Biogeochemistry最新文献

Black carbon has been shown to suppress microbial methane production by promoting anaerobic oxidation of organic carbon, diverting electrons from methanogenesis. This finding represents a new process through which black carbon, such as wildfire char and biochar, can impact the climate. However, the mechanism and capacity of black carbon to support metabolism remained unclear. We hypothesized black carbon could support microbial growth exclusively through its electron storage capacity (ESC). The electron contents of a wood biochar was quantified through redox titration with titanium(III) citrate before and after Geobacter metallireducens growth, with acetate as an electron donor and air-oxidized biochar as an electron acceptor. Cell number increased 42-fold, from 2.8(± 0.6) × 10⁸ to 1.17(± 0.14) × 10¹⁰, in 8 days based on fluorescent cell counting and the result was confirmed by qPCR. The qPCR results also showed that most cells existed in suspension, whereas cell attachment to biochar was minimal. Graphite, which conducts but does not store electrons, did not support growth. Through electron balance and use of singly ¹³C-labeled acetate (¹³CH₃COO^–), we showed (1) G. metallireducens could use 0.86 mmol/g, or ~ 19%, of the biochar's ESC for growth, (2) 84% and 16% of the acetate was consumed for energy and biosynthesis, respectively, during biochar respiration and (3) ca. 80 billion electrons were deposited into biochar for each cell produced. This is the first study to establish electron balance for microbial respiration of black carbon and to quantitatively determine the mechanism and capacity of biochar-supported growth.

Graphical Abstract

The Caribbean region is experiencing seasonal inundation of the shoreline by large mats of pelagic Sargassum spp. (Sargassum) leading to novel impacts to ecological communities. Where Sargassum becomes trapped along the shoreline, leachates turn the water a brown color, coined Sargassum Brown Tide (Sbt). We conducted monthly sampling at six sites along the offshore mangrove keys of Jobos Bay, PR between April 2022 to July 2023 to collect temperature, pH, salinity, dissolved oxygen, total nitrogen (TN), total phosphorus (TP), chlorophyll a (chl a), total suspended solids (TSS), and volatile suspended solids (VSS) at nearshore, midshore, and offshore zones along transects running perpendicular to the shoreline. We also collected data on submerged aquatic vegetation (SAV) community dynamics along transects at each site. We found significantly higher chl a and lower dissolved oxygen concentrations within the nearshore zone during Sbt events but the differences did not extend out to the midshore and offshore zones. Total suspended solids were also higher at nearshore zones compared to offshore zones when a Sbt event occurred. In addition, sites that experienced Sbt had higher turbidity and lower pH. Total percent cover of SAV was different between sites impacted by Sbt and control sites depending on transect zone, with higher SAV percent cover for control sites within the 5 m zone and often within the 15 m zone. Our data suggest that Sbt has significant impacts to nearshore water quality, chl a, and SAV percent cover; however, most impacts are not seen beyond 45 m in well flushed systems.

Climate-related events and bark beetle outbreaks influenced hydrological dynamics and nitrogen cycling in three Central European forest catchments in the GEOMON network. Since 1994, distinct environmental phases were observed at studied catchments. Initially, nitrate (NO₃^⁻) concentrations declined at Anenský potok and Polomka due to reduced acid deposition, while remaining stable at Pluhův bor. From 2015 onwards, drought and extensive spruce dieback caused significant hydrological disruptions, including over a 200% increase in runoff at Anenský potok. In contrast, moderated hydrological impacts due to differences in the evapotranspiration-to-precipitation ratio was observed at Polomka. At Pluhův bor, gradual deforestation combined with climate change effects, such as rising temperatures and decreasing precipitation, resulted in stable runoff compared to the abrupt changes in the other two catchments. Despite these differences, disturbances across all catchments intensified nitrate leaching and disrupted nitrogen retention. This led to substantial dissolved inorganic nitrogen (DIN) export, particularly at Polomka, which is characterized by a low soil carbon-to-nitrogen ratio (C/N). These findings highlight the vulnerability of forest ecosystems to nitrogen loss under environmental stressors and underscore the importance of effective management strategies to mitigate nitrogen cycle disruptions in the context of ongoing climate change.

