Horizons Of Forest Soils Research Articles

Contents of Potentially Toxic Elements in Forest Soils of the Jizera Mountains Region

In central Europe, the region termed ‘the Black Triangle’ corresponds to an area of concentrated burning of fossil fuels during the period between early 1950s up to the mid 1980s. Although major polluting activities have ceased, effects of atmospheric deposition are still evident. The aims of this study were to determine potentially toxic element (PTE) concentrations in organic and mineral horizons of forest soils in the Jizera Mountains region and to assess the relationship between their distributions and stand factors (altitude, grass cover, forest type). One hundred thirty-eight samples were taken from 98 positions, comprising O, A, E and B horizon samples. Target elements (Cu, Cd, Pb, Zn, Mn) were extracted using 2 M HNO3 and then analysed by FAAS. Basic statistical parameters were determined, and correlation, t test and ANOVA were used to assess the relationship to stand factors. Maps were created using ArcMap 9.1. Two map creation techniques were used—kriging and inverse distance weighting. Highest mean metal contents (except for Mn) were found in organic horizons, with Cu and Pb being particularly concentrated in the upper layers. Strong positive correlation exists between Cd content and altitude, while negative correlation exists for Mn. Cadmium concentration was also significantly higher in areas of grass cover and under spruce canopy as opposed to beech. Surface maps indicated a similar source of pollution with highest concentrations corresponding also to relief and the prevailing wind direction. Overall, mean PTE contents were not excessive. Top enrichment factors proved the anthropogenic origin of Cd, Cu, Pb and Zn, whereas Mn is probably of geologic origin. Analysis of stand factors showed a statistically significant influence of altitude, grass cover and forest type on cadmium concentration in forest soils. Spatial distribution of metals showed a similar pattern for Cd, Cu, Pb and Zn in O horizon soil, which points toward a single source of pollution.

The effect of stand species composition on water storage capacity of the organic layers of forest soils

The dynamics of litterfall and its quantitative differentiation in stands with different species composition suggest that the origin of the organic matter accumulated in the organic horizons of forest soils affects their physical properties, and thus, their ability to retain rainwater. The main aim of the study was to determine the physical properties, the degree of decomposition and capillary capacity of individual ectohumus sublevels of mountain forest soils, formed under fir stands (Abies alba Mill.) and beech stands (Fagus sylvatica L.), and to compare them with the physical and retention properties of the organic horizons of spruce stands [Picea abies (L.) H. Karst], as determined by Kucza (2007). The study was conducted on soil monoliths, sampled in a way that allowed preserving their natural structure. For individual ectohumus sublevels contained in the monoliths, the content and degree of decomposition of organic matter, bulk density, total porosity and capillary capacity were determined. It has been shown that the capillary capacity of the litter layer (Ol) differed significantly between beech, fir and spruce stands, assuming average values equal to 1.60 (±0.10), 2.76 (±0.11) and 4.44 (±0.10) mm H2O in the layer of 1 cm, respectively. In the case of detritus (Ofh) horizons, the smallest water storage capacity characterized beech stands, wherein the capillary capacity was approximately 1.39 mm lower than in fir stands and over twice lower as compared to spruce stands.

Lead migration in smelter-impacted deciduous and coniferous organic soil horizons based on a long-term in-situ implantation and laboratory column experiments

Lead (Pb) contamination of forest soils constitute a serious threat against soil organisms and wildlife and the transport of previously deposited Pb from surface soils is of high environmental relevance. We studied the migration of Pb in highly contaminated deciduous and coniferous soils in a smelting area. A mixture of fermented/humified (F+H) deciduous and coniferous soil horizons highly contaminated by Pb smelting operations were implanted to the same horizon types in an area of low Pb atmospheric input for 6months. The implantation was accompanied with mechanical turbation, which caused changes in the soil parameters, i.e., CEC (cation exchange capacity), Corg. (organic carbon) or pH. The target soil horizons F+H (and partly A) were enriched with Pb, compared to background concentrations. The retention of Pb in smelter-impacted coniferous forest soil horizons L (raw litter), F+H, A (organo-mineral) and C (mineral) was studied using a column experiment.As a result of the Pb addition with a specific isotope composition (American galena) it was found that with the exception of the L horizon, all of the added Pb was completely retained in soil horizons. The isotope composition of Pb in eluate from the L horizon was represented by linear mixing between the original and added Pb sources. The majority of Pb would be eluted from the L horizon after less than 5years (using linear approximation).

