Coniferous Forest Soils Research Articles

In situ gross nitrogen transformations differ between temperate deciduous and coniferous forest soils

Despite long-term enhanced nitrogen (N) inputs, forests can retain considerable amounts of N. While rates of N inputs via throughfall and N leaching are increased in coniferous stands relative to deciduous stands at comparable sites, N leaching below coniferous stands is disproportionally enhanced relative to the N input. A better understanding of factors affecting N retention is needed to assess the impact of changing N deposition on N cycling and N loss of forests. Therefore, gross N transformation pathways were quantified in undisturbed well-drained sandy soils of adjacent equal-aged deciduous (pedunculate oak (Quercus robur L.)) and coniferous (Scots pine (Pinus sylvestris L.)) planted forest stands located in a region with high N deposition (north Belgium). In situ inorganic 15N labelling of the mineral topsoil (0–10 cm) combined with numerical data analysis demonstrated that (i) all gross N transformations differed significantly (p < 0.05) between the two forest soils, (ii) gross N mineralization in the pine soil was less than half the rate in the oak soil, (iii) meaningful N immobilization was only observed for ammonium, (iv) nitrate production via oxidation of organic N occurred three times faster in the pine soil while ammonium oxidation was similar in both soils, and (v) dissimilatory nitrate reduction to ammonium was detected in both soils but was higher in the oak soil. We conclude that the higher gross nitrification (including oxidation of organic N) in the pine soil compared to the oak soil, combined with negligible nitrate immobilization, is in line with the observed higher nitrate leaching under the pine forest.

Nitrogen cycling in forest soils across climate gradients in Eastern China

A 15N tracing study was carried out to investigate the potential gross nitrogen (N) dynamics in thirteen forest soils in Eastern China ranging from temperate to tropical zones (five coniferous forests, six deciduous broad-leaf forests, one temperate mixed forest, one evergreen broad-leaf forests ecosystems), and to identify the major controlling factors on N cycling in these forest ecosystems. The soil pH ranged from 4.3 to 7.9 and soil organic carbon (SOC) ranged from 6.6 g kg−1 to 83.0 g kg−1. The potential gross N transformation rates were quantified by 15N tracing studies where either the ammonium or nitrate pools were 15N labeled in parallel treatments. Gross mineralization rates ranged from 0.915 μg N g−1 soil day−1 to 2.718 μg N g−1 soil day−1 in the studied forest soils. The average contribution of labile organic-N (MNlab) to total gross mineralization (MNrec+MNlab) was 86% (58% to 99%), indicating that turnover of labile organic N plays a dominant role in the studied forest ecosystems. The gross mineralization rates in coniferous forest soils were significantly lower (ranging between 0.915 and 1.228 μg N g−1 soil day−1) compared to broad-leaf forest soils (ranging from 1.621 to 2.718 μg N g−1 soil day−1) (p < 0.01). Thus, the dominant vegetation may play an important role in regulating soil N mineralization. Nitrate production (nitrification) occurred via two pathways, oxidation of NH4+ and organic N the forest soils. Correlations with soil pH indicated that this is a key factor controlling the oxidation of NH4+ and organic N in theses forest ecosystems. NH4+ oxidation decreased with a decline in pH while organic N oxidation increased. The climatic conditions (e.g. moisture status) at the various sites governed the NO3−-N consumption processes (dissimilatory NO3− reduction to NH4+ (DNRA) or immobilization of NO3−). Total NO3− consumption and the proportion of total NO3− consumption to total NO3− production decreased with an increase in the drought index of ecosystems, showing that strong interactions appear to exist between climatic condition (e.g. the drought index), N mineralization and the rate of DNRA. Interactions between vegetation, climatic conditions govern internal N cycling in these forests soils.

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils

AbstractDepth distribution profiles of environmental radionuclides (137Cs and 210Pb) have been investigated in soil to elucidate the underlying environment of semi-natural temperate deciduous and/or coniferous forest soils in Slovenia (Žirovski vrh, Idrija, Kočevski Rog, Pohorie, Gorišnica and Rakitna). Surface enrichment of both nuclides was observed at all the sites investigated in this study, suggesting that the soils had undergone little natural or anthropogenic disturbance for at least the last several decades. Apparent annual burial rates of 137Cs (0.1–0.2 cm y−−1) were estimated to be about 1.3 times higher than those of 210Pb at individual sites of different lithology, which suggests strong affinity of 210Pb to soil organic matter. Variability of the vertical distribution profiles of these nuclides depends not only on “in situ” pedology but also on geographical and meteorological conditions, especially precipitation and wind direction.

