Three thousand years of Hg pollution recorded in mangrove wetland sediments from South China.

Mercury (Hg) is known to affect aquatic, terrestrial ecosystems as well as human health, through biomagnification. Mangrove wetlands are potential Hg sinks because of their low tidal velocity, fast sedimentation rate, strong reducing condition and high organic matter content. The spatial and temporal distribution of Hg has been a hot topic of recent studies in mangrove wetlands. In this study, we investigated Hg concentration, accumulation rate and isotopes to reconstruct the Hg pollution history and to differentiate its potential sources in the Gaoqiao mangrove wetland (Guangdong province), which is part of the largest mangrove area in China. We reconstructed a first, continuous, high-resolution Hg pollution history over the last 3000 years in South China. Our findings show that mangrove wetland sediments are more enriched in Hg than the adjacent grasslands. The increased Hg concentration and δ202Hg in recent sediments mirror the enhanced anthropogenic impacts; Hg concentrations in areas with high levels of anthropogenic disturbance are up to 5× higher than the average background value (9.9 ± 1.2 µg kg-1). Compared to mangroves in coastal areas of South China and around the world, the Hg concentration in Gaoqiao is much lower. The significant increase of Hg since the 1950s and the major Hg peak since the 1980s were the evidence of the human activities influences and indicated the possible start date of Anthropocene. After 2007 CE, a decline in Hg pollution occurs due to the effective implementation of the mangrove protection policy. Three potential sources were identified by the Hg isotope traces including urban gaseous Hg, industrial Hg, and regional soil and leaf litter Hg input.

Lignocellulolytic Potential of Microbial Consortia Isolated from a Local Biogas Plant: The Case of Thermostable Xylanases Secreted by Mesophilic Bacteria.

Lignocellulose biomasses (LCB), including spent mushroom substrate (SMS), pose environmental challenges if not properly managed. At the same time, these renewable resources hold immense potential for biofuel and chemicals production. With the mushroom market growth expected to amplify SMS quantities, repurposing or disposal strategies are critical. This study explores the use of SMS for cultivating microbial communities to produce carbohydrate-active enzymes (CAZymes). Addressing a research gap in using anaerobic digesters for enriching microbiomes feeding on SMS, this study investigates microbial diversity and secreted CAZymes under varied temperatures (37 °C, 50 °C, and 70 °C) and substrates (SMS as well as pure carboxymethylcellulose, and xylan). Enriched microbiomes demonstrated temperature-dependent preferences for cellulose, hemicellulose, and lignin degradation, supported by thermal and elemental analyses. Enzyme assays confirmed lignocellulolytic enzyme secretion correlating with substrate degradation trends. Notably, thermogravimetric analysis (TGA), coupled with differential scanning calorimetry (TGA-DSC), emerged as a rapid approach for saccharification potential determination of LCB. Microbiomes isolated at mesophilic temperature secreted thermophilic hemicellulases exhibiting robust stability and superior enzymatic activity compared to commercial enzymes, aligning with biorefinery conditions. PCR-DGGE and metagenomic analyses showcased dynamic shifts in microbiome composition and functional potential based on environmental conditions, impacting CAZyme abundance and diversity. The meta-functional analysis emphasised the role of CAZymes in biomass transformation, indicating microbial strategies for lignocellulose degradation. Temperature and substrate specificity influenced the degradative potential, highlighting the complexity of environmental-microbial interactions. This study demonstrates a temperature-driven microbial selection for lignocellulose degradation, unveiling thermophilic xylanases with industrial promise. Insights gained contribute to optimizing enzyme production and formulating efficient biomass conversion strategies. Understanding microbial consortia responses to temperature and substrate variations elucidates bioconversion dynamics, emphasizing tailored strategies for harnessing their biotechnological potential.

The effects of biochar on soil organic matter pools are not influenced by climate change.

