Mineral Soil Material Research Articles

Carbon distribution in restored and reference marshes at Blackwater National Wildlife Refuge

Tidal marshes are important for the ecosystem of the Chesapeake Bay, east coast USA. They have the capacity to sequester large amounts of carbon as they accrete with sea-level rise. The purpose of this study was to evaluate carbon distributions in a marsh restored using coarse mineral and organic sediments in 2003 and a natural reference marsh. Soil cores were collected across transects in each marsh to a depth of 1 m. Samples were divided by horizon and analyzed for bulk density and carbon concentration. The restored marsh had wider ranges of bulk density and C concentrations due to the presence of both organic and mineral soil materials. Horizons from the restored marsh had a mean bulk density of 0.50 g cm−3 while the reference marsh averaged 0.09 g cm−3. Carbon concentrations were greater in the reference marsh (30%) than the restored marsh (13%). The average carbon content in the restored marsh was 35 kg m−2 while the reference marsh has only 24 kg m−2 due to a greater bulk density. New organic material deposited over the dredge material represents surface carbon accumulation of 1.8 Mg C ha−1 yr−1. Evaluating restoration and carbon dynamics are difficult without knowledge of site characteristics prior to restoration.

Comparison of different nano- and micro-focus X-ray computed tomography set-ups for the visualization of the soil microstructure and soil organic matter

This study explores the potential of different X-ray computed tomography (X-ray CT) set-ups for the discrimination of soil mineral matter, soil organic matter (OM) and the pore phase. Different X-ray sources, detectors and filtering methods were investigated. Use of a low-energy detector as well as a Cu-filter decreased the potential for phase segmentation in X-ray CT images of an artificial sand–OM mixture. A mid-range X-ray detector showed to hold more potential. Results obtained for an artificial sand–OM sample showed that an attenuation coefficient (AC) grey-value histogram-based single threshold was unsuitable for automated phase segmentation. A dual thresholding approach enabled a better separation of the different phases. Secondly, the minimal measurable pore size class in a clay loam soil aggregate was compared using micro-focus and state-of-the-art nano-focus X-ray CT. The resolution of the scanned images depends on the spot size of the X-ray source, the resolution of the detector and the magnification used. Reliable discrimination of pore and solid phases was expected to be limited by the X-ray tube's focal spot size to 2.5 μm, in contrast to the voxel size of 0.84 μm actually obtained using nano-focus CT. Although this study was limited in its extent, indications were found that more fine porosity is visible at higher resolutions and that large connected pore spaces may be observed. This fine porosity seems to be very locally autocorrelated. Further fundamental research into AC grey-value automated segmentation of OM from the mineral and pore phases, as well as the truly achievable minimal pore size class using artificial calibration samples, is necessary.

Nitrogen Mineralization and Microbial Activity in Oil Sands Reclaimed Boreal Forest Soils

Organic materials including a peat-mineral mix (PM), a forest floor-mineral mix (L/S), and a combination of the two (L/PM) were used to cap mineral soil materials at surface mine reclamation sites in the Athabasca oil sands region of northeastern Alberta, Canada. The objective of this study was to test whether LFH provided an advantage over peat by stimulating microbial activity and providing more available nitrogen for plant growth. Net nitrification, ammonification, and N mineralization rates were estimated from field incubations using buried bags. In situ gross nitrification and ammonification rates were determined using the 15N isotope pool dilution technique, and microbial biomass C (MBC) and N (MBN) were measured by the chloroform fumigation-extraction method. All reclaimed sites had lower MBC and MBN, and lower net ammonification and net mineralization rates than a natural forest site (NLFH) used as a control, but the reclamation treatment using LFH material by itself had higher gross and net nitrification rates. A positive correlation between in situ moisture content, dissolved organic N, MBC, and MBN was observed, which led us to conduct a moisture manipulation experiment in the laboratory. With the exception of the MBN for the L/S treatment, none of the reclamation treatments ever reached the levels of the natural site during this experiment. However, materials from reclamation treatments that incorporated LFH showed higher respiration rates, MBC, and MBN than the PM treatment, indicating that the addition of LFH as an organic amendment may stimulate microbial activity as compared to the use of peat alone.

