noted in the Introduction, the resolution of 13 C analysis becomes limited when the δ 13 C values of the input plastic and soil overlap, even partially, making carbon-source partitioning and consequently, priming effect quantification unreliable.. 63 This limitation was demonstrated in our study, where the AMS data showed that the δ 13 C values of the MPs and soil overlapped (Table S3). To overcome this limitation, 14 C analysis was employed for distinguishing fossil-derived plastic carbon (0 pMC) from SOM carbon (~ 99 pMC). Compared with 13 C analysis, 14 C analysis enables unambiguous source tracking even when δ 13 C signatures overlap extensively, for example, when differentiating fossil-based plastics (− 36 to − 24‰) from SOM in C3-vegetated soils (− 35 to − 25‰). 31 . The resolution power of 14 C analysis is further enhanced several orders of magnitude by AMS sensitivity, which can detect 14 C up to zeptomole (10 − 21 ) level, 64 allowing reliable CO 2 partitioning and quantification of priming effects on the SOM induced by biodegradable plastics. Although our study examined a clear-cut case of fossil-based plastics (Type 2), this approach can be extended to more complex systems, such as bio-/fossil-based polymer blends with intermediate pMC values. These materials are increasingly commercialized following the paradigm shift toward sustainable materials and are more likely to exhibit a broader δ 13 C range due to their complex compositions, making 14 C analysis a preferred choice over 13 C analysis for evaluating the impact of biodegradable MPs on soil carbon dynamics. A reliable AMS-based 14 C analysis requires an effective CO 2 capture system during the biodegradation of MPs in soil. Two standardized biodegradation tests based on ISO 14855-2 (cumulative sampling) and ASTM D5988 (individual sampling) are commonly used (Fig. 4 ). 23 , 65 , 66 In the cumulative sampling system, CO 2 -free air is continuously supplied to the incubation chamber, and the CO 2 outflow from soil microbial metabolism is captured in an alkaline column trap (Fig. 4 A). This approach has been previously applied for AMS-based 14 C analysis to monitor the biodegradation of PBS, although its priming effects were not examined. 67 However, the system requires complex equipment, high operation costs, and precise control of CO 2 -free inflow and stable soil conditions. Furthermore, because CO 2 accumulates in a single trap, the carbon signal is integrated over the entire incubation period. This makes it challenging to resolve biogenic and fossil-derived carbon fractions at specific time intervals. In contrast, the individual sampling system offers a simpler and lower-cost alternative for collecting CO 2 using an alkaline trapping solution in sealed jars. The trapping solution can be easily replaced, and the soil can be aerated at predetermined sampling time points. This approach allows the monitoring of CO 2 emissions and quantification of biogenic and fossil-based carbon fractions at discrete time points, thereby enabling a time-resolved evaluation of the priming effect throughout the biodegradation process. This setup is also particularly advantageous for slowly degrading polymers such as PBAT, as it eliminates the need for a prolonged, continuous CO 2 -free air supply and soil conditioning. It also enables the identification of temporal shifts in priming effects (e.g., negative to positive), which would otherwise be obscured under cumulative sampling. We note that the ASTM D5988 protocol quantifies CO 2 by titrating the alkaline trapping solution with an acid that releases CO 2 during the process, making it impossible to recover carbon in a solid form for further treatment and analysis (Fig. 4 C). To enable downstream 14 C analysis, we replaced this titration step with precipitation. Specifically, CO 2 absorbed in the alkaline solution was converted to stable BaCO 3 by reacting with barium chloride (BaCl 2 ). The resulting precipitate was graphitized and analyzed for 14 C by AMS (Fig. 4 D). Implications and Limitation of This Study The priming effects observed in this study should not be taken as universally representative, as they may vary across different soil types, environmental conditions, and the physicochemical properties of the MPs introduced to the soil (e.g., structural composition and particle size). 68 – 70 Prior studies on PLA illustrate this variability: positive priming effects have been reported in sandy soil, whereas negative priming effects have been observed in paddy soils, with soil pH identified as one of key controlling factors. 30 , 34 , 56 We emphasize here again that these studies partitioned carbon sources using 13 C analysis. Due to its limitation as discussed above, these reported differences in the priming effects may reflect analytical limitations rather than true biological responses. Furthermore, our results highlight that priming should not be evaluated solely from net cumulative outcomes. Although we demonstrated that the net priming effect of biodegradable MPs was negative, time-resolved measurements revealed transient positive shifts owing to microbial substrate switching and nutrient demands. However, under different soil and environmental conditions, the opposite can be observed. Furthermore, this study employed an elevated incubation temperature (50°C) representative of industrial composting conditions to promote the growth of thermophilic microorganisms. This temperature also reflects natural biological self-heating processes in soils during winter, where microbial degradation of SOM generates heat up to ~ 70°C, to warm plant roots, facilitate nutrient cycling, and suppress pathogens. 40 This elevated temperature was applied to accelerate polymer degradation and enable measurable CO 2 evolution within a short laboratory timeframe, particularly for slow-degrading polymers such as PBAT. These conditions differ from typical field environments, where lower temperatures, slower microbial activity, and extended degradation timescales may alter both MP degradation kinetics and associated priming effects. Consequently, the magnitude and temporal patterns of priming observed here may not directly translate to natural soils. We also used a relatively high MP concentration, exceeding the typical values reported for intensively managed agricultural soil, 17 to ensure detectable and distinguishable CO 2 production between MP-amended and unamended soils. Furthermore, capturing CO 2 in a closed system prevented atmospheric exchange and allowed accurate quantification. Therefore, scaling this study to field conditions would require a more robust CO 2 capture system that minimizes atmospheric contamination while accommodating much lower CO 2 fluxes from both MP mineralization and MP-induced priming relative to the substantially larger CO 2 background from SOM decomposition. Because the difference in CO 2 yields between control and MP-contaminated soils in the field is expected to be extremely small compared with that under optimized laboratory conditions, overcoming the CO 2 capture bottleneck would make radiocarbon analysis particularly advantageous. The minute sample requirement and high sensitivity of AMS-based 14 C analysis provide reliable source partitioning over the IRMS-based 13 C analysis. Additionally, while the 14 C analysis provides a clear-cut distinction between carbon derived from fossil-based plastics and that from soil, assessing the priming effects of biobased biodegradable plastics (Type 1) can be more challenging as their radiocarbon signatures are often similar to those of the soil (both being biogenic carbon). In such cases, it is necessary to maximize/optimize the zeptomol resolution of AMS to resolve the δ 14 C between plastic- and soil-derived CO 2 . Complementary 13 C analysis can be employed to provide a more definite conclusion, for example by partitioning carbon from C4-plant-derived bioplastics and C3-vegetated soils. Alternatively, radioactive isotopic labeling can be used to give the input bioplastic a distinct isotopic profile relative to the soil to improve the 14 C analysis resolution. Although this study represents an early-stage effort, it establishes a methodological foundation for future investigations into the priming effects of biodegradable plastics on SOM using AMS-based radiocarbon analysis. Further research is still required to elucidate MP–soil interactions in shaping the priming response. Importantly, the ability of 14 C analysis to reveal priming effects highlights an important consideration for biodegradation studies: without accounting for change in SOM mineralization upon plastic addition, the extent of plastic degradation in soil can be under- or overestimated. Finally, the more reliable interpretation of the priming effect enabled by 14 C analysis over 13 C analysis is particularly significant in shaping environmental policies regarding the use of biodegradable plastic products in soils, such as agricultural mulch films. Positive priming leading to SOM loss may justify restrictions on their use, whereas negative priming may indicate short-term enhancement of soil carbon retention. Overall, this study demonstrated that AMS-based radiocarbon analysis provides a robust approach for quantifying priming effects in soils amended with fossil-derived biodegradable MPs. In contrast to conventional 13 C analysis-based methods, which are constrained by overlapping isotopic signatures, 14 C analysis enables unambiguous separation of plastic-derived carbon from biogenic SOM. Utilizing a modified ASTM D5988 protocol involving CO 2 capture and precipitation, we achieved time-resolved resolution of both short- and longer-term priming dynamics. Under the laboratory conditions examined, we showed that PCL and PBAT MPs induced a net negative priming effect, with transient positive priming phases, likely driven by microbial substrate switching and nutrient mining. While these findings are yet to generalize environmental impacts on soil carbon dynamics induced by biodegradable MPs, this study provides an analytical framework transferrable across multiple plastics–soil systems for studying their interactions. Furthermore, it offers a tool