The sustainability of Mediterranean croplands is threatened by climate warming and rainfall reduction. The use of biochar as an amendment represents a tool to store organic carbon (C) in soil. The vulnerability of soil organic C (SOC) to the joint effects of climate change and biochar application needs to be better understood by investigating its main pools. Here, we evaluated the effects of partial rain exclusion (∼30%) and temperature increase (∼2 °C), combined with biochar amendment, on the distribution of soil organic matter (SOM) into particulate organic matter (POM) and the mineral-associated organic matter (MAOM). A set of indices suggested an increase in thermal stability in response to biochar addition in both POM and MAOM fractions. The MAOM fraction, compared to the POM, was particularly enriched in labile substances. Data from micro-Raman spectroscopy suggested that the POM fraction contained biochar particles with a more ordered structure, whereas the structural order decreased in the MAOM fraction, especially after climate manipulation. Crystalline Fe oxides (hematite) and a mix of ferrihydrite and hematite were detected in the POM and in the MAOM fraction, respectively, of the unamended plots under climate manipulation, but not under ambient conditions. Conversely, in the amended soil, climate manipulation did not induce changes in Fe speciation. Our work underlines the importance of discretely taking into account responses of both MAOM and POM to better understand the mechanistic drivers of SOC storage and dynamics.

Near Infared Circularly Polarized Luminescence From Water Stable Organic Nanoparticles Containing a Chiral Yb(III) Complex.

We report the first example of very efficient NIR Circularly Polarized Luminescence (CPL) (around 970 nm) in water, obtained thanks to the combined use of a chiral Yb complex and of poly lactic-co-glycolic acid (PLGA) nanoparticles. [YbL(tta)2 ]CH3 COO (L=N, N'-bis(2-pyridylmethylidene)-1,2-(R,R+S,S) cyclohexanediamine and tta=2-thenoyltrifluoroacetonate) shows good CPL in organic solvents, because the tta ligands efficiently sensitize Yb NIR luminescence and the readily prepared chiral ligand L endows the complex with the necessary dissymmetry. PLGA nanoparticles incorporate the complex and protect the metal ion from the intrusion of solvent molecules, while ensuring biocompatibility, water solubility and stability to the complex. Hydrophilic NIR-CPL optical probes can find applications in the field of NIR-CPL bio-assays.

Iron Speciation in Organic Matter Fractions Isolated from Soils Amended with Biochar and Organic Fertilizers.

The role and distribution of iron (Fe) species in physical soil fractions have received remarkably little attention in field-scale systems. Here, we identify and quantify the Fe phases into two fractions (fine sand, FSa, and fine silt and clay, FSi + Cl), isolated from an agricultural soil unamended and amended with different organic materials, by Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The linear combination fitting and wavelet transform of EXAFS data revealed noticeable differences between unamended FSa and FSi + Cl fractions. Specifically, the FSi + Cl fraction was mainly characterized by ferrihydrite (48%) and Fe(III)-soil organic matter (SOM) complexes (37%), whereas in the FSa fraction, ferrihydrite still represented a major phase (44%), with a lower contribution from Fe(III)-SOM (18%). In the FSa fraction, the addition of the organic amendments resulted in an increase of Fe-SOM complexes (31-35%) and a decrease of ferrihydrite (28-29%). By contrast, in the amended FSi + Cl fractions, the added organic matter led to negligible changes in percent ferrihydrite. Therefore, regardless of the amendment type, the addition of organic matter to soil increased the capability of the coarse fraction (FSa) to stabilize organic carbon, thus pointing out that the role of FSa in carbon sequestration in agricultural soils at a global scale may be overlooked.

Testate amoeba records indicate regional 20th-century lowering of water tables in ombrotrophic peatlands in central-northern Alberta, Canada.