Effects of surface fire on litter decomposition and occurrence of microfungi in a Cymbopogon polyneuros dominated grassland

Litter decomposition rate, changes in macronutrients such as nitrogen (N), phosphorus (P) and potassium (K) from different grades of litter decomposition and occurrence of soil microfungi were investigated in a Cymbopogon polyneuros-dominated tall grass ecosystem from a burned and an unburned site in southern India. The litter decomposition rate was higher at the burned site than at the unburned site. This rate was also higher when the litter was mixed with the mineral soil material than leaving the litter unaffected on the soil surface. The concentrations of N, P, and K in the litter decreased as a result of progressed litter decomposition. Occurrence of microfungi identified from the different decomposition grades of the Cymbopogon polyneuros litter was higher at the burned site compared to the unburned site. Microfungal species present at both sites showed only minor differences.

Comparison of different isotherm models for dissolved organic carbon (DOC) and nitrogen (DON) sorption to mineral soil

The concentration of dissolved organic matter (DOM) in the soil solution is predominantly determined by sorption processes to mineral surfaces. We compared four models describing DOM sorption isotherms to mineral soil material using the results of batch experiments for dissolved organic carbon (DOC) and nitrogen (DON) sorption to different horizons of a podsol. The Initial Mass and modified Langmuir isotherms could be fit to the data points in all cases. The three curvilinear models (Langmuir, Freundlich and exponential models) were found to result in similar goodness-of-fit and parameter estimates. We found that the most widely used, linear model (the Initial Mass isotherm) could be used for horizons with very small sorption capacity and horizons almost saturated with DOM, but failed to describe sorption in the deeper, DOM-unsaturated horizons characterized by a curvilinear shape of the sorption isotherm. The modified Langmuir isotherm was found to describe DOM sorption to mineral soil best and gave realistic parameter estimates, including a measure for maximum sorption capacity of the soil. Comparing the results of the sorption experiments with DOM concentrations in soil solution in the field indicated that the sorption isotherms can serve as a basis for larger DOM leaching models.

Fire Effects on Stable Isotopes in a Sierran Forested Watershed

This study tested the hypothesis that stable C and N isotope values in surface soil and litter would be increased by fire due to volatilization of lighter isotopes. The hypothesis was tested by: (1) performing experimental laboratory burns of organic and mineral soil materials from a watershed at combinations of temperature ranging 100 to 600 degrees C and duration ranging from 1 to 60 min; (2) testing field samples of upland soils before, shortly after, and 1 yr following a wildfire in the same watershed; and (3) testing field soil samples from a down-gradient ash/sediment depositional area in a riparian zone following a runoff event after the wildfire. Muffle furnace results indicated the most effective temperature range for using stable isotopes for tracing fire impacts is 200 to 400 degrees C because lower burn temperatures may not produce strong isotopic shifts, and at temperatures>or=600 degrees C, N and C content of residual material is too low. Analyses of field soil samples were inconclusive: there was a slightly significant effect of the wildfire on delta15N values in upland watershed analyses 1 yr postburn, while riparian zone analyses results indicated that delta13C values significantly decreased approximately 0.71 per thousand over a 9 mo post-fire period (p=0.015), and ash/sediment layer delta13C values were approximately 0.65 per thousand higher than those in the A horizon. The lack of field confirmation may have been due to overall wildfire burn temperatures being <200 degrees C and/or microbial recovery and vegetative growth in the field. Thus, the muffle furnace experiment supported the hypothesis, but it is as yet unconfirmed by actual wildfire field data.

