21. 题目: Alteration of mixture toxicity in nonferrous metal mine tailings treated by biochar
Nonferrous metal mining activities produce enormous amounts of tailings that contain high concentrations of toxic chemicals threatening human health and the environment. This risk could be alleviated using remediation agents such as biochar, as proposed by others. However, contradictory evidence indicates that biochar can increase or sometimes decrease bioavailable concentrations depending on the selection of metal(loid)s in mine tailings. Here three biochars derived from different raw stocks were used to treat mine tailings samples. Chemical analyses indicated that all biochars favored the stabilization of Cd, Cr, Cu, Pb, and Zn, as well as the mobilization of As and Sb. The barley root elongation bioassay showed that the tailings toxicity was only partially diminished (up to 55.8%) or even elevated (up to 20.7%) by biochar treatment. Similar results were also observed from microbial enzyme assays (increased up to 28.3% or decreased up to 24.0%). Further analyses showed that these toxic effects correlated well with the relative toxicity index (R2 = 0.66 to 0.88). Toxicity testing coupled with the use of a toxicity prediction model presented here suggested that the release of As and Sb from tailings compromised the favorable effects of biochar treatment on toxic cationic metals. Such information is of paramount importance when taking countermeasures for improving bioremediation technologies.
22. 题目: Cadmium mediated phytotoxic impacts in Brassica napus: Managing growth, physiological and oxidative disturbances through combined use of biochar and Enterobacter sp. MN17
Cadmium (Cd) is a toxic heavy metal with unknown biological role. Interactive effect of Enterobacter sp. MN17 and biochar was studied on the growth, physiology and antioxidant defense system of Brassica napus under Cd contaminated soil. A multi-metal tolerant endophytic bacterium, Enterobacter sp. MN17, was able to grow in tryptic soy agar (TSA) medium with up to 160, 200, 300, 700, 160 and 400 μg mL−1 of Cd, Cu, Cr, Pb, Ni and Zn, respectively. Paper and pulp waste biochar was prepared at 450 °C and applied to pots (7 kg soil) at a rate of 1% (w/w), while Cd was spiked at 80 mg kg−1 soil. Application of Enterobacter sp. MN17 and biochar, alone or combined, was found effective in the amelioration of Cd stress. Combined application of Enterobacter sp. MN17 and biochar caused the maximum appraisal in shoot and root length (52.5 and 76.5%), fresh and dry weights of shoot (77.1 and 70.7%) and root (81.2 and 57.9%), photosynthetic and transpiration rate (120.2 and 106.6%), stomatal and sub-stomatal conductance (81.3 and 75.5%), chlorophyll content and relative water content (RWC) (78.4 and 102.9%) than control. Their combined use showed a significant decrease in electrolyte leakage (EL), proline, malondialdehyde (MDA), catalase (CAT), glutathione peroxidase (GPX), glutathione S transferase (GST) and superoxide dismutase (SOD) by 39.3, 39.4, 39.5, 37.0, 39.0 42.1 and 30.8%, respectively, relative to control. Likewise, the combined application of bacterial strain MN17 and biochar reduced Cd in soil by 45.6%, thereby decreasing its uptake in root and shoot by 40.1 and 38.2%, respectively in Cd contaminated soil. The application of biochar supported the maximum colonization of strain MN17 in the rhizosphere soil, root and shoot tissues. These results reflected that inoculation with Enterobacter sp. MN17 could be an effective approach to accelerate biochar-mediated remediation of Cd contaminated soil for sustainable production of crops.
23. 题目: Extracellular organic matter (EOM) distribution characteristic in algae electro-dewatering process
The work evaluated the influence of different operating conditions (voltage, ionic strength and mechanical pressure) on algae electro-osmotic dewatering effect and extracellular organic matter (EOM) regionalization. It was found that the algae electro-dewatering effect became better as the voltage and ionic strength increased, but electro-dewatering effect was decreased when ionic strength was more than 0.006gNaCl/gTSS, this indicated that too high ionic strength will reduce algae electro-dewatering effect. In addition, electro-osmosis effect first increases and then weakens when the pressure was increased. The content of dissolved organic materials (DOM) in the filtrate of both electrodes was increased when the voltage and ionic strength enhanced, the DOM content of filtrate at cathode and anode were increased from 42.9 mg/L, 36.7 mg/L to 68.2 mg/L, 85.3 mg/L when ionic strength raised from 0gNaCl/gTSS to 0.01gNaCl/gTSS, this indicated that a large amount of EOM dissolution as the voltage and ionic strength increased. The DOM content of both electrodes did not change significantly when mechanical pressure changed, anodic oxidation can oxidize and decompose macromolecular weight substances into mid-molecular weight and low molecular weight substances.