to inform end-of-life management strategies and evidence-based policies governing the use of biodegradable plastics in agroecosystems. Experimental Reagents PCL (average M n = 80,000 g mol − 1 ), PS (average M w 35,000), glucose, potassium hydroxide (≥ 85%), and barium chloride dihydrate (≥ 99%) were purchased from Sigma-Aldrich (USA). PBAT was purchased from Ankor Bioplastics (S. Korea). All reagents were stored according to the manufacturer’s instructions and used as received. Deionized water was purified using a Milli-Q Integral 3 system (Millipore, USA), with a final resistivity of 18.0 MΩ cm at 25°C. Microplastics MPs were prepared by cryogenic-grinding polymer pellets using a horizontal 6875 Freezer/Mill (Spex SamplePrep, Antylia Scientific, USA) for 15 min in liquid nitrogen. The resulting powder was passed through a 125 µm standard test sieve (BS0125-75, LK Labkorea) to collect PMs of uniform sizes. Soil Soil used for the biodegradation experiment was obtained from Jisaengto (S. Korea). The soil was ground and sieved to < 2 mm using a standard test sieve (BS2000, LK Labkorea). Its basic physicochemical properties were analyzed at Cheillab and are listed in Table S1 . Biodegradation and CO 2 Capture Setup Biodegradation and CO 2 trapping experiments were conducted in sealed glass vessels following the ASTM D5988 with suitable modifications. All treatments were performed in triplicate. Each vessel contained 200 g of soil amended with MPs or left unamended as a control. Prior to MP addition, the microbial activity was activated by adding glucose (1 wt% relative to soil) and incubating the soil at 50°C in airtight glass vessels sealed with O-rings and split-ring closures in a temperature-controlled incubator (BF-250IN, Biofree, Korea), with moisture inside the vessel maintained using an open vial of deionized water. Evolved CO 2 was captured in an open vial containing 2 M KOH aqueous solution (50 mL). The soil was aerated every 3 d by stirring, and deionized water was added to maintain > 80 wt% water content as needed. Once CO 2 evolution stabilized, 0.4 g of PCL, PBAT, or PS (nonbiodegradable control) MPs were added to the soil. Evolved CO 2 was captured in an open vial containing 1 M KOH aqueous solution, which was replaced daily during the first 7 d, then every 3 d thereafter. The soil containing MPs was aerated daily, and moisture was maintained by adding deionized water as needed. To quantify the pMC of the evolved CO 2 during biodegradation, the CO 2 absorbed in KOH was precipitated as barium carbonate (BaCO 3 ) by dropwise addition of saturated BaCl 2 solution. Precipitation was controlled to avoid coprecipitation of barium hydroxide [Ba(OH) 2 ]. The resulting BaCO 3 was dried in vacuo at ambient temperature. The dried BaCO 3 was used both to calculate CO 2 evolution and for AMS analysis of pMC. Graphitization/Reduction of BaCO 3 Carbon atoms in BaCO 3 [C(IV)] were converted to graphite [C(0)] through sequential acid hydrolysis, vaporization, and catalytic reduction. Briefly, BaCO 3 (~ 19.7 mg) was reacted with phosphoric acid (H 3 PO 4 , 5 mL) in a Schlenk flask sealed with a gas-tight stopcock connected to a vacuum manifold. The flask was incubated in a hot water bath at 90°C for 1 h to facilitate the reaction. The evolved CO 2 was first cold-trapped twice using a dry ice–ethanol bath at − 76°C under vacuum to remove water vapor and volatile contaminants. Subsequently, the outlet CO 2 was cryogenically trapped in another tube using liquid nitrogen at − 196°C under 3 × 10 − 6 torr. The collected CO 2 was then transferred to a sealed borosilicate reactor containing precombusted iron powder (325 mesh; 5 mg) as a catalyst and reduced to graphite under excess hydrogen gas (H 2 :CO 2 molar ratio ~ 3:1) at 650°C for 10 h. The resulting graphite (~ 1 mg) was recovered, compacted in a sample holder, and analyzed by AMS for radiocarbon isotopic composition. 71 AMS measurements were conducted in triplicate for each sample. AMS Carbon isotopes ( 14 C, 13 C, and 12 C) were analyzed using AMS (MICADAS, Ionplus AG, Switzerland). BaCO 3 -derived graphitized carbon was packed into aluminum cathodes and ionized using a cesium sputter cation beam. The generated carbon anions were accelerated and separated based on their atomic mass-to-charge ratios using a high-energy analyzing magnet. 12 C and 13 C isotopes were quantified as ion currents with multi-Faraday cups, whereas the 14 C atoms were detected as discrete events using a solid-state detector equipped with a semiconductor absorber for energy discrimination and background suppression. The 14 C was measured relative to the US National Institute of Standards and Technology (NIST) oxalic acid II (SRM 4990C) and IAEA-C7 as modern and fossil reference standards, respectively, and expressed as the pMC. AMS analyses were done in triplicate for each sample. Priming Effect Calculation The biogenic carbon content obtained from AMS was attributed to carbon derived from the soil. The priming effect was calculated based on the total amount of CO 2 released and the biocarbon content determined by AMS analysis as follows: Soil priming (mmol) =(C sample ✕ B)/100)−C soil where C soil is the total CO 2 released from the control (mmol), C sample is the total CO 2 released from the sample (mmol), and B is the normalized biogenic carbon content of the sample relative to that of soil (%). GPR GPR was employed to model the evolution of experimentally measured biogenic carbon content as a continuous function of time. For each observation, the measured response was expressed as the sum of an underlying latent function and random noise. Specifically, for each day time, i = 1, 2, ..., n , the modeling framework is y i = f ( x i ) + ε i , where y i is the experimentally observed biogenic carbon content, x i is the measurement time (day) and ε is the random noise. The latent function f ( x ) was modeled as a zero-mean Gaussian process, f ( x )∼GP(0, k ( x , x′ )), with a squared exponential covariance function that encodes temporal smoothness through the distance between observation times. The kernel includes a length-scale parameter that determines how the function varies with time. Given the limited number of observations and their irregular temporal spacing, GPR provides a flexible nonparametric framework capable of capturing nonlinear temporal trends without assuming a predefined functional form. Model predictions were obtained from the posterior distribution of the Gaussian process, where the posterior mean represents the predicted value and the posterior variance quantifies the associated uncertainty. In addition to point estimates, GPR provides predictive uncertainty. The mean prediction and the associated 70% confidence intervals were obtained from the posterior distribution. Declarations Authors Sungbin Ju - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; https://orcid.org/0000-0003-3224-5929 Lam Tan Hao - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; https://orcid.org/0000-0001-9791-6071 Semin Kim - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea Minkyung Lee - Technical Support Center for Chemical Industry, Korea Research Institute of Chemical Technology (KRICT); Ulsan 44429, Republic of Korea Hyo Jeong Kim - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; Advanced Materials & Chemical Engineering, Korea National University of Science and Technology (UST), Daejeon 34113, Republic of Korea; https://orcid.org/0000-0002-5331-5407 Author Contributions S.J. and L.T.H. performed the experiments, analyzed the data, and wrote the manuscript. S.J., L.T.H, and D.X.O. prepared the figures. S.K. and M.L. performed AMS analysis. H.J.K. validated the manuscript. H.J., J.P., and D.X.O. conceived, designed, and directed the project. Notes The authors declare no competing financial interest. Acknowledgment This work was supported by the National Research Foundation (NRF) of Korea, funded by the Ministry of Science and ICT (RS-2024-00408795), and by the Korea Institute of Marine Science & Technology Promotion (KIMST), funded by the Ministry of Oceans and Fisheries (RS-2025-02305544). H.J. acknowledges the support from the Technology Innovation Program funded by the Ministry of Trade Industry & Energy (MOTIE), Republic of Korea (RS-2025-02313873), and from the Korea Research Institute of Chemical Technology core project (KS2642-10). References Friedlingstein P, Jones MW, O’Sullivan M, Andrew RM, Bakker DCE, Hauck J, Le Quéré C, Peters GP, Peters W, Pongratz J et al (2022) Global carbon budget 2021. 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Supplementary Files PrimingmanuscriptSI.docx GA.png As biodegradable plastics become more commonly integrated to the modern economy, soil contamination by biodegradable microplastics (MPs) has raised concerns owing to their potential to alter soil organic matter (SOM), an important carbon reservoir, through priming effects. Priming effects refer to the acceleration (positive) or suppression (negative) of SOM decomposition following external carbon input. Previous studies have relied on carbon-13 isotope analysis, which lacks the resolution required for precise carbon tracing, to study the priming effects of biodegradable MPs. Herein, we present a robust approach combining accelerator mass spectrometry-based radiocarbon (carbon-14) analysis with a closed-jar incubation system to quantify the priming effects of two fossil-based biodegradable MPs, poly(ε-caprolactone) (PCL) and poly(butylene adipate--terephthalate) (PBAT). This method enables high-resolution time-resolved partitioning of biogenic and fossil-derived carbons. Both biodegradable MPs show a net negative priming effect (up to − 35.4 µg C g soil for PCL and − 9.6 µg C g soil for PBAT) over a 50-d incubation period, with transient positive priming observed at certain time points. This study provides a robust approach for accurate assessment of plastic–SOM interactions and offers an important analytical framework to devise end-of-life management strategies for biodegradable plastics in agroecosystems. