Biogeochemistry最新文献

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.

Fellaster zelandiae, a sand dollar endemic to Aotearoa New Zealand, follows other echinoderms in producing Mg-calcite. Their skeletons, however, show mineralogical variation at different levels of scale: nanostructure, body part, individual, and population. Atomic-level imaging highlighted differences in skeletal ultrastructure with varying levels of consistency in elemental composition. Teeth, the deepest internal skeletal structures in the individual and vital for feeding, showed the greatest compositional variation at the nanoscale, whereas tests and spines were both more consistent in Mg concentrations. Mg incorporation is, approximately, a function of proximity to seawater, with levels highest in layers further away from the marine environment. Body part variation within individuals of a populations was relatively low (Maximum SD_x̄ = ± 0.19 wt% MgCO₃, n = 9) while average variation was ± 0.14 wt% MgCO₃ (n = 670), reflecting genetic variability. Population variation across a range of latitudes indicated both well-known and novel environmental influences. Skeletal mineralogy in a population in Tauranga, North Island, New Zealand at 38°S (mean = 8.5, SD = 0.07, n = 50) is significantly different (p < 0.0001) from a population in Timaru, South Island, New Zealand at 44°S (mean = 8.2, SD = 0.07, n = 62). Populations across the country showed that external parts (spines) were most affected by temperature and classical environmental factors, while internal parts (Aristotle’s lanterns) were not swayed by abiotic factors. Intermediate structures (tests) were unexpectedly influenced by wave energy, where increases in Mg content among populations was correlated to higher wave-energy beaches. While intrinsic, phylogenetic, and extrinsic factors can individually influence skeletal carbonate mineralogy, these data show that accounting for the cumulative individual- and population-level factors affecting mineralogy provides an extremely nuanced understanding of biomineralization within a single species.

While it is well acknowledged that both light irradiance and biofilm age influence daytime nutrient cycling in streams, it remains unclear how these factors interact and affect nighttime nutrient dynamics together with dissolved organic matter (DOM) composition. The understanding of these interactions is crucial for comprehending overall nutrient dynamics in stream ecosystems. In this study, we assess the interplay of biofilm age (one, i.e. younger, and three, i.e. older, weeks old) under three levels of light irradiance (high, low, and no light) on the daytime and nighttime dynamics of dissolved inorganic nitrogen (NO₃–N and NH₄–N), soluble reactive phosphorus (SRP), and DOM molecular fractions in streamside flumes. Daytime NO₃–N demand by younger biofilms increased with irradiance, with no net-uptake without light. Moreover, both daytime and nighttime NO₃–N net-uptake increased with biofilm age under higher light incidence, but at lower rates for nighttime net-uptake. Older biofilms acted as daytime sources of DOM (humic-like molecular fractions) and of SRP, while protein-like DOM fractions were consumed both during daytime and nighttime by both younger and older biofilms. Our results reveal distinct daytime and nighttime nutrient dynamics influenced by light irradiance and biofilm age, emphasizing the importance of nighttime processes for a comprehensive assessment of nutrient cycling in streams.

There is substantial variation in estimates of the respiratory quotient (RQ), i.e., molar ratio of produced CO₂ and consumed O₂ during microbial mineralization of organic matter (OM). While several studies have examined RQ's controlling factors in terrestrial or aquatic ecosystems, there are no broader cross-ecosystem comparisons, and there is a lack of general understanding of the extrinsic (environmental) and intrinsic (organic matter composition) controls on RQ. In this study, we examine RQ across a broad range of environments, including soils, aquatic sediments, lake and coastal water. We measured CO₂ production and O₂ consumption using membrane inlet mass spectrometry (MIMS). We also assessed the microbial metabolic profiles using BIOLOG EcoPlates and determined the energy content of the natural OM with bomb calorimetry and its elemental composition. We show that RQ differs significantly between the ecosystem types and strongly deviates from the frequently assumed value of 1. In addition, microbial mineralization across the different studied ecosystems is correlated with the bulk energy content of the OM (kJ g⁻¹ organic carbon). Finally, RQ was correlated to the metabolic profiles of microorganisms, as estimated based on BIOLOG EcoPlates. We argue that an increased use of cross-ecosystem experimental studies will enhance the understanding of the factors controlling carbon cycling.

Trace metal micronutrients are known to play an important role in the optimal functioning of aquatic microorganisms involved in the sequestration of atmospheric carbon dioxide. Understanding the biogeochemical cycling of trace metal micronutrients in the global ocean has been a focus of intense research over several decades. Conversely, investigations into the cycling of trace metals in lakes have been relatively rare. This study investigated the biogeochemical cycling of five biologically important trace metals, namely manganese, cobalt, nickel, copper and zinc in three New Zealand lakes of different trophic state. The surface water in the three lakes was sampled monthly over a year, during which depth profile samples were collected twice. The samples were analysed to examine how trace metal speciation and phytoplankton productivity interact in the three lakes over time. The cycling of the metals was driven by the different physicochemical and biogeochemical factors distinctive for each lake, including water column oxygen concentrations and the extent to which each metal was bound to particulates. Intriguingly, increased biological uptake or limitation of growth during times of high phytoplankton growth was not observed for any of the investigated trace metals. This is of interest, especially as many of the trace metals investigated were present in sub-nanomolar bioavailable concentrations. The results from this study emphasise the important role biogeochemical cycling plays in regulating the distributions and bioavailability of trace metals in lakes.

To date, research on the role of organic matter dynamics in maintaining the health of (sub)tropical Andisols (i.e., volcanic ash-derived soils) is limited. High concentrations of poorly and noncrystalline minerals in these soils favor greater soil organic matter (SOM) accumulation than in phyllosilicate-dominant soils, yet SOM abundance and composition vary across volcanic landscapes. In this study, we measured the effects of moisture regime and current land use on soil health and SOM physical fractions and identified the carbon (C) and nitrogen (N) fractions that best predicted soil health scores in Andisols. We collected soil samples across humid (Udands) and dry (Ustands) moisture regimes and three land uses (croplands, pastures, forests) on Hawaiʻi Island. We measured nine dynamic soil properties and integrated them into a soil health score using a structural equation model. Then, we quantified the C and N contents of SOM physical fractions, including light particulate organic matter (LPOM), coarse heavy associated organic matter (CHAOM), and mineral associated organic matter (MAOM). We found that pastures and Udand forests scored highest in soil health while Ustand croplands scored lowest. Pastures contained greater proportions (% of total element) and contents (mg/g soil) of C and N in the CHAOM fraction, suggesting differences in CHAOM composition across ecosystems. All three physical fractions collectively explained 81% of soil health score variation, with MAOM-C explaining substantially more variation than LPOM-N and CHAOM-N. Our framework, which links soil C and N fractions to dynamic soil health properties, holistically captures the unique attributes of (sub)tropical Andisols rich in poorly and noncrystalline minerals.