Soil microbial communities play a pivotal role in controlling soil carbon cycling and its climate feedback. Accurately predicting microbial respiration in soils has been challenged by the intricate resource heterogeneity of soil systems. This makes it difficult to formulate mathematical expressions for carbon fluxes at the soil bulk scale which are fundamental for soil carbon models. Recent advances in characterizing and modeling soil heterogeneity are promising. Yet they have been independent of soil structure characterizations, hence increasing the number of empirical parameters needed to model microbial processes. Soil structure, intended as the aggregate and pore size distributions, is, in fact, a key contributor to soil organization and heterogeneity and is related to the presence of microsites and associated environmental conditions in which microbial communities are active. In this study, we present a theoretical framework that accounts for the effects of microsites heterogeneity on microbial activity by explicitly linking heterogeneity to the distribution of aggregate sizes and their resources. From the soil aggregate size distribution, we derive a mathematical expression for heterotrophic respiration that accounts for soil biogeochemical heterogeneity through measurable biophysical parameters. The expression readily illustrates how various soil heterogeneity scenarios impact respiration rates. In particular, we compare heterogeneous with homogeneous scenarios for the same total carbon substrate and microbial biomass and identify the conditions under which respiration in heterogeneous soils (soils having non-uniform distribution of carbon substrate and microbial biomass carbon across different aggregate size classes) differs from homogeneous soils (soils having uniform distribution of carbon substrate and microbial biomass carbon across different aggregate size classes). The proposed framework may allow a simplified representation of dynamic microbial processes in soil carbon models across different land uses and land covers, key factors affecting soil structure.

Colonization by pioneer plants, among which the arctic willow (Salix polaris) is one of the most important, accelerates soil development after deglaciation. This is achieved through the increased input of organic matter from plant biomass and the exudation of low molecular mass organic compounds (LMMOA), predominantly organic acids, which facilitate mineral dissolution and nutrient release. These exudates support microbial activity and contribute to the formation of soil organic matter. While there is quite a lot of data on the exudation and acceleration of microbial activity in the rhizosphere of various plants, similar data concerning arctic plants, including willow, are scarce. Furthermore, there is a lack of data on the effect of C, N, P root stoichiometry on nutrient content in exudates and the rhizosphere microbiome during soil succession after deglaciation. In this study, we analysed various habitats of high-arctic tundra in Petuniabukta (Billefjorden, Svalbard), representing different stages of vegetation development. Our objectives were (i) to assess soil and rhizosphere carbon and nutrient content and availability, as well as microbial biomass CNP; (ii) to evaluate the rhizosphere effect on nutrient availability and the microbiome of arctic willow; and (iii) to measure root and exudation CNP and quality, primarily LMMOA, in arctic willow from the studied habitats. The exudates released to deionised water were analysed for LMMOA and inorganic anions (ion chromatography) as well as the total content of C and N. The plants roots were analysed for CNP content. Soil chemical properties (e.g. pH, organic C, total and exchangeable content of elements, water extractable PO₄³⁻) and microbial parameters (microbial biomass and quantity of bacteria and fungi) were assessed in both rhizosphere and bulk soils, with the rhizosphere effect calculated accordingly. The most abundant LMMOA species in willow exudates were lactate, acetate, formate, malate and citrate, followed by pyruvate, quinate and oxalate, collectively representing approximately 2% of the total exuded C. The rhizosphere effect of willows on nutrient availability and microbial parameters was the most significant at sites with early soil development and diminished with increasing vegetation cover. A link was observed between nitrogen and phosphorus exudation and plant root stoichiometry. These trends underscored the essential role of root exudation in overcoming microbial nutrient limitations during early soil development, particularly in sites with lower nitrogen availability by reducing the soil C/N ratio.

Understanding the effects of prescribed burning management practices in combination with anthropogenic nitrogen (N) deposition on soil carbon (C) storage capacity is of crucial importance in Mediterranean mountain shrublands. To address this issue, an experiment was conducted to assess the effects of prescribed burning (Burn, B / No Burn, NB), N additions (0, 15, and 50 kg N·ha⁻¹·year⁻¹, N0, N15, N50) and their interactive effects on various soil parameters in a shrubland located in the mountain range of Madrid over 2-year period. The results of the study confirmed that both low-intensity prescribed burning and short-term N additions did not alter the C stocks in the soil and floor shrubs. Furthermore, the combination of these two factors did not lead to an increase in soil C accumulation. However, the prescribed fire treatment caused divergent responses in soil parameters and fluxes. Specifically, it caused transient changes including decreased soil respiration (Rs), alterations in the soil microbial community, increased soil water content, temperature, and soil pH, and changes in NH₄, NH₃, and available P. Moreover, the cumulative amount of N added gradually depressed Rs, and microbial biomass. Additionally, the interaction between prescribed burning and N fertilisation did not modify the effects associated with fire. The findings indicate that prescribed burning, as implemented in the experiment, can be effectively employed in Mediterranean shrublands, as it did not significantly affect soil C storage under both current and future N deposition scenarios.

As with most aquatic ecosystems, reservoirs play an important role in the global carbon (C) cycle and emit greenhouse gases (GHG) as carbon dioxide (CO₂) and methane (CH₄). However, GHG emissions from reservoirs are poorly quantified, especially in temperate systems, resulting in high uncertainty. We compared reservoir C emission estimates and uncertainty of diffusive, ebullitive, and degassing pathways in six hydropower reservoirs in the southeastern United States among four data sources: two field-based surveys and two models (including the GHG Reservoir “G-res” Tool). We found that CH₄ diffusion was most similar across data sources (modeled minus observed, bias = − 21 g CO_2-eq m⁻² y⁻¹) and had low relative uncertainty (coefficient of variation, CV = 0.98). On the other hand, CO₂ diffusion was least consistent across data sources (bias = − 518 g CO_2-eq m⁻² y⁻¹). Both field surveys indicated strong negative CO₂ diffusion (i.e., CO₂ uptake) at all reservoirs, while G-res estimated positive CO₂ diffusion. By extension, total C emissions showed similar discrepancies, leading to high uncertainty in upscaling and interpreting reservoir source-sink dynamics. Finally, CH₄ ebullition had the highest relative uncertainty (CV = 2.77) due to high variability across sites. We discuss limitations of field surveys and these models, including temperature-based annualization methods, varying definitions of ebullition zones, low sampling resolution, and lack of dynamism. Future field efforts focused on capturing variability in CO₂ diffusion and CH₄ ebullition will be especially valuable in reducing uncertainty and improving models to advance our understanding reservoir GHG emissions.

Biomass production in the lowland wet tropical forest is greater than in any other biome, and it is typically limited by soil phosphorus (P) availability. However, the mechanisms involved in the P cycle remain poorly represented in Earth System Models (ESMs). Soil P sorption processes are key in the P cycle and for understanding the extent of P limitation for plant productivity. Currently, a few ESMs include isotherm equations to model these processes. Although the Langmuir equation is widely cited, other isotherm equations may better describe sorption in tropical soils. Here, we use a diverse range of soil samples from Puerto Rico to test the validity of the Langmuir, Freundlich, and Temkin equation. We found that across four soil orders (Inceptisols, Mollisols, Oxisols, Ultisols), and forested and cultivated land use types, the Freundlich equation best represented soil P sorption. Furthermore, the Langmuir and the Temkin equations poorly represent soil P adsorption, especially at low P concentrations. Specifically, the Langmuir equation underestimated soil P adsorption by 40% and the Temkin equation overestimated adsorption by 76%. We also found, as expected, that soil clay content and pH were the most important parameters explaining the variability of the Freundlich (K_f) constant. Greater clay content and lower pH, common in highly weathered Ultisols and Oxisols which are abundant in the tropics, led to greater K_f values. Overall, our results suggest that a diversity of soils can prompt underestimation of P sorption when using the Langmuir isotherm, which leads to an overestimation of available P that can have repercussions on ESM predictions of the P cycle and tropical forest productivity.