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 17 May, 2026 Reviews received at journal 16 May, 2026 Reviews received at journal 15 May, 2026 Reviews received at journal 15 May, 2026 Reviews received at journal 05 May, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers agreed at journal 26 Apr, 2026 Reviewers agreed at journal 25 Apr, 2026 Reviewers agreed at journal 24 Apr, 2026 Reviewers agreed at journal 24 Apr, 2026 Reviewers invited by journal 24 Apr, 2026 Editor assigned by journal 11 Apr, 2026 Submission checks completed at journal 11 Apr, 2026 First submitted to journal 10 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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(B) Priming effect schematic of fossil-derived biodegradable microplastics on SOM via \u003csup\u003e14\u003c/sup\u003eC analysis. Biogenic carbon in SOM contains \u003csup\u003e12\u003c/sup\u003eC, \u003csup\u003e13\u003c/sup\u003eC, and \u003csup\u003e14\u003c/sup\u003eC isotopes (collectively marked in green), whereas fossil-derived plastics do not contain \u003csup\u003e14\u003c/sup\u003eC (marked in gray). Soil microorganisms metabolize both SOM and biodegradable plastics, producing CO\u003csub\u003e2\u003c/sub\u003e derived from both sources. The evolved CO\u003csub\u003e2\u003c/sub\u003e is collected and analyzed to determine the fraction of \u003csup\u003e14\u003c/sup\u003eC in soil alone and soil with added plastics, allowing for the evaluation of positive or negative priming effects.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/7647d1ff25097ce94c705338.png"},{"id":108537165,"identity":"24b65019-dc10-4a9b-accf-1d97df92f371","added_by":"auto","created_at":"2026-05-05 17:28:37","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":764562,"visible":true,"origin":"","legend":"\u003cp\u003eDaily CO\u003csub\u003e2\u003c/sub\u003e emissions from soils amended with (A) PCL and (B) PBAT MPs with their predicted partitioning into SOM- and plastic-derived fractions over the biodegradation period. Partitioning is modeled using GPR based on percent modern carbon values obtained from AMS \u003csup\u003e14\u003c/sup\u003eC measurements at selected representative time points. Values derived from actual measurements are indicated by red lines and points.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/ef614d16c5fd817463790c21.png"},{"id":108804278,"identity":"15f255a4-404b-41db-acf4-4eb7b4d2fef3","added_by":"auto","created_at":"2026-05-08 15:18:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":616631,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Bar graph of the absolute priming effects on SOM induced by fossil-derived PCL and PBAT MPs at selected time points following MP amendment. (B) Schematics depicting the distinct mechanisms underlying the negative priming effects caused by biodegradable vs nonbiodegradable plastics through their influences on soil microbial activity.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/06d4b845a1fa7f46282cb30c.png"},{"id":108537168,"identity":"b7120ee8-4aa0-4c10-87d1-33874707f1f2","added_by":"auto","created_at":"2026-05-05 17:28:37","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":689576,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of CO\u003csub\u003e2\u003c/sub\u003e capture methods used in biodegradation experiments. (A) Open-system setup following ISO14855-2, where CO\u003csub\u003e2\u003c/sub\u003e released from sample incubation is continuously carried by CO\u003csub\u003e2\u003c/sub\u003e-free air flow and cumulatively collected in an alkaline column. (B) Closed-system setup following ASTM D5988, where CO\u003csub\u003e2\u003c/sub\u003e is trapped using an alkaline solution in a sealed jar. The alkaline solution can be refreshed at the desired time point, allowing time-resolved sampling. (C) Titration-based (conventional ASTM D5988) and (D) precipitation (modified ASTM D5988) method for CO\u003csub\u003e2\u003c/sub\u003e quantification and obtaining material for graphitization and AMS analysis.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/33e535122de33d8de91326db.png"},{"id":108809570,"identity":"834074f4-8bd1-447a-8857-35157e72c323","added_by":"auto","created_at":"2026-05-08 15:53:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3072428,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/c4a59dfe-39cf-4ee8-b348-ef5b179b49d7.pdf"},{"id":108804916,"identity":"7e3c0e21-05d1-4164-90c3-a90a27082cf4","added_by":"auto","created_at":"2026-05-08 15:24:14","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3907079,"visible":true,"origin":"","legend":"","description":"","filename":"PrimingmanuscriptSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/1778c9cff5d7c9a1afbae54e.docx"},{"id":108804379,"identity":"5bbea5d7-9c12-428f-b2dc-ca33d90bab1a","added_by":"auto","created_at":"2026-05-08 15:20:00","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":167237,"visible":true,"origin":"","legend":"\u003cp\u003eAs biodegradable plastics become more commonly integrated to the modern economy, soil contamination by biodegradable microplastics (MPs) has raised concerns owing to their potential to alter soil organic matter (SOM), an important carbon reservoir, through priming effects. Priming effects refer to the acceleration (positive) or suppression (negative) of SOM decomposition following external carbon input. Previous studies have relied on carbon-13 isotope analysis, which lacks the resolution required for precise carbon tracing, to study the priming effects of biodegradable MPs. Herein, we present a robust approach combining accelerator mass spectrometry-based radiocarbon (carbon-14) analysis with a closed-jar incubation system to quantify the priming effects of two fossil-based biodegradable MPs, poly(ε-caprolactone) (PCL) and poly(butylene adipate--terephthalate) (PBAT). This method enables high-resolution time-resolved partitioning of biogenic and fossil-derived carbons. Both biodegradable MPs show a net negative priming effect (up to \u0026amp;minus;\u0026amp;thinsp;35.4 \u0026amp;micro;g C g soil for PCL and \u0026amp;minus;\u0026amp;thinsp;9.6 \u0026amp;micro;g C g soil for PBAT) over a 50-d incubation period, with transient positive priming observed at certain time points. This study provides a robust approach for accurate assessment of plastic\u0026amp;ndash;SOM interactions and offers an important analytical framework to devise end-of-life management strategies for biodegradable plastics in agroecosystems.\u003c/p\u003e","description":"","filename":"GA.png","url":"https://assets-eu.researchsquare.com/files/rs-9383674/v1/9cb36d77ff2cb2b3ec9ee62a.png"}],"financialInterests":"No competing interests reported.","formattedTitle":"Time-Resolved Investigation of the Priming Effect of Biodegradable Plastics on Soil Organic Matter Using Radiocarbon Analysis","fulltext":[{"header":"Synopsis","content":"\u003cp\u003eThis study employs radiocarbon analysis using accelerator mass spectrometry to investigate the priming effect of biodegradable microplastics on soil organic matter, highlighting the need for their management strategies in agroecosystems.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eThe Earth\u0026rsquo;s carbon cycle has been increasingly disrupted by human activities since industrialization. In particular, fossil fuel combustion and land use changes (such as deforestation and agricultural practices) annually emit over 13 Gt of carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) into the atmosphere, significantly contributing to global warming.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e As an important terrestrial carbon reservoir, soil stores approximately 2344 Gt of carbon but is susceptible to anthropogenic disturbances (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA).\u003csup\u003e\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e The loss of soil carbon can accelerate atmospheric CO\u003csub\u003e2\u003c/sub\u003e accumulation and intensify climate change.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA key anthropogenic influence on soil carbon dynamics is the introduction of external carbon inputs through a process known as the priming effect, in which foreign organic matter alters the decomposition rate of native soil organic matter (SOM).\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e Positive priming accelerates SOM decomposition, releasing additional CO\u003csub\u003e2\u003c/sub\u003e into the atmosphere and intensifying global warming, whereas negative priming slows SOM breakdown, enhancing carbon retention in soil, and supporting soil biota and ecosystem functions.\u003csup\u003e\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003ePlastic pollution in soil has become one of the most pervasive environmental challenges. A major concern is the accumulation of microplastics (MPs; 0.1\u0026ndash;5,000 \u0026micro;m) and nanoplastics (NPs; 1\u0026ndash;100 nm), where concentrations can reach up to 2830 particles kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil.\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e These particles represent a growing persistent carbon input that not only alters soil physical structure but also influences SOM dynamics through priming effects.\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eTo address plastic pollution, bioplastics have been developed. Together with conventional plastics, these materials are classified according to feedstock origin (bio-based vs. fossil-based) and biodegradability into four types.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Type 1 comprises bio-based biodegradable plastics, such as polylactide (PLA), polyhydroxyalkanoate (PHA), and starch-based plastics. Type 2 includes fossil-based biodegradable plastics, represented by poly(butylene adipate-\u003cem\u003eco\u003c/em\u003e-terephthalate) (PBAT), poly(ε-caprolactone) (PCL), and poly(butylene succinate) (PBS). Type 3 refers to bio-based nonbiodegradable plastics, including bio-poly(ethylene terephthalate) (bio-PET), bio-polyethylene (bio-PE), bio-polypropylene (bio-PP), and isosorbide-based polymers. Type 4 consists of conventional fossil-based, nonbiodegradable plastics, such as polyethylene (PE), polypropylene (PP), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polystyrene (PS). Under this classification, biodegradable plastics correspond to Types 1 and 2, whereas bioplastics encompass Types 1\u0026ndash;3.