Biogeochemistry最新文献

The processes involved in the carbon cycle are essential for marine trophic networks and global climate regulation. Interactions within the microbial loop play key roles in carbon transformation and transport across the food web. The Argentine Patagonian Shelf in the Southwestern Atlantic Ocean is a hotspot for carbon sequestration. However, our understanding of microbial impacts on carbon cycling in this area remains limited. This study examines the microbial community structure and its role in the carbon transformation during a progression of the spring bloom along the Patagonian shelf-break and adjacent ocean. This progression was studied in a latitudinal track where we observed a gradient of Dissolved Organic Matter (DOM) complexity. In the northern area, the bloom termination was characterised by low Chlorophyll-a concentrations, with smaller organisms (Synechococcus) dominating the autotrophic plankton biomass, and high viral concentrations. DOM showed high humification and aromaticity, indicating an intensified microbial activity by heterotrophic bacteria that followed the production of phytoplankton-derived DOM. In the southern area, high Chlorophyll-a was mainly attributed to large protist plankton, accompanied by abundant heterotrophic bacteria and bioavailable DOM from recent phytoplankton blooms. These results showed that during bloom termination, bacterial production of refractory compounds significantly immobilises carbon, suggesting a potential pathway for carbon sequestration. Additionally, data suggest high carbon retention on the shelf side of the front by microbial transformation and efficient trophic transfer within the microbial community, while the side influenced by the Malvinas Current, presents high carbon export by advection and a higher degree of unutilised carbon from bacterial origin. These findings highlight rapid shifts in carbon dynamics driven by microbial successions during different bloom phases.

The increased mining of metals required to meet future demands also generates vast amounts of waste rock that depending on the ore, can contain substantial amounts of metal sulfides. Unconstrained storage of these mining biproducts results in the release of acidic metal laden effluent (termed ‘acid rock drainage’) that causes serious damage to recipient ecosystems. This study investigated the development of 16S rRNA gene based microbial communities and physiochemical characteristics over two sampling occasions in three age classes of rock, from newly mined to > 10 years in a boreal metal sulfide waste repository. Analysis of the waste rocks showed a pH decrease from the youngest to oldest aged waste rock suggesting the development of acid rock leachate. The microbial communities differed between the young, mid, and old samples with increasing Shannon’s H diversity with rock age. This was reflected by the young age microbial community beta diversity shifting towards the mid aged samples suggesting the development of a community adapted to the low temperature and acidic conditions. This community shift was characterized by the development of iron and sulfur oxidizing acidophilic populations that likely catalyzed the dissolution of the metal sulfides. In conclusion, the study showed three potential microbial community transitions from anaerobic species adapted to underground conditions, through an aerobic acidophilic community, to a more diverse acidophilic community. This study can assist in understanding acid rock drainage generation and inform on strategies to mitigate metal and acid release.

Boreal peatlands store abundant carbon (C) belowground because of saturated conditions and cold temperatures, which inhibit the enzymatic release of dissolved organic carbon (DOC) from organic matter. However, metals may also bind DOC, as well as nitrogen (N) and phosphorus (P), and their impact may vary among peatlands with differing hydrology. To assess variation of metal-C-nutrient interactions within and among peatlands and with depth, we sampled cores from seven peatlands in the Marcell Experimental Forest, Minnesota, including bogs, poor fens, and a rich fen. We extracted peat with sodium sulfate to release elements bound with exchangeable metals such as calcium (Ca) or aluminum (Al), and with sodium dithionite to release elements bound with the redox-active metals iron (Fe) and manganese (Mn). We compared extracted elements to long-term peat porewater measurements. Mean DOC extracted by sulfate or dithionite in the bogs and poor fens was 5 or 8 times greater, respectively, than porewater DOC, and in the rich fen it was 8 or 38 times greater. Similarly, N and P extracted by sulfate and dithionite were 10–24 times higher than porewater in the bogs and poor fens and 7–55 times higher in the rich fen. The ratio and absolute values of redox-sensitive and ion-exchangeable elements varied by element among peatland types and with peat depth and values were not always greater in fens than bogs. We conclude that both redox-active (Fe) and non-redox-active (Ca and Al) metals bind important pools of peatland C and nutrients regardless of peatland hydrologic type and despite the very low total mineral content of these boreal peats.

