Mineral Soil Samples Research Articles

Soil organic carbon turnover following forest restoration in south China: Evidence from stable carbon isotopes

As over half of the world’s tropical forests are reforested or afforested, understanding the resilience of carbon (C) pool in these forests is critical for global C balance. While most previous studies on the reforested lands have focused on C stock recovery, soil C turnover has largely been overlooked. We evaluated soil C turnover rate by calculating the isotopic enrichment factors of α (defined as the slope of the regression between the δ13C difference and ln-transferred C concentrations in mineral soil samples relative to the surface litter) and β (defined as the slope of the regression between δ13C and log-transferred C concentrations) along 0–30 cm soil profiles in a 400-year-old monsoon evergreen broad-leaved forest (MEBF), a 51-year-old mixed-native plantation (NP1), a 31-year-old mixed-native plantation (NP2), a 31-year-old Acacia mangium plantation (AP), a 31-year-old mixed-conifer plantation (CP), and a 31-year-old secondary forest with natural restoration (SF). Results showed that soil C stocks did not differ among the six forests. The estimated α values ranged from 1.0023 to 1.0086 and increased in the order of MEBF = NP1 < NP2 = AP = CP < SF. The estimated β values ranged from −19.70 to −5.22 but showed an opposite trend to α values. Additionally, changes of the α and β values among these forests were mainly regulated by soil water content and bulk density. Our findings demonstrate that forest restoration could enhance soil C stock equivalent to the undisturbed old-growth forests within a few decades, but the rate of soil C turnover in these restored forests were still higher.

Molecular Identification of Water-Extractable Organic Carbon from Thermally Heated Soils: C-13 NMR and Accurate Mass Analyses Find Benzene and Pyridine Carboxylic Acids.

To simulate the effects of wildfire on the combustion process in soils and their potential to leach organic compounds into streams and groundwater, mineral soil samples were heated at temperatures of 150-550 °C. Then, the soils were leached with deionized water, filtered, and analyzed for dissolved organic carbon. The water extract was concentrated by both XAD-8 and XAD-4 resins and analyzed by C-13 nuclear magnetic resonance and liquid chromatography time-of-flight mass spectrometry. Approximately 15-20% of the water-extractable organic carbon was identified as benzene dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acid isomers, commonly called BPCAs. Also identified were isomers of pyridine dicarboxylic acids and tricarboxylic acids (PCAs). The conversion of soil organic carbon to BPCAs occurs at 250 °C and reaches a maximum between 350 and 450 °C. At higher temperatures (>450 °C), the BPCA concentrations decrease, suggesting decarboxylation and conversion to carbon dioxide and water. This is the first report of BPCAs and PCAs in water-extractable organic carbon from thermally altered soil and suggest that these compounds are possible candidates for further water-quality studies in watersheds affected by wildfire. Finally, BPCAs and PCAs could contribute to the black carbon and nitrogen in seawater and are worthy of future investigation.

A comparison of cation exchange capacity of organic soils determined by ammonium acetate solutions buffered at some pHs ranging between around field pH and 7.0

Cation exchange capacity (CEC) and exchangeable cations are among two of the most important measures for determining soil characteristics and soil quality. There are various methods of measuring CEC, including the ammonium acetate method of Schollenberger and Dreibelbis (1930) which is buffered at pH 7.0 and the barium chloride-triethanolamine method of Mehlich (1938) which is buffered at pH 8.2. These CEC measurements can result in values very different from the CEC of the soil at its field pH (effective CEC or CECe), especially in acidic soils, such as organic soils, with pH-dependent CEC. Therefore, the focus of this article is the comparison of CEC of organic soils obtained using the different pH level of the extraction solution. Five organic soil and two mineral soil samples were used in this experiment. The variables tested were CEC and exchangeable cations using ammonium acetate solutions buffered at several pHs; field pHs (acidic) of 3.8, 4.2, 4.8 and neutral (7.0). Each soil sample and pH level were replicated three times. The decomposition rate of the five organic soil samples was determined using the pyrophosphate color method, which proved to be sapric. The results indicated a positive relationship between pH and CEC value, the higher the pH buffer the much higher the CEC measured. There was a considerable difference of CEC values produced from the varying pHs of extraction solution. However, the pH of the extraction had no substantial effect on measured exchangeable cations.