Predicting the Concentration of Total Mercury in Mineral Horizons of Forest Soils Varying in Organic Matter and Mineral Fine Fraction Content

The level of mercury (Hg) concentration in soils can be estimated using certain predictors such as the content of organic carbon (Corg) or the fine fractions (FFs) such as silt and clay. This study was focused on the potential use of Corg and FF contents as the predictors of Hg concentration at the spatial meso-scale in forest soils derived from Triassic sandstones and claystones, Quaternary sands derived from weathering sandstones and Quaternary sands of fluvioglacial origin. To understand the importance of Corg and FF contents for Hg retention in mineral soil, the allocation of Hg in physically separated fractions of soil samples was also tested. The experiment was designed over a regular 200 × 200-m grid, where 275 plots were established. The results implied that the concentration of total Hg in mineral soil may vary by several orders of magnitude because of the natural variation in Corg content. The model where the Corg content was the only variable explained 44 % of Hg concentration variability in soil, and other significantly correlated variables were the FF content and the C/N ratio. Detailed analysis revealed that the particulate organic matter fraction accumulated more Hg per unit of Corg than in the organic matter associated with FF. The content of Corg, FF and C/N ratio allowed, for the local soils, a satisfactory prediction of the spatial distribution and the magnitude of total Hg concentration in soils.

A new approach to analysis of relationships between 137Cs activity concentrations in forest soil horizons.

The measurements results of 137Cs activity concentrations in forest soil profiles are discussed. In studies some simplifications were considered. First of them concerns disregarding of soil subtype in data analysis. However initially this parameter was considered in data analysis, it was finally ignored. The second assumption drops information about specific soil horizon. Description of 137Cs accumulation is based on relationships between its relative activity concentrations in soil layers. The model formulation was based on the results of exploratory data analysis of the relative 137Cs activity concentrations. In studies the methods designed for compositional data analysis were used. The results of analysis showed that the relationships between the relative activity concentrations of 137Cs in soil layers, due to their nature, might be divided into two groups. The first of them concerns layers located close to soil surface. The relative activity concentrations of 137Cs in these layers are proportional to each other, and distribution mechanism of cesium within them has the characteristics of the process leading to thermodynamic equilibrium. The second group is related to layers that are located deeper. The calculation results suggest lack of thermodynamic equilibrium between these layers and layers situated above. Utilization of a linear model for description of changes in relative activity concentrations of 137Cs in deeper layers supposes that these changes occur much slower than in layers lying above.

Impact of clear cutting on soil microbial communities and bioavailable nutrients in the LFH and Ae horizons of Boreal Plain forest soils

Soil productivity is, to a large extent, governed by the microbial communities inhabiting the soil and is an important priority within the forestry industry. This study assessed community level changes in microbial community size and composition in conjunction with nutrient bioavailability to clear cutting. Soils from the Boreal Plain of central Alberta were sampled from the LFH and mineral Ae horizons using a time series approach. Phospholipid fatty acid analysis was utilized to determine changes in microbial community size and composition in soils of a cutblock area over three growing seasons spanning pre- and post-harvest conditions, and in situ N, P, K, and Ca were measured. Results indicated that there was no loss of microbial biomass detected until 2yrs post-harvest, while the community composition was altered immediately post-harvest in both the LFH and Ae. A post-harvest ‘flush’ of N, P and K was observed in these soils, though soil C, moisture content and microbial biomass did not indicate significant change over the three growing seasons post-harvest. Nutrient and microbial differences observed between the LFH and Ae horizons indicate that for objectives seeking relative comparisons, homogenization is sufficient, but for those seeking absolute values, distinct horizons should be analyzed separately.