Testate amoebae are abundant in the surface layers of northern peatlands. Analysis of their fossilized shell (test) assemblages allows for reconstructions of local water-table depths (WTD). We have reconstructed WTD dynamics for five peat cores from peatlands ranging in distance from the Athabasca bituminous sands (ABS) region in western Canada. Amoeba assemblages were combined with plant macrofossil records, acid-insoluble ash (AIA) fluxes and instrumental climate data to identify drivers for environmental change. Two functional traits of testate amoebae, mixotrophy and the tendency to integrate xenogenic mineral matter in test construction, were quantified to infer possible effects of AIA flux on testate amoeba presence. Age-depth models showed the cores each covered at least the last ~315 years, with some spanning the last millennium. Testate amoeba assemblages were likely affected by permafrost development in two of the peatlands, yet the most important shift in assemblages was detected after 1960 CE. This shift represents a significant apparent lowering of water tables in four out of five cores, with a mean drop of ~15 cm. Over the last 50 years, assemblages shifted towards more xerophilous taxa, a trend which was best explained by increasing Sphagnum s. Acutifolia and, to a lesser extent, mean summer temperature. This trend was most evident in the two cores from the sites located farthest away from the ABS region. AIA flux variations did not show a clear effect on mineral-agglutinating taxa, nor on S. s. Acutifolia presence. We therefore suggest the drying trend was forced by the establishment of S. s. Acutifolia, driven by enhanced productivity following regional warming. Such recent apparent drying of peatlands, which may only be reconstructed by appropriate indicators combined with high chronological control, may affect vulnerability to future burning and promote emissions of CO2 .

Peat Bogs Document Decades of Declining Atmospheric Contamination by Trace Metals in the Athabasca Bituminous Sands Region.

Peat cores were collected from five bogs in the vicinity of open pit mines and upgraders of the Athabasca Bituminous Sands, the largest reservoir of bitumen in the world. Frozen cores were sectioned into 1 cm slices, and trace metals determined in the ultraclean SWAMP lab using ICP-QMS. The uppermost sections of the cores were age-dated with 210Pb using ultralow background gamma spectrometry, and selected plant macrofossils dated using 14C. At each site, trace metal concentrations as well as enrichment factors (calculated relative to the corresponding element/Th ratio of the Upper Continental Crust) reveal maximum values 10 to 40 cm below the surface which shows that the zenith of atmospheric contamination occurred in the past. The age-depth relationships show that atmospheric contamination by trace metals (Ag, Cd, Sb, Tl, but also V, Ni, and Mo which are enriched in bitumen) has been declining in northern Alberta for decades. In fact, the greatest contemporary enrichments of Ag, Cd, Sb, and Tl (in the top layers of the peat cores) are found at the control site (Utikuma) which is 264 km SW, suggesting that long-range atmospheric transport from other sources must be duly considered in any source assessment.

Persistent high temperature and low precipitation reduce peat carbon accumulation.

Extreme climate events are predicted to become more frequent and intense. Their ecological impacts, particularly on carbon cycling, can differ in relation to ecosystem sensitivity. Peatlands, being characterized by peat accumulation under waterlogged conditions, can be particularly sensitive to climate extremes if the climate event increases soil oxygenation. However, a mechanistic understanding of peatland responses to persistent climate extremes is still lacking, particularly in terms of aboveground-belowground feedback. Here, we present the results of a transplantation experiment of peat mesocosms from high to low altitude in order to simulate, during 3 years, a mean annual temperature c. 5 °C higher and a mean annual precipitation c. 60% lower. Specifically, we aim at understanding the intensity of changes for a set of biogeochemical processes and their feedback on carbon accumulation. In the transplanted mesocosms, plant productivity showed a species-specific response depending on plant growth forms, with a significant decrease (c. 60%) in peat moss productivity. Soil respiration almost doubled and Q10 halved in the transplanted mesocosms in combination with an increase in activity of soil enzymes. Spectroscopic characterization of peat chemistry in the transplanted mesocosms confirmed the deepening of soil oxygenation which, in turn, stimulated microbial decomposition. After 3 years, soil carbon stock increased only in the control mesocosms whereas a reduction in mean annual carbon accumulation of c. 30% was observed in the transplanted mesocosms. Based on the above information, a structural equation model was built to provide a mechanistic understanding of the causal connections between peat moisture, vegetation response, soil respiration and carbon accumulation. This study identifies, in the feedback between plant and microbial responses, the primary pathways explaining the reduction in carbon accumulation in response to recurring climate extremes in peat soils.