24. 题目: The river–groundwater interface as a hotspot for arsenic release
25. 题目: Superoxide-driven autocatalytic dark production of hydroxyl radicals in the presence of complexes of natural dissolved organic matter and iron
We introduced superoxide as potassium superoxide (KO2) to artificial lake water containing dissolved organic matter (DOM) without or with introduced ferric iron complexes (DOM-Fe), and monitored the production rate of hydroxyl radicals as well as changes in the absorption and fluorescence properties of DOM. The introduction of KO2 decreased the absorption by DOM but increased the spectral slope coefficient of DOM more with complexed ferric Fe than without it. The introduction of KO2 increased the fluorescence of humic-like components in DOM without introduced ferric Fe but resulted in the loss of fluorescence in DOM with introduced ferric Fe. A single introduction of 13 μmol L−1 KO2 produced 10 μmol L−1 and 104 μmol L−1 hydroxyl radicals during a week-long experiment without and with the introduced DOM-Fe complexes, respectively. The production rate of hydroxyl radicals decreased exponentially with time but levelled off and continued several days in DOM with introduced ferric Fe. These findings suggest that in the presence of DOM-Fe complexes, superoxide can trigger an autocatalytic Fenton reaction that produces hydroxyl radicals and breaks down DOM.
26. 题目: Early diagenetic pyrite cementation influences molecular composition of sedimentary organic matter in the Dongying Depression, China
Micro-variations of lipid hydrocarbons and biomarkers in well-laminated shales have not been extensively documented, especially within different rock textures, fabrics and mineralogies. Comparison of a pyrite cemented zone and its surrounding sediment may offer a new perspective on mineral control on preservation of hydrocarbons and organic carbon. A black well-laminated shale comprising two adjacent and contrasting calcareous (light) and pyrite (dark) laminae at the millimetre scale was selected from the Eocene Shahejie Formation, Dongying Depression, Bohai Bay Basin. It was horizontally sliced to separate a pyrite cemented concretion from the unaltered laminated shale, and investigated using geochemical techniques to assess the heterogeneity of elements, minerals, microfossils and hydrocarbons within the two slices. Micro-scale changes in source inputs were noted. For instance, the 4α-methylsteranes, dinosteranes and the triaromatic dinosteranes show varying distributions between the two slices, attributed to slight differences in dinoflagellate contributions. Similarly, variation in the amount of bacterial sulfate reduction is indicated by variations in the aryl isoprenoid ratio, relative amount of isorenieratane, long-chain n-alkane carbon isotopic composition and other molecular indicators including the relative amounts of dibenzothiophene, dibenzofuran, methyldibenzothiophene and methyltrimethyltridecylchromans. The primary control on these variations appears to be different euxinic water conditions, but diagenesis has also influenced the distributions. Differential anaerobic bacterial reworking of organic matter and pyrite concretion protection are responsible for organic geochemical variations on a millimetre-scale in the shale. The pyrite concretion has an altered record of its thermal history, but has a more accurate record of the organic geochemistry of microfossils and water column conditions. This study shows the potential for future investigations of closely-spaced vertical variation in organic geochemical parameters that may shed light on rapid temporal variation in organic matter input and depositional environment.