Storm flow flushing in a structured soil changes the composition of dissolved organic matter leached into the subsoil

Dissolved organic matter increases typically in streams draining forested catchments during heavy rainstorms and snowmelt. Tracer methods and model calculations suggest that the storm flow flushing of dissolved organic matter is either due to lateral near-surface flow, i.e. within the organic forest floor, or preferential flow (funnelling) through the mineral soil. Both pathways should deliver forest floor-derived dissolved organic matter to streams that is hardly changed because of little to no interaction with mineral soil material and microorganisms. Here, we investigated the effect of rain storm induced vertical flushing through the mineral soil on the composition of dissolved organic matter in a structured Rendzic Leptosols under 90-year-old European beech ( Fagus sylvatica L.). During two rainstorm periods in autumn 1998 with elevated transport of organic C, N, P and S from the forest floor into the subsoil, we sampled dissolved organic matter in forest floor leachates (sampled by zero-tension plate lysimeters), subsoil solutions (sampled by suction cups at 90 cm depth) and subsoil seepage (sampled by zero-tension plate lysimeters at 90 cm depth). The chemical composition of dissolved organic matter was characterised by fractionation with XAD-8 macroreticular resin, wet-chemical analyses of carbohydrates and lignin-derived phenols, and determination of the δ 13C. During both rainstorm periods, all tested chemical features of dissolved organic matter in forest floor leachate and subsoil seepage matched each other greatly. In contrast, dissolved organic matter in soil solution contained smaller portions of XAD-8-adsorbable organic C, less lignin-derived phenols, more carbohydrates and showed smaller δ 13C values than that in forest floor leachates and subsoil seepage. These results suggest a rather direct transfer of organic solutes from the forest floor into the subsoil and probably further to ground and surface waters during heavy rainstorms. Dissolved organic matter leaving the soil in heavy rainstorms by rapid water flow through macropores is likely less biodegradable, more UV-digestible and more reactive towards metals and organic pollutants than that released from soil at low rainfall intensity by matric flow.

The interaction of heavy metals with urban soils: sorption behaviour of Cd, Cu, Cr, Pb and Zn with a typical mixed brownfield deposit

This study investigated the sorption characteristics and release of selected heavy metals (Cd, Cu, Cr, Pb and Zn) from a typical urban soil material from a derelict brownfield site in Western Scotland, UK. The study aimed to evaluate contaminant interactions with an urban substrate, comprising a mix of mineral soil and residue materials (e.g. brick, concrete, wood). This type of material has received little consideration in the literature to date. Soil samples were subject to a sequence of test involving batch equilibration and dynamic leaching, in single (non-competitive) and multi-element (competitive) solutions. The batch experiments were carried out in unadjusted and close to soil field pH conditions (pH 2 and 7, respectively). The equilibrium adsorption capacity for heavy metals was measured and extrapolated using the Langmuir isotherm. The parameters of the isotherms x m (the maximum amount adsorbed per unit mass of adsorbent (mg/g)) and b (adsorption constant (m 3/g)) were calculated for Cd, Cu, Cr, Pb as single-element and multi-element solutions. The adsorption from the single-element solution was more effective than adsorption under multi-element conditions, due to competitive effects. For example, the adsorption of copper from a single-element solution was over four times greater than for a multi-element solution. In the case of Cr and Zn, migration of metal from soil to solution was observed. Adsorption capacity at pH 2 followed the order Cr>Cu>Pb>Cd and at pH 7 Cd>Zn, with precipitation affecting Cu and Pb behaviour. During the column leaching experiment, most of the heavy metals were irreversibly bound to the soil, but in the case of Cr some movement from soil into solution was observed. The results also showed that Cd, Cu, Pb and Zn were removed from the solution and adsorbed on the soil. No significant difference in the metal removal from single- and multi-element solutions was observed. Overall, the urban residue behaved in a similar manner to mineral soils despite a significant component of anthropogenic solid materials.