Airborne Petcoke Dust is a Major Source of Polycyclic Aromatic Hydrocarbons in the Athabasca Oil Sands Region.

Oil sands mining has been linked to increasing atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) in the Athabasca oil sands region (AOSR), but known sources cannot explain the quantity of PAHs in environmental samples. PAHs were measured in living Sphagnum moss (24 sites, n = 68), in sectioned peat cores (4 sites, n = 161), and snow (7 sites, n = 19) from ombrotrophic bogs in the AOSR. Prospective source samples were also analyzed, including petroleum coke (petcoke, from both delayed and fluid coking), fine tailings, oil sands ore, and naturally exposed bitumen. Average PAH concentrations in near-field moss (199 ng/g, n = 11) were significantly higher (p = 0.035) than in far-field moss (118 ng/g, n = 13), and increasing temporal trends were detected in three peat cores collected closest to industrial activity. A chemical mass-balance model estimated that delayed petcoke was the major source of PAHs to living moss, and among three peat core the contribution to PAHs from delayed petcoke increased over time, accounting for 45-95% of PAHs in contemporary layers. Petcoke was also estimated to be a major source of vanadium, nickel, and molybdenum. Scanning electron microscopy with energy-dispersive X-ray spectroscopy confirmed large petcoke particles (>10 µm) in snow at near-field sites. Petcoke dust has not previously been considered in environmental impact assessments of oil sands upgrading, and improved dust control from growing stockpiles may mitigate future risks.

Sphagnum mosses from 21 ombrotrophic bogs in the athabasca bituminous sands region show no significant atmospheric contamination of "heavy metals".

Sphagnum moss was collected from 21 ombrotrophic (rain-fed) peat bogs surrounding open pit mines and upgrading facilities of Athabasca bituminous sands in Alberta (AB). In comparison to contemporary Sphagnum moss from four bogs in rural locations of southern Germany (DE), the AB mosses yielded lower concentrations of Ag, Cd, Ni, Pb, Sb, and Tl, similar concentrations of Mo, but greater concentrations of Ba, Th, and V. Except for V, in comparison to the "cleanest", ancient peat samples ever tested from the northern hemisphere (ca. 6000-9000 years old), the concentrations of each of these metals in the AB mosses are within a factor of 3 of "natural, background" values. The concentrations of "heavy metals" in the mosses, however, are proportional to the concentration of Th (a conservative, lithophile element) and, therefore, contributed to the plants primarily in the form of mineral dust particles. Vanadium, the single most abundant trace metal in bitumen, is the only anomaly: in the AB mosses, V exceeds that of ancient peat by a factor of 6; it is therefore enriched in the mosses, relative to Th, by a factor of 2. In comparison to the surface layer of peat cores collected in recent years from across Canada, from British Columbia to New Brunswick, the Pb concentrations in the mosses from AB are far lower.

Soil organic matter dynamics and stability: Climate vs. time.

