Biogeochemistry最新文献

Shifts in precipitation patterns with less frequent rain events accompanied by global warming will trigger soil drying and rewetting, even in humid regions. Because rewetting of dried soil provokes pulse carbon dioxide (CO₂) emissions from soils, the chronic soil dry-wet cycle (DWC) in humid regions may provide positive feedback, contributing to global warming. In this study, we aimed to reveal the effects of repeated DWCs on soil CO₂ emissions, and the factors affecting emissions after rewetting in humid temperate forests. Experimentation included incubation of soils under five sequential DWCs. CO₂ emissions from the soils were measured throughout the incubation period, except during periods of drying. Soil extractable organic carbon (EOC) and microbial biomass carbon (MBC) were also measured at three hours and at five days after the first, third, and fifth rewetting. Rewetting of dried soil significantly increased CO₂ emissions during the first DWC, whereas the size of the pulse CO₂ emissions after rewetting decreased with an increasing number of subsequent cycles. Soil rewetting decreased soil MBC and increased EOC, and the EOC concentration decreased during each subsequent wet period. Based on path analysis, MBC three hours after rewetting was strongly and positively correlated with CO₂ emissions in the following five days in the dry-wet treatment (regression coefficient β = 0.710, p < 0.001). The results suggest that microbial survivability to soil DWCs, rather than sudden labile carbon supply, determines the response of pulse CO₂ emissions from soils after rewetting during repeated soil DWCs in humid regions.

White-sand forests contribute significantly to dissolved organic matter (DOM) production in the central Amazon, forming blackwater rivers that dominate organic matter export from the Amazon basin to the ocean. Despite their importance in controlling DOM export, white-sand forests are understudied, and it remains unclear whether systematic changes in the formation of blackwater DOM occur and how seasonal variations and extremes like El Niño-associated droughts impact them. We collected soil porewater from two central Amazon white-sand forests for 2 years, spanning a wet La Niña year followed by an El Niño drought year. The molecular composition of DOM was analyzed using high-resolution mass spectrometry, and correlation network analysis was employed to identify ecologically meaningful DOM subsets. Using additional chemical characterization, database annotations, correlation with ¹⁴C-age of DOM and climatic variables, and ecological null modeling, we propose five distinct DOM sources: plant litter and throughfall, soil organic matter (SOM) decomposition, root exudation, and two drought response subsets of likely microbial and plant origin. During drought conditions, aboveground plant-derived compounds decreased, while SOM products, root exudates, and drought response compounds increased. These drought responses were qualitatively similar in both years but notably amplified in the drier El Niño year. Drought amplified deterministic control over DOM composition, indicating that DOM reflected directed biological responses and that future droughts are likely to generate similar shifts. Overall, drought substantially altered belowground carbon cycling by shifting DOM sources and inducing stress responses, effects expected to recur and potentially intensify under future climate scenarios.

The substrate production process for the edible mushroom Agaricus bisporus offers a controlled model environment to investigate organic matter transformation. Despite the central role of humic substances (HS) in organic matter dynamics, detailed insights into their compositional changes during decomposition are limited. We investigated the formation and transformation of dissolved and solid phase HS during microbial composting and subsequent mycelial growth of A. bisporus. Total carbon and nitrogen were analyzed in both bulk material and HS fractions. Additionally, bulk material was analyzed for carbohydrates, fatty acids, and lignin content and composition. Pyrolysis–GC–MS was used to characterize humic acids (HA), fulvic acids (FA), and the bulk material. Throughout microbial composting HS formed, with HA as main fraction followed by FA. The formation of HS coincided with substantial degradation of cellulosic components and enrichment of organic nitrogen. HA was particularly enriched in lignin(derived) and nitrogen-containing compounds. During early mycelial growth of A. bisporus HS and particularly HA decreased, thus HS are an accessible source of carbon and nitrogen for fungal metabolism.