What influences upland soil chemistry in the Amazon basin, Brazil? Major, minor and trace elements in the upper rhizosphere

Increasing land transformation in the Amazon basin, from forest to post-forest usage such as pastureland, agriculture and agroforestry, triggers significant changes in hydrology, soil fertility and regional climatology. However, relatively little is known about Amazon basin soil chemistry in general and about its possible alteration with recent land-use change.We present robust pedogeochemical data for 65 elements and oxides, and evidence for modification due to recent deforestation and post-forest land use on upland soils in Amazonas state, Brazil. Differences emerge in median element concentrations between these two land-cover types, and between central and southern parts of the basin. These new data, a product of the bi-national EcoRespira-Amazon (ERA) project, are based on triplicate sampling under different seasonal conditions at 29 sites, representing ca. 740,000km2 and average annual meteorological conditions. Mineral soil samples (TOP: 0–20cm; BOT: 30–50cm) characterize the active upper rhizosphere. Data were obtained with very tight quality control from sampling to analysis (following GEMAS protocols), using various overlapping analytical methods. Some major, minor and trace element concentrations deviate strongly from established world soil averages, including the recent PEGS2.Geological (lithological) and weathering boundary conditions define the primary soil chemical signal. This is overprinted by biogeochemical forces (ecosystem feedbacks), and recently by human intervention (change of land cover, deforestation). The general assumption of depleted tropical soils is not justified as such – a more differentiated view is needed, since carbon and macronutrients such as nitrogen and phosphorous, albeit not always plant-available, do often occur in relatively high concentrations (median values TOP: 1.9, 0.15 and 0.02wt%). Calcium, magnesium and potassium are truly depleted (median values TOP: 0.025, 0.095 and 0.065wt%), albeit with noticeable variance. Trace elements, from silver to zirconium and including REE, show highly differentiated responses. Most are relatively enriched in post-forest soils; a subtle signal that is interpreted as reduced plant-soil interaction. BOT concentrations are generally higher than those in TOP soil, reflecting weathering conditions and biogeochemical cycling – with interesting exceptions (Br, Cd, Rb).

Geogenic influence and impact of mining activities on water soil and plants in surrounding areas of Morila Mine, Mali

The Morila Gold mine, a joint venture between AngloGold Ashanti and Randgold Resources, is one of the 10 operating mines in Mali. The mine is located at 180 km southeast of Bamako, Mali, and has been operating since 2001. With the depletion of the orebody, a closure plan was established by the government and shareholders since 2012, and rehabilitation strategies are currently operating. The concentration of major, minor and traces elements were analyzed in 90 water samples (45 water supply boreholes, 13 shallow wells, 20 piezometers of the mine and 12 surface water), 46 stream sediment samples, 10 mine soil samples and 57 plant samples. All the samples were collected from June 2015 to December 2016 in three study areas: Morila mine, an intermittent stream at downstream of the mine and a controlled geochemical background area free of mining activities (located 15 to 20 km upstream of the mine). Chemical water analyses show that arsenic (As: 0.8 to 132 ppb), manganese (Mn: 2.52 to 5200 ppb) and total iron (Fe: 0.462 to 78 ppm) are present at high levels. The ANOVA tests demonstrate significant differences between the three sites for most major ions and trace metals in water, stream sediments and mine soils. The mean concentrations within the mine were significantly higher than those outside mine boundaries. Factor analysis and cluster analysis show a geogenic and pollution factors influencing the soils and the water quality in the study area.Arsenic values were mostly found in groundwater of the village of Sanso (the nearest village to the Morila mine), where 7 of the 10 sources of drinking water boreholes had arsenic contents higher than the standard value of 10 ppb. This arsenic contamination in groundwater and those located in background area could not be linked to mining activities, and attributed to geogenic influences.In stream sediments and soil samples, the values of the analyzed elements were ranged bellow the maximum allowed concentration except for As, Fe, Al and S. Mine soils have high Fe (~10 wt%) and high Al (~3 wt%) concentrations, likely derived from naturally sources. Sulfur contents in soil and stream sediments were high only in the mining environment, and derive from sulfide mineral oxidation. Arsenic contents were elevated in most plant species samples, and concentrations of samples located within the mine were higher than those of the background area. This study indicates that most of the metals and toxic contaminations were from geogenic origin, but mining activities likely also play a substantial role by increasing the level of these contaminants in water, soil and plants within the mining environment.