\u003c/p\u003e \u003cp\u003eBiodegradable plastics are designed to be broken down by microorganisms into water and CO\u003csub\u003e2\u003c/sub\u003e (under aerobic conditions) or CH\u003csub\u003e4\u003c/sub\u003e (under anaerobic conditions). Their environmental effects have recently become controversial, as once introduced to soil, biodegradable plastics fragment into MPs and NPs (during the early stages of biodegradation) that can persist temporarily before complete mineralization.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e Unlike their nonbiodegradable counterparts that are inert, biodegradable MPs and NPs can act as carbon sources accessible to microorganisms.\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e As soil microorganisms generally prefer labile organic matter, low concentrations of easily metabolizable substrates (such as glucose) added to soil generally suppress SOM breakdown (negative priming).\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e By contrast, higher concentrations stimulate microbial activity, triggering nutrient mining, in which microorganisms decompose SOM to access other nutrients such as nitrogen or phosphorus (positive priming).\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Similarly, biodegradable MPs and their decomposition products may induce priming effects, thereby influencing soil carbon cycling and ecosystem processes.\u003c/p\u003e \u003cp\u003eUnderstanding the priming effects of biodegradable MPs is therefore essential for improving the end-of-life management strategies for biodegradable plastics in agroecosystems. As these materials become increasingly prevalent in the modern economy, research on their soil\u0026ndash;carbon interactions has intensified over the past few years..\u003c/p\u003e \u003cp\u003eElucidating the priming effect of plastics on SOM requires identifying the source of CO\u003csub\u003e2\u003c/sub\u003e evolved after MP addition (i.e., whether CO\u003csub\u003e2\u003c/sub\u003e originates from plastics or SOM decomposition) and comparing SOM-derived CO\u003csub\u003e2\u003c/sub\u003e with that from unamended soil. Stable isotope (carbon-13, \u003csup\u003e13\u003c/sup\u003eC) analysis via isotope-ratio mass spectrometry (IRMS) has been commonly used for this purpose.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e This technique relies on differences in the natural abundance of \u003csup\u003e13\u003c/sup\u003eC (expressed as δ\u003csup\u003e13\u003c/sup\u003eC: \u003csup\u003e13\u003c/sup\u003eC/\u003csup\u003e12\u003c/sup\u003eC atomic ratio), which varies between bioplastics and soil. Fossil-based plastics typically exhibit δ\u003csup\u003e13\u003c/sup\u003eC values between \u0026minus;\u0026thinsp;36 and \u0026minus;\u0026thinsp;24\u0026permil;, while bio-based plastics derived from C4 plants such as maize range from \u0026minus;\u0026thinsp;14 to \u0026minus;\u0026thinsp;10\u0026permil;. Soil δ\u003csup\u003e13\u003c/sup\u003eC values usually reflect the vegetation type, ranging from \u0026minus;\u0026thinsp;35 to \u0026minus;\u0026thinsp;25\u0026permil; for C3 plants, and \u0026minus;\u0026thinsp;14 to \u0026minus;\u0026thinsp;10\u0026permil; for C4 plants.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e Most studies investigating priming effects of biodegradable plastics, such as PLA,\u003csup\u003e32\u0026ndash;34\u003c/sup\u003e (PHA),\u003csup\u003e33\u003c/sup\u003e PBS,\u003csup\u003e35\u003c/sup\u003e and (PBAT),\u003csup\u003e33\u003c/sup\u003e have relied on this \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC isotope approach. Although their reported priming effects vary (depending on substrates and soil biotic/abiotic factors), the method itself has a critical limitation. The resolution of \u003csup\u003e13\u003c/sup\u003eC analysis becomes inadequate when the δ\u003csup\u003e13\u003c/sup\u003eC ranges of the input plastic and soil overlap, such as fossil-derived plastics in C3-vegetated soils or C4 plant-derived bioplastics in C4-vegetated soils. The complexity further increases with blends of fossil- and bio-based plastics in soil influenced by mixed vegetation types, making CO\u003csub\u003e2\u003c/sub\u003e source attribution and priming effect interpretation highly uncertain. To address this issue, carbon isotope-labeled substrates have been used to create distinct isotopic profiles with that of soil for improving CO\u003csub\u003e2\u003c/sub\u003e tracing.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e However, isotope labeling is technically demanding and may lead to biased positive priming, as many catabolytic microorganisms preferentially metabolize lighter isotopes (\u003csup\u003e12\u003c/sup\u003eC), leading to underrepresentation of the heavy carbon isotopes in decomposition products.\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e Therefore, approaches based on natural isotope abundance remain more reliable for accurately assessing the priming effects of plastics in soils.\u003c/p\u003e \u003cp\u003eA higher-resolution alternative for tracing CO\u003csub\u003e2\u003c/sub\u003e sources is radiocarbon analysis based on the natural abundance of carbon-14 (\u003csup\u003e14\u003c/sup\u003eC). \u003csup\u003e14\u003c/sup\u003eC is a radioactive isotope continuously produced in the atmosphere with a half-life (\u003cem\u003et\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e) of approximately 5700\u0026thinsp;\u0026plusmn;\u0026thinsp;30 y.\u003csup\u003e38\u003c/sup\u003e Living organisms maintain equilibrium with atmospheric \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC (δ\u003csup\u003e14\u003c/sup\u003eC: \u003csup\u003e14\u003c/sup\u003eC/\u003csup\u003e12\u003c/sup\u003eC\u0026thinsp;~\u0026thinsp;1\u0026ndash;1.5\u0026times; 10\u003csup\u003e\u0026ndash;12\u003c/sup\u003e), but this exchange stops after death, and the decay of \u003csup\u003e14\u003c/sup\u003eC over time renders fossil-derived carbon as \u003csup\u003e14\u003c/sup\u003eC-free.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e The clear distinction in δ\u003csup\u003e14\u003c/sup\u003eC between biogenic and fossil carbon, combined with the high sensitivity of radiocarbon analysis, allows unambiguous source distinction, even when their δ\u003csup\u003e13\u003c/sup\u003eC signatures overlap.\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e Despite these advantages, \u003csup\u003e14\u003c/sup\u003eC analysis has not yet been applied to study the priming effects of biodegradable plastics on SOM.\u003c/p\u003e \u003cp\u003eRadiocarbon measurements are typically performed by liquid scintillation counting (LSC) or accelerator mass spectrometry (AMS) (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). LSC detects \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC by measuring light pulses generated from beta emissions during radioactive decay that interact with a liquid scintillator. This method offers low instrumentation costs but is limited by its low sensitivity and precision.\u003csup\u003e\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e In contrast, AMS provides exceptionally high sensitivity and accuracy by ionizing the sample, accelerating and separating the ions, and directly counting individual \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC atoms, thereby enabling the detection of minute \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC concentrations. AMS is therefore better suited for resolving small changes in CO\u003csub\u003e2\u003c/sub\u003e sources, but it has not been applied to investigate the priming effects of biodegradable plastics on SOM.\u003c/p\u003e \u003cp\u003eHerein, we investigated the priming effects of fossil-based biodegradable MPs (Type 2) on SOM using AMS-based radiocarbon analysis. The fossil δ\u003csup\u003e14\u003c/sup\u003eC signature of MPs (~\u0026thinsp;0) allows for a clear distinction from the biogenic δ\u003csup\u003e14\u003c/sup\u003eC of SOM (~\u0026thinsp;1.2 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;12\u003c/sup\u003e), enabling precise source partitioning of evolved CO\u003csub\u003e2\u003c/sub\u003e from MP degradation and SOM mineralization. To achieve time-resolved sampling, we employed a modified ASTM D5988 biodegradation test protocol\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e to capture CO\u003csub\u003e2\u003c/sub\u003e in sealed incubation jars using an alkaline solution and replacing the absorbent at defined intervals, The captured CO\u003csub\u003e2\u003c/sub\u003e was precipitated as barium carbonate (BaCO\u003csub\u003e3\u003c/sub\u003e), graphitized, and analyzed by AMS. This setup not only accurately traces CO\u003csub\u003e2\u003c/sub\u003e sources but also captures short-term variations in priming effect dynamics. Our study offers a robust framework for understanding the effects of biodegradable MPs on soil carbon and helps devise strategies for managing biodegradable plastics in terrestrial environments.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eBiodegradation and CO\u003csub\u003e2\u003c/sub\u003e Partitioning\u003c/h2\u003e \u003cp\u003eThe biodegradation of fossil-based MPs was conducted following ASTM D5988 (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Treatments included soil only (negative controls) and soil amended with biodegradable poly(ε-caprolactone) (PCL) and poly(butylene adipate-\u003cem\u003eco\u003c/em\u003e-terephthalate) (PBAT) MPs. Polystyrene (PS) MPs were used as a nonbiodegradable control. Key physicochemical properties of the soil are summarized in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e (initial organic matter content of 17.63 wt%, an average moisture content of 28%, and a C/N ratio of 12.5).