Nutrient limitations to soil microbial biomass and activity in loblolly pine forests

We performed an assay of nutrient limitations to soil microbial biomass in forest floor material and intact cores of mineral soil collected from three North Carolina loblolly pine ( Pinus taeda) forests. We added solutions containing C, N or P alone and in all possible combinations, and we measured the effects of these treatments on microbial biomass and on microbial respiration, which served as a proxy for microbial activity, during a 7-day laboratory incubation at 22 °C. The C solution used was intended to simulate the initial products of fine root decay. Additions of C dramatically increased respiration in both mineral soil and forest floor material, and C addition increased microbial biomass C in the mineral soil. Additions of N increased respiration in forest floor material and increased microbial biomass N in the mineral soil. Addition of P caused a small increase in forest floor respiration, but had no effect on microbial biomass.

Instrumental neutron activation analysis as a tool for assessing the solubility of soil mineral matter in strong acid

Fifty samples of natural surface soils with high but variable organic matter content were analyzed for 13 elements (Na, Al, K, Sc, V, Cr, Mn, Fe, Co, Zn, Sr, Ba, La) by INAA. The same samples were analyzed for the “total-recoverable” fraction of these elements by ICP-OES after decomposition with 7M HNO3, and the results are compared. The data are discussed separately for two groups of samples with organic matter contents of respectively >80% and Mn (77)>La (60)>Fe=Zn (53)>V (33)>Cr (29)>Sc (25)>Al=Ba (17)>Sr (13)>K (5)>Na (2). The results are in good agreement with corresponding literature data for mineral soils in the case of Al, K, Sc, V, Cr, Fe, and La. In the case of Na, Mn, Co, Zn, Sr, and Ba the present surface soils showed significantly higher “total-recoverable” fractions than the previously studied subsoils. Possible reasons for these differences are discussed. INAA remains a convenient reference technique for determination of total concentrations with the rapidly increasing use of strong mineral acids in environmental studies of elements.

Sediment subsidy: effects on soil–plant responses in a rapidly submerging coastal salt marsh

The tidal energy subsidy hypothesis postulates that the high primary productivity of coastal salt marshes is the result of an energy subsidy provided by the tides. The sediment component of this subsidy is especially important in contributing to the elevation increase of the marsh surface, a process essential for the sustainability of salt marshes during periods of sea level rise. This research tested the hypothesis that sediment subsidies have an ameliorating effect on sea level rise-induced impacts to salt marsh vigor. We assessed the plant structural and soil physico-chemical responses to different intensities of sediment subsidy in a salt marsh experiencing a high rate of relative sea level rise. Sediments were hydraulically dredged with a high fluid to solids ratio (85%:15%) from the Gulf of Mexico and dispersed into a Spartina alterniflora dominated salt marsh. Approximately 2 years after this fluid-sediment-enrichment, maximum sediment elevation did not exceed 30 cm above ambient and both plant cover and aboveground biomass responded positively. Sediment subsidy increased soil mineral matter, and, in turn, soil fertility and marsh elevation, and thereby reduced nutrient deficiency, flooding, and interstitial sulfide stresses. Thus, sediment subsidy generated a more favorable environment for plant growth and potentially, marsh sustainability.

Solid-solution partitioning of Cd, Cu, Ni, Pb, and Zn in the organic horizons of a forest soil.

We report the solid-liquid partitioning of Cd, Cu, Ni, Pb, and Zn in 60 organic horizon samples of forest soils from the Hermine Watershed (St-Hippolyte, PQ, Canada). The mean Kd values are respectively 1132, 966, 802, 3337 and 561. Comparison of those Kd coefficients to published compilation values show that the Kd values are lower in acidic organic soil horizons relative to the overall mean Kd values compiled for mineral soils. But, once normalized to a mean pH of 4.4, the Kd values in organic soil horizons demonstrate the high sorption affinity of organic matter, which is either as good as or up to 30 times higher than mineral soil materials for sorbing trace metals. Regression analysis shows that, within our data set, pH and total metal contents are not consistent predictors of metal partitioning. Indeed, metal sorption by the solid phase must be studied in relation to complexation by dissolved organic ligands, and both processes may sometime counteract one another.

