Biogeochemistry最新文献

As the interface between plants and soil, the organic horizon is the foundation of forest ecosystems. Two potential predictors of O-horizon properties, vegetation and mineral soil type, are difficult to separate because they typically covary. We conducted a factorial study involving four canopy tree species and two soil types with different hydrology and topographic position to parse patterns in chemistry and microbiota of the O-horizon in a north-temperate deciduous forest. There were frequent strong effects of tree species. Organic horizon properties under white ash frequently differed from the other trees: e.g., lower cation exchange capacity and exchangeable acidity, thinner Oi horizon, lower %C and C:N, and, from phospholipid fatty acids, more AM fungi and less gram positive bacteria. These patterns, presumably due to species-specific attributes of leaf litter quality, root exudates, and microbial associations, must arise over decades, given that the forest stands that we studied were established only 85—100 years ago. We also found patterns in the O-horizon related to underlying soil type, independent of tree species: e.g., Bh podzols, compared to typical podzols, had higher trace metals, thicker Oa horizon, and more AM fungi. Relationships between mineral soil type and the organic horizon could arise because landscape features that influence hydrology and therefore soil formation over centuries also influence biogeochemistry of the organic horizon over decades. It could also involve bioturbation by organisms across horizons. There is basic and applied value in better understanding of properties of the O-horizon based on vegetation and soil types.

Atmospheric methane (CH₄) uptake in subarctic and Arctic mineral soils is significant for the CH₄ budget of high-latitude regions, but its response to warming is not well understood. The effect of soil warming on net CH₄ uptake was studied in situ across a natural warming gradient (ambient to +  57.5 °C) in a geothermal area in Southwest Iceland. The study site represented a subarctic grassland on mineral soil with field measurements conducted in summer and fall 2021. Combined automatic and manual dynamic chamber CH₄ flux measurements across the warming transect showed that net CH₄ uptake increased with 0.26 nmol CH₄ m⁻² s⁻¹ per 1 °C of soil warming from ambient soil temperature up to about + 4 °C of soil warming. Soil warming above + 4 °C resulted in a gradual decrease of net CH₄ uptake corresponding to 0.1 nmol CH₄ m⁻² s⁻¹ per 1 °C of soil warming up to + 13 °C . With further soil warming, in situ net CH₄ fluxes were probably affected by geogenic emissions during the effective study period. These trends of enhanced in situ net CH₄ uptake with mild soil warming followed by a decreasing uptake rate with further warming were confirmed in a laboratory incubation experiment showing that the in situ response to temperature <  + 13 °C was biogenic rather than geogenic. It is still not known whether the observed trends are due to adaptation of the community structure to temperature, differential regulation of activity or abundance. Our findings point to a window of future soil warming up to about + 4 °C where net CH₄ uptake in subarctic grassland mineral soils is likely to increase, while further soil warming may result in a decrease of this important CH₄ sink below ambient level. To expand the representativeness of these findings, we encourage future studies to include similar incubation experiments of the warming response for soils across the Arctic.

Ex situ incubations are the primary method used to quantify rates of gross methane production and consumption, which together determine net wetland methane emissions. However, a clear framework for interpreting these data is lacking, and it remains uncertain whether ex situ rates and their environmental drivers conform to expectations from in situ ecological theory. We synthesized published rates of methanogenesis, aerobic methane oxidation, and anaerobic methane oxidation and used boosted regression tree models to identify key drivers. We found median aerobic methane oxidation rates were 2.7 times greater than those of methanogenesis—a paradox given wetlands are net methane sources. This discrepancy arises from methodological artifacts: aerobic methane oxidation is measured as a potential rate, resulting in overestimation, whereas methanogenesis is largely measured as a substrate-limited rate, resulting in underestimation. This conclusion is grounded in our finding that potential methanogenesis rates were an order of magnitude higher than their substrate-limited counterparts (p < 0.001). Our driver analysis indicates that 1. rates of methanogenesis are strongly controlled by labile carbon availability from the soil surface, 2. the balance between methanogenesis and anaerobic methane oxidation is shifting with warming, and 3. species-specific plant effects structure all pathways of methane production and consumption via rhizosphere interactions. This synthesis demonstrates the value of ex situ data for generating mechanistic hypotheses while highlighting the need for future research to prioritize in situ measurements to obtain accurate rate estimates.