Heavy Metal Pollution in Topsoil and Vegetables in the Typical Mining Area Near Gannan, Jiangxi Province, China

Abstract To provide a theoretical basis for soil management in mining areas, soil and vegetable samples were collected from the vegetable fields at a depth of 0–20 cm near the tungsten mining area ...

DYNAMICS OF SOIL NUTRIENT STATUS OF HIGHBUSH BLUEBERRY IN LATVIA, 2006-2017

In Latvia, the first commercial highbush blueberry (Vaccinium corymbosum L.) plantings have been established on a few hectares at the end of the 1990th. Since then, a remarkable growth has noticed and today the total cultivated area reaches 280 hectares. An increasing market demand for fresh and processed berries provides a future upward trend in the development of blueberry crop in Latvia. In general, blueberry is a highly specialized crop that has definite soil agrochemical and climatic requirements. There are two main soil types used for blueberry cultivation in Latvia: well-drained acid sandy soils with high organic matter content and sphagnum peat soils. Evaluation and management of plant mineral nutrition in such diverse soils are based on guidelines for the particular type of growing medium. A long-term study (2006-2017, divided into three periods: 2006-2009, 2010-2013, 2014-2017) was done to find out the nutrient status of blueberry soils in Latvia. In total, 330 mineral and peat soil samples were collected from the upper layer of soils (0 - 20 cm) across blueberry plantations in Latvia and tested on plant available nutrients (N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, Mo, B), as well as soil pHKCl and electrical conductivity. In general, more than 50% of blueberry soils had low content of N, S, Mo and B, as well as a high level of Mn over the study period of 2006-2017. Less than 25% of samples in the optimum range indicated on N as the most deficient nutrient.

Bioflocculant production and heavy metal sorption by metal resistant bacterial isolates from gold mining soil

Two bioflocculant producing bacterial isolates from mining soil samples were investigated for their application in heavy metal removal. The bacterial isolates were identified as Pseudomonas koreensis and Pantoea sp. using 16S rRNA gene. Cadmium resistant genes cadA and CzcD were detected in Pantoea sp. while P. koreensis harbor CzcD and chrA responsible for Cd and Cr resistance respectively. The isolates showed maximum flocculating activity of 71.3% and 51.7% with glucose and yield of 2.98 g L−1 and 3.26 g L−1 for Pantoea sp. and P. koreensis respectively. The optimum flocculating activity was achieved at pH 7.5 and temperature of 30 °C. Fourier transform infrared analysis of the bioflocculants produced by the two isolates showed the presence of carboxyl, hydroxyl and amino groups characteristic of polysaccharide and protein. Heavy metal sorption by bioflocculant of Pantoea sp. removed 51.2% Cd, 52.5% Cr and 80.5% Pb while that of P. koreensis removed 48.5% Cd, 42.5% Cr and 73.7% Pb. The bioflocculants produced have potential in metal removal from industrial wastes.

Effects of season and interval of prescribed burns on pyrogenic carbon in ponderosa pine stands in the southern Blue Mountains, Oregon, USA

In ponderosa pine (Pinus ponderosa) forests of the western United States, prescribed burns are used to reduce fuel loads and restore historical fire regimes. The season of and interval between burns can have complex consequences for the ecosystem, including the production of pyrogenic carbon (PyC). PyC plays a crucial role in soil carbon cycling, displaying turnover times that are orders of magnitude longer than unburned organic matter. This work investigated how the season of and interval between prescribed burns affects soil organic matter, including the formation and retention of PyC, in a ponderosa pine forest of eastern Oregon. In 1997 a prescribed burn study was implemented in Malheur National Forest to examine the ecological effects of burning at 5 and 15-year intervals in either the spring or fall. In October 2015, both O-horizon and mineral soil (0–15 cm) samples were collected and analyzed for PyC concentration, content, and structure using the benzene polycarboxylic acid (BPCA) method. O-horizon depth, carbon and nitrogen concentration and content, pH, and bulk density were also measured. Plots burned in the spring and fall had lower C and N stocks in the O-horizon compared to the unburned controls due to a reduction in O-horizon depth; however, we did not observe any differences in O-horizon concentration of C or N. Moreover, the concentrations and stocks of C and N in the mineral soil of plots burned in the spring or fall were the same as or only very slightly different from the unburned controls, suggesting that the prescribed burns on these sites have not adversely affected SOM quantity in the surface mineral soil carbon pools over the course of this 18-year experiment. Compared to unburned controls, we estimate that fall burns increased the mean PyC concentration of the mineral soil by 8.42 g BPCA/kg C. We did not detect a difference in mean PyC concentration of the mineral soil between the spring burns and the unburned controls; however, the spring burn plots did contain a number of isolated pockets with very high concentrations of PyC, suggesting a patchier burn pattern for these plots. In general, there was no detectable difference in any of the response variables when comparing the various prescribed burn treatments to one another. Reestablishing fire in these forests resulted in minor effects on the PyC concentration and pH, which may have beneficial impacts on soil carbon and available nutrients, while having few effects on other soil characteristics. This suggests that the application of low severity prescribed fires should result in little detrimental change to soils of ponderosa pine forests of the Southern Blue Mountains, while achieving management objectives such as reduction of surface fuels.

