Biogeochemistry最新文献

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.

In the nutrient-poor soils of the Amazon rainforest, phosphorus (P) emerges as a critical limiting factor for ecosystem productivity. Despite these limitations, the Amazon exhibits remarkable productivity that is maintained by its efficient nutrient recycling mechanisms. Central to this process is the role of organic matter, particularly its dissolved (DOM) fraction, which serves as a crucial nutrient reservoir for both plants and microorganisms. This study delves into the dynamics of nutrient-containing DOM within the soils of two contrasting rainforest ecosystems: clayey terra firme forests, known for their robust nutrient recycling and presumed P-limitation, and sandy white-sand forests, characterized by reduced nutrient recycling capacity and presumed nitrogen (N)-limitation. Utilizing ultra-high resolution mass spectrometry (HR-MS), we analyzed the molecular composition of dissolved organic nutrient species. We evidenced nutrient limitation applying innovative concepts: (1) assessing nutrient depletion in DOM via nutrient-to-carbon ratios, (2) comparing the composition of nutrient-enriched DOM pools across soil depth profiles to infer microbial nutrient processing, and (3) examining the temporal variability of nutrient-containing DOM as an indicator of nutrient uptake and production. Our results corroborate the hypothesis of P-limitation in terra firme forests, with significant processing of N-containing DOM also observed, indicating a synergistic demand for both P and N. Surprisingly, white-sand soils exhibited no signs of N-limitation but instead sulfur (S)-limitation, a novel finding for these ecosystems. This study highlights the diversity of potential nutrient limitations in the central Amazon and the importance of the bioavailable “black box” DOM for tropical nutrient cycles.

There are major gaps in our understanding of how Mediterranean ecosystems will respond to anticipated changes in precipitation. In particular, limited data exists on the response of deep soil carbon dynamics to changes in climate. In this study we wanted to examine carbon and nitrogen dynamics between topsoils and subsoils along a precipitation gradient of California grasslands. We focused on organic matter composition across three California grassland sites, from a dry and hot regime (~ 300 mm precipitation; MAT: 14.6 (boldsymbol{^circ{text{C}} })) to a wet, cool regime (~ 2160 mm precipitation/year; MAT: 11.7 (boldsymbol{^circ{text{C}} })). We determined changes in total elemental concentrations of soil carbon and nitrogen, stable isotope composition (δ¹³C, δ¹⁵N), and composition of soil organic matter (SOM) as measured through Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) to 1 m soil depth. We measured carbon persistence in soil organic matter (SOM) based on beta (({varvec{beta}})), a parameter based on the slope of carbon isotope composition across depth and proxy for turnover. Further, we examined the relationship between δ¹⁵N and C:N values to infer SOM’s degree of microbial processing. As expected, we measured the greatest carbon stock at the surface of our wettest site, but carbon stocks in subsoils converged at Angelo and Sedgwick, the wettest and driest sites, respectively. Soils at depth (> 30 cm) at the wettest site, Angelo, had the lowest C:N and highest δ¹⁵N values with the greatest proportion of simple plant-derived organic matter according to DRIFTS. These results suggest differing stabilization mechanisms of organic matter at depth across our study sites. We infer that the greatest stability was conferred by associations with reactive minerals at depth in our wettest site. In contrast, organic matter at our driest site, Sedgwick, was subject to the most microbial processing. Results from this study demonstrate that precipitation patterns have important implications for deep soil carbon storage, composition, and stability.

Wetlands are the largest natural source of methane (CH₄), but spatial variability in fluxes complicates prediction, budgeting, and mitigation efforts. Despite the many environmental factors identified as CH₄ drivers, the overall influence of wetland spatial heterogeneity on CH₄ fluxes remains unclear. We identified five dominant patch types—submersed aquatic vegetation (SAV), emergent forbs, sedges/rushes, grasses, and open water—within a freshwater wetland in Maryland, USA, and measured CH₄ fluxes using a combined chamber and eddy covariance approach from June to September 2021. Because patch types integrate co-occurring environmental factors, we hypothesized that CH₄ flux is best characterized at the patch scale. Chamber measurements from representative patches showed distinct CH₄ signals; fluxes from grasses and sedges/rushes were highest, while fluxes from SAV and forbs were lower but skewed, suggesting episodic emission pulses. Open water had the lowest fluxes. Differences between patches were consistent over time, and spatial variability was greater between patches than within them, highlighting patches as key drivers of flux variability. By combining chamber fluxes with eddy covariance data in a Bayesian framework, we provide evidence that patch-type fluxes scale over space and time. Understanding spatial heterogeneity is essential for quantifying wetland contributions to global biogeochemical cycles and predicting the impacts of environmental change on wetland ecosystem processes. Our study demonstrates the importance of vegetation patch types in structuring spatial variability and supports a patch-explicit representation to reduce uncertainty in wetland CH₄ fluxes.