27. 题目: Solar irradiation combined with chlorine can detoxify herbicides
The solar/chlorine process is an energy-efficient advanced oxidation process that can produce reactive species such as hydroxyl radical, reactive chlorine species and ozone. This study investigated the process' ability to detoxify the typical herbicides atrazine and mecoprop (methylchlorophenoxypropionic acid). Both herbicides are resistant to direct solar photolysis or chlorination alone, but they can be degraded by the solar/chlorine process effectively. Atrazine inhibited the development of Arabidopsis thaliana, but such inhibition was negligible after solar/chlorine treatment of an atrazine solution. The transformation of atrazine in the process was shown to be through hydroxylation, hydrogen abstraction and dechlorination but did not involve chlorine substitution or addition. Cl• reacts with atrazine and mecoprop with rate constants of 6.87 × 109 M−1s−1 and 1.08 × 1010 M−1s−1, respectively, while ClO• reacts with mecoprop with a rate constant of 1.11 × 108 M−1s−1. The degradation kinetics of atrazine and mecoprop by solar/chlorine was simulated by modeling, which fitted the experimental results well. Hydroxyl radicals (HO•) mainly contributed to the degradation of atrazine by solar/chlorine at pH 7 with the contribution of 65%, whereas ClO• and O3 were main species responsible for the degradation of mecoprop with the contribution of 72% and 17%, respectively. The pseudo-first-order rate constants (k′s) of the two degradations increased substantially (by 28.8% for atrazine and by 198% for mecoprop) when the chlorine dosage was increased from 50 μM to 200 μM. The k′s decreased with increasing pH. The presence of natural organic matter inhibited the degradation of both herbicides, while the presence of bromide enhanced their degradation. This work reveals a feasible method for the detoxifying herbicides by combining chlorine with solar radiation.
28. 题目: Temperature-induced iron (III) reduction results in decreased dissolved organic carbon export in subalpine wetland soils, Colorado, USA
Concentrations of dissolved organic carbon (DOC) in surface waters have rapidly increased across Europe and North America over the past few decades. The causes for such trends have yet to be fully understood, although several factors including elevated temperatures and decreased atmospheric deposition of acid, nitrogen and sulfur, are considered responsible for the release of carbon from soils into streams. In order to determine how seasonal temperature patterns and soil physical and chemical characteristics influence iron (Fe)(III) reduction and DOC release to pore-water in subalpine wetland soils, we measured potential Fe(II) and DOC export rates at low (6˚C) and high (18˚C) temperatures using flow-through reactors containing undisturbed wetland soils sampled in the Fraser Experimental Forest (Colorado, USA) in two wetland types and at two depths.
Higher temperature, soil organic matter, nitrogen, and extractable Fe concentrations, but lower soil C:N ratios and extractable manganese concentrations promoted Fe(II) export from soil to water. Additionally, Fe(III) reduction was 1.5-5 times more responsive to temperature in shallow, organic matter-rich soils, compared to organic-poor deeper soils. Conversely, DOC export declined at higher temperature in all soils, consistent with a temperature-related increase in carbon respiration by Fe(III)-reducers. While higher temperature is expected to reduce carbon storage in wetland soils, our findings suggest that temperature-related increase in Fe(III) reduction will not generate additional release of DOC from soils to rivers.
29. 题目: Metrics that matter for assessing the ocean biological carbon pump
30. 题目: The Effects of pH, Temperature, and Humic-Like Substances on Anaerobic Carbon Degradation and Methanogenesis in Ombrotrophic and Minerotrophic Alaskan Peatlands
31. 题目: The combined application of organic and inorganic fertilizers increases soil organic matter and improves soil microenvironment in wheat-maize field
32. 题目: Balanced nutrient stoichiometry of organic amendments enhances carbon priming in a poorly structured sodic subsoil
Application of organic amendments (OAs), nutrients and gypsum to sodic subsoils is of great interest to improve soil functionality and crop yield. However, controversy remains about the impact of the priming effect (PE) on native soil organic carbon (SOC), and the mechanisms governing the dynamics of the PE by OAs (with variations in nutrient stoichiometry). To address these gaps in knowledge, this nine-month study applied C4-plant-derived OAs in a C3-plant-derived soil at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients (nitrogen and/or phosphorus) or gypsum. Across the treatments, the cumulative PE was between 135 and 475 mg CO2–C kg−1 soil over the nine months, equivalent to 2.3–8.2% of native SOC loss. In the first two months, the positive PE by the OAs could be attributed to co-metabolism and nitrogen (N) mining. These theories were supported by (i) the enhanced growth of microbial biomass associated with increased soil labile C (such as dissolved organic C); and (ii) the decreased soil mineral N availability, likely via microbial N immobilization, particularly with the inputs of sorghum stubble or sugarcane bagasse. Towards the end of the incubation, the relative PE (i.e. PE ÷ SOC mineralization in the control) was higher in the OA treatments (sorghum stubble and sugarcane bagasse) where nutrients were added to lower the C: nutrient stoichiometric ratios. These results support the theory of microbial stoichiometric decomposition of SOC, which may have become the dominant mechanism of PE over time. The application of gypsum, together with OAs (sorghum stubble or sugarcane bagasse), did not significantly change the magnitude or direction of the PE. In conclusion, the significant native SOC losses and N immobilization induced by the OAs, particularly where we balanced the nutrient stoichiometric ratios, indicate the vulnerability of subsoil SOC, and the potential of C sequestration in a sodic subsoil following amendment by OAs may be limited.