\u003c/p\u003e \u003cp\u003eSoil microbial activity was first activated by adding 1 wt% glucose\u003csup\u003e46\u0026ndash;50\u003c/sup\u003e and preincubating for about three weeks at 50\u0026deg;C until the CO\u003csub\u003e2\u003c/sub\u003e released from SOM stabilized. After the preconditioning phase, MPs (\u0026lt;\u0026thinsp;125 \u0026micro;m; Figure S2) were added at 0.2 g MP 100 g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil. This level exceeds the typical field concentrations (~\u0026thinsp;4.5 mg MP kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil),\u003csup\u003e17\u003c/sup\u003e and was intentionally chosen to simulate an extreme contamination scenario and ensure sufficient CO\u003csub\u003e2\u003c/sub\u003e evolution for quantifying priming effects within a practical lab time scale. CO\u003csub\u003e2\u003c/sub\u003e sampling was done daily during the first week and then twice weekly thereafter to assess the initial and longer-term priming effects, respectively.\u003c/p\u003e \u003cp\u003eReleased CO\u003csub\u003e2\u003c/sub\u003e captured and precipitated as BaCO\u003csub\u003e3\u003c/sub\u003e was quantified to assess the biodegradation progress of the MPs. Soil amended with PCL and PBAT consistently released more cumulative CO\u003csub\u003e2\u003c/sub\u003e than the unamended control soil, indicating active microbial degradation (Figure S3). PCL-amended soil released 7.49 mmol more CO\u003csub\u003e2\u003c/sub\u003e than the control by day 7 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and 10 mmol more by day 47 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In comparison, PBAT-amended soil produced 3.3 mmol more CO\u003csub\u003e2\u003c/sub\u003e than the control by day 7 (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) and 17 mmol more by day 48, respectively (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). PCL degraded faster than PBAT, likely due to its lower melting point (~\u0026thinsp;55\u0026ndash;60\u0026deg;C) and simpler chemical structure, facilitating enhanced microbial accessibility.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e In contrast, the PS-amended soil released 16 mmol less cumulative CO\u003csub\u003e2\u003c/sub\u003e than the untreated soil (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Figure S5).\u003c/p\u003e \u003cp\u003eSubsequently, we calculated the first derivatives of the cumulative CO\u003csub\u003e2\u003c/sub\u003e release to evaluate the biodegradation dynamics and select suitable time points for AMS analysis (Figure S4). In the PCL treatment, a sharp peak (~\u0026thinsp;4.4 mmol d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was observed within the first 5 d, followed by a steady decline until day 9, indicating rapid initial mineralization by soil microorganisms. In contrast, PBAT showed a sustained CO\u003csub\u003e2\u003c/sub\u003e release rate over 50 d, with notable peaks at days 3 (~\u0026thinsp;2.6 mmol d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and 24 (~\u0026thinsp;1.6 mmol d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Based on these trends, BaCO\u003csub\u003e3\u003c/sub\u003e sampling for AMS analysis was conducted on days 3, 5, and 9 for PCL and on days 2, 3, and 24 for PBAT. Additionally, samples were collected on day 2 for PCL and day 1 for PBAT post-MP addition to capture the early priming effects, which are typically the most pronounced immediately following external carbon input.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe AMS data were first used to partition CO\u003csub\u003e2\u003c/sub\u003e emissions into SOM- and plastic-originated fractions based on the δ\u003csup\u003e14\u003c/sup\u003eC and percent modern carbon (pMC) values, using oxalic acid as the reference standard (Table S2). The δ\u003csup\u003e14\u003c/sup\u003eC value of the soil used was ~\u0026thinsp;1.2\u0026times; 10\u003csup\u003e\u0026ndash;12\u003c/sup\u003e, corresponding to 99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35 pMC, which is close to the modern atmospheric level (~\u0026thinsp;100 pMC). In contrast, added MPs showed\u0026thinsp;\u0026lt;\u0026thinsp;0.1 pMC, consistent with their fossil origin (Table S3).\u003c/p\u003e \u003cp\u003eBecause of the substantial time and cost required for radiocarbon sample pretreatment and AMS, measurements were not feasible for all samples across all collection time points over the 50-d incubation period. To estimate carbon source contribution throughout the entire PCL and PBAT biodegradation period, we applied Gaussian process regression (GPR) to the pMC data from representatively sampled time points to interpolate the CO\u003csub\u003e2\u003c/sub\u003e partitioning results for unsampled time points (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This approach balanced analytical rigor with practical feasibility over extended timeframes. The results revealed that biogenic carbon remained the dominant source of daily CO\u003csub\u003e2\u003c/sub\u003e release and confirmed that PCL degraded more rapidly than PBAT.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003ePriming Effect Quantification\u003c/h3\u003e\n\u003cp\u003eBased on CO\u003csub\u003e2\u003c/sub\u003e fractionation data, the priming effects of fossil-derived biodegradable MPs were calculated as the difference in SOM-derived CO\u003csub\u003e2\u003c/sub\u003e production between MP-amended and unamended soils (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), reported in \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil. Following the addition of biodegradable MPs, an initial negative priming effect was observed, with 35.4 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil for PCL (day 2) and 7.2 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil for PBAT (day 1) (absolute values). Throughout the incubation period, priming effects remained predominantly negative, except for brief positive responses, on day 5 for PCL and day 2 for PBAT. For PCL, the positive priming effect was weaker than its initial negative response. Toward the end of the incubation, strong negative priming effects for both MPs reemerged, with 26.6 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil for PCL (day 9) and 9.6 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil for PBAT (day 24) (absolute values). In contrast, PS exhibited consistent negative priming (21.6 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at day 2, 32.58 \u0026micro;g C g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at day 9) throughout the incubation period (Figure S6). Because PS is not biodegradable, all CO\u003csub\u003e2\u003c/sub\u003e released in PS-amended soil originated solely from SOM, allowing direct calculation of priming effects without AMS-based carbon partitioning..\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe magnitude and mechanisms of the priming effect depended on the type of MP. Among the biodegradable MPs, PCL induced a stronger and more immediate negative priming effect than PBAT, likely due to its higher biodegradability (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA).\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan additionalcitationids=\"CR53\" citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e Its simple molecular structure and low melting point (\u003cem\u003eT\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e ~55\u0026ndash;60\u0026deg;C) facilitated rapid chain scission and hydrolysis, generating degradation intermediates readily assimilated by soil microorganisms. This preferential utilization of PCL-derived carbon reduces microbial reliance on SOM, thereby enhancing the negative priming effect. The intermittent shifts between positive and negative priming observed during the incubation can be attributed to microbial substrate switching, as microorganisms alternated between the SOM and MP-derived carbon depending on nutrient availability.\u003csup\u003e\u003cspan additionalcitationids=\"CR56\" citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e This was indirectly supported by changes in biodegradation kinetics for both PCL and PBAT. Following the brief positive priming (day 5 for PCL and day 2 for PBAT), the relative contribution of biogenic carbon from SOM increased compared with fossil-derived carbon from MPs, as indicated by the GPR-based partitioning (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This shift suggests a temporary reduction in plastic degradation as microorganisms increasingly utilized SOM. Because the tested MPs lack nitrogen, the temporary positive priming effects likely resulted from microbial mining of SOM to acquire nitrogen.\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e As the degradation progressed and labile MP-derived compounds accumulated, they increasingly served as carbon sources and reinforced the negative priming effect. In contrast, PS induced a net negative priming effect through a different mechanism (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). As a non-biodegradable MP, PS acted as a nutrient adsorber or chelator, reducing nutrient bioavailability without providing assimilable carbon.\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e This suppressed microbial growth and activity, resulting in a negative priming effect throughout the incubation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB).\u003csup\u003e\u003cspan additionalcitationids=\"CR60\" citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFurther evidence of priming effect dynamics and nutrient mining was provided by SOM analysis (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Comparison between the pre- and post-incubation samples revealed a decrease in SOM (%C from 17.6% to 17.1%) in the control and PCL-amended soil samples, indicating microbial mineralization of organic matter. In contrast, PBAT- and PS-amended soil samples exhibited an apparent increase in the SOM content (%C from 17.6% to 17.8%), likely attributed to residual PBAT and non-degraded PS MPs remaining in the soil contributing to the measured organic fraction Furthermore, an increase in the C/N ratio (from 12.5 to 13.6\u0026ndash;15.8) in the MP-amended soil supports the nitrogen mining by soil microorganisms in response to MP addition.\u003c/p\u003e\n\u003ch3\u003eTechnological Advances in Investigating the Priming Effects of Biodegradable MPs on SOM\u003c/h3\u003e\n\u003cp\u003eRecent studies have increasingly investigated the ecological impacts of biodegradable MPs, particularly their priming effects on SOM, with most relying on \u003csup\u003e13\u003c/sup\u003eC analysis to distinguish carbon sources between biodegradable plastics and soil.