Modelling and Mapping of Critical Loads of Acidification and Eutrophication on Forest Ecosystems in Latvia

Modelling and Mapping of Critical Loads of Acidification and Eutrophication on Forest Ecosystems in Latvia The Very Simple Dynamic model (VSD), which has been developed as the simplest extension of steady-state models, has been used for dynamic modelling of critical loads to forest ecosystems. The model consisting of a set of mass balance equations describes the soil input and output data relationships and fluxes, and soil properties. The mapping of critical loads of acidity and eutrophication effects is performed on 25562 deciduous, coniferous and mixed forest soil receptor polygons (area &gt; 0.01 km2). The results have been mapped in the geographical units of EMEP grid (50 × 50 km2).

Biodegradation and chemical characteristics of hot-water extractable organic matter from soils under four different vegetation types in the Wuyi Mountains, southeastern China

Water extractable organic carbon (WEOC) is the most active soil organic carbon and plays an important role in global C cycling. Our aim was to investigate the biodegradability and the chemical characteristics of hot-water extractable organic matter (HWEOM) from soils under different vegetation types, including evergreen broad-leaved forest (EBF), coniferous forest (CF), dwarf forest (DF) and alpine meadow (AM), across an altitude gradation in the Wuyi Mountains of southeastern China. We quantified the biodegradability in a 90 day incubation experiment by measuring the loss of hot-water extractable organic carbon (HWEOC) and calculated the sizes of labile and stable HWEOC pool and the respective decomposition rate constants by a double exponential model. We used UV and fluorescence spectroscopic techniques to characterize the structural properties of HWEOM and measured the contents of carbohydrates, phenols and hydrophilic carbon of HWEOM solution. The extent of HWEOC biodegradation was higher in EBF and DF soils with about 20% HWEOC loss, and the labile C accounted for 13–15% of the total HWEOC. HWEOC from CF soils was the least degradable with only 12% HWEOC loss. The estimated mean residence time of the labile HWEOC pool was 8–10 days, whereas that of the stable HWEOC pool ranged from 3 to 6 years. The biodegradability of HWEOC increased with decreasing soil C/N ratio, aromaticity and humification indices, proportion of phenols and increasing proportion of hydrophilic carbon.

Effects of decreasing water potential on gross ammonification and nitrification in an acid coniferous forest soil

Abstract Changes in the soil water regime, predicted as a consequence of global climate change, might influence the N cycle in temperate forest soils. We investigated the effect of decreasing soil water potentials on gross ammonification and nitrification in different soil horizons of a Norway spruce forest and tested the hypotheses that i) gross rates are more sensitive to desiccation in the Oa and EA horizon as compared to the uppermost Oi/Oe horizon and ii) that gross nitrification is more sensitive than gross ammonification. Soil samples were adjusted by air drying to water potentials from about field capacity to around −1.0 MPa, a range that is often observed under field conditions at our site. Gross rates were measured using the 15N pool dilution technique. To ensure that the addition of solute label to dry soils and the local rewetting does not affect the results by re-mineralization or preferential consumption of 15N, we compared different extraction and incubation times. T0 times ranging from 10 to 300 min and incubation times of 48 h and 72 h did not influence the rates of gross ammonification and nitrification. Even small changes of water potential decreased gross ammonification and nitrification in the O horizon. In the EA horizon, gross nitrification was below detection limit and the response of the generally low rates of gross ammonification to decreasing water potentials was minor. In the Oi/Oe horizon gross ammonification and nitrification decreased from 37.5 to 18.3 mg N kg−1 soil d−1 and from 15.4 to 5.6 mg N kg−1 soil d−1 when the water potential decreased from field capacity to −0.8 MPa. In the Oa horizon gross ammonification decreased from 7.4 to 4.0 mg N kg−1 soil d−1 when the water potential reached −0.6 MPa. At such water potential nitrification almost ceased, while in the Oi/Oe horizon nitrification continued at a rather high level. Hence, only in the Oa horizon nitrification was more sensitive to desiccation than ammonification. Extended drought periods that might result from climate change will cause a reduction in gross N turnover rates in forest soils even at moderate levels of soil desiccation.