Modelling the pH dependency of dissolved calcium and aluminium in O, A and B horizons of acid forest soils

The molar ratio of the calcium (Ca) and aluminium (Al) activities (Ca/Al ratio) in soil water is an important indicator for forest health conditions, with values less than 1 indicating negative conditions for forest growth. Here we used and calibrated a simple model, with only modest parameter requirement, to describe the Ca activity in soil water of acid forest soils according to the Gaines–Thomas exchange equation. Next, the model was combined with the Al(OH)3 equilibrium model, applicable at pH>pHthreshold, and the recently developed Al solubility model (based on organic complexation theory, applicable at pH<pHthreshold) proposed by Gruba and Mulder (2008). The pHthreshold is the pH of the soil above which the Al(OH)3 equilibrium model and below which the organic complexation model control the Al solubility.Calibration of the Gaines–Thomas selectivity coefficient for calcium–aluminium exchange resulted in LogKCa-Al(gt) close to zero. A combined model, including the Gaines–Thomas equation and an aluminium solubility model, was tested subsequently for internal consistency, using a set of 32 samples each from A and B horizons of forest soils (Cambisols) located in Southern Poland (pHH2O range 3.3–5.4). The observed relationship between pHH2O and CaX for a large number of O, A and B horizons from Polish lowland soils, as reported in a second data set, was in accordance with the general curvi-linear pattern predicted by the models. The observations in data set II also indicate that at any given CaX, the value of pHH2O increased in the order O<A<B horizon. Probably, this order is explained by the increase in pHKCl and the decrease in Ca activity. Model predictions suggested that molar Ca/Al<1 occurred at levels of exchangeable Ca smaller than 4%.

Pedogenic processes of placic and spodic horizons in subtropical subalpine forest soils with contrasting textures

Placic (Bsm) and spodic (Bhs) horizons are common in subalpine or alpine forest soils in Taiwan. Bsm horizons are found more usually in finer textured soils than those with Bhs horizons. To understand the different formation processes in Bsm and Bhs horizons in a humid subtropical ecosystem, we identified micro-morphological features by using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and electron probe micro-analysis (EPMA), and determined the physiochemical properties by chemical extractions and clay mineralogy. The study included four pedons with well-developed Bsm horizons from our previous study and four with well-developed Bhs horizons at other sites. Both sites were in subtropical mountain forests with similar climate, topography and general geology but over regoliths with distinctly different textures. Micro-morphology revealed a vughy (small cavities lined with in-washed materials) microstructure in Bsm horizons but a granular structure with bridge microstructures between coarse grains in Bhs horizons. Chemical analysis revealed more free pedogenic iron (Fed) and aluminium (Ald) in Bsm than in Bhs horizons, but more organically complexed Al (Alp) in Bhs horizons. Energy dispersive spectrometry revealed predominant Fe, oxygen (O) and carbon (C) in the matrix of the Bsm horizons, whereas Al, silicon (Si) and C were the major elements of interstitial materials in Bhs horizons. Polarizing microscopy and EPMA spectra confirmed the illuvial nature of organic Al complexes in Bhs horizons. The transformation of clay minerals showed more intense podzolization in Bhs horizons than in Bsm horizons. The different formation mechanisms in Bsm and Bhs horizons result from contrasting texture; redox processes are predominant in Bsm horizons because of the clayey texture whereas podzolization is predominant in sandy Bhs horizons.

Fate of Decomposed Fungal Cell Wall Material in Organic Horizons of Old-Growth Douglas-fir Forest Soils

Organic horizons of old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] forests are colonized by ectomycorrhizal fungi, which can form large patches or mats. Respiration, N mineralization, chitinase activity, and amino sugar C and N turnover are higher in soils colonized by ectomycorrhizal mats. To test if microbial activity in mat soil is driven by decomposition of fungal biomass, we incubated mat and non-mat soil with ¹³C¹⁵N-labeled, chitin-enriched fungal cell wall material. Cell wall material was readily decomposed during 22-d incubations in both soils, and cell-wall-derived ¹³C and ¹⁵N were traced into mineralized pools, extractable organic pools, microbial biomass, and microbial phospholipid fatty acids (PLFAs). Basal microbial activity was higher in mat soils. Although total respiration was higher in mat soils with cell walls added, more cell wall C was mineralized in non-mat than mat soils; this was inferred to reflect greater preferential respiration of cell wall C over soil organic matter (SOM). Mineralization of N from cell wall material was low, with no difference between soils, and positive priming of N mineralization from SOM occurred after 3 wk. Both the proportion of cell wall N assimilated and N growth yield efficiency (GYE) were higher than for cell wall C. The relative abundance of fungi was higher in cell-wall-amended soils, and cell-wall-derived ¹³C was found in fungal and Gram-negative bacterial PLFAs. Cell wall C assimilation and C GYE were higher in mat soils, which could be linked to greater mineralization of SOM or to differential activity of select microbial taxonomic groups. Chitin-rich fungal cell wall material was utilized as both a microbial N and C source; N was predominantly assimilated and C was predominantly metabolized. It is possible that fungal necromass may contribute to N stabilization in these soils.