Soil Carbon Storage in Douglas‐Fir Forests of Western Oregon and Washington Before and After Modern Timber Harvesting Practices

Core Ideas Nine forest stands in the Pacific Northwest were selected to detect at least a 5% change in mineral soil carbon. Change in mineral soil carbon content following harvest was negligible (+2% ns). There was an increase of 184% in forest floor carbon resulting from harvest residue inputs. Conventional methods of timber harvesting do not cause substantial short‐term loss in mineral soil carbon. Forest soil carbon represents a large, but slowly changing pool of carbon in forests. Understanding the response of soil carbon to forest management, including harvesting, is critical for determining overall stand and/or landscape carbon balance. This longitudinal study on nine randomly selected sites was designed to detect a 5% or greater change in mineral soil carbon storage following harvest. Soil samples were collected both pre‐harvest and 3 to 3.5 yr post‐harvest at 300 sample points on a fixed grid from each stand. A forest floor sample and mineral soil samples in depth increments of 0 to 15 and 15 to 30 cm were collected at every point. A soil sample at 30 to 100 cm (or 30–60 cm at two sites) was collected at 200 points. Each mineral soil depth fraction was separated into size fractions of &lt;2 mm and 2 to 4.75 mm for analysis. At each site, these samples were spatially grouped into 25 composites by depth and size for the efficient analysis of carbon concentration. Soil mass and carbon concentrations were multiplied to calculate the carbon content in the soil per unit area. Across all sites combined, we found negligible change (+2% ns) in mineral soil carbon content following harvest and a 184% increase in forest floor carbon resulting from harvest residue inputs. This indicates that conventional timber harvesting methods in the Pacific Northwest do not cause substantial short‐term losses in mineral soil carbon, but the longer‐term trajectory of soil carbon storage following harvest remains to be investigated.

Temporal changes in magnetic signal of burnt soils – A compelling three years pilot study

Wildfires strongly affect soils, including iron biogeochemical cycling and carbon storage. Thus, it is important to reveal the dynamics of iron oxide synthesis and transformations during and after a wildfire. This study investigates the temporal stability of strongly magnetic minerals appearing after a wildfire. Following a designed experimental fire, samples from vegetation ash and mineral soil were taken immediately after and at progressively longer time intervals. The magnetic susceptibility monitoring of samples during three years period demonstrates an initial increase in magnetic signal of ash-rich material taken immediately after the fire followed by a gradual decrease over time. The behavior of samples collected later after the fire showed only a moderate decrease. It is suggested that the magnetic susceptibility rise during the laboratory storage could be due to the increased availability of nutrients and microbial activity immediately after the fire and related intense redox reactions involving iron oxide particles. The decreasing trend in magnetic susceptibility is ascribed to the oxidation of ultrafine magnetite particles with time. All mineral soil samples from the deeper level showed an initial susceptibility increase, assigned to a similar process. Magnetic susceptibility monitoring was also carried out on samples gathered shortly after natural wildfires. The soil samples affected by strong and long wildfires show a decrease in magnetic susceptibility with time. This effect is more pronounced in the surface black-colored ash layer. The ash material from a site disturbed by a strong short wildfire demonstrates behavior similar to the ash from the experimental fire. It is supposed that the temporal evolution of magnetic susceptibility of the mineral alteration products of wildfires is influenced by the grain size of the produced iron oxide particles, their redox reactions mediated by the heterotrophic bacteria, as well as the amplifying role of pyrogenic carbon for intensification of the redox reactions.