33. 题目: Responses of physiological groups of tropical heterotrophic bacteria to temperature and DOM additions: food matters more than warming
Compared to higher latitudes, tropical heterotrophic bacteria may be less responsive to warming because of strong bottom‐up control. In order to separate both drivers we determined the growth responses of bacterial physiological groups to temperature after adding dissolved organic matter (DOM) from mangroves, seagrasses and glucose to natural seawater from the Great Barrier Reef. Low (LNA) and high (HNA) nucleic acid content, membrane‐intact (Live) and membrane‐damaged (Dead) plus actively respiring (CTC+) cells were monitored for 4 days. Specific growth rates of the whole community were significantly higher (1.9 d−1) in the mangrove treatment relative to the rest (0.2–0.4 d−1) at in situ temperature and their temperature dependence, estimated as activation energy, was also consistently higher. Strong bottom‐up control was suggested in the other treatments. Cell size depended more on DOM than temperature. Mangrove DOM resulted in significantly higher contributions of Live, HNA and CTC+ cells to total abundance while the seagrass leachate reduced Live cells below 50%. Warming significantly decreased Live and CTC+ cells contributions in most treatments. Our results suggest that only in the presence of highly labile compounds, such as mangroves DOM, can we anticipate increases in heterotrophic bacteria biomass in response to warming in tropical regions.
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34. 题目: Modeling Spatiotemporal Patterns of Ecosystem Metabolism and Organic Carbon Dynamics Affecting Hypoxia on the Louisiana Continental Shelf
The hypoxic zone on the Louisiana Continental Shelf (LCS) forms each summer due to nutrient enhanced primary production and seasonal stratification associated with freshwater discharges from the Mississippi/Atchafalaya River Basin (MARB). Recent field studies have identified highly productive shallow nearshore waters as an important component of shelf‐wide carbon production contributing to hypoxia formation. This study applied a three‐dimensional hydrodynamic‐biogeochemical model named CGEM (Coastal Generalized Ecosystem Model) to quantify the spatial and temporal patterns of hypoxia, carbon production, respiration, and transport between nearshore and middle shelf regions where hypoxia is most prevalent. We first demonstrate that our simulations reproduced spatial and temporal patterns of carbon production, respiration, and bottom‐water oxygen gradients compared to field observations. We used multiyear simulations to quantify transport of particulate organic carbon (POC) from nearshore areas where riverine organic matter and phytoplankton carbon production are greatest. The spatial displacement of carbon production and respiration in our simulations was created by westward and offshore POC flux via phytoplankton carbon flux in the surface layer and POC flux in the bottom layer, supporting heterotrophic respiration on the middle shelf where hypoxia is frequently observed. These results support existing studies suggesting the importance of offshore carbon flux to hypoxia formation, particularly on the west shelf where hypoxic conditions are most variable.
35. 题目: Variations in the profile distribution and protection mechanisms of organic carbon under long-term fertilization in a Chinese Mollisol
Long term fertilization may have a significant effect on soil organic carbon (SOC) fractions and profile distribution. However, previous research mostly explored the SOC in the topsoil and provided little or no information about its distribution in deeper layers and various protection mechanisms particularly under long-term fertilization. The present study investigated the contents and profile distribution (0–100 cm) of distinct SOC protection mechanisms in the Mollisol (black soil) of Northeast China after 35 years of mineral and manure application. The initial Organic Matter content of the topsoil (0–20 cm) ranged from 26.4 to 27.0 g kg−1 soil, and ploughing depth was up to 20 cm. A combination of physical-chemical fractionation methods was employed to study various SOC fractions. There were significant variations throughout the profile among the various fractions and protection mechanisms. In topsoil (to 40 cm), mineral plus manure fertilization (MNPK) increased the total SOC content and accounted for 16.15% in the 0–20 cm and 12.34% in the 20–40 cm layer, while the manure alone (M) increased the total SOC by 56.14%, 48.73% and 27.73% in the subsoil (40–60, 60–80 and 80–100 cm, respectively). Moreover, MNPK and M in the topsoil and subsoil, respectively increased the unprotected coarse particulate organic carbon (cPOC) (48% and 26%, respectively), physically protected micro-aggregate (μagg) (20% and 18%, respectively) and occluded particulate organic carbon (iPOC) contents (279% and 93%, respectively) compared with the control (CK). A positive linear correlation was observed between total SOC and the cPOC, iPOC, physico-biochemically protected NH-μSilt and physico-chemically protected H-μSilt (p < 0.01) across the whole profile. Overall, physical, physico-biochemical and physico-chemical protection were the predominant mechanisms to sequester carbon in the whole profile, whereas the biochemical protection mechanisms were only relevant in the topsoil, thus demonstrating the differential mechanistic sensitivity of fractions for organic carbon cycling across the profile.
