Nitrous oxide emission from Swedish forest soils in relation to liming and simulated increased N-deposition

Fluxes of N₂O were studied in a Norway spruce forest in the southwest of Sweden. Three differently treated catchments were compared: Limed (6 t dolomite ha^–1), Nitrex (additional N-deposition corresponding to 35 kg ha^–1 year^–1, in small doses) and Control (used as control site). The N-retention was still high (95%) after 2years of N-addition at the Nitrex site when the flux measurements were performed. Each catchment contained both well-drained and poorly drained soils (covered with Sphagnum sp.). The emissions of N₂O were in general low with both a high spatial and temporal variation for all three sites. The measured emissions were 25, 71 and 96 (gN₂O-N ha^–1 year^–1) for the well-drained Limed, Control and Nitrex sites, respectively. The average emissions of N₂O from the wet areas were significantly higher than the well-drained areas within the catchments. For the wet areas the measured emissions were larger: 90, 118 and 254 (g N₂O-N ha^–1 year^–1) for the Limed, Control and Nitrex sites, respectively. Comparison between treatments showed the wet Nitrex site to have a significantly higher emission than all other sites. The increased N-deposition at the Nitrex site increased the N₂O emissions by 0.2% of the added N for the well-drained soils and about 1% for the wet areas, compared with the control site. Since the wet areas represented only a small part of the forest, their larger emissions did not contribute significantly to the overall emission of the forest. Neither temperature nor water content of the soil was well correlated with the N₂O emissions. Soil gas samples showed that most of the N₂O was produced below a 0.3-m depth in the soil. Received: 27 September 1996     

Effects of N sources and methane concentrations on methane uptake potential of a typical coniferous forest and its