宁夏贺兰山、六盘山典型森林类型土壤主要肥力特征

采用野外调查结合室内分析的方法,对该区域典型森林类型下土壤的主要剖面肥力特征进行了研究,并对主要理化指标进行了因子分析。结果表明:受森林凋落物的累积、分解和成土母质、气候条件的影响,贺兰山、六盘山主要森林土壤的剖面肥力具有明显差异。其中,土壤孔隙度 (54.50%-72.22%,剖面均值,下同) 受有机质影响显著,随土层加深逐渐减小,容重 (0.72-1.21 g/cm³)、比重 (2.55-2.68 g/cm³) 随土层加深显著增大,且六盘山各样地比重大于贺兰山。受有机质归还作用影响,有机碳 (24.03-65.37 g/kg)、全N (1.48-3.49 g/kg)、NO^-₃-N (1.88-10.50 mg/kg)、NH⁺₄-N (5.02-11.01 mg/kg)、全P (0.37-1.19 g/kg)、有效P (4.82-13.38 mg/kg)、速效K含量 (82.03-244.62 mg/kg) 均随土层加深逐渐降低;全K含量 (18.92-26.14 g/kg) 随土层加深逐渐增大,且六盘山各样地全K含量大于贺兰山。土壤C/N (11.74-19.88) 呈现B层>C层>A层,且贺兰山各样地C/N大于六盘山。土壤CEC (23.94-40.30 cmol/kg) 受有机质的主导作用明显,随土层加深显著减小,pH值 (7.09-8.09)、ESP (0.59%-2.47%)及BSP (51.24%-80.57%) 均随土层加深逐渐增大,且贺兰山各样地pH值、ESP大于六盘山。粘粒 (5.46%-10.20%)、TDS (0.33-1.12 g/kg) 及CaCO₃ (1.44-14.23 g/kg) 均未出现明显积聚,且贺兰山各样地TDS、CaCO₃含量大于六盘山。因子分析显示,对于该区域各样地土壤的肥力特征,可以应用有机质因子、环境因子和NO^-₃-N因子进行综合描述。其中青海云杉、山杨混交林下土壤的有机质因子得分最高,贺兰山各样地环境因子得分显著大于六盘山,NO^-₃-N因子得分则以小叶金露梅灌丛和华北落叶松天然林最高。;The main areas of forest in Ningxia Province lie in the Helan and Liupan mountain ranges. These forests have important ecological and economic significance. The fertility of forest soil in these areas has not been systematically studied. The objective of this study was to evaluate soil fertility under six forest types in the Su-Yukou forest zone of the Helan mountain range and in the Xi-Xia and Die-Diegou forest zones of the Liupan mountain range. The natural forest types were <em>Pinus tabulaeformis</em> × <em>Populus davidiana</em>, <em>Picea crassifolia</em> × <em>Populus davidiana</em>, <em>Potentilla parvifolia</em>, and <em>Larix principis-rupprechtii</em>. The planted forest types were <em>Quercus liaotungensis</em> and <em>Larix principis-rupprechtii</em>. Five separate profiles (replications) were sampled in an 'S' pattern for each soil type. The profiles were divided into A, B, and C horizons and then sampled, making a total of 18 soil samples. Soil physical and chemical properties were measured with conventional methods. The results were analyzed using univariate analysis of variance. Differences among forest types and soil horizons were analyzed with Duncan's test (SSR). Soil fertility characteristics were evaluated using principal component analysis. The results indicated significant differences in soil fertility under the six forest types. These differences can probably be attributed to differences in the accumulation and decomposition of forest litter, in soil parent material, or in climatic conditions. Soil porosity ranged from 54.5 to 72.2% and decreased as soil depth increased. Soil bulk density ranged from 0.72 to 1.21 g/cm³ and particle density ranged from 2.55 to 2.68 g/cm³. Soil bulk density and particle density both increased as soil depth increased. Soil particle density in the Liupan mountains was higher than that in the Helan mountains. Soil organic C (24.03-65.37 g/kg), total N (1.48-3.49 g/kg), NO^-₃-N (1.88-10.50 mg/kg), NH⁺₄-N (5.02-11.01 mg/kg), total P (0.37-1.19 g/kg), available P (4.82-13.38 mg/kg), and available K (82.03-244.62 mg/kg) increased as soil depth increased. Total K (18.92-26.14 g/kg) increased as soil depth increased. Total K concentrations were higher in soil from the Liupan mountains than in soil from the Helan mountains. The soil C : N ratio (11.74 to 19.88) tended to be highest in the B horizon followed by the C and A horizons. The cation exchange capacity (23.94-40.30 cmol/kg) decreased as soil depth increased. In contrast, soil pH (7.09-8.09), exchangeable sodium percentage (0.59%-2.47%) and base saturation percentage (51.24%-80.57%) increased as soil depth increased. Clay content (5.46%-10.20%), total dissolved salt, (0.33-1.12 g/kg), and CaCO₃ content (1.44-14.23 g/kg) did not change significantly with soil depth. The soil C : N ratio, pH, exchangeable sodium percentage, total dissolved salt, and CaCO₃ content of soil from the Helan mountains was higher than that of soil from the Liupan mountains. Factor analysis was used to describe soil fertility under the six forest types. Three soil fertility components (organic matter factor, environmental factor, and NO^-₃-N factor) were derived from 14 physico-chemical soil properties. Component scores showed significant differences among the three fertility components under different forest types. The soil under the <em>Picea crassifolia</em> × <em>Populus davidiana</em> forest had the highest component score for the organic matter factor. Soils from the Helan mountain range had the highest component score for the environmental factor, and soil from the natural <em>Potentilla parvifolia</em> and <em>Larix principis-rupprechtii</em> forest had the highest component score for the NO^-₃-N factor.