Paddy soils are a significant source of methane (CH₄) affecting the global climate. Therefore, it is important to investigate both emission mitigation strategies and the underlying biogeochemical processes. The application of biochar into paddy soils has emerged as a promising measure to mitigate CH₄ emissions. However, it has not yet been clarified why such effects are usually weaker in field studies than in laboratory incubations and which properties of biochar specifically decrease the production of CH₄. We conducted two incubation experiments, one with 1.5% addition of untreated biochars and one with same amounts, but pH-levelled, rinsed biochars. According to the common experimental design of existing incubation studies (experiment 1) biochar addition induced a mean soil pH increase of 0.28 after anaerobic incubation compared to the contro. In these treatments, biochar significantly extended the pre-methanogenic stage (mean 24.23%). However, this effect was weakened or even reversed when pH-levelled, rinsed biochars were amended in experiment 2, which was intended to mimic the persistent long-term effects in the field. This indicated that the provision of electron accepting capacities to suppress methanogenesis may be less important than previously thought. The addition of biochar significantly lowered CH₄ production rates m in both experiments with no significant influence of the pH (mean 25.89%), though. Our study demonstrated that incubation studies on CH₄ production in paddy soils can be improved by separating the pre-methanogenic and the methanogenic stage. This facilitates future research to compare characteristics of biochar, but also combinations of measures to optimise CH₄ mitigation strategies.

Climate and atmospheric deposition interact with watershed properties to drive dissolved organic carbon (DOC) concentrations in lakes. Because drivers of DOC concentration are inter-related and interact, it is challenging to assign a single dominant driver to changes in lake DOC concentration across spatiotemporal scales. Leveraging forty years of data across sixteen lakes, we used structural equation modeling to show that the impact of climate, as moderated by watershed characteristics, has become more dominant in recent decades, superseding the influence of sulfate deposition that was observed in the 1980s. An increased percentage of winter precipitation falling as rain was associated with elevated spring DOC concentrations, suggesting a mechanistic coupling between climate and DOC increases that will persist in coming decades as northern latitudes continue to warm. Drainage lakes situated in watersheds with fine-textured, deep soils and larger watershed areas exhibit greater variability in lake DOC concentrations compared to both seepage and drainage lakes with coarser, shallower soils, and smaller watershed areas. Capturing the spatial variability in interactions between climatic impacts and localized watershed characteristics is crucial for forecasting lentic carbon and nutrient dynamics, with implications for lake ecology and drinking water quality.

Rare earth elements (REE) are important resources, but REE in the environment are also deemed to be a new class of pollutant. Phytoremediation, using the hyperaccumulator Dicranopteris pedata, offers a promising approach for reclaiming and recycling REE from mining tailings. However, how in situ leaching affects the topsoil characteristics of mining areas and the absorption of REE by D. pedata remains elusive. To address these issues, an in situ leached hill and an un-leached hill were selected for comparison. This study revealed the following: (1) a significant increase in total REE, heavy REE (HREE), and available REE at the leached hill by 47.28%, 100.74%, and 108%, respectively; (2) a marked elevation in the contents of REE in D. pedata of the leached hill, especially HREE in rhizomes, stems, and foliage by 634.45%, 232.63%, and 156.8%, respectively; and (3) a Pearson correlation analysis indicating that the enhanced uptake of REE by D. pedata at the leached hill is related to available REE in the topsoil. This study illuminates the mining-induced dynamics of soil REE migration and plant uptake, reinforcing the feasibility of phytoremediation for REE tailings.