Soil structure and characteristics of organic matter in two orchards differing in earthworm activity

By consuming plant remains and soil, earthworms incorporate organic matter (OM) into the soil and form biogenic soil structures, which can affect OM dynamics. We carried out a (micro)morphological study of soil structure development and OM distribution in two orchards (45 year) in a Dutch calcareous marine loam: RI − without, and KR + with high earthworm activity, the result of different levels of heavy metal contamination from fungicides. In both soils, sedimentary–stratification was absent to 60 cm depth and equal amounts of biogenic calcite spheroids were counted, suggesting similar earthworm activity in the past. In RI − the current vol.% of worm-worked groundmass in thin sections was 6% in the Ah and 7% in the Bw horizon compared with 51% in the Ah and 16% in the Bw horizon of KR +. Disappearance of earthworms with time in RI − gave rise to a compacted physicogenic soil structure with angular and prismatic aggregates and the absence of earthworm biopores. Due to restricted fragmentation and incorporation of OM fragments in casts, a litter layer formed at the soil surface. OM coatings were present in fissures and root pores of the Ah horizon, indicating the absence of mixing of organic and mineral soil materials. OM fragments were relatively coarse (>50 μm) and heterogeneously distributed through the Ah groundmass. Stronger decalcification in RI − than in KR + could be ascribed to higher production of organic acids in the litter layer of RI − and the absence of soil homogenisation by earthworms. In KR + earthworm activity was high, which has resulted in a biogenic structure with granular and subangular blocky aggregates and many worm casts and biopores. Particulate OM was relatively fine (<50 μm) and encapsulated with clayey material in casts and micro-aggregates. The organic C content was not significantly ( P<0.05) higher in the Ah horizon of KR +, than in the Ah horizon of RI − (15.7 and 13.7 g kg −1, respectively). The lower C mineralization rates in KR + below 6 cm depth, however, might be an indication of higher microbial substrate-use efficiency or physical protection of OM against decomposition. The latter explanation would accord with the observed encapsulation of OM in micro-aggregates, and with studies on other management systems that favour biogenic aggregate formation. The quality of the soil macro- and microstructures, degree of soil compaction and decalcification and soil OM dynamics were strongly determined by the occurrence of earthworms in soils.

The weathering of mineral soil by natural soil solutions

Chemical weathering is an important neutralisation process and sourceof cations in forest soil. The presence of dissolved organic matter in the soil solution can have a considerable influence on weathering release. The aim of this study is to compare the weathering potentialof natural soil solutions, collected from Norway spruce, Scots pine and birch sites, to release Al, Ca, Mg, K, Na, and Si from the fine fraction in the C horizon of a podzol. Residual organic matter in the mineral soil was removed with H2O2. The <0.06 mm fraction of the mineral soil was suspended in soil solution, collected from the three sites, for 11 days with continuous agitation. Ultrapure water was used as a control. The pH of the suspensions was maintained at 5.4 by bubbling with CO2. The initial mean DOC concentrations in the soil solutions were 65, 56 and 40 mg L-1 for the spruce, pine and birch sites, respectively. The presence of DOM in the soil solution did not significantly enhance the capacity to weather mineral soil material, and no systematic differences were found between the three sites. However, Al release from the mineral soil was slightly higher in the soil solutions containing DOM compared to the control solution with no DOM. The proportions of DOM fractions capable of enhancing weathering were comparable with those reported in earlier studies. The weathering of metals was found to be primarily due to pH-driven processes. The lack of considerable weathering enhancement by DOM could be due to the fact that the cation-binding sites of the organic ligands were already saturated by e.g. Al and Fe in the soil solution derived from these podzolic, Al- and Fe-rich soils.