Organic soils provide evidence of spatial variation in human‐induced vegetation change following European occupation of Tasmania

AbstractAimWe test the hypothesis that the European destruction of western Tasmanian Aboriginal society, and consequent changes in burning patterns, resulted in succession towards rain forest near the coast, and an increase in the area of more fire‐resistant sedgeland in inland areas.LocationSouth‐western and western Tasmania, Australia.MethodsAttributes of organic soils (surface and underlying dominant horizons) beneath rain forest and sedgeland were described and measured from 559 soil pits in areas with highly siliceous surface geology. Multiple logistic regression was used to discriminate the dominant horizons of rain forest and sedgeland soils. This equation was used to derive scores for all soil pits. The hypothesis that change was greater near existing boundaries was tested using correlation. The hypothesis that change was greater at coastal than inland locations was tested using ANOVA.ResultsBoth upper horizons of the soils under the fire‐sensitive rain forest (14C‐dated to be younger than 60 years) and dominant horizons of these soils had significantly higher organic contents, lower bulk density and more nitrogen than the soils under the fire‐requiring sedgeland. Twenty‐nine per cent of the soils under sedgeland had dominant horizons that indicated past rain forest. One‐quarter of the soils under rain forest had dominant horizons characteristic of sedgeland soils. Although results were heterogeneous in both locations, the former difference was more common inland and the latter near the coast. Change was not higher close to present boundaries.Main conclusionsThe characteristics of the dominant horizons and the post‐colonial surface horizon give a strong indication of the vegetation that formed them. Changes in fire regimes, caused by the displacement of Tasmanian Aborigines by Europeans, appear to have caused vegetation changes that differed within and between the coast and inland areas. Thus, there has been a strong human role in determining the distributions of vegetation types in the region.