Climate and time are among the most important factors driving soil organic carbon (SOC) stability and accrual in mineral soils; however, their relative importance on SOC dynamics is still unclear. Therefore, understanding how these factors covary over a range of soil developmental stages is crucial to improve our knowledge of climate change impact on SOC accumulation and persistence. Two chronosequences located along a climate gradient were investigated to determine the main interactions among time (age) and climate (precipitation and temperature) on SOC stability and stock with depth. Considering a common depth (0-15 or 0-30 cm), in the drier chronosequence, the older soil showed the highest SOC stock, while the younger exhibited the lowest carbon accumulation. Considering the whole profile, the SOC stock increased with age. In the wetter chronosequence, the younger soil showed the highest SOC stock considering a common depth, whereas, when the entire profile is taken into account, the older one accumulated 2-3 times more SOC than the others. In both chronosequences, significant stocks of SOC (∼42 %) were accumulated below 30 cm. Soil organic matter stability, assessed by thermal analysis and heterotrophic respiration, increases with depth and age only in the drier chronosequence. Soils from the wetter chronosequence were instead characterized by a greater quantity of labile and/or not-stabilized SOC; here, the amorphous Fe/Al-rich secondary mineral weathering products showed an essential predictor function of SOC storage, although they do not seem to be involved in SOC stabilization mechanisms. Otherwise, the interaction of SOC with fine particles, short-range order minerals, and organo-metal complexes represent the significant stabilization mechanisms in soils from drier climate. The results highlighted how the age factor plays an unassuming role in geochemical processes influencing SOC dynamics; however, climate determines different trajectories of soil development and SOC dynamics for a given soil age. Thus, soil age shows a key role in SOC stabilization especially in drier climatic conditions, while wetter conditions determine an accumulation of a higher yet more labile amount of SOC.

Using diatoms and physical and chemical parameters to monitor cow-pasture impact in peat cores from mountain mires.

Peatlands play a crucial role in carbon (C) sequestration and biodiversity conservation. However, these environments are highly vulnerable, and Europe has lost >60 % of its peatland habitat in recent decades. Cattle grazing and trampling contribute to peatland degradation, which generally result in a shift from moss-dominated vegetation to vascular plants and in lower C sequestration rates. Overgrazing poses also a significant threat to habitat integrity and biodiversity, especially in the Alpine area, where close-to-pristine mires with high ecological integrity are becoming extremely rare. Thus, a more in depth understanding of how cattle grazing and trampling are threatening Alpine mires is strongly needed for a sustainable management and conservation of these habitats. The objective of this study was to examine the impact of grazing on the physical, chemical, and biological characteristics of peat, with a focus on diatoms. To answer such a question, seven 50-cm deep cores were collected from mires located in the Adamello-Brenta Nature Park (North of Italy) along a grazing-induced disturbance gradient. Results indicated that grazing primarily affected at least the upper 15 cm of the peat, resulting in increased density and reduced water content, due to compaction, and lower C-to­nitrogen ratio, possibly caused by both cow manure inputs and increased peat mineralization. Moreover, almost 200 diatom taxa were recorded across the 7 cores, with several of them falling under threat categories in the Red List for central Europe. The higher percentage of eutraphentic species in highly-grazed areas was related to the increase in nutrients caused by cattle manure. Finally, intense grazing increased the share of taxa that are more likely to survive in environments with unstable water availability (= aerial species). We showed that diatom data, supported by physical and chemical parameters, can be a refined tool to inform mire protection and rehabilitation.

Human activity has increasingly affected recent carbon accumulation in Zhanjiang mangrove wetland, South China.

Mangrove wetlands are an important component of blue carbon (C) ecosystems, although the anthropogenic impact on organic C accumulation rate (OCAR) in mangrove wetlands is not yet clear. Three sediment cores were collected from Zhanjiang Gaoqiao Mangrove Reserve in Southern China, dated by 210Pb and 137Cs, and physico-chemical parameters measured. Results show that the OCARs in mangroves and grasslands have significantly increased by 4.4 and 1.3 times, respectively, since 1950, which is consistent with the transformation of organic C sources and the increase of sedimentation rate. This increment is due to increased soil erosion and nutrient enrichment caused by land use change and the discharge of fertilizer runoff and aquaculture wastewater. This study provides clear evidence for understanding the changes in organic C accumulation processes during the Anthropocene and is conducive to promoting the realization of C peak and neutrality targets.

Transcranial alternating current stimulation (tACS) at gamma frequency: an up-and-coming tool to modify the progression of Alzheimer's Disease.

