Publications

In-vitro incubation of environmental samples is a common approach to estimate CH4 oxidation potential. Here we developed and verified an in-situ method utilizing passive diffusion chambers (PDC, silicone tubes) to deliver 13C-labeled CH4 into peat for the determination of the CH4 oxidation potential based on 13C excess of CO2. To target CH4 oxidation under semi-aerobic and anaerobic conditions, we installed 20 PDCs (30 ml volume) below the water table in profiles from 35-cm to 2-m depths of a peatland in north-eastern Sweden in July 2017 using a peat auger. 13C-labeled CH4 was injected into PDCs through tubing twice during 12 days (day 0 and 6) and samples were collected at days 1, 3, 6, 8 and 11. Background (non-labeled) δ13C of CO2 ranged from −7.3 (35 cm) to +5.7‰ (200 cm) with depth. These δ13C values rose to +110 and + 204‰ after the CH4 injection. The estimated CH4-derived C in CO2 was the lowest at the bottom of the profile (0.3 μmol L−1), whereas the maximum was at 100 cm (6.1 μmol L−1) at five days after the second labeling. This corresponded to 1.5–7.2% of the total CH4 pool to be oxidized, depending on depth. This novel approach with belowground in-situ 13C labeling of gases demonstrated the suitability of tracing the transformations of these gases in soil depth by PDCs and for the first time verified the in-situ occurrence of a deep-peat CH4 oxidation.

Tussock microhabitat is a universal phenomenon in wetlands, where soil and plant properties differ from their surrounding lawns. This study aims to investi

Biodegradable microplastics (MPs), which are starting to be used in large quantities in croplands, may affect the mineralization of soil organic carbon (SOC). These priming effects induced by biodegradable MPs are a very new issue, and their mechanisms as well as consequences for various soils are nearly unknown. Using stable carbon isotope signature (δ13C), we quantified the priming effects by adding corn (C4 plant) -based polylactic acid (PLA, δ13C = 11.9‰) MPs to three paddy soils with solely C3 signature: Ferralsol, Alfisol and Mollisol at two rates (0.5 and 1.0 wt%, based on the mass of MPs). After the incubation (180 days), PLA-MPs reduced the SOC mineralization in all three soils, triggering a negative priming effect. This negative priming effect was strongest in Mollisol (210–220 mg CO2–C kg−1). The net C balance in Mollisol was positive and clearly larger than the C amounts initially added with PLA-MPs to soils, indicating C accrual. The two main mechanisms of the negative priming effects were: i) sorptive protection of SOC and especially of dissolved organic carbon (DOC) by PLA-MPs, and ii) reduction of microbial biomass and fungal diversity after PLA-MPs addition. Additionally, “switching of microbial decomposition from SOC to PLA-MPs” was pronounced in Mollisol, indicated by more PLA-MPs being mineralized. PLA-MPs thus changed the soil C stock and dynamics mediated in part by the changes of microbial biomass, diversity, and community composition, switch of utilization to new resources and decrease of SOC mineralization, all of them leading to C accumulation in soil.

No abstract is provided for this article.

Microplastic threats to biodiversity, health and ecological safety are adding to concern worldwide, but the real impacts on the functioning of organisms and ecosystems are obscure owing to their inert characteristics. Here we investigated the long-lasting ecological effects of six prevalent microplastic types: polyethylene (PE), polypropylene (PP), polyamide (PA), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) on soil bacteria at a 2 % (w/w) level. Due to the inertia and lack of available nitrogen of these microplastics, their effects on bacteriome tended to converge after one year and were strongly different from their short-term effects. The soil volumes around microplastics were very specific, in which the microplastic-adapted bacteria (e.g., some genera in Actinobacteria) were enriched but the phyla Bacteroidetes and Gemmatimonadetes declined, resulting in higher microbial nitrogen requirements and reduced organic carbon mineralization. The reshaped bacteriome was specialized in the genetic potential of xenobiotic and lipid metabolism as well as related oxidation, esterification, and hydrolysis processes, but excessive oxidative damage resulted in severe weakness in community genetic information processing. According to model predictions, microplastic effects are indirectly derived from nutrients and oxidative stress, and the effects on bacterial functions are stronger than on structure, posing a heavy risk to soil ecosystems.