Heterogeneity of the chemical composition and thermal stability of particulate organic matter in French forest soils

In temperate forests, soils contain a significant part of the ecosystem carbon (C) stock that can be subjected to C losses upon global changes. In forest soils, particulate organic matter (POM) is a major contributor to the labile C pool and its dynamics can significantly influence the overall total soil organic carbon stock. However, POM has been overlooked in forest soils, specifically in deep horizons.We isolated the POM fraction of mineral soil samples collected in 52 French forest sites, using a size- (> 50 μm) and density- (< 1.6 g·cm−3) fractionation scheme. These soil samples presented variability in terms of depth (0–10 cm; 40–80 cm), soil class (dystric Cambisol, eutric Cambisol, entic Podzol) and vegetation type (deciduous, coniferous). First, we determined the POM chemical composition and thermal stability using elemental analysis, mid infrared-attenuated total reflectance spectroscopy and Rock-Eval thermal analysis. Then, we assessed how depth, soil class and vegetation type influenced POM chemistry and thermal stability in these temperate forest soils.Depth, soil class and vegetation type were all important factors influencing POM chemistry and thermal stability. Variations in POM chemistry (higher C/N ratio, lower ether + alcohol and carbonyl + carboxyl ratios and decrease in hydrogen-rich compounds) and increase in thermal stability with depth suggested different POM input sources for the surface and deep soil layers and an increased biogeochemical stability of POM in deep soil layers. Whatever the vegetation, POM in eutric Cambisols had lower aliphatic and higher aromatic ratios than POM in dystric Cambisols. POM in soils under deciduous trees had higher aliphatic and carbonyl + carboxyl ratios and lower aromatic ratio, more hydrogen-rich and less oxygen-rich compounds than POM in soils under coniferous trees, reflecting the difference in litter chemistry between the two vegetation types. POM from deciduous plots was also significantly more thermally stable than from coniferous plots, suggesting a higher biogeochemical stability for POM in deciduous forest soils.This study highlights the variations in POM chemistry and thermal stability existing within and among soil profiles and the role of depth, soil class and vegetation type in these variations. It appears that if POM can be regarded as a labile carbon fraction in soils, its lability varies depending on the ecosystem (soil, vegetation) and depth considered.

Distribution of nutrients and trace elements in forest soils of Singapore

Information on chemical fertility status and on trace element concentrations for Singapore soils is sparse. In this study, concentration and distribution of nutrients and trace elements in forest soils of Singapore, and the effect of geology on the current conditions of soils, were evaluated. Litter and mineral soil samples (0–10 cm, 10–20 cm, 20–50 cm) were divided into three groups according to geology (sedimentary rocks, Neogene-Quaternary sediments and igneous rocks). Basic soil properties, exchangeable cations including cation exchange capacity (CEC), and pseudototal concentrations of 17 elements including nutrients and potentially toxic elements (PTE; As, Cd, Cu, Cr, Ni, Pb, Zn) were determined. Results showed that the soils of Singapore were acidic (pH 3.7–6.2) and characterised by a low CEC (maximum mean value: 100 mmolc kg−1) and low P concentrations (mean values of 0.28 g kg−1 or less) irrespective of geology. Pseudototal concentrations of PTE were also low, except for As. However, significantly (p < 0.05) higher concentrations of soil organic carbon, total P, base forming elements, exchangeable base cations and PTE (except As and Cd) were found in soils developed on sedimentary rocks and Neogene-Quaternary sediments compared to those developed on igneous rocks. Although total N and S concentrations did not differ significantly between the three geological groups, the differences in nutrient status were more pronounced than in trace element levels across geology. The properties of forest soils, which are mainly unaffected by anthropogenic activities, vary depending on the parent material, i.e. igneous or sedimentary rocks and Neogene-Quaternary sediments.