The last decades have witnessed huge efforts devoted to deciphering the pathological mechanisms underlying Alzheimer's Disease (AD) and to testing new drugs, with the recent FDA approval of two anti-amyloid monoclonal antibodies for AD treatment. Beyond these drug-based experimentations, a number of pre-clinical and clinical trials are exploring the benefits of alternative treatments, such as non-invasive stimulation techniques on AD neuropathology and symptoms. Among the different non-invasive brain stimulation approaches, transcranial alternating current stimulation (tACS) is gaining particular attention due to its ability to externally control gamma oscillations. Here, we outline the current knowledge concerning the clinical efficacy, safety, ease-of-use and cost-effectiveness of tACS on early and advanced AD, applied specifically at 40 Hz frequency, and also summarise pre-clinical results on validated models of AD and ongoing patient-centred trials.

Sources, spatial-distributions and fluxes of PAH-contaminated dusts in the Athabasca oil sands region.

Atmospheric deposition of polycyclic aromatic hydrocarbons (PAHs) has increased in northern Alberta, Canada, due to industrial development in the Athabasca oil sands region (AOSR). However, the sources, summertime deposition fluxes and associated spatial patterns are poorly characterized, and the magnitude of contamination has not been directly contrasted with comparable measurements around large Canadian cities. PAHs were measured in Sphagnum moss collected from 30 bogs in the AOSR and compared with reference moss collected from various remote, rural and near-urban sites in Alberta and Ontario. At all 39 locations, strong correlations between depositional fluxes of PAHs and accumulation rates of ash (n = 117, r = 0.877, p < 0.001) implied that the main source of PAHs to moss was atmospheric deposition of particles. Average PAH concentrations at near-field AOSR sites (mean [SD], 62.4 [24.3] ng/g) were significantly higher than at far-field AOSR sites (44.9 [20.8] ng/g; p = 0.038) or the 7 reference sites in Alberta (20.6 [3.5] ng/g; p < 0.001). In fact, average PAH concentrations across the entire AOSR (7,850 km2) were approximately twice as high as in London, Ontario, or near petroleum upgrading and major traffic corridors in Edmonton, Alberta. A chemical mass balance model estimated that both delayed petcoke (33 % of PAHs) and fine tailings (38 % of PAHs) were the major sources of PAHs in the AOSR. Over the 2015 summer growing season, we estimate that 101-110 kg of PAHs (on 14,300-17,300 tonnes of PAH-containing dusts) were deposited to the AOSR within a 50 km radius of surface mining. Given that the highest PAH deposition was to the northern quadrant of the AOSR, which includes the First Nations community of Fort MacKay, further dust control measures should be considered to protect human and environmental health in the region.

Evaluating the potential of hydrochar as a soil amendment.

In this study, hydrochar (HC), a carbon-rich product originated from hydrothermal conversion treatment (HTC), was obtained from wastes of the wine and dairy industries. The effect of mixing secondary char and compost was tested, before and after the aerobic mixing of compost (COM) and HC at increasing doses (from 15 to 75 Mg ha-1 DM), in an effort to lower the HC phytotoxicity due to potential phytotoxic compounds of secondary char. The results indicated that, after the aerobic stabilization, the mix HC/COM was able to double the plant growth in comparison to COM alone. The presence of easily degradable organic compounds probably led to poor stability of HC, increased microbial activity and, consequently, root anoxia when used at high doses. Chemical, spectroscopic and thermal investigation confirmed this hypothesis. In particular, HC shows a high content of dissolved organic matter, characterized by the presence of small molecules, which is negatively correlated with the growth index of lettuce. Furthermore, thermal characterization suggests a higher proportion of less complex and thermally stable molecular compounds in HC in comparison to COM. Therefore, co-composting of HC allows obtaining a useful amendment to support soil organic matter and fertility.

Effect of the alkali vs iron ratio on glass transition temperature and vibrational properties of synthetic basalt-like glasses.