Plastic film mulching and nitrogen (N) fertilization are two important field management practices used to increase crop yields in rain-fed agriculture in arid and semi-arid areas. These two practices, however, can have opposing effects on soil organic carbon (SOC) stock and turnover. To clarify and analyze the combined effects of these practices, we conducted a 7-year continuous maize cultivation experiment with four treatments: (1) no plastic film mulching without N fertilization (Control), (2) plastic film mulching without N fertilization (PFM), (3) N fertilization without plastic film mulching (N), and (4) plastic film mulching with N fertilization (PFM + N). The 13C natural abundance of in the light and heavy fractions of organic carbon (LFOC and HFOC) was used to differentiate "old" (>7 years) and "new" (<7 years) C in the soil after C3 to C4 vegetation change. PFM increased soil temperature and moisture content over 7 years and led to a 150 % and 108 % increase in the above-ground and root biomass of maize, respectively. Hot and wet conditions under PFM accelerated the decomposition of both labile C (i.e., LFOC) and persistent C (i.e., HFOC), as measured by CO2 efflux from the soil. PFM decreased the LFOC and HFOC pools due to the fast decomposition of "old" C and inadequate stabilization of "new" C. Furthermore, PFM accelerated HFOC decomposition to a greater extent than that of LFOC. The Q10 values of SOC decomposition remained similar both in the presence and absence of PFM. Nitrogen fertilization increased the aboveground and root biomass of maize by 54 % and 40 %, respectively. In the control soil, microorganisms decomposed organic N owing to limited availability of mineral N and in the absence of any from replenishment by fertilizer N. Thus, the increase in LFOC content under N fertilization, was primarily attributed to the reduced decomposition of "old" C. The use of N fertilization produced a similar HFOC content as that of the control soil, while also accelerating the decomposition of "old" C and promoting the stabilization of "new" C, resulting in a faster turnover rate. Consequently, the impact of N fertilization on SOC turnover was negligible owing to the contrasting effects on LFOC and HFOC. The application of N fertilization resulted in a reduction of the Q10 value as compared to control. The combination of PFM and N fertilization accelerated the decomposition of HFOC and SOC, while having absent effect on SOC, labile C and persistent C contents. This indicates that 7 years weren't long enough to trigger a response to the combination of PFM and N fertilization from SOC and HFOC contents. In summary, PFM led to a decline in the SOC content by accelerating the decomposition of both LFOC and HFOC. Conversely, N fertilization maintained SOC content by inhibiting LFOC decomposition and enhancing HFOC decomposition.

Respiration of soil heterotrophs—mainly of bacteria and fungi—is a substantial part of carbon balance in terrestrial ecosystems, which tie up organic matter decomposition with the rise of atmospheric CO2 concentration. Deep understanding and prediction of seasonal and interannual variation of heterotrophic and autotrophic components of CO2 efflux from soil is limited by the lack of long-term, full-year measurements. To better understand the impact of current climate changes on CO2 emissions from soils in the mixed forest and mowed grassland, we measured CO2 efflux every week for 2 years. Heterotrophic (SOM-derived + leaf litter) and root-associated (root with rhizosphere microorganisms) components were partitioned by the root exclusion method. The total CO2 efflux from soil was averaged 500 g C m−2 yr−1 in the forest and 650 g C m−2 yr−1 in the grassland, with shares of the no-growing cold season (Nov–Mar) of 22% and 14%, respectively. The heterotrophic component of CO2 efflux from the soil averaged 62% in the forest and 28% in the grassland, and it was generally stable across seasons. The redistribution of the annual precipitation amounts as well as their deficit (droughts) reduced soil respiration by 33–81% and heterotrophic respiration by 24–57% during dry periods. This effect was more pronounced in the grassland (with an average decline of 56% compared to 39% in the forest), which is related to lower soil moisture content in the grassland topsoil during dry periods.

Glomalin related soil proteins (GRSP) produced by arbuscular mycorrhizal fungi are important stabilizing components of soil aggregates, and consequently helping to entrap organic matter and encapsulate it from microbial decomposition. Grasslands provide excellent opportunity to study GRSP effects because arbuscular mycorrhiza responsible for GRSP production is well development on roots of grasses. Fast GRSP production will accelerate soil organic carbon (SOC) accumulation, but the contribution of GRSP to particulate organic C (POC) and mineral-associated organic C (MAOC) pool remain unclear. We investigated GRSP content and thermal stability of POC and MAOC in topsoil (0–10 cm) as dependent on grassland restoration. SOC content had a nonlinear rise tendency with grassland restoration, and SOC changes were largely dependent on MAOC (>64 %). The POC content decreased by 58 %, while the MAOC content increased by 34 % after 40 years of restoration, microbial transformation of POC plays important role for MAOC formation. The GRSP content contributed 1.7 times more to MAOC (15 %) content than to POC (9 %), but the potential accumulation of GRSP in POC was higher than that in MAOC. The GRSP in the POC pool (less protected) is more sensitive to grassland restoration than in the MAOC pool (more protected). Thermally easily decomposable and refractory organic matter was quantified in POC and MAOC. Thermal stability of MAOC was higher than POC, and GRSP contribute to increase in SOC thermal stability. The GRSP content and thermal stability of POC pool gradually decreased with grassland restoration, reflecting production of more organic matter available for microorganisms and with fast turnover. In conclusion, we must account for the role of GRSP in maintaining SOC thermal stability, and the potential for GRSP sequestration during grassland restoration.

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