Wildfire effects on soil properties in fire-prone pine ecosystems: Indicators of burn severity legacy over the medium term after fire

The aim of this study was to determine the effects of burn severity on soil properties (chemical, biochemical and microbiological) in fire-prone pine ecosystems three years after fire. To achieve these goals, we selected two large wildfires that occurred in summer 2012 within the Iberian Peninsula: the Sierra del Teleno wildfire, which burned 119 km2 dominated by Pinus pinaster forests developed over acidic soils, and the Cortes de Pallás wildfire, which burned 297 km2, part of them dominated by Pinus halepensis ecosystems with calcareous soils. We classified the burned areas into low or high burn severity categories using spectral indices. Three years after the wildfires, we distributed 56 field plots proportionally to the extent of each severity category. In each field plot, we collected samples of mineral soil from a depth of 0–3 cm. We analysed soil chemical (pH, electrical conductivity, organic carbon, total nitrogen, available phosphorus) biochemical (β-glucosidase, urease and acid phosphatase enzymatic activities) and microbiological (microbial biomass carbon) properties in each soil sample. The relationship between burn severity and soil properties was analysed by a Permutational Multivariate Analysis of Variance and Generalized Linear Models. The results showed a significant influence of the original ecosystem and of burn severity on the overall soil status over the medium term after fire. Available P content increased with burn severity in the acidic soils of the P. pinaster ecosystem. However, the three enzymatic activities and microbial biomass carbon decreased with burn severity in both types of pine ecosystems. β-glucosidase, urease and microbial biomass carbon showed common patterns in relation to burn severity in the two different Pinus ecosystems (acidic and calcareous soils), and therefore we suggest that they could be potential indicators of the burn severity legacy on soils over the medium term after fire in fire-prone pine Mediterranean forests. Available P and acid phosphatase could be potential indicators in the P. pinaster ecosystem. This study provides useful knowledge for developing hazard reduction and restoration strategies after large wildfires.

Litter quality, land-use history, and nitrogen deposition effects on topsoil conditions across European temperate deciduous forests

Topsoil conditions in temperate forests are influenced by several soil-forming factors, such as canopy composition (e.g. through litter quality), land-use history, atmospheric deposition, and the parent material. Many studies have evaluated the effects of single factors on physicochemical topsoil conditions, but few have assessed the simultaneous effects of multiple drivers. Here, we evaluate the combined effects of litter quality, land-use history (past land cover as well as past forest management), and atmospheric deposition on several physicochemical topsoil conditions of European temperate deciduous forest soils: bulk density, proportion of exchangeable base cations, carbon/nitrogen-ratio (C/N), litter mass, bio-available and total phosphorus, pHKCl and soil organic matter. We collected mineral soil and litter layer samples, and measured site characteristics for 190 20 × 20 m European mixed forest plots across gradients of litter quality (derived from the canopy species composition) and atmospheric deposition, and for different categories of past land cover and past forest management. We accounted for the effects of parent material on topsoil conditions by clustering our plots into three soil type groups based on texture and carbonate concentration. We found that litter quality was a stronger driver of topsoil conditions compared to land-use history or atmospheric deposition, while the soil type also affected several topsoil conditions here. Plots with higher litter quality had soils with a higher proportion of exchangeable base cations, and total phosphorus, and lower C/N-ratios and litter mass. Furthermore, the observed litter quality effects on the topsoil were independent from the regional nitrogen deposition or the soil type, although the soil type likely (co)-determined canopy composition and thus litter quality to some extent in the investigated plots. Litter quality effects on topsoil phosphorus concentrations did interact with past land cover, highlighting the need to consider land-use history when evaluating canopy effects on soil conditions. We conclude that forest managers can use the canopy composition as an important tool for influencing topsoil conditions, although soil type remains an important factor to consider.

Conversion from tussock grassland to pine forest: effect on soil phytoliths and phytolith-occluded carbon (PhytOC)