\u003csup\u003e\u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e,\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e,\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e However, as noted in the Introduction, the resolution of \u003csup\u003e13\u003c/sup\u003eC analysis becomes limited when the δ\u003csup\u003e13\u003c/sup\u003eC values of the input plastic and soil overlap, even partially, making carbon-source partitioning and consequently, priming effect quantification unreliable..\u003csup\u003e63\u003c/sup\u003e This limitation was demonstrated in our study, where the AMS data showed that the δ\u003csup\u003e13\u003c/sup\u003eC values of the MPs and soil overlapped (Table S3).\u003c/p\u003e \u003cp\u003eTo overcome this limitation, \u003csup\u003e14\u003c/sup\u003eC analysis was employed for distinguishing fossil-derived plastic carbon (0 pMC) from SOM carbon (~\u0026thinsp;99 pMC). Compared with \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis, \u003csup\u003e14\u003c/sup\u003eC analysis enables unambiguous source tracking even when δ\u003csup\u003e13\u003c/sup\u003eC signatures overlap extensively, for example, when differentiating fossil-based plastics (\u0026minus;\u0026thinsp;36 to \u0026minus;\u0026thinsp;24\u0026permil;) from SOM in C3-vegetated soils (\u0026minus;\u0026thinsp;35 to \u0026minus;\u0026thinsp;25\u0026permil;).\u003csup\u003e31\u003c/sup\u003e. The resolution power of \u003csup\u003e14\u003c/sup\u003eC analysis is further enhanced several orders of magnitude by AMS sensitivity, which can detect \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC up to zeptomole (10\u003csup\u003e\u0026minus;\u0026thinsp;21\u003c/sup\u003e) level,\u003csup\u003e64\u003c/sup\u003e allowing reliable CO\u003csub\u003e2\u003c/sub\u003e partitioning and quantification of priming effects on the SOM induced by biodegradable plastics. Although our study examined a clear-cut case of fossil-based plastics (Type 2), this approach can be extended to more complex systems, such as bio-/fossil-based polymer blends with intermediate pMC values. These materials are increasingly commercialized following the paradigm shift toward sustainable materials and are more likely to exhibit a broader δ\u003csup\u003e13\u003c/sup\u003eC range due to their complex compositions, making \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis a preferred choice over \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis for evaluating the impact of biodegradable MPs on soil carbon dynamics.\u003c/p\u003e \u003cp\u003eA reliable AMS-based \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis requires an effective CO\u003csub\u003e2\u003c/sub\u003e capture system during the biodegradation of MPs in soil. Two standardized biodegradation tests based on ISO 14855-2 (cumulative sampling) and ASTM D5988 (individual sampling) are commonly used (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e,\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e In the cumulative sampling system, CO\u003csub\u003e2\u003c/sub\u003e-free air is continuously supplied to the incubation chamber, and the CO\u003csub\u003e2\u003c/sub\u003e outflow from soil microbial metabolism is captured in an alkaline column trap (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). This approach has been previously applied for AMS-based \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis to monitor the biodegradation of PBS, although its priming effects were not examined.\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e However, the system requires complex equipment, high operation costs, and precise control of CO\u003csub\u003e2\u003c/sub\u003e-free inflow and stable soil conditions. Furthermore, because CO\u003csub\u003e2\u003c/sub\u003e accumulates in a single trap, the carbon signal is integrated over the entire incubation period. This makes it challenging to resolve biogenic and fossil-derived carbon fractions at specific time intervals.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn contrast, the individual sampling system offers a simpler and lower-cost alternative for collecting CO\u003csub\u003e2\u003c/sub\u003e using an alkaline trapping solution in sealed jars. The trapping solution can be easily replaced, and the soil can be aerated at predetermined sampling time points. This approach allows the monitoring of CO\u003csub\u003e2\u003c/sub\u003e emissions and quantification of biogenic and fossil-based carbon fractions at discrete time points, thereby enabling a time-resolved evaluation of the priming effect throughout the biodegradation process. This setup is also particularly advantageous for slowly degrading polymers such as PBAT, as it eliminates the need for a prolonged, continuous CO\u003csub\u003e2\u003c/sub\u003e-free air supply and soil conditioning. It also enables the identification of temporal shifts in priming effects (e.g., negative to positive), which would otherwise be obscured under cumulative sampling.\u003c/p\u003e \u003cp\u003eWe note that the ASTM D5988 protocol quantifies CO\u003csub\u003e2\u003c/sub\u003e by titrating the alkaline trapping solution with an acid that releases CO\u003csub\u003e2\u003c/sub\u003e during the process, making it impossible to recover carbon in a solid form for further treatment and analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). To enable downstream \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis, we replaced this titration step with precipitation. Specifically, CO\u003csub\u003e2\u003c/sub\u003e absorbed in the alkaline solution was converted to stable BaCO\u003csub\u003e3\u003c/sub\u003e by reacting with barium chloride (BaCl\u003csub\u003e2\u003c/sub\u003e). The resulting precipitate was graphitized and analyzed for \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC by AMS (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD).\u003c/p\u003e\n\u003ch3\u003eImplications and Limitation of This Study\u003c/h3\u003e\n\u003cp\u003eThe priming effects observed in this study should not be taken as universally representative, as they may vary across different soil types, environmental conditions, and the physicochemical properties of the MPs introduced to the soil (e.g., structural composition and particle size).\u003csup\u003e\u003cspan additionalcitationids=\"CR69\" citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e\u003c/sup\u003e Prior studies on PLA illustrate this variability: positive priming effects have been reported in sandy soil, whereas negative priming effects have been observed in paddy soils, with soil pH identified as one of key controlling factors.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e We emphasize here again that these studies partitioned carbon sources using \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis. Due to its limitation as discussed above, these reported differences in the priming effects may reflect analytical limitations rather than true biological responses. Furthermore, our results highlight that priming should not be evaluated solely from net cumulative outcomes. Although we demonstrated that the net priming effect of biodegradable MPs was negative, time-resolved measurements revealed transient positive shifts owing to microbial substrate switching and nutrient demands. However, under different soil and environmental conditions, the opposite can be observed.\u003c/p\u003e \u003cp\u003eFurthermore, this study employed an elevated incubation temperature (50\u0026deg;C) representative of industrial composting conditions to promote the growth of thermophilic microorganisms. This temperature also reflects natural biological self-heating processes in soils during winter, where microbial degradation of SOM generates heat up to ~\u0026thinsp;70\u0026deg;C, to warm plant roots, facilitate nutrient cycling, and suppress pathogens.\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e This elevated temperature was applied to accelerate polymer degradation and enable measurable CO\u003csub\u003e2\u003c/sub\u003e evolution within a short laboratory timeframe, particularly for slow-degrading polymers such as PBAT. These conditions differ from typical field environments, where lower temperatures, slower microbial activity, and extended degradation timescales may alter both MP degradation kinetics and associated priming effects. Consequently, the magnitude and temporal patterns of priming observed here may not directly translate to natural soils.\u003c/p\u003e \u003cp\u003eWe also used a relatively high MP concentration, exceeding the typical values reported for intensively managed agricultural soil,\u003csup\u003e17\u003c/sup\u003e to ensure detectable and distinguishable CO\u003csub\u003e2\u003c/sub\u003e production between MP-amended and unamended soils. Furthermore, capturing CO\u003csub\u003e2\u003c/sub\u003e in a closed system prevented atmospheric exchange and allowed accurate quantification. Therefore, scaling this study to field conditions would require a more robust CO\u003csub\u003e2\u003c/sub\u003e capture system that minimizes atmospheric contamination while accommodating much lower CO\u003csub\u003e2\u003c/sub\u003e fluxes from both MP mineralization and MP-induced priming relative to the substantially larger CO\u003csub\u003e2\u003c/sub\u003e background from SOM decomposition. Because the difference in CO\u003csub\u003e2\u003c/sub\u003e yields between control and MP-contaminated soils in the field is expected to be extremely small compared with that under optimized laboratory conditions, overcoming the CO\u003csub\u003e2\u003c/sub\u003e capture bottleneck would make radiocarbon analysis particularly advantageous. The minute sample requirement and high sensitivity of AMS-based \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis provide reliable source partitioning over the IRMS-based \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis.\u003c/p\u003e \u003cp\u003eAdditionally, while the \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis provides a clear-cut distinction between carbon derived from fossil-based plastics and that from soil, assessing the priming effects of biobased biodegradable plastics (Type 1) can be more challenging as their radiocarbon signatures are often similar to those of the soil (both being biogenic carbon). In such cases, it is necessary to maximize/optimize the zeptomol resolution of AMS to resolve the δ\u003csup\u003e14\u003c/sup\u003eC between plastic- and soil-derived CO\u003csub\u003e2\u003c/sub\u003e. Complementary \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis can be employed to provide a more definite conclusion, for example by partitioning carbon from C4-plant-derived bioplastics and C3-vegetated soils. Alternatively, radioactive isotopic labeling can be used to give the input bioplastic a distinct isotopic profile relative to the soil to improve the \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC analysis resolution.\u003c/p\u003e \u003cp\u003eAlthough this study represents an early-stage effort, it establishes a methodological foundation for future investigations into the priming effects of biodegradable plastics on SOM using AMS-based radiocarbon analysis. Further research is still required to elucidate MP\u0026ndash;soil interactions in shaping the priming response. Importantly, the ability of \u003csup\u003e14\u003c/sup\u003eC analysis to reveal priming effects highlights an important consideration for biodegradation studies: without accounting for change in SOM mineralization upon plastic addition, the extent of plastic degradation in soil can be under- or overestimated. Finally, the more reliable interpretation of the priming effect enabled by \u003csup\u003e14\u003c/sup\u003eC analysis over \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis is particularly significant in shaping environmental policies regarding the use of biodegradable plastic products in soils, such as agricultural mulch films. Positive priming leading to SOM loss may justify restrictions on their use, whereas negative priming may indicate short-term enhancement of soil carbon retention.\u003c/p\u003e \u003cp\u003eOverall, this study demonstrated that AMS-based radiocarbon analysis provides a robust approach for quantifying priming effects in soils amended with fossil-derived biodegradable MPs. In contrast to conventional \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC analysis-based methods, which are constrained by overlapping isotopic signatures, \u003csup\u003e14\u003c/sup\u003eC analysis enables unambiguous separation of plastic-derived carbon from biogenic SOM. Utilizing a modified ASTM D5988 protocol involving CO\u003csub\u003e2\u003c/sub\u003e capture and precipitation, we achieved time-resolved resolution of both short- and longer-term priming dynamics. Under the laboratory conditions examined, we showed that PCL and PBAT MPs induced a net negative priming effect, with transient positive priming phases, likely driven by microbial substrate switching and nutrient mining. While these findings are yet to generalize environmental impacts on soil carbon dynamics induced by biodegradable MPs, this study provides an analytical framework transferrable across multiple plastics\u0026ndash;soil systems for studying their interactions. Furthermore, it offers a tool to inform end-of-life management strategies and evidence-based policies governing the use of biodegradable plastics in agroecosystems.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eReagents\u003c/h2\u003e \u003cp\u003ePCL (average \u003cem\u003eM\u003c/em\u003e\u003csub\u003en\u003c/sub\u003e = 80,000 g mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), PS (average \u003cem\u003eM\u003c/em\u003e\u003csub\u003ew\u003c/sub\u003e 35,000), glucose, potassium hydroxide (\u0026ge;\u0026thinsp;85%), and barium chloride dihydrate (\u0026ge;\u0026thinsp;99%) were purchased from Sigma-Aldrich (USA). PBAT was purchased from Ankor Bioplastics (S. Korea). All reagents were stored according to the manufacturer\u0026rsquo;s instructions and used as received. Deionized water was purified using a Milli-Q Integral 3 system (Millipore, USA), with a final resistivity of 18.0 MΩ cm at 25\u0026deg;C.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMicroplastics\u003c/h3\u003e\n\u003cp\u003eMPs were prepared by cryogenic-grinding polymer pellets using a horizontal 6875 Freezer/Mill (Spex SamplePrep, Antylia Scientific, USA) for 15 min in liquid nitrogen. The resulting powder was passed through a 125 \u0026micro;m standard test sieve (BS0125-75, LK Labkorea) to collect PMs of uniform sizes.\u003c/p\u003e\n\u003ch3\u003eSoil\u003c/h3\u003e\n\u003cp\u003eSoil used for the biodegradation experiment was obtained from Jisaengto (S. Korea). The soil was ground and sieved to \u0026lt;\u0026thinsp;2 mm using a standard test sieve (BS2000, LK Labkorea). Its basic physicochemical properties were analyzed at Cheillab and are listed in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eBiodegradation and CO\u003csub\u003e2\u003c/sub\u003e Capture Setup\u003c/h2\u003e \u003cp\u003eBiodegradation and CO\u003csub\u003e2\u003c/sub\u003e trapping experiments were conducted in sealed glass vessels following the ASTM D5988 with suitable modifications. All treatments were performed in triplicate. Each vessel contained 200 g of soil amended with MPs or left unamended as a control. Prior to MP addition, the microbial activity was activated by adding glucose (1 wt% relative to soil) and incubating the soil at 50\u0026deg;C in airtight glass vessels sealed with O-rings and split-ring closures in a temperature-controlled incubator (BF-250IN, Biofree, Korea), with moisture inside the vessel maintained using an open vial of deionized water. Evolved CO\u003csub\u003e2\u003c/sub\u003e was captured in an open vial containing 2 M KOH aqueous solution (50 mL). The soil was aerated every 3 d by stirring, and deionized water was added to maintain\u0026thinsp;\u0026gt;\u0026thinsp;80 wt% water content as needed.\u003c/p\u003e \u003cp\u003eOnce CO\u003csub\u003e2\u003c/sub\u003e evolution stabilized, 0.4 g of PCL, PBAT, or PS (nonbiodegradable control) MPs were added to the soil. Evolved CO\u003csub\u003e2\u003c/sub\u003e was captured in an open vial containing 1 M KOH aqueous solution, which was replaced daily during the first 7 d, then every 3 d thereafter. The soil containing MPs was aerated daily, and moisture was maintained by adding deionized water as needed.\u003c/p\u003e \u003cp\u003eTo quantify the pMC of the evolved CO\u003csub\u003e2\u003c/sub\u003e during biodegradation, the CO\u003csub\u003e2\u003c/sub\u003e absorbed in KOH was precipitated as barium carbonate (BaCO\u003csub\u003e3\u003c/sub\u003e) by dropwise addition of saturated BaCl\u003csub\u003e2\u003c/sub\u003e solution. Precipitation was controlled to avoid coprecipitation of barium hydroxide [Ba(OH)\u003csub\u003e2\u003c/sub\u003e]. The resulting BaCO\u003csub\u003e3\u003c/sub\u003e was dried \u003cem\u003ein vacuo\u003c/em\u003e at ambient temperature. The dried BaCO\u003csub\u003e3\u003c/sub\u003e was used both to calculate CO\u003csub\u003e2\u003c/sub\u003e evolution and for AMS analysis of pMC.\u003c/p\u003e \u003cp\u003e \u003cb\u003eGraphitization/Reduction of BaCO\u003c/b\u003e \u003csub\u003e \u003cb\u003e3\u003c/b\u003e \u003c/sub\u003eCarbon atoms in BaCO\u003csub\u003e3\u003c/sub\u003e [C(IV)] were converted to graphite [C(0)] through sequential acid hydrolysis, vaporization, and catalytic reduction. Briefly, BaCO\u003csub\u003e3\u003c/sub\u003e (~\u0026thinsp;19.7 mg) was reacted with phosphoric acid (H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e, 5 mL) in a Schlenk flask sealed with a gas-tight stopcock connected to a vacuum manifold. The flask was incubated in a hot water bath at 90\u0026deg;C for 1 h to facilitate the reaction. The evolved CO\u003csub\u003e2\u003c/sub\u003e was first cold-trapped twice using a dry ice\u0026ndash;ethanol bath at \u0026minus;\u0026thinsp;76\u0026deg;C under vacuum to remove water vapor and volatile contaminants. Subsequently, the outlet CO\u003csub\u003e2\u003c/sub\u003e was cryogenically trapped in another tube using liquid nitrogen at \u0026minus;\u0026thinsp;196\u0026deg;C under 3 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e torr. The collected CO\u003csub\u003e2\u003c/sub\u003e was then transferred to a sealed borosilicate reactor containing precombusted iron powder (325 mesh; 5 mg) as a catalyst and reduced to graphite under excess hydrogen gas (H\u003csub\u003e2\u003c/sub\u003e:CO\u003csub\u003e2\u003c/sub\u003e molar ratio\u0026thinsp;~\u0026thinsp;3:1) at 650\u0026deg;C for 10 h. The resulting graphite (~\u0026thinsp;1 mg) was recovered, compacted in a sample holder, and analyzed by AMS for radiocarbon isotopic composition.\u003csup\u003e\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e\u003c/sup\u003e AMS measurements were conducted in triplicate for each sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eAMS\u003c/h2\u003e \u003cp\u003eCarbon isotopes (\u003csup\u003e14\u003c/sup\u003eC, \u003csup\u003e13\u003c/sup\u003eC, and \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003eC) were analyzed using AMS (MICADAS, Ionplus AG, Switzerland). BaCO\u003csub\u003e3\u003c/sub\u003e-derived graphitized carbon was packed into aluminum cathodes and ionized using a cesium sputter cation beam. The generated carbon anions were accelerated and separated based on their atomic mass-to-charge ratios using a high-energy analyzing magnet. \u003csup\u003e12\u003c/sup\u003eC and \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC isotopes were quantified as ion currents with multi-Faraday cups, whereas the \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC atoms were detected as discrete events using a solid-state detector equipped with a semiconductor absorber for energy discrimination and background suppression. The \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003eC was measured relative to the US National Institute of Standards and Technology (NIST) oxalic acid II (SRM 4990C) and IAEA-C7 as modern and fossil reference standards, respectively, and expressed as the pMC. AMS analyses were done in triplicate for each sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003ePriming Effect Calculation\u003c/h2\u003e \u003cp\u003eThe biogenic carbon content obtained from AMS was attributed to carbon derived from the soil. The priming effect was calculated based on the total amount of CO\u003csub\u003e2\u003c/sub\u003e released and the biocarbon content determined by AMS analysis as follows:\u003c/p\u003e \u003cp\u003eSoil priming (mmol) =(C\u003csub\u003esample\u003c/sub\u003e ✕ B)/100)\u0026minus;C\u003csub\u003esoil\u003c/sub\u003e\u003c/p\u003e \u003cp\u003ewhere C\u003csub\u003esoil\u003c/sub\u003e is the total CO\u003csub\u003e2\u003c/sub\u003e released from the control (mmol), C\u003csub\u003esample\u003c/sub\u003e is the total CO\u003csub\u003e2\u003c/sub\u003e released from the sample (mmol), and B is the normalized biogenic carbon content of the sample relative to that of soil (%).