Erratum to: The importance of amino sugar turnover to C and N cycling in organic horizons of old-growth Douglas-fir forest soils colonized by ectomycorrhizal mats

Erratum to: The importance of amino sugar turnover to C and N cycling in organic horizons of old-growth Douglas-fir forest soils colonized by ectomycorrhizal mats

Geochemical position of thallium in soils from a smelter-impacted area

The study complements our previous research, focused on metal contamination of soils in the area historically affected by Zn smelting near Olkusz (Silesia–Krakow region, southern Poland) and provides complex data on the geochemistry of anthropogenic Tl in soils with contrasting land use. Significant differences in Tl concentrations and chemical fractionation were observed between forest and grassland soil profiles, indicating the effect of land use on Tl behavior. Our findings proved the ability of forest soils to concentrate high amounts of Tl, particularly within the organic layers. A comparison of Tl concentrations in the upper (O or A) and the bottom horizons (C) of forest and grassland soils clearly demonstrates vertical mobility of Tl. The results of the sequential extraction procedure indicated the important role of soil organic matter in Tl mobilization, probably as a result of long-term alteration/dissolution of smelter-derived particles followed with Tl release; up to ~20% of total Tl amount was associated with the exchangeable/acid-extractable fraction in forest soils. The Tl concentrations detected in grassland soils were up to an order of magnitude lower than in forest soils. Taking into account the dominant bonding of Tl to the residual fraction, Tl present in grassland soils poses lower environmental hazard with respect to the potential mobilization or uptake by plants. Nevertheless, further research on Tl dynamics with emphasis to the environmental stability of Tl-bearing phases is essential for precise understanding of Tl behavior in such polluted (agro)systems.

Tomographic method of studying soil pore space: Current perspectives and results for some Russian soils

The methods and results of tomographic soil studies are discussed. A brief history of the development of the tomographic method and its application in soil science are described, and the major results obtained with the use of this method are outlined. An experience of the application of X-ray microtomography for studying the structure of undisturbed samples of some Russian soils is also considered. Three-dimensional images of soil aggregates and soil pore space with a resolution of 15.8 μm have been obtained for the upper horizons of gray forest and soddy-podzolic soils. On the basis of these data, the merits and demerits of the tomographic method in comparison with the traditional method for studying soil pedality and pore space in thin sections are discussed. Certain advantages of the tomographic method provide good possibilities to study soil processes at a qualitatively new level. Priority directions of the development of tomographic studies in soil science are outlined.

The importance of amino sugar turnover to C and N cycling in organic horizons of old-growth Douglas-fir forest soils colonized by ectomycorrhizal mats

Amino sugar dynamics represent an important but under-investigated component of the carbon (C) and nitrogen (N) cycles in old-growth Douglas-fir forest soils. Because fungal biomass is high in these soils, particularly in areas colonized by rhizomorphic ectomycorrhizal fungal mats, organic matter derived from chitinous cell wall material (or the monomeric building block of chitin, N-acetylglucosamine (NAG)) could be a significant source of C or N to the soil microbiota, and thus an important driver of microbial C and N processing. This paper reports the results of incubation experiments initiated to measure chitin degradation, NAG utilization, and the contribution of these substrates to soil respiration and N mineralization rates in mat-colonized and non-mat soil organic horizons. Amendments of chitin and NAG stimulated respiration, N mineralization, and biomass accumulation in mat and non-mat soils, and responses to NAG amendment were stronger than to chitin amendment. NAG-induced respiration was consistently two-fold higher in mat soils than non-mat soils, but induced N mineralization was similar between the two soil patch types. Assimilation of both C and N into microbial biomass was apparent, biomass C:N ratio decreased in all treatments, and microbial N use efficiency (treatment means 0.25 ± 0.06–0.50 ± 0.05) was greater than C use efficiency (treatment means 0.12 ± 0.04–0.32 ± 0.02). NAGase enzyme response was non-linear and showed the same pattern in chitin and NAG amendments. Responses to NAG and chitin amendment differed between mat and non-mat soils, indicating different mechanisms driving NAG and chitin utilization or differences in saprotrophic community composition between the two soil patch types. Net chitin and NAG processing rates were 0.08–3.4 times the basal respiration rates and 0.07–14 times the ambient net N mineralization rates, high enough for the turnover of total soil amino sugars to potentially occur in days to weeks. The results support the hypotheses that amino sugars are important microbial C and N sources and drivers of C and N cycling in these soils.