36. 题目: Optimal biochar amendment rate reduced the yield-scaled N2O emissions from Ultisols in an intensive vegetable field in South China
Nitrous oxide (N2O) emissions, vegetable yields, and soil microbial properties were studied in response to different rates of rice-straw biochar applied to an intensive vegetable soil (Ultisol) in South China. The study was conducted over a one-year period as a block-designed field experiment (n = 3) with two successive crops and five harvests in total. Biochar was applied at rates of 0, 10, 20, 30 and 40 Mg ha−1 and splits of nitrogen (N) fertilizer were added in the form of urea (1010 kg N in total). References without biochar and N fertilization were included. Biochar significantly decreased the cumulative annual N2O emissions by 34–67%, which concurred with decreased denitrification enzyme activity and increased nosZ gene abundance in the vegetable soil. The absolute N2O mitigation increased with increasing flux rates, which were positively correlated to soil temperature and water-filled pore space. Conversely, weak increases of N2O emissions were recurrently induced by biochar when the soil temperature was lower than 20 °C and the absolute fluxes were low. A significant 17–29% increase in vegetable yield was induced by biochar, which also ameliorated soil fertility by increasing the soil carbon content and the cation exchange capacity. Overall, biochar significantly decreased the yield-scaled N2O emissions by 44–71% with the lowest yield-scaled N2O emissions for the intermediate biochar application rate of 20 Mg ha−1. Higher biochar application rates failed to further decrease the yield-scaled N2O emissions, but rather caused weak increases. Based on the present results, a biochar application rate of 20 Mg ha−1 combined with N fertilization seemed to be recommendable to achieve highest vegetable yield with lowest N2O emissions in intensive vegetable production in South China.
37. 题目: Photolability of pyrogenic dissolved organic matter from a thermal series of laboratory-prepared chars
While pyrogenic dissolved organic matter (pyDOM) is known to be photolabile, the rates and components of pyDOM that are lost via photochemical degradation, and how these vary with pyrogenic source, are poorly understood. Thus, pyDOM was leached from an oak thermal series and a grass chars (250–650 °C) and photoirradiated in a solar simulator. About 10–20% of oak char leachate organic C was mineralized over five days, with greater proportions lost from leachates of higher temperature parent chars. Ultraviolet and fluorescence spectroscopy suggested that mainly aromatic components (e.g., fulvic-, humic-, aromatic-like) were lost. Quantification of benzenepolycarboxylic acids (BPCAs), molecular markers indicated that 75–94% of condensed aromatic C was lost during the first five days of photoincubation, with preferential loss of larger aromatic clusters. Using a 2-component exponential decay model, this most photolabile fraction was calculated to have experimental half-lives of about 1 day. It represented 16 to 23% of the dissolved C, was primarily condensed aromatics, and was likely lost through primary photoreactions. A non-condensed component was lost at half-lives of about 1–2 d, likely through radical-driven propagation reactions. Using the same model, about 43% of pyrogenic C was predicted to be photomineralized over the course of 1 year. These results highlight the contrasting reactivity of condensed and non-condensed portions of pyDOM, and both should be considered when evaluating the potential of pyDOM to alter aquatic ecology and the environmental mobility of priority pollutants.
38. 题目: Removal of heavy metal ions by ultrafiltration with recovery of extracellular polymer substances from excess sludge
To solve the difficult problem of separating extracellular polymeric substances (EPSs) with adsorbed heavy metal ions (HMIs) from aqueous solutions, EPS recovery and HMI adsorption were combined into dead-end ultrafiltration (EPS-enhanced ultrafiltration, EPS-UF). First, an EPS solution was concentrated via UF into a cake on the membrane, which was then used to filter heavy-metal-containing wastewater. EPS-UF could effectively remove HMIs in wastewater, with a 94.8% Pb2+ removal efficiency and 85.5% EPS recovery efficiency with concentrations of 0.1 g/L EPS and 10 μM Pb2+. During concentration, the filtration resistance increased with increasing filtration pressure because of the high compressibility of the EPS cake and as filtration proceeded. During removal, a high filtration pressure (200 kPa) could not increase the filtration rate, and the removal efficiency of Pb2+ decreased markedly (78.88%). Ca2+ was proposed as a strategy for controlling membrane fouling because it was completely released from the cake after adsorbing Pb2+ and barely affected the characteristic groups in EPS. Fourier transform infrared and X-ray photoelectron spectroscopy revealed that carboxyls or esters from carboxylate and uronic acids in EPS bonded with HMIs via ion exchange or complexation, and the main characteristic groups in EPS remained unchanged, while more complex proteins formed.
39. 题目: The roles of vegetation, tide and sediment in the variability of carbon in the salt marsh dominated tidal creeks
Combined effects of vegetation, tide and sediment on the carbon dynamics in the intertidal creek-marsh systems remain unclear. We investigated the variability of dissolved organic (DOC) and inorganic carbon (DIC), and particulate organic (POC) and inorganic carbon (PIC) in the tidal creeks within the Poaceae and Cyperaceae communities on flood-ebb cycle in a salt marsh of eastern China. In the Poaceae creek with high plant biomass and soil carbon stock, the DOC concentrations were higher by on average 1.00–1.48 times than that in the Cyperaceae creek across all seasons and spring and neap tide stages, while the difference of DIC was not notable. The POC and PIC concentrations were lower in the Poaceae creek compared to the Cyperaceae creek. Spring tides increased the carbon concentrations (except for PIC) in both creeks by on average 7–40%, relative to neap tides. Seasonal variations of sedimentary rate within the communities probably result in the discrepancy of particulate carbon loading between the creeks. The Poaceae creek functioned as a source of DOC and DIC throughout a year but as a sink of POC and PIC in summer and autumn, while it turned to a weak source of PIC in winter and spring. The Cyperaceae creek exhibited as a source of all carbon components throughout a year. We suggest that vegetation type (with soil carbon stocks), tidal regimes and sedimentary dynamics would synergistically determine the fate of carbon in the creeks. Our results are helpful in reliable estimates of carbon transport between the coastal marsh and the adjacent ocean.
40. 题目: Microbial release of apatite- and goethite-bound phosphate in acidic forest soils
Phosphorus (P) is an element crucial for plant nutrition. P can be bound in primary minerals such as apatites or to secondary minerals, such as metal(hydr-)oxides. Microorganisms are capable of releasing mineral-bound P, and thus, transforming it into plant-available forms. This study examined the potential of native microbial communities of five beech forest soils to release P either from hydroxyapatite or P-loaded goethite. Incubation experiments with soil extracts, either with or without glucose, were conducted. Desorption of phosphate from goethite was less effective than the solubilization of phosphate from hydroxyapatite. We found that the net P solubilization from hydroxyapatite was driven by the microbial production of low molecular weight organic acids (LMWOAs), such as D-gluconic and 2-keto-D-gluconic acids, and differed among the microbial communities extracted from the five forest soils. In contrast, the net P desorption rates from goethite did not vary significantly among the microbial communities extracted from the different soils. Microbial acidification of the solution increased the adsorption of phosphate to goethite, whereas less acidic conditions promoted progressive desorption of phosphate. Microbial communities in soil extracts incubated with P-loaded goethite downregulated the release of organic acids, which reduced acidification. The net P solubilization rates from hydroxyapatite and the net P desorption rates from goethite were strongly increased by the addition of glucose, suggesting that microbial P mobilization from minerals is strongly carbon limited. In conclusion, the study shows that microbial communities from acidic beech forest soils are much more efficient at releasing phosphate from hydroxyapatite than from goethite.