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eGPR\u003c/h2\u003e \u003cp\u003eGPR was employed to model the evolution of experimentally measured biogenic carbon content as a continuous function of time. For each observation, the measured response was expressed as the sum of an underlying latent function and random noise. Specifically, for each day time, \u003cem\u003ei\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1, 2, ..., \u003cem\u003en\u003c/em\u003e, the modeling framework is \u003cem\u003ey\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e = \u003cem\u003ef\u003c/em\u003e(\u003cem\u003ex\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e) + \u003cem\u003eε\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e, where \u003cem\u003ey\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e is the experimentally observed biogenic carbon content, \u003cem\u003ex\u003c/em\u003e\u003csub\u003ei\u003c/sub\u003e is the measurement time (day) and ε is the random noise. The latent function \u003cem\u003ef\u003c/em\u003e(\u003cem\u003ex\u003c/em\u003e) was modeled as a zero-mean Gaussian process, \u003cem\u003ef\u003c/em\u003e(\u003cem\u003ex\u003c/em\u003e)\u0026sim;GP(0, \u003cem\u003ek\u003c/em\u003e(\u003cem\u003ex\u003c/em\u003e,\u003cem\u003ex\u0026prime;\u003c/em\u003e)), with a squared exponential covariance function that encodes temporal smoothness through the distance between observation times. The kernel includes a length-scale parameter that determines how the function varies with time.\u003c/p\u003e \u003cp\u003eGiven the limited number of observations and their irregular temporal spacing, GPR provides a flexible nonparametric framework capable of capturing nonlinear temporal trends without assuming a predefined functional form. Model predictions were obtained from the posterior distribution of the Gaussian process, where the posterior mean represents the predicted value and the posterior variance quantifies the associated uncertainty. In addition to point estimates, GPR provides predictive uncertainty. The mean prediction and the associated 70% confidence intervals were obtained from the posterior distribution.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSungbin Ju\u003c/strong\u003e - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; https://orcid.org/0000-0003-3224-5929\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLam Tan Hao\u003c/strong\u003e - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; https://orcid.org/0000-0001-9791-6071\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSemin Kim\u003c/strong\u003e - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMinkyung Lee\u003c/strong\u003e - Technical Support Center for Chemical Industry, Korea Research Institute of Chemical Technology (KRICT); Ulsan 44429, Republic of Korea\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHyo Jeong Kim\u003c/strong\u003e - Research Center for Bio-based Chemistry, Korea Research Institute of Chemical Technology (KRICT), Ulsan 44429, Republic of Korea; Advanced Materials \u0026amp; Chemical Engineering, Korea National University of Science and Technology (UST), Daejeon 34113, Republic of Korea; https://orcid.org/0000-0002-5331-5407\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eS.J. and L.T.H. performed the experiments, analyzed the data, and wrote the manuscript. S.J., L.T.H, and D.X.O. prepared the figures. S.K. and M.L. performed AMS analysis. H.J.K. validated the manuscript. H.J., J.P., and D.X.O. conceived, designed, and directed the project.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Research Foundation (NRF) of Korea, funded by the Ministry of Science and ICT (RS-2024-00408795), and by the Korea Institute of Marine Science \u0026amp; Technology Promotion (KIMST), funded by the Ministry of Oceans and Fisheries (RS-2025-02305544). H.J. acknowledges the support from the Technology Innovation Program funded by the Ministry of Trade Industry \u0026amp; Energy (MOTIE), Republic of Korea (RS-2025-02313873), and from the Korea Research Institute of Chemical Technology core project (KS2642-10).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eFriedlingstein P, Jones MW, O\u0026rsquo;Sullivan M, Andrew RM, Bakker DCE, Hauck J, Le Qu\u0026eacute;r\u0026eacute; C, Peters GP, Peters W, Pongratz J et al (2022) Global carbon budget 2021. Earth Syst Sci Data 14:1917\u0026ndash;2005\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eInternational Energy Agency (2008) World energy outlook 2008. World Energy Outlook; OECD,\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrumbore SE (1997) Potential responses of soil organic carbon to global environmental change. 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Radiocarbon 43:299\u0026ndash;304\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"priming effect, biodegradable plastic, soil, carbon-14, soil organic matter, acceleration mass spectrometry","lastPublishedDoi":"10.21203/rs.3.rs-9383674/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9383674/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"As biodegradable plastics become more commonly integrated to the modern economy, soil contamination by biodegradable microplastics (MPs) has raised concerns owing to their potential to alter soil organic matter (SOM), an important carbon reservoir, through priming effects. Priming effects refer to the acceleration (positive) or suppression (negative) of SOM decomposition following external carbon input. Previous studies have relied on carbon-13 isotope analysis, which lacks the resolution required for precise carbon tracing, to study the priming effects of biodegradable MPs. Herein, we present a robust approach combining accelerator mass spectrometry-based radiocarbon (carbon-14) analysis with a closed-jar incubation system to quantify the priming effects of two fossil-based biodegradable MPs, poly(ε-caprolactone) (PCL) and poly(butylene adipate--terephthalate) (PBAT). This method enables high-resolution time-resolved partitioning of biogenic and fossil-derived carbons. Both biodegradable MPs show a net negative priming effect (up to \u0026minus;\u0026thinsp;35.4 \u0026micro;g C g soil for PCL and \u0026minus;\u0026thinsp;9.6 \u0026micro;g C g soil for PBAT) over a 50-d incubation period, with transient positive priming observed at certain time points. This study provides a robust approach for accurate assessment of plastic\u0026ndash;SOM interactions and offers an important analytical framework to devise end-of-life management strategies for biodegradable plastics in agroecosystems.","manuscriptTitle":"Time-Resolved Investigation of the Priming Effect of Biodegradable Plastics on Soil Organic Matter Using Radiocarbon Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-05 17:28:31","doi":"10.21203/rs.3.rs-9383674/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-17T14:05:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-16T17:57:01+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T10:21:10+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T08:39:29+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T07:52:11+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"338738491410751862652645049011538948189","date":"2026-04-26T17:12:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"197174347581911313523958212617592623359","date":"2026-04-26T12:36:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"227883819706349228133583953291297501511","date":"2026-04-26T03:19:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"176943859466958669655746553417686723988","date":"2026-04-24T12:50:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"18615553495625393227539496708154623989","date":"2026-04-24T11:28:49+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-24T11:18:33+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-11T12:48:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-11T12:48:31+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymers and the Environment","date":"2026-04-11T01:19:53+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymers-and-the-environment","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jooe","sideBox":"Learn more about [Journal of Polymers and the Environment](https://www.springer.com/journal/10924)","snPcode":"10924","submissionUrl":"https://submission.nature.com/new-submission/10924/3","title":"Journal of Polymers and the Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"621839d8-ead2-4330-8804-59545bad0daf","owner":[],"postedDate":"May 5th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-17T14:05:04+00:00","index":26,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-16T17:57:01+00:00","index":25,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T10:21:10+00:00","index":24,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-15T08:39:29+00:00","index":23,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-05T07:52:11+00:00","index":22,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-05T17:28:31+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-05 17:28:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9383674","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9383674","identity":"rs-9383674","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}