Effects of Vegetation Succession on Soil Fertility Within Farming-Plantation Ecotone in Ziwuling Mountains of the Loess Plateau in China

To further understand the relationship between vegetation succession and soil fertility within farming-plantation ecotone in Ziwuling Mountains of the Loess Plateau, nine kinds of widely distributed communities at different succession stages were selected, and the effects of vegetation succession on soil fertility were studied through the methods of comparing two hierarchical clustering (similarity index: ▪) and other multivariate analysis. The results showed that: (i) the similarity in clustering pattern of nine communities which classified by plant species and soil nutrients respectively showed a trend of ▪ overall plant-soil 0–10 cm> ▪ overall plant-soil 10–20 cm> ▪ overall plant-soil 20–40 cm, and for the top soil, it showed a trend of ▪ grass-soil 0–10 cm> ▪ shrub-soil 0–10 cm> ▪ tree-soil 0–10 cm; (ii) soil fertility increased during the succession process from abandoned land to forest community, and the soil fertility of forest community showed an increased order of coniferous forest →mixed forest →broadleaf forest; (iii) during the process of vegetation succession, the variation of topsoil fertility was higher than that of the subsurface soil (coefficient of variation: CV 0–10 cm > CV 10–20 cm > CV 20–40 cm), and when the succession developed into the stages of shrub and forest communities, the top soil fertility had been improved significantly; and (iv) for the subsurface soil of the communities at the advanced succession stages, the soil fertility also increased to some extent. Our results suggested that the method of comparing two hierarchical clustering reflected the similarity level of different cluster patterns, therefore, it was helpful to study the relationship between vegetation succession and soil fertility. There was a corresponding relationship between the change process of soil fertility from the top soil to subsurface soil and the process of vegetation succession from the early stages to the advanced stage. The differentiations of soil fertility in vertical space and horizontal space were both caused by vegetation succession, which was significant for both the shrub and forest communities. The improved level of forest soil fertility was related to forest vegetation types and the improved fertility level of broad-leaved forest-soil community was higher than that of the coniferous forest soil. In the practice on soil fertility ecological restoration of the loess plateau, it is important to carry out reasonably artificial forestation so as to enhance the restoration and improvement of soil fertility.

Change in Bacterial Community Structure in Response to Disturbance of Natural Hardwood and Secondary Coniferous Forest Soils in Central Taiwan

Forest management often results in changes in the soil and its microbial communities. In the present study, differences in the soil bacterial community caused by forest management practices were characterized using small subunit (SSU) ribosomal RNA (rRNA) gene clone libraries. The communities were from a native hardwood forest (HWD) and two adjacent conifer plantations in a low-elevation montane, subtropical experimental forest at the Lienhuachi Experimental Forest (LHCEF) in central Taiwan. At this locality, the elevation ranges from 600 to 950 m, the mean annual precipitation is 2,200 mm, the mean annual temperature is 20.8 °C, and the soil pH is 4. The conifer forests included a Cunninghamia konishii Hay (CNH) plantation of 40 years and an old growth Calocedrus formosana (Florin) Florin (CLC) forest of 80 years. A total of 476 clones were sequenced and assigned into 12 phylogenetic groups. Proteobacteria-affiliated clones (53%) predominated in the library from HWD soils. In contrast, Acidobacteria was the most abundant phylum and comprised 39% and 57% in the CLC and CNH libraries, respectively. Similarly, the most abundant OTUs in HWD soils were greatly reduced or absent in the CLC and CNH soils. Based on several diversity indices, the numbers of abundant OTUs and singletons, and rarefaction curves, the diversity of the HWD community (0.95 in evenness and Shannon diversity indices) was somewhat less than that in the CNH soils (0.97 in evenness and Shannon diversity indices). The diversity of the community in CLC soils was intermediate. The differences in diversity among the three communities may also reflect changes in abundances of a few OTUs. The CNH forest soil community may be still in a successional phase that is only partially stabilized after 40 years. Analysis of molecular variance also revealed that the bacterial community composition of HWD soils was significantly different from CLC and CNH soils (p = 0.001). These results suggest that the disturbance of forest conversion and tree species composition are important factors influencing the soil bacterial community among three forest ecosystems in the same climate.