Microbial processes controlling P availability in forest spodosols as affected by soil depth and soil properties

Because carbon dioxide (CO2) concentration is rising, increases in plant biomass and productivity of terrestrial ecosystems are expected. However, phosphorus (P) unavailability may disable any potential enhanced growth of plants in forest ecosystems. In response to P scarcity under elevated CO2, trees may mine deeper the soil to take up more nutrients. In this scope, the ability of deep horizons of forest soils to supply available P to the trees has to be evaluated. The main objective of the present study was to quantify the relative contribution of topsoil horizons and deep horizons to P availability through processes governed by the activity of soil micro-organisms. Since soil properties vary with soil depth, one can therefore assume that the role of microbial processes governing P availability differs between soil layers. More specifically, our initial hypothesis was that deeper soil horizons could substantially contribute to total plant available P in forested ecosystems and that such contribution of deep horizons differs among sites (due to contrasting soil properties). To test this hypothesis, we quantified microbial P and mineralization of P in ‘dead’ soil organic matter to a depth of 120 cm in forest soils contrasting in soil organic matter, soil moisture and aluminum (Al) and iron (Fe) oxides. We also quantified microbiological activity and acid phosphomonoesterase activity. Results showed that the role of microbial processes generally decreases with increasing soil depth. However, the relative contribution of surface (litter and 0–30 cm) and deep (30–120 cm) soil layers to the stocks of available P through microbial processes (51–62 kg P ha−1) are affected by several soil properties, and the contribution of deep soil layers to these stocks vary between sites (from 29 to 59%). This shows that subsoils should be taken into account when studying the microbial processes governing P availability in forest ecosystems. For the studied soils, microbial P and mineralization of P in ‘dead’ soil organic matter particularly depended on soil organic matter content, soil moisture and, to a minor extent, Al oxides. High Al oxide contents in some sites or in deep soil layers probably result in the stabilization of soil organic compounds thus reducing microbiological activity and mineralization rates. The mineralization process in the litter also appeared to be P-limited and depended on the C:P ratio of soil organic matter. Thus, this study highlighted the effects of soil depth and soil properties on the microbial processes governing P availability in the forest spodosols.

Carbon delivery to deep mineral horizons in Hawaiian rain forest soils

[1] This study aimed to better understand the mechanisms for soil organic matter delivery to and accumulation in mineral horizons of tropical rain forest, volcanic soils. We used soil morphology, lysimetry, isotopes, and spectroscopy to investigate the role of preferential flow paths in the delivery of carbon (C) to the subsoil. High rainfall, high primary productivity, and the dominance of highly reactive, short-range-order minerals combine to sequester substantial stocks of soil C with long mean residence times. The soils have large peds, separated by wide cracks, which form a network of channels propagating downward through the top 40 to 60 cm, facilitating macropore flow. The channel infillings and crack surfaces were enriched in organic material (OM) with lower C:N ratios, and had higher ammonium oxalate-extractable Al, and lower ammonium oxalate-extractable Fe than the adjacent mineral bulk soil. CP MAS 13C-NMR spectra of OM accumulating at depth showed strong signal intensities in the carboxyl and carbonyl C regions, indicative of organic acids, while decaying roots showed greater contributions of aromatic and O-alkyl C. The ratios of alkyl-to-O-alkyl C in the organic infillings were more similar to those of the bulk Bh and to dissolved organic matter than to those of decaying roots. Radiocarbon-based ages of OM infillings at >50 cm depth were significantly younger than the mineral soil (2000 years versus 7000 years). Respired CO2 from incubated soils showed that OM accumulating at depth is a mixture of modern and much older C, providing further evidence for the downward movement of fresh C.