Photolith morphotypes differ between plant species which can be utilized to reconstruct past vegetation. More recently, the role of phytoliths in soil carbon (C) storage and soil C and silicon (Si) cycling has received increasing attention. The aim of this study was to investigate the impact of recent land cover change on soil phytolith assemblage, soil phytolith concentration, and phytolith-occluded carbon (PhytOC) storage. Mineral soil samples (0–10 cm) were collected from a tussock grassland (n = 18) and an adjacent 32-year-old pine forest (n = 21) in Otago, New Zealand. The pine forest was established on tussock grassland. Microwave digestion was followed by sedimentation and flotation procedures to obtain a purified phytolith extract to identify soil phytolith morphotypes by microscopy and to quantify PhytOC concentrations using an elemental analyzer. Soil phytolith assemblage was similar under tussock grassland and pine forest. Bulliform and short cells which were derived from grass species accounted for more than 80% of the phytoliths. Woody plant-derived phytoliths found under tussock grassland (1) may originate from shrubs which are encroaching into the tussock grassland and/or (2) are a legacy of the past woody-dominated vegetation. Soil phytolith concentration ranged between 1 and 3%. Soil PhytOC storage was 0.15 kg C/m2 and 0.14 kg C/m2 under tussock grassland and pine forest, respectively, and accounted for around 3% of total soil carbon storage. Soil phytolith assemblage, soil phytolith concentration, and soil PhytOC storage did not differ significantly between the tussock grassland and the pine forest that was converted from tussock grassland recently. The dominance of grass-derived phytoliths under the pine forest may reflect the legacy of the tussock vegetation which dominated the study site before the afforestation with pine in 1992. This study also revealed that the intrinsic feature of tussock grass species and the accumulation of phytoliths over centuries is likely the cause for the high soil phytolith and PhytOC concentrations.

Cytotoxic and antibacterial activities of biologically synthesized gold nanoparticles assisted by Micrococcus yunnanensis strain J2

Abstract In the present study the capability of Micrococcus yunnanensis J2 (isolated from Sarcheshme mine soil samples and identified by 16S rDNA sequencing) for biosynthesis of gold nanoparticles (Au NPs) was evaluated. The produced biogenic Au NPs were characterized using UV–visible spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), thermal gravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) methods. The related TEM and SEM images of biogenic Au NPs indicated spherical shaped and well dispersed nanostructures with the average particle size of 53.8 nm. Zeta potential analysis of as-synthesized Au NPs showed a peak at − 17.6 ± 1.8 mV. The XRD profile of the biogenic Au NPs contained five peaks positioned at 2θ of 38.2°, 45.8°, 63.7°, 77.6°, and 82.1° due to (111), (200), (220), (311), and (222) lattice planes, respectively, which clearly indicated the crystalline structure of the obtained Au NPs. Cytotoxic activity of biologically synthesized Au NPs (assisted by MTT-based colorimetric assay) revealed IC50 (µg/mL) of 73.6 ± 1.9, 85.6 ± 2.9, 63.5 ± 2.1, 65.2 ± 1.9, 105.3 ± 1.7, and 88.4 ± 2.1 against six cancer cell lines of U87, HT1080, PC12, Caco2, MCF7, and A549, respectively. However, two normal cells of 3T3 and Vero inhibited by 85% in the presence of 500 µg/mL of the biogenic Au NPs. Evaluation of antibacterial effect of the produced Au NPs and Au3+ ions against three Gram-positive and four Gram-negative bacterial strains exhibited lower inhibitory activity of Au NPs compared to that of Au3+ ions.

Quantifying Changes in Total and Pyrogenic Carbon Stocks Across Fire Severity Gradients Using Active Wildfire Incidents

Positive feedbacks between wildfire emissions and climate are expected to increase in strength in the future; however, fires not only release carbon (C) from terrestrial to atmospheric pools, they also produce pyrogenic C (PyC) which contributes to longer-term C stability. Our objective was to quantify wildfire impacts on total C and PyC stocks in California mixed-conifer forest, and to investigate patterns in C and PyC stocks and changes across gradients of fire severity, using metrics derived from remote sensing and field observations. Our unique study accessed active wildfires to establish and measure plots within days before and after fire, prior to substantial erosion. We measured pre- and post-fire aboveground forest structure and woody fuels to calculate aboveground biomass, C and PyC, and collected forest floor and 0–5 cm mineral soil samples. Immediate tree mortality increased with severity, but overstory C loss was minimal and limited primarily to foliage. Fire released 85% of understory and herbaceous C (comprising <1.0% of total ecosystem C). The greatest C losses occurred from downed wood and forest floor pools (19.3 ± 5.1Mg ha−1 and 25.9 ± 3.2Mg ha−1, respectively). Tree bark and downed wood contributed the greatest PyC gains (1.5 ± 0.3Mg ha−1 and 1.9 ± 0.8Mg ha−1, respectively), and PyC in tree bark showed non-significant positive trends with increasing severity. Overall PyC losses of 1.9 ± 0.3Mg ha−1 and 0.5 ± 0.1Mg ha−1 occurred from forest floor and 0–5 cm mineral soil, with no clear patterns across severity. Fire resulted in a net ecosystem PyC gain (1.0 ± 1.0Mg ha−1) across aboveground and belowground components of these forests, and there were no differences among severity levels. Carbon emissions represented only 21.6% of total forest C; however, extensive conversion of C from live to dead pools will contribute to large downed wood C pools susceptible to release in a subsequent fire, indicating that there may be a delayed relationship between fire severity and C emissions. This research advances understanding of forest C loss and stabilization as PyC in wildfires; however, poor relationships between C and PyC gains or losses and fire severity highlight the complexity of fire impacts on forest C.