Soil microbial community structure in European forests in relation to forest type and atmospheric nitrogen deposition

The objective of the present study was to evaluate the combined effect of vegetation and N deposition on microbial community composition in forest soils. For this, microbial biomass and community structure were assessed by ester linked fatty acid methyl ester (EL-FAME) analyses for 12 European forest sites representing different forest types (coniferous/deciduous) and differing in annual N loads (2–40 kg N ha−1). Microbial community composition was affected by vegetation as indicated by a higher proportion of the marker for arbuscular mycorrhiza (AM) fungi—16:1 11ω—in deciduous forest soils (1.2%–5.7% of total EL-FAMEs) compared to acidic coniferous forest soils (0.5%–1.6%). The two pine forest sites investigated showed the highest proportion of fungi (up to 28% of total EL-FAMEs) and the lowest proportions of Gram-negative and Gram-positive bacteria of all study sites. Nitrogen deposition rates were highly correlated with the ratios of cyclopropyl fatty acids to their precursors (r = 0.82; P 30 kg N ha−1a−1).

Formation, fate and leaching of chloroform in coniferous forest soils

Chloroform is a common groundwater pollutant but also a natural compound in forest ecosystems. Leaching of natural chloroform from forest soil to groundwater was followed by regular analysis of soil air and groundwater from multilevel wells at four different sites in Denmark for a period of up to 4 a. Significant seasonal variation in chloroform was observed in soil air 0.5 m below surface ranging at one site from 120 ppb by volume in summer to 20 ppb during winter. With depth, the seasonal variation diminished gradually, ranging from 30 ppb in summer to 20 ppb during winter, near the groundwater table. Chloroform in the shallowest groundwater ranged from 0.5–1.5 μg L−1 at one site to 2–5 μg L−1 at another site showing no clear correlation with season. Comparing changes in chloroform in soil air versus depth with on-site recorded meteorological data indicated that a clear relationship appears between rain events and leaching of chloroform. Chloroform in top soil air co-varied with CO2 given a delay of 3–4 weeks providing evidence for its biological origin. This was confirmed during laboratory incubation experiments which further located the fermentation layer as the most chloroform producing soil horizon. Sorption of chloroform to soils, examined using 14C–CHCl3, correlated with organic matter content, being high in the upper organic rich soils and low in the deeper more minerogenic soils. The marked decrease in chloroform in soil with depth may in part be due to microbial degradation which was shown to occur at all depths by laboratory tests using 14C–CHCl3.

Spectroscopic characterization of hot-water extractable organic matter from soils under four different vegetation types along an elevation gradient in the Wuyi Mountains

Water extractable organic carbon (WEOC) is the most active component in global carbon cycle and its chemical and structural characteristics most likely influence its biodegradation. Our objective was to investigate the structural characteristics of hot-water extractable organic matter (HWEOM) from soils collected at various depths (S1, S2, S3) under four different vegetation types, i.e. evergreen broad-leaved forest (EBF), coniferous forest (CF), dwarf forest (DF) and alpine meadow (AM) along an elevation gradient in the Wuyi Mountains, and to relate its structural characteristics to soil properties and biological properties. Here we examine the structural characteristics of HWEOM by UV, fluorescence and Fourier-transform infrared (FTIR) spectroscopic techniques. In the synchronous fluorescence spectra of all HWEOM samples, the main emission peaks were aromatic amino acid-like fluorophores, fulvic acid-like fluorophores and polycyclic aromatic structures with a high degree of conjugation. FTIR spectroscopy showed that HWEOM featured aliphatic C–H, aromatic C=C and carbohydrate C–O functional groups. The aromaticity, the humification indices (HIXem, HIXsyn) and the fluorescence efficiency of HWEOM from the S1 layer were significantly higher in CF than those in the other three vegetation types and, in all cases they decreased with depth in the soil profile. Soil C/N ratio was highly correlated with UV absorption, humification indices and fluorescence efficiency of HWEOM. Soil metabolic quotient (qCO 2) was highly negatively correlated with UV absorption and humification indices of HWEOM. The ratio of microbial biomass C to total organic C was significantly correlated with humification indices and fluorescence efficiency of HWEOM. Our results indicate that the HWEOM from CF soils contain more highly condensed aromatic and/or heterocyclic compounds and, at the same time, the high molecular weight and complex molecules are less mobile, leading to being preferentially retained in the upper soil layer.

