Biogeochemistry最新文献

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.

Understanding the biogeochemical cycling of phosphorus (P), particularly organic P (OP) in soils, under varying land use and soil development processes is essential for optimizing P usage under P fertilizer crisis. However, the complexity of OP impedes the mechanistic understanding. Therefore, by using well-documented organic carbon (OC) and total nitrogen (TN) cycling, we studied their stoichiometric correlation with P in soil fractions to indicate soil organic matter (SOM) and P turnover under two land uses (Cropland VS. Grassland) in Germany. Our results showed that grassland soils on the hillslope have higher OC and TN stocks than cropland soils. Total P (TP) stocks were unaffected by land use. However, grassland topsoil exhibited higher OP stocks and OP/TP proportions than cropland, with a constant IP stock throughout the soil profile, as this was determined by soil development processes in the subsoil. This proves that the flood plain soils are decoupled from hillslope soils due to different soil development processes. The stoichiometric assessment revealed a higher enrichment of OP in fine fractions of grassland soils, indicating stronger resistance to P loss by soil degradation. Mechanistic insights from OC:OP ratio of fine fractions indicate two potential OP cycling pathways: a ratio similar to microbial biomass C:P ratio suggesting a greater OP stabilization within microbial biomass/necromass; whereas a narrower ratio indicating more OP associated directly with mineral surfaces. This study illuminates the complex interplay between land use and soil development processes on OC, TN and P cycling, emphasizing the potential of stoichiometric assessment in soil fractions to understand OP biogeochemical cycling.

The stability of carbon (C) stocks in peatlands is intricately linked to phosphorus (P) bioavailability. Given that organic P compounds (P_o) can make up to 89% of total soil P in these ecosystems, it is vital to understand their role in regulating plant productivity and organic matter decomposition. Despite this significance, the mechanisms controlling P bioavailability remain poorly understood. Plants and soil microorganisms primarily regulate the release of soil P via low-molecular-weight organic acids (LMWOAs) and modulate the hydrolysis of P_o through phosphatase enzymes, particularly phosphomonoesterase, phytase, and phosphodiesterase. This study investigated the role of LMWOAs, derived from root exudates of dominant vascular plants and Sphagnum leachates in a temperate montane peatland, in facilitating the release of P. We also quantified the ability of these plants to hydrolyze P_o from various LMWOA-extracted fractions by adding phosphomonoesterase, phytase, and phosphodiesterase. The results show that peatland plants predominantly exuded muconic, azelaic, 3-hydroxybutyric, and malonic acids. The concentration of enzymatically hydrolyzed P_o in the water-extracted fraction was 8.1 ± 3.4 mg kg⁻¹. Notably, azelaic and malonic acids were effective in releasing over 58% of soil P (330–798 mg kg⁻¹), with more than 88% of this P being in organic form. In the azelaic and malonic acid-extracted fractions, the concentration of enzymatically hydrolyzed P_o concentration was 123.7 ± 32.1 mg kg⁻¹, accounting for 23% of the LMWOA-extracted P_o. Phytase, the most important phosphatase enzyme, accounts for 66% (47–88%) of the enzymatically hydrolyzed P_o (81.9 ± 20.9 mg kg⁻¹). Our study demonstrates that LMWOA-mediated release of P_o is an essential prerequisite for enzymatic hydrolysis of P_o in organic peat soils. However, only a small portion of LMWOA-extracted P_o can be hydrolyzed by phosphatase enzymes. The different composition and efficacy of LMWOAs from species of different plant functional types highlight the necessity to consider changes in vegetation composition, as this could significantly impact P dynamics in peatlands and, consequently, the stability of their C stocks.

An important control on long-term soil organic carbon (SOC) storage is the adsorption of SOC by short-range-ordered (SRO) minerals. SRO are commonly quantified by measuring oxalate-extractable metals (M_ox = Al_ox + ½ Fe_ox), which many studies have shown to be positively correlated with SOC. It remains uncertain if this organo-mineral relationship is robust at the global scale, or if capturing regional differences is needed to maximize model accuracy. We used a global synthesis of Al_ox and Fe_ox data to test their role in controlling SOC abundance across regions. We compiled 37,344 individual soil horizon measurements, with soil depth ranging between 0 and 200 cm, from 11,122 profiles. We used the Holdridge Life Zones, which are characterized by biotemperature, precipitation, and potential evapotranspiration, to group the soil profiles by their climatic conditions that also correlate with other important soil-forming factors. Based on linear mixed-effects models, we found a positive relationship between M_ox and SOC across regions and depths, accounting for 49% of the SOC variation. This relationship is strongest in wetter regions and at depths between 20 and 100 cm. Across all environmental conditions, Al_ox is a stronger predictor of SOC than Fe_ox. Our analysis suggests oxalate-extractable metals are good proxies for mineral-induced SOC protection at the global scale. However, our findings also indicate that the importance of organo-mineral interactions at the global scale varies with climatic conditions and depth. The underlying mechanisms need to be considered when incorporating these relationships as proxies for mineral sorption capacity into soil C models.