Correlating phosphorus extracted by simple soil extraction methods with foliar phosphorus concentrations of Picea abies (L.) H. Karst. and Fagus sylvatica (L.)

AbstractPhosphorus (P) concentrations in needles and leaves of forest trees are declining in the last years in Europe. For a sustainable forest management the knowledge of site specific P nutrition/availability in forest soils is vital, but we are lacking verified simple methods for the estimation of plant available P. Within this study, four soil P extraction methods [water ( ), double‐lactate (Plac), citric acid (Pcit), and sodium bicarbonate ( )], as well as total P content of the soil (Ptot) were tested to investigate which method is best correlated with foliar P concentrations of spruce [Picea abies (L.) H. Karst.] and beech [Fagus sylvatica (L.)]. Mineral soil samples from 5 depth levels of 48 forest sites of the Bavarian sample set of the second National Forest Soil Inventory (BZE II) were stratified according to tree species (spruce and beech) and soil pH (pH &lt; 6.2 and &gt; 6.2), covering the whole range of P nutrition. The extractable amount of P per mass unit of soil increased in the order &lt;&lt; Plac &lt; &lt; Pcit, decreased with soil depth, and was higher in soils with pH &lt; 6.2. Citric acid extracted up to 10% of Ptot in acidic soils. Whereas Pcit delivers adequate regression models for P nutrition in the case of spruce (R2 up to 0.53) and beech (R2 up to 0.58) for acidic soils, shows good results for spruce growing on acidic soils (R2 up to 0.66) and for beech on soils with pH &gt; 6.2 (R2 up to 0.57). Plac produces adequate models only for beech on high pH soils (R2 up to 0.64), while did not produce acceptable regression models. Ptot seems suitable to explain the P nutrition status of beech on acidic (R2 up to 0.62) and alkaline soils (R2 up to 0.61). Highest R2s are obtained mostly in soil depths down to 40 cm. As and Pcit showed good results for both investigated tree species, they should be considered preferentially in future studies.

Woody encroachment and soil carbon stocks in subalpine areas in the Central Spanish Pyrenees

Woody encroachment has been an ongoing process in the subalpine belt of Mediterranean mountains, after land abandonment, the disappearance of the transhumant system and the decrease of the livestock number. The main objectives of this study were: (i) to identify land use/land cover (LULC) changes from 1956 to 2015, and (ii) to investigate the effects of LULC changes in physical and chemical soil properties and soil organic carbon (SOC) and nitrogen (N) stocks. It is hypothesized that woody encroachment in the subalpine belt may lead to significant changes in soil properties, and will generate an increase in the SOC stocks. A land use gradient was identified in the subalpine belt of the Central Spanish Pyrenees: (i) subalpine grasslands, (ii) shrublands, (iii) young forests, and (iv) old forests. Mineral soil samples were collected every 10 cm, down to 40 cm, at three points per each LULC and a total of 48 samples were analyzed. The results showed that (i) woody encroachment has occurred from 1956 to 2015 due to the expansion of coniferous forests and shrublands (at the expense of grasslands), (ii) land cover and soil depth had significant effects on soil properties (except for pH), being larger in the uppermost 0–10 cm depth, (iii) SOC and N contents and stocks were higher in the grassland sites, and (iv) the woody encroachment process initially produced a decrease in the SOC stocks (shrublands), but no differences were observed considering the complete soil profile between grasslands and young and old forests. Further studies, describing SOC stabilization and quantifying above-ground carbon (shrub and tree biomass) are required.