Wildfire and Charcoal Enhance Nitrification and Ammonium‐Oxidizing Bacterial Abundance in Dry Montane Forest Soils

All forest fire events generate some quantity of charcoal, which may persist in soils for hundreds to thousands of years. However, few studies have effectively evaluated the potential for charcoal to influence specific microbial communities or processes. To our knowledge, no studies have specifically addressed the effect of charcoal on ammonia-oxidizing bacteria (AOB) in forest soils. Controlled experiments have shown that charcoal amendment of fire-excluded temperate and boreal coniferous forest soil increases net nitrification, suggesting that charcoal plays a major role in maintaining nitrification for extended periods postfire. In this study, we examined the influence of fire history on gross nitrification, nitrification potential, and the nature and abundance of AOB. Soil cores were collected from sites in the Selway-Bitterroot wilderness area in northern Idaho that had been exposed twice (in 1910, 1934) or three times (1910, 1934, and 1992) in the last 94 yr, allowing us to contrast soils recently exposed to fire to those that experienced no recent fire (control). Charcoal content was determined in the O horizon by hand-separation and in the mineral soil by a chemical digestion procedure. Gross and net nitrification, and potential rates of nitrification were measured in mineral soil. Analysis of the AOB community was conducted using primer sets specific for the ammonia mono-oxygenase gene (amoA) or the 16S rRNA gene of AOB. Denaturing gradient gel electrophoresis was used to analyze the AOB community structure, while AOB abundance was determined by quantitative polymerase chain reaction. Recent (12-yr-old) wildfire resulted in greater charcoal contents and nitrification rates compared with sites without fire for 75 yr, and the more recent fire appeared to have directly influenced AOB abundance and community structure. We predicted and observed greater abundance of AOB in soils recently exposed to fire compared with control soils. Interestingly, sequence data revealed that Clusters 3 and 4, and not Cluster 2, of genus Nitrosospira dominated these forest soils, with a shift toward Cluster 3 in recently burned sites.

Multi-residue analysis of PAH, PCB, and OCP optimized for organic matter of forest soil

Analyzing organic pollutants in forest soil is challenging because they are strongly physical and chemical bound to soil organic matter (SOM). Within the framework of a forest soil inventory, an analytical protocol for the determination of polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), and organochlorine pesticides (OCP) should be established and validated using one and the same extraction and cleanup procedure. The protocol should be applicable for reliable analysis of a high number of samples in a short timeframe. Two different soil samples representative for the humic layer from a typical mixed and coniferous forest soil had been used for the analysis. Three solvents of different polarity, namely cyclohexane (CH), ethylacetate (EA)/CH (1/1, v/v), and acetone (AC)/CH (2/1, v/v), and the six standard extraction techniques (pressurized liquid extraction (PLE), soxhlet extraction, fluidized bed extraction, sonication, shaking, and one-step extraction recommended for analyzing agricultural soil in Germany (VDLUFA 2008)) were compared concerning their extraction efficiency. For additional matrix separation, two different cleanup procedures (gel permeation chromatography (GPC) and solid-phase extraction (SPE) with different sorbents) were tested. Quantification was carried out using gas chromatography combined with mass spectrometry (GC–MS) and two different injection systems (split/splitless injection and programmable temperature vaporizer (PTV) injection). Labeled internal standards, added prior to extraction, were used for method evaluation. For the simultaneous extraction of PAH, PCB, and OCP from organic forest soil PLE with acetone/cyclohexane (2/1, v/v) provided the highest extraction efficiency. A two-step cleanup procedure consisting of GPC followed by SPE with silica gel was entirely sufficient for the separation of humic substances without discrimination of analytes. Recovery rates for the different extraction and cleanup steps ranged between 89% and 106%. For quantification, a GC–MS method was developed using two different injection systems and two capillary columns of different selectivity. By comparing six standard extraction techniques for PAH, PCB, and OCP from forest soil, we obtained the highest extraction efficiency when using PLE with AC/CH (2/1). For sample injection, we achieved best results using an optimized PTV injection system as it highly reduced the breakdown of thermolabile pesticides. Using this combination of technical equipment, it is possible to determine a concentration of the analytes in the trace level range of 1–2 μg kg−1 in humic soil.