Effects of Seedbed Substrate on Moisture Conditions and Germination of Pinus sylvestris Seeds in a Clearcut

The objective of the investigation was to describe moisture conditions and germination of Scots pine (Pinus sylvestris L.) seeds in different seedbed substrates (feather mosses, mineral soil, humus and ground organic material) with and without irrigation during 2 weeks, in a clearcut in northern Sweden. Without irrigation no seeds germinated, which could be explained as an effect of the low moisture conditions of the seedbed substrates. This was shown in the seeds' low moisture content, with highest values in mineral soil, 10-20%, and for the other seedbed substrates 5-15%. The moisture conditions were highest during the night and lowest in the afternoon. With irrigation, moisture conditions improved (seed moisture content 20-50%) and diurnal changes were moderated. Seeds germinated in all substrates with most seedlings in mineral soil (60% of sown germinable seeds). The moisture conditions of the seedbed substrates proved to be in poor agreement with the seeds' requirement for germination, especially during warm weather with no precipitation.

Lead exposure of small herbivorous vertebrates from atmospheric pollution

Concentrations of Pb in livers of willow grouse ( Lagopus lagopus), black grouse ( Tetrao tetrix), and hare ( Lepus timidus) were determined in samples collected during the period 1990–92 from 77 locations distributed across Norway. Our objective was to elucidate the impact of long-range atmospheric transport on the Pb exposure of the animals. The moss Hylocomium splendens was measured for atmospheric Pb deposition and Pb in soil at 60-cm depth was determined to reflect the natural geochemical background at the study locations. Strong positive relationships were found between Pb in liver and atmospheric deposition of Pb for all species and age groups studied. Results indicate that long-range atmospheric transport was the main source of Pb in the animals studied. This conclusion was supported by Pb analysis of typical food plants for the animals. Correlation between Pb in liver and Pb in soil mineral matter was observed only when considering sites with very low impact of atmospheric deposition. Even though the observed liver Pb concentrations may seem low (⩽12 μg g −1 dw) they approach levels where sub-lethal effects cannot be ignored.

NITROGEN TRANSFORMATIONS IN FALLEN TREE BOLES AND MINERAL SOIL OF AN OLD-GROWTH FOREST

I measured net N transformation rates of well-decayed boles and adjacent mineral soil under field conditions in an old-growth Douglas-fir/western hemlock/western red cedar stand in the central Oregon Cascades. Additionally, laboratory assays and in- cubations were used to elucidate the controls on net N transformations in these materials. Net N mineralization under field conditions was similar for well-decayed boles and mineral soils (0.83 and 0.61 g N m-2 material-yr-1, respectively). Laboratory rates of net N min- eralization per mass of total N were similar or higher in well-decayed boles compared to mineral soil. These results are surprising, given that the C:N ratio of well-decayed boles was much greater than that of mineral soil (117 vs. 26, respectively), and given the vastly different physical structure of these materials. Higher field and laboratory rates of net N mineralization relative to total N in boles compared to mineral soil suggest either that organically bound N contained in boles is in a more readily mineralizable form or that C compounds in well-decayed bole material are less readily metabolized by microbial het- erotrophs (i.e., C availability is lower) than in mineral soil, resulting in a higher ratio of net-to-gross N mineralization because of reduced N demand by a C-limited microflora. A lower microbial respiration rate and smaller microbial biomass C relative to the total C pool in well-decayed boles than in mineral soil support the latter hypothesis. Furthermore, bole material exhibited a higher specific respiration rate (respired C per unit microbial biomass C), suggesting either a lower C-use efficiency of bole microflora or a lower C availability in boles compared to mineral soil. Both well-decayed bole and mineral soil materials showed low annual rates of net nitrification under field conditions. Using an estimate of the mass of class 4 and 5 boles in similar forest stands in the Pacific Northwest, I estimate that well-decayed boles contribute about 0.16-0.25 g N.m-2 yr-I of plant-available N. This N flux is lower than other internal N fluxes within this forest, as well as lower than the rate of N input from the atmosphere. Total plant uptake in a nearby old-growth Douglas-fir forest has been estimated at about 4.0 g Nm-2_yr- 1, suggesting that well-decayed boles may contribute about 4-6% of plant N uptake. Results from this study indicate that the C:N ratio is a poor predictor of net N release from contrasting forest detrital pools.