Plant and soil properties determine microbial community structure of shared Pinus-Vaccinium rhizospheres in petroleum hydrocarbon contaminated forest soils

Rhizosphere communities are critical to plant and ecosystem function, yet our understanding of the role of disturbance in structuring these communities is limited. We tested the hypothesis that soil contamination with petroleum hydrocarbons (PHCs) alters spatial patterns of ecto- (ECM) and ericoid (ERM) mycorrhizal fungal and root-associated bacterial community structure in the shared rhizosphere of pine (Pinus contorta var. latifolia) and lingonberry (Vaccinium vitis-idaea) in reconstructed sub-boreal forest soils. Pine seeds and lingonberry cuttings were planted into containers with an organic (mor humus, FH or coarse woody debris, CWD) layer overlying sandy mineral horizons (Ae and Bf) of forest soils collected from field sites in central British Columbia, Canada. After 4 months, 219 mg cm-2 crude oil was applied to the soil surface of half of the systems; systems were sampled 1 or 16 weeks later. Composition, relative abundance and vertical distribution of pine ECMs were assessed using light microscopy; community profiles were generated using LH-PCR of ribosomal DNA. Multivariate analysis revealed that plant and soil factors were more important determinants of community composition than was crude oil treatment. Fungal communities differed between pine and lingonberry roots; ECM communities were structured by soil layer whereas ERM communities varied between FH and CWD soil systems. Bacterial communities varied between plants and soil layers, indicating properties of ECM and ERM rhizospheres and the soil environment influence bacterial niche differentiation. This integration of mycorrhizal and bacterial community analysis contributes to a greater understanding of forest soil sustainability in forest ecosystems potentially contaminated with PHCs.

Oxidability of Soil Organic Matter of Forest Soils Assessed Using 33 mM of Potassium Permanganate

The main objective of this research was to study the oxidizability of soil organic matter (SOM). Forty-one surface horizons of forest soils under Fagus sylvatica L. developed on different lithologies (limestones, sandstones, marlstones, and shales) were sampled. The oxidizability of SOM was assessed by reacting air-dried samples with 33 mmol/L of potassium permanganate for different incubation times (1, 3, 6, and 24 h). None of the soil properties analyzed (including organic C content and oxidizability of SOM) showed significant differences (P 0.850). The cumulative amount of OCper increased with time following an asymptotic trend that fitted to a power model (r2 > 0.700); oxidation rates showed that the first hour was the most reactive (0.069-0.094 g of C g-1 of soil h-1). On average, 9% of the total initial organic C was oxidized at 1 h, 12% at 3 h, 15% at 6 h, and 23% at 24 h, which are values comparable to those found in previous studies. Principal component analysis revealed that the samples were composed of two groups of soils. Both groups showed an increase in total soil organic C content (and oxidizability) with increasing contents of reactive soil colloids (clay and metal-SOM complexes) but had different slopes in their relationship to the scores of the first principal component, suggesting different dynamics. Copyright © 2011 by Lippincott Williams & Wilkins.

Determination of total organic halogen (TOX) in humic acids after microwave-induced combustion

Chemically chlorinated organic matter as well as natural background humic acids contain significant amounts of organically bound halogens that must be determined for assessment of environmental pollution. In this work the use of ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed for the determination of total organic Cl, Br and I concentration in humic acids extracted from various forest soil horizons after a single digestion by microwave-induced combustion (MIC). Samples were pressed as pellets and combusted using 20 bar of oxygen and ammonium nitrate solution as igniter. Analytes were absorbed in diluted alkaline solution (50 mM (NH 4) 2CO 3) and a reflux step was applied after combustion to improve analyte recoveries (5 min, microwave power of 1400 W). The accuracy was evaluated using certified reference materials (CRM) and spiked samples. Using MIC the agreement with CRM values and spike recoveries was higher than 97% for all analytes. As an advantage over conventional procedures, using MIC it was possible to digest up to eight samples in only 25 min, obtaining a single solution suitable for all halogens determination in humic acids samples by different techniques (IC and ICP-MS). The limit of detection (3 σ) for Cl, Br and I obtained by IC was 1.2, 2.5 and 4.3 μg g −1 and by ICP-MS it was 1.4, 0.03 and 0.002 μg g −1, respectively.