River floodplain systems are challenged by drought, which may trigger excess nutrient concentrations and greenhouse gas emissions. Increasingly frequent short-term droughts may exacerbate both problems by altering hydrological connectivity and thereby restructuring microbial communities and dissolved organic matter (DOM), which, in combination, may regulate sediment phosphorus and methane release. However, the combined effects of drought and connectivity on phosphorus and methane release via changes in DOM composition and microbial activity remain poorly understood. We incubated sediments from three floodplain sites along a hydrological connectivity gradient to the River Elbe and subjected them to two short-term drought intensities, corresponding to sediment moisture losses of 0.5–2.5% (moderate drought) and 19–21% (intense drought), followed by rewetting. Drought had surprisingly limited effects on phosphorus and methane release, while the site had a consistently higher impact and shaped the direction and magnitude of drought effects. Moreover, our results suggest that fluxes may be more pronounced at sites that were formerly well-connected to the river. Phosphorus was released under oxic conditions and was linked to heterotrophic microbial carbon use and humic-like DOM, implying that the effects of DOM-mediated microbial activity on phosphorus release need to be considered in future research efforts. Our findings suggest that long-term changes in hydrological connectivity, like lower discharge and changed DOM delivery, could have stronger effects on nutrient dynamics and microbial processes than short-term drought. Preserving floodplain connectivity is therefore critical to limiting nutrient and greenhouse gas release under climate change.

Understanding the stability of soil organic matter (SOM) is central to predicting soil carbon persistence and informing sustainable land management. We combined thermal, chemical, and biological approaches to evaluate SOM stability in 108 soils spanning diverse ecozones in Canada, New Zealand, Scotland, and the Subarctic. Thermal stability was measured using Rock–Eval (RE) pyrolysis, chemical composition was characterized with X-ray absorption near-edge structure (XANES) spectroscopy, and biological stability was assessed through 98-day C mineralization assays. Across soils, thermal stability (T50) was strongly and negatively correlated with mineralized C, indicating that stronger bond structures reduce biodegradability. Importantly, our results demonstrate that T50 not only reflects SOM quality but also serves as a proxy for the extent of organo-mineral associations that contribute to stabilization. The Hydrogen Index (HI) showed a positive relationship with mineralized C, confirming its role as a reliable indicator of labile SOM. XANES results further revealed that alkyl-C and the alkyl/O-alkyl-C ratio were positively related to thermal stability, whereas ketones and aromatic groups correlated negatively with T50, suggesting they are labile byproducts of microbial decomposition or contributions from lignin and tannins, rather than highly recalcitrant aromatic compounds typically associated with stable SOM. Together, these findings highlight that SOM persistence is shaped by both intrinsic chemical composition and extrinsic mineral protection. Rock–Eval pyrolysis and XANES spectroscopy thus provide complementary insights into SOM stability and, when combined with biological assays, offer generalizable tools for evaluating soil carbon resilience across ecosystems.

Turbid coastal waters are dynamic systems where fine-grained sediments interact with organic matter, significantly influencing the fate of both the components. We investigated the seasonal dynamics of particulate (POC) and dissolved (DOC) organic carbon pools along a suspended particulate matter (SPM) gradient from nearshore to offshore waters in a mid-latitude coastal zone. To assess temporal and spatial variations in POC composition, we quantified the relative contributions of phytoplankton (POC_phyto), heterotrophs (POC_het), detritus (POC_det), and mineral-associated organic matter (POC_mineral) to the bulk POC pool. In nearshore waters, frequent tidal resuspension and high SPM concentrations led to elevated POC_det and POC_mineral fractions, masking the increase in POC_phyto, despite the higher primary productivity during the spring bloom. In contrast, offshore waters exhibited a greater relative contribution of POC_phyto, with seasonal POC increases corresponding to elevated chlorophyll a (Chla) levels in spring and summer, similar to the open-ocean dynamics. These trends were further reflected in particulate organic carbon to nitrogen (POC:PON) ratios and POC:Chla ratios, commonly used to assess sources and quality of organic matter. The cross-shore gradient in organic matter partitioning, with dominance of POC nearshore and DOC offshore, highlights the role of particle resuspension and phytoplankton production in controlling organic carbon distribution between the two pools. Overall, our findings underscore the complex interplay between biological production, nutrient cycling, hydrodynamic forces, and SPM in shaping the composition and fate of organic carbon in turbid coastal systems.