Silicon is a major driver of global primary productivity and CO₂ sequestration, and is a beneficial element for the growth and environmental stress mitigation of many terrestrial and aquatic plants. However, only a few studies have examined the occurrence of silicon in seagrasses, and its function within seagrass ecosystems and the role of seagrasses in silicon cycling remain largely unexplored. This study uses for the first time two methods, the wet-alkaline digestion and the hydrofluoric acid digestion, to quantify silicon content in seagrass leaves using the species Zostera marina and elaborates on the potential role of silicon in seagrass biogeochemistry and ecology, as well as the role of seagrass ecosystems as a silicon reservoir. The results revealed that seagrass leaves contained 0.26% silicon:dry-weight, which is accumulated in two forms of silica: a labile form digested with the alkaline method and a resistant form digested only with acid digestion. These findings support chemical digestions for silicon quantification in seagrass leaves and provide new insights into the impact of seagrasses on the marine silicon cycle. Labile silica will be recycled upon leaf degradation, benefiting siliceous organisms, while refractory silica will contribute to the ecosystem’s buried silica stock and coupled carbon sequestration. In the Bay of Brest (France), the seagrass silicon reservoir was estimated at 0.18 ± 0.07 g Si m⁻², similar to that of benthic diatoms, underscoring the potential role of seagrasses in silicon biogeochemistry in the land–ocean continuum, where they might act as a buffer for silicon transport to the ocean.

Soil solution is the liquid phase of soil containing nutrients that are essential for vegetation’s health and growth. As such, soil solution chemistry is directly related to nutrient cycling and productivity in forest ecosystems. However, the long-term impacts of elevated N deposition on boreal forest soil solution composition remain uncertain. In this study, we investigate the effects of two decades of ammonium nitrate addition applied at rates of 3 (LN treatment) and 10 (HN treatment) times the ambient N deposition on soil solution collected weekly during the snow-free period at a black spruce boreal forest site located in eastern Canada. We show that N addition corresponding to 60 years (LN treatment) and 200 years (HN treatment) of accelerated ambient N deposition had nearly no important nor lasting impacts on soil solution NO₃⁻ and NH₄⁺ concentrations. This reveals that N deposition will most likely not significantly impact Canadian boreal forests soil solution inorganic N concentration in the future. Based on these results and along with NOx emissions data measured globally in North America and on NO₃–N deposition recorded at our experimental forest site, it is also likely that N deposition never affected Canadian forests’ soil chemistry in the past, even at the peak of N emission in North America in the 70 s. Our results indicate a surprisingly strong and widespread resilience of the eastern Canadian boreal forest soil solution chemistry and inorganic N content to long-term N deposition. This resilience can be partially explained by an important N-limitation in high-latitude forest ecosystems.

Global soils play a critical role in carbon (C) cycling and storage, and even minor disturbances to soil C flux can cause CO₂ release to the atmosphere, exacerbating the greenhouse effect. This study investigates the long-term effects of forest detrital manipulation on soil CO₂ efflux at a temperate forest site in Oregon’s western Cascade Mountains. We assessed the variation in seasonal and diurnal autotrophic and heterotrophic contributions to in situ soil CO₂ efflux after 25 + years of detritus additions and removals and found slight increases in soil CO₂ efflux rates concurrent with slight increases in soil C stocks, relative to C input rates, that may reflect underlying changes to C cycling in this system resulting from sustained detritus manipulation coupled with environmental change. Total CO₂ efflux experienced increased contributions from functionally autotrophic root and rhizosphere respiration relative to the heterotrophic component. Seasonal and diurnal differences between soil respiration rates by treatment suggest a soil moisture buffering effect provided by the extra woody detritus that may support vegetative growth at times when seasonal drought would ordinarily slow plant and soil microbial metabolic activity. Overall, this research highlights the long-term effects of sustained litter additions and removals on soil CO₂ efflux, which can help illuminate the response of C cycling in forests to current and future global change.