Stratigraphic Approach to Alteration in Mineral Soils: The Heavy Metal Example

AbstractQuantifying post‐depositional alteration of mineral soil material is complicated by the fact that many soils consist of layered parent materials with varying indigenous composition. Part of our study site in the Steigerwald Mountains of northern Bavaria was cultivated during the Middle Ages and later reforested. Soil erosion removed the upper materials, exposing a deposit to contamination from the surface, whereas nearby, the deposit remained protected by overlying layers. We compared heavy metal concentrations within that deposit across this boundary of varying protection. No significant results were obtained for Cd; however, the concentrations of Pb and Cu increase by about 100% or more where the protecting cover thins. The Pb and Cu values provide a measure of the gross post‐depositional alteration of that deposit. We expect this procedure can help quantify various pedogenic alterations by comparison with essentially the same, unaltered parent material.

Carbon dioxide and methane fluxes by a forest soil under laboratory-controlled moisture and temperature conditions

Carbon dioxide and methane are important greenhouse gases whose exchange rates between soils and the atmosphere are controlled strongly by soil temperature and moisture. We made a laboratory investigation to quantify the relative importance of soil moisture and temperature on fluxes of CO 2 and CH 4 between forest soils and the atmosphere. Forest floor and mineral soil material were collected from a mixed hardwood forest at the Harvard Forest Long-Term Ecological Research Site (MA) and were incubated in the laboratory under a range of moisture (air-dry to nearly saturated) and temperature conditions (5–25°C). Carbon dioxide emissions increased exponentially with increasing temperature in forest floor material, with emissions reduced at the lowest and highest soil moisture contents. The forest floor Q 10 of 2.03 (from 15–25°C) suggests that CO 2 emissions were controlled primarily by soil biological activity. Forest floor CO 2 emissions were predicted with a multiple polynomial regression model ( r 2=0.88) of temperature and moisture, but the fit predicting mineral soil respiration was weaker ( r 2=0.59). Methane uptake was controlled strongly by soil moisture, with reduced fluxes under conditions of very low or very high soil moisture contents. A multiple polynomial model accurately described CH 4 uptake by mineral soil material ( r 2=0.81), but only weakly ( r 2=0.45) predicted uptake by forest floor material. The mineral soil Q 10 of 1.11 for CH 4 uptake indicates that methane uptake is controlled primarily by physical processes. Our work suggests that inclusion of both moisture and temperature can improve predictions of soil CO 2 and CH 4 exchanges between soils and the atmosphere. Additionally, global change models need to consider interactions of temperature and moisture in evaluating effects of global climate change on trace gas fluxes.

Influence of Norway spruce seedlings on the nutrient availability in mineral soil and forest floor material

A greenhouse experiment was performed to evaluate the effect of Norway spruce (Picea abies (L.) Karst.) seedlings on net nutrient availability in five different growing media containing F- or H-layer and mineral soil originating from a haplic podzol in northern Sweden. The initial total amounts of eight nutrient elements (N, K, P, Ca, Mg, Mn, Fe, Zn) and exchangeable amounts of the same elements were analyzed in pots with or without spruce seedlings. In the planted pots seedling nutrient uptake was also estimated. After 26 weeks, higher net nutrient availability with seedlings was found in 25 out of the 40 (62%) growing media and nutrient element combinations. A positive seedling effect on net nutrient availability might be explained by rhizodeposition stimulating the soil microorganism activity and accelerating the weathering of minerals or by seedling roots promoting the nutrient providing processes through changes in soil chemical and physical properties. Nitrogen availability was primarily affected by what part of the forest floor the growing medium contained although the positive response to seedling presence was apparent. The positive net availability response of P, Ca, Mg, Mn, Fe and Zn to seedling presence was on the other hand relatively strong. In the case of P, K, and Zn the growing medium composition (if the F- and H-layer was pure or mixed with mineral soil) was also an important factor for the estimated net availability. Pure F-and H-layer provided greater P- and K-availability while the availability of Zn increased when mineral soil was added. The influence of growing plants ought to be considered when soil samples are used for assessing the nutrient availability.