Fungal and Bacterial Activity in Northern Peatlands

Selective inhibition of substrate-induced respiration with antibiotics cycloheximide and streptomycin sulphate provided insight into eukaryotic versus prokaryotic activities in surface peat soil of three Canadian peatlands. Prokaryotic and eukaryotic communities in peatlands are important in the net sequestration of atmospheric carbon dioxide and therefore play a unique role in global carbon cycling. Selective inhibition techniques were generally successful, with a maximum non-target inhibition of only 17%. Assuming that eukaryotic and prokaryotic activities were dominated by fungi and bacteria respectively, across 3 ecologically and hydrologically diverse and spatially dispersed peatlands, we demonstrated bacterial dominance in a bog and a poor fen both with acidic and primarily Sphagnum derived peat soil and in a near pH neutral wetter rich fen with sedge peat (fungal to bacterial activity ratio = 0.31 to 0.68). These results differ in that in other acidic environments, such as conifer forest soils, fungal to bacterial activity ratios are mostly greater than 1 indicative of fungal dominance.

Active organic carbon pool of coniferous and broad-leaved forest soils in the mountainous areas of Beijing

In order to explore the effects of different forest types on active soil carbon pool, the amounts and density of soil organic carbon (SOC) were studied at different soil horizons under typical coniferous and broad-leaved forests in the mountainous area of Beijing. The results showed that the amount of total SOC, readily oxidizable carbon and particulate organic carbon decreased with increasing depths of soil horizons and the amounts at depths of 0–10 cm and 10–20 cm in broad-leaved forest was clearly higher than that in coniferous forests. The trend of a decrease in SOC density with increasing depth of the soil horizon was similar to that of the amount of SOC. However, no regular trend was found for SOC density at different depths between coniferous forest and broad-leaved forests. The ratio of readily oxidizable carbon to total amount of SOC ranged from 0.36–0.45 and the ratio of particulate organic carbon to total amount of SOC from 0.28–0.73; the ratios decreased with increasing depths of soil horizons. Active SOC was significantly correlated with total SOC; the relationship between readily oxidizable carbon and particulate organic carbon was significant. A broad-leaved forest may produce more SOC than a coniferous forest.

Activity of nematodes and enchytraeids, bacterial community composition, and functional redundancy in coniferous forest soil

Soil faunal activity stimulates terrestrial carbon and nutrient cycling and maintains soil physical structure. Interestingly, the effects of faunal activity on soil microbial community composition and activity is less clear, although the microbial community evidently is the key element of terrestrial decomposition processes and nutrient cycling. We manipulated the composition of soil fauna in mesh bags with various mesh sizes (5, 45, and 1,000 µm) to exclude faunal groups based on body size. Our experiment indicated that feeding and foraging activity of nematodes and enchytraeids modified the physical–chemical properties of the soil and had long-term effects on soil bacterial community composition (measured by denaturing gel electrophoresis, colony-forming unit counts, and phospholipid fatty acid pattern). However, microbial enzyme (phosphomonoesterase, butyrate-esterase, s-glucosidase, N-acetyl-glucosamidase, and s-cellobiosidase) activities (measured by fluorogenic model substrates), decomposition rate of woody and cellulose material, or C and N status of the soil were not altered by the faunal treatment. Instead, enzyme activity was reduced by soil drying. Our results give support to ideas that functional redundancy is a common characteristic of the soil organisms, but no support was found for the idea that the community composition of soil decomposers had a strong link to the regulation of C and N cycles in the soil.

Effect of Charcoal Quantity on Microbial Biomass and Activity in Temperate Soils

Wildfire‐produced charcoal is a common component of soils, affecting a range of important abiotic and biotic soil processes. Our ability to predict the effects of charcoal addition to soil is currently limited, however, by our understanding of how charcoal affects the soil microbial community mediating many of these processes. This study sought to improve our understanding of the relationship between charcoal addition and soil microbial biomass and activity among temperate soils. Charcoal was added to four distinct temperate soils, a Mollisol, an Alfisol, an Entisol, and a Spodosol, at five application levels ranging from 0 to 0.1 kg charcoal kg−1 soil, and incubated at 25°C with measurements at approximately 0, 1.5, and 3 mo. We hypothesized that microbial biomass and activity would increase with increasing charcoal application in all soils, but the relative magnitude of the response would depend on the texture and fertility of each soil. As hypothesized, microbial biomass and activity and Bray P increased significantly with increasing charcoal application, while extractable N decreased. The coniferous forest soil provided a notable exception to the general patterns of N availability, having the highest total extractable N at the highest charcoal application level. Our results suggest that charcoal additions affected microbial biomass, microbial activity, and nutrient availability in relatively similar ways in all four soils that we studied, suggesting considerable predictability in response to charcoal application. Differences in the magnitude of the microbial response, however, appeared dependent on differences in nutrient availability among soils.