Dissolved organic matter (DOM) consists of dissolved molecules, biopolymers, and aggregates with a broad range of molecular sizes. In freshwater and seawater environments, spontaneous self-assembly of DOM forms hydrated particulate organic matter (POM) networks. This conversion from DOM to POM affects carbon transfer through microbial and particle food webs and export to sediments. Particle food webs are based on the direct POM ingestion by zooplankton species. This DOM assembly occurs when the inter-polymer or inter-colloid distances allow chemical (covalent) or physical (e.g., electrostatic, hydrogen) bonds. Here we explore the underlying mechanisms of self-assembly using lake waters with different concentrations of polyanionic DOM with humic content and calcium (Ca) and iron (Fe) crosslinking. We experimentally adjusted the cations by chelating and/or increasing the concentration of calcium or iron. To monitor the self-assembly of DOM, we employed homodynamic laser scattering. Results indicate that DOM self-assembly and physical gel-particle formation result from low-energy Ca⁺² and Fe⁺³ counterion bonding. It can be readily reversed by Ca and Fe chelators, resulting in the disassembly of the network and dispersion of DOM polymers. Calcium cations appear to promote a higher level of self-assembly, reaching larger hydrodynamic sizes during stabilization, compared to iron cations. Our results indicate that the chemical environmental context critically affects the formation of POM from DOM, influencing ecosystem processes such as carbon sedimentation and storage, and providing alternative pathways for heterotrophic consumers (i.e., food webs based on particles).

The 11 BIOGEOMON (International Symposium on Ecosystem Behavior) conferences span 37 years of research in ecosystem science. Here we discuss the history of BIOGEOMON in two parts. In Part 1 we focus on the structure of the conference over the years: its inception, the demographics of attendees, the major biomes and ecosystems studied, and the evolution of dominant topics and themes. We argue that the fundamental goal of understanding the response of ecosystems to perturbations has remained the same over the meetings, but the drivers of change focused upon have evolved over time, reflecting the emergence of new issues and the development of scientific understanding. Each conference is therefore partly a snapshot of the important topics of the day, and partly the core themes that define BIOGEOMON: the cycling and transformations of the major biogeochemical elements on land, and the investigative techniques of monitoring, modelling, and catchment manipulation. We conclude with some reflections on the conference from BIOGEOMON attendees over the years.

The 11 BIOGEOMON (International Symposium on Ecosystem Behaviour) conferences span 37 years of research in ecosystem science.  In this set of papers, we discuss the history of BIOGEOMON in two parts.  In Part 2 we consider the development in understanding of three topics over successive conferences:  acid deposition, peatland biogeochemistry, and isotope geochemistry. Using these three topics as examples, we show how the BIOGEOMON conferences both reflect, and lead, advances in biogeochemistry research.  Using published papers from conference special issues, conference proceedings, and other publications from BIOGEOMON delegates, we highlight the changing importance of these research strands over the years, and consider the questions, insights, and surprises, played out in the meetings.

Ocean acidification due to anthropogenic carbon dioxide (CO₂) uptake threatens marine ecosystems, but coastal waters have complex and highly variable carbonate system dynamics. More coastal time series are therefore needed to better constrain coastal pH dynamics, but especially in the tropics such time series are rare. Southeast Asia’s Sunda Shelf Sea has exceptionally high marine biodiversity and rapidly increasing anthropogenic pressures, but we have little knowledge of coastal carbonate system dynamics in the region. We analyzed 7-years of monthly carbonate system data from the Singapore Strait in the central Sunda Shelf. Our results show consistently low seawater pH (total scale; pH_T; < 8.0) and aragonite saturation state (Ω_Ar, usually < 3.0), but with a clear seasonal pH_T variation by 0.11–0.19 units. The observed seasonality reflects the monsoon-driven advection of water masses that have been shaped by different biogeochemical processes. Specifically, during the southwest monsoon, remineralization of terrestrial dissolved organic carbon originating from regional peatlands lowers pH_T, while calcium carbonate (CaCO₃) formation and dissolution are more important during other seasons. Comparing our data to predicted values for purely conservative mixing of river water and seawater shows that these non-conservative biogeochemical processes are dominant drivers. Our time series shows a significant decreasing trend in pH_T of –0.043 units per decade, exceeding the theoretical trend detection time (TDT) of 5.0 ± 1.3 years. However, the seasonal pH_T variability itself shows interannual variability, and pH_T is also correlated with the El Niño Southern Oscillation. This longer-term climatic control may complicate trend quantification. Our study highlights how terrestrial dissolved organic carbon remineralization may enhance future ocean acidification in Sunda Shelf region, emphasizing the importance of continuing the time series to better quantify climatic drivers and long-term trends.