Volcanic eruptions generate huge amounts of material with a wide range of compositions and therefore different physicochemical properties. We present a combined Raman and calorimetric study carried out on four synthetic basaltic glasses with different alkali vs iron ratio which spans the typical compositions of basalts on Earth. Differential scanning calorimetry shows that changes of this ratio modify the glass transition interval whereas Raman spectra allow to gain insight about the structure of the glass in the microscopic and macroscopic range. Indeed, our Raman analysis is extended from the high frequency region, characterized by the molecular peaks, to the very low frequency region where glasses exhibit the boson peak. Spectra show a variation of the non-bridging oxygens number that affects the medium range order of the glass and the network interconnections. In the considered substitution interval, the boson peak shape is conserved while its position shift upwards. This means that increasing the alkali vs iron content, the elastic medium hardens but it does not change nature. This study emphasizes the importance of considering the full-range spectra when analysing multicomponent or natural systems with small chemical variations.

Phosphorus Acquisition Efficiency and Transcriptomic Changes in Maize Plants Treated with Two Lignohumates.

Lignohumates are increasing in popularity in agriculture, but their chemistry and effects on plants vary based on the source and processing. The present study evaluated the ability of two humates (H1 and H2) to boost maize plant performance under different phosphorus (P) availability (25 and 250 µM) conditions in hydroponics, while understanding the underlying mechanisms. Humates differed in chemical composition, as revealed via elemental analysis, phenol and phytohormone content, and thermal and spectroscopic analyses. H1 outperformed H2 in triggering plant responses to low phosphorus by enhancing phosphatase and phytase enzymes, P acquisition efficiency, and biomass production. It contained higher levels of endogenous auxins, cytokinins, and abscisic acid, likely acting together to stimulate plant growth. H1 also improved the plant antioxidant capacity, thus potentially increasing plant resilience to external stresses. Both humates increased the nitrogen (N) content and acted as biostimulants for P and N acquisition. Consistent with the physiological and biochemical data, H1 upregulated genes involved in growth, hormone signaling and defense in all plants, and in P recycling particularly under low-P conditions. In conclusion, H1 showed promising potential for effective plant growth and nutrient utilization, especially in low-P plants, involving hormonal modulation, antioxidant enhancement, the stimulation of P uptake and P-recycling mechanisms.

Soil organic carbon sequestration as affected by afforestation: the Darab Kola forest (north of Iran) case study.

Following the ratification of the Kyoto Protocol, afforestation of formerly arable lands and/or degraded areas has been acknowledged as a land-use change contributing to the mitigation of increasing atmospheric CO(2) concentration in the atmosphere. In the present work, we study the soil organic carbon sequestration (SOCS) in 21 year old stands of maple (Acer velutinum Bioss.), oak (Quercus castaneifolia C.A. Mey.), and red pine (Pinus brutia Ten.) in the Darab Kola region, north of Iran. Soil samples were collected at four different depths (0-10, 10-20, 20-30, and 30-40 cm), and characterized with respect to bulk density, water content, electrical conductivity, pH, texture, lime content, total organic C, total N, and earthworm density and biomass. Data showed that afforested stands significantly affected soil characteristics, also raising SOCS phenomena, with values of 163.3, 120.6, and 102.1 Mg C ha(-1) for red pine, oak and maple stands, respectively, vs. 83.0 Mg C ha(-1) for the control region. Even if the dynamics of organic matter (OM) in soil is very complex and affected by several pedo-climatic factors, a stepwise regression method indicates that SOCS values in the studied area could be predicted using the following parameters, i.e., sand, clay, lime, and total N contents, and C/N ratio. In particular, although the chemical and physical stabilization capacity of organic C by soil is believed to be mainly governed by clay content, regression analysis showed a positive correlation between SOCS and sand (R = 0.86(**)), whereas a negative correlation with clay (R = -0.77(**)) was observed, thus suggesting that most of this organic C occurs as particulate OM instead of mineral-associated OM. Although the proposed models do not take into account possible changes due to natural and anthropogenic processes, they represent a simple way that could be used to evaluate and/or monitor the potential of each forest plantation in immobilizing organic C in soil (thus reducing atmospheric C concentration), as well as to select more appropriate species during forestation plan management at least in the north of Iran.