Pedobacter nyackensis sp. nov., Pedobacter alluvionis sp. nov. and Pedobacter borealis sp. nov., isolated from Montana flood-plain sediment and forest soil

Three Gram-negative, rod-shaped, non-spore-forming eubacterial strains were isolated in western Montana, USA, and subjected to taxonomic studies. Strains NWG-II14(T) and NWER-II11(T) were isolated from hyporheic sediments of a large alluvial flood plain, whereas strain G-1(T) was isolated from a conifer forest soil. On the basis of 16S rRNA gene sequence similarity, strains NWG-II14(T), NWER-II11(T) and G-1(T) were shown to belong to the family Sphingobacteriaceae and are most closely related to various species of the genus Pedobacter. The results of molecular, physiological and biochemical tests allowed genotypic and phenotypic differentiation of these three strains from 23 Pedobacter species with validly published names. The three isolates therefore represent novel species, for which the names Pedobacter nyackensis sp. nov. (type strain NWG-II14(T) =DSM 19625(T) =LMG 24260(T)), Pedobacter alluvionis sp. nov. (type strain NWER-II11(T) =DSM 19624(T) =LMG 24258(T)) and Pedobacter borealis sp. nov. (type strain G-1(T) =DSM 19626(T) =LMG 24259(T)) are proposed.

Soil greenhouse gas and nutrient dynamics in fertilized western Canadian plantation forests

We explored the impacts of fertilization on soil greenhouse gas fluxes and underlying soil nutrient transformations using short-term (up to 7 months) simulated operational fertilization with urea-nitrogen or nitrogen, phosphorus, potassium, and micronutrients in lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), western hemlock ( Tsuga heterophylla (Raf.) Sarge.), and Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) forests in British Columbia. Urea appeared to be rapidly mineralized to ammonium, and nitrification (relative to controls) was only observed at the lodgepole pine site and represented only 0.5% of added nitrogen. All sites were small net sinks for atmospheric methane, and fertilization effects, both stimulatory and inhibitory, were short-lived. Across all sites and treatments, soils were as likely to consume as emit nitrous oxide, and among treatment replicates, rates were never significantly different from 0, with the exception of one efflux rate of 1.5 µg·m–2·h–1on the warmest day in the study. We conclude from this pilot study that in acidic, unpolluted (with regard to nitrogen deposition) upland conifer forest soils in western Canada fertilized once or infrequently with urea, ammonium, or a combination of nutrients, the dynamics of soil greenhouse-gas fluxes are generally not disturbed over the short-term, with soils remaining small sinks for atmospheric methane and neutral with regard to flux of nitrous oxide.

Temperature Sensitivity Indicates That Chlorination of Organic Matter in Forest Soil Is Primarily Biotic

Old assumptions that chloride is inert and that most chlorinated organic matter in soils is anthropogenic have been challenged by findings of naturally formed organochlorines. Such natural chlorination has been recognized for several decades, but there are still very few measurements of chlorination rates or estimates of the quantitative importance of terrestrial chlorine transformations. While much is known about the formation of specific compounds, bulk chlorination remains poorly understood in terms of mechanisms and effects of environmental factors. We quantified bulk chlorination rates in coniferous forest soil using 36Cl-chloride in tracer experiments at different temperatures and with and without molecular oxygen (O2). Chlorination was enhanced by the presence of O2 and had a temperature optimum at 20 degrees C. Minimum rates were found at high temperatures (50 degrees C) or under anoxic conditions. The results indicate (1) that most of the chlorination between 4 and 40 degrees C was biotic and driven by O2 dependent enzymes, and (2) that there is also slower background chlorination occurring under anoxic conditions at 20 degrees C and under oxic conditions at 50 degrees C. Hence, while oxic and biotic chlorination clearly dominated, chlorination by other processes including possible abiotic reactions was also detected.