Phosphorus (P) is often a limiting nutrient in highly weathered soils. Fire is a major driver of nutrient redistribution and can temporarily increase the pool of plant-available P in P-limited ecosystems. Yet, the long-term effects of frequent fire on soil P in montane grasslands remain poorly understood. We investigated how fire regime influences soil P pools using data from a long-term fire experiment in the South African Drakensberg. Total soil P, moderately labile organic and inorganic P and plant-available P were measured across five prescribed fire regimes varying in frequency (annual, biennial or infrequent) and season of burn (autumn or spring). We hypothesised that frequent fire would not alter total P in the topsoil, but expected it would increase inorganic P and plant-available P. Infrequent and biennial burns had little effect on total P; however, total P was significantly higher under annual spring burns than the other treatments, particularly the infrequent burns and annual or biennial autumn burns. In contrast, plant-available P did not respond to any fire treatment. Frequent spring burns generally increased organic P relative to inorganic P, indicating a shift in the composition of soil P pools with fire frequency and season. Overall, despite changes in topsoil total and organic P, plant-available P remained constrained, reflecting a bottleneck in the P cycle likely driven by the high P-retention capacity of these acidic Andosols. These findings highlight the complex and sometimes counterintuitive effects of fire on nutrient dynamics in montane grasslands.

Understanding the biogeochemical consequences of fire and land-use history in tropical upland systems is essential for sustainable soil management. We investigated the vertical distribution of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in soils under rotational shifting cultivation (RSC) in Northern Thailand. Three fields with distinct land-use histories were analyzed: a continuously fallow site for seven years (CF-7Y), a six-year fallow RSC site (RSC-6Y), and a twelve-year fallow RSC site (RSC-12Y). The RSC-6Y and RSC-12Y fields were left fallow for 6 and 12 years, respectively, with both fields burned in 2022 and entered a new two-year fallow phase. By contrast, CF-7Y field was last burned in 2017 and has remained under continuous fallow since that time. In 2024, soil samples were collected from upper, middle, and lower slope positions to analyze total organic carbon (TOC), total nitrogen (TN), TOC:TN, and δ¹³C and δ¹⁵N signatures across the 0–100 cm soil profile. Results revealed that longer fallow periods (RSC-12Y) enhanced vertical movement and stabilization of TOC and TN, with more enriched δ¹³C and δ¹⁵N values at depth—indicative of legacy fire effects and microbial transformation. The CF-7Y field showed high surface TOC and more negative δ¹³C values, reflecting active C₃ vegetation inputs and minimal decomposition. The δ¹³C values were significantly affected by both site and slope position, suggesting independent influences of land-use history and topography on soil carbon dynamics. In contrast, δ¹⁵N was shaped by a significant interaction between site and slope, indicating that nitrogen cycling processes vary with the combined effects of land use and topographic gradient. The δ¹⁵N values consistently increased with depth across all fields, particularly in lower slope positions, suggesting deposition of ¹⁵N-enriched material and persistent alteration of nitrogen pools post-fire. Slope position significantly influenced nutrient distribution, with lower slopes acting as nutrient sinks and upper slopes experiencing erosion-driven losses. These findings underscore the decoupled recovery of soil carbon and nitrogen cycles after disturbance, highlighting the need for slope-sensitive and nutrient-aware restoration strategies.

Understanding how soil organic matter (SOM) fractions, such as mineral-associated organic matter (MAOM) and particulate organic matter (POM), respond to nutrient management practices is essential for improving soil health and advancing sustainability in agroecosystems. In particular, there is a need for strategies that sustain and enhance soil fertility while simultaneously reducing nitrogen (N) losses and greenhouse gas emissions. Co-applying compost and fertilizer has the potential to improve soil health by building SOM and increasing fertilizer N retention in the soil, which can be especially beneficial for low nutrient-demanding crops like olives. In a two-year field study conducted in a super-high-density olive orchard, we investigated the effects of compost application and N fertilization rate on SOM fractions down to 90-cm depth and on nitrous oxide (N₂O) emissions. Using ¹⁵N-labeled fertilizer, we traced fertilizer N in the soil over time. Compost application increased the concentration of carbon (C) and N in topsoil, including in MAOM and POM, with the largest effects occurring in the first year. We also observed greater concentrations of C and N within MAOM at deeper soil layers with compost, but compost did not increase the concentration of fertilizer N remaining in the soil over two years. Compost significantly reduced N₂O emissions, especially background emissions. These effects may have been mediated by increased soil C from compost application, particularly dissolved organic C, which may have driven SOM turnover, MAOM formation, and N₂O reduction. Together, these results suggest that compost application can be an effective strategy for sustainable nutrient management and building soil health, particularly in low-input perennial tree crop systems.

Carbon dioxide removal (CDR) via enhanced rock weathering (ERW) strongly depends on rock particle size. While ERW models typically link finer particle size to greater CDR, their tendency to aggregate with soil components such as organic matter (OM) may impede weathering. The inconsistent effects of ERW on soil OM storage in recent studies reinforce the need to clarify underlying mechanisms. We thus tested if finer basaltic rock promotes organo-mineral association while lowering CDR through incubation experiments (rock alone and rock-plant residue-sand mixture) under water regimes with or without weekly leaching. After six months, we analyzed total carbon, extractable metal(loid)s, organo-mineral aggregate formation (by density fractionation), and inorganic carbon contents (by XANES and leachates). Coarse basaltic rock (106–150 μm) showed faster abiotic and biologically induced weathering. Contrarily, fine basaltic rock (20–38 μm) led to greater organo-mineral aggregation and OM accrual, which was attributable to higher particle numbers, geometric surface area, and binding agents (inherent and increased reactive metal(loid)s). The amount of organic carbon stabilized in meso-density aggregates by basaltic rock was one order of magnitude higher than the estimated CDR, regardless of the water regimes. These results exhibit the first direct evidence that rock particle size could induce the trade-off between CO₂ removal and OM stabilization, which implies that the current ERW models may severely overestimate CDR potential due to basaltic rock interaction with OM and its weathering products. Further research into rock interactions with soil components is essential for improving model prediction and optimizing ERW applications.

Fluctuating groundwater levels in drained peatlands create a transition zone with seasonally changing oxygen availability. This zone drives dynamic iron (Fe) and sulphur (S) cycling under alternating anoxic and oxic conditions, influencing decomposition rates. This study investigated how Fe and S affect decomposition rates and resulting carbon dioxide (CO₂) emissions under fluctuating redox conditions in transition zone. In a controlled laboratory experiment, peat samples from two drained Dutch coastal peatlands were amended with ferric iron (Fe³⁺) and sulphate (SO₄²⁻) and incubated anoxically to mimic high groundwater tables. This was followed by an oxic phase simulating groundwater table drops. The cycle was repeated with lactate addition to replenish labile carbon. Carbon dioxide emission rates were monitored continuously throughout the anoxic–oxic cycles. Water soluble Fe and S concentrations, exoenzyme activities, and pH were measured before and after the experiment. Carbon dioxide emission rates increased under anoxic conditions with Fe³⁺ and SO₄²⁻ amendments potentially due to stimulation of microbial activity using these compounds as alternative electron acceptors. Short-term oxygenation suppressed emissions compared to controls without amendments. Water-soluble Fe remained stable across treatments, while water-soluble S concentrations changed significantly from initial levels. Exoenzyme activities were primarily influenced by pH, with minimal effects from amendments. The findings show that transition zone is an active redox zone where decomposition dynamics are determined by available electron acceptors in the system, influencing greenhouse gas (GHG) emissions from managed peatlands. This zone should be integrated into future models to improve the accuracy of reporting national GHG emissions.

Nitrogen (N) and phosphorus (P) concentrations in many northern prairie rivers have been increasing due to anthropogenic activities. While long-term trends in total N and P have been well documented, there remains limited knowledge regarding trends in dissolved fractions as well as the associated effects of shifting nutrient loadings on nutrient stoichiometry (i.e., N:P) of river water. We assessed long-term (25-year) trends in total and dissolved N and P concentrations and N:P at 11 monitoring stations situated on five rivers within the Red-Assiniboine River Basin in North America. We found that N and P concentrations and stoichiometry were changing through time at a majority of stations. Spatial patterns of trends were variable with no consistent directional changes in either nutrient concentrations or stoichiometry among stations, suggesting the importance of localized nutrient sources, such as wastewater treatment plants. Changes associated with catchment characteristics were the primary contributors to observed trends in nutrient concentrations and stoichiometry, whereas alterations in the streamflow regime played a comparatively minor role. Variations in the relative quantities of nutrients in the basin’s rivers may be influencing the potential for nutrient depletion, with some rivers undergoing stoichiometric shifts in the depleted nutrient. Consequently, nutrient management may need to occur at the sub-basin scale to mitigate point source nutrient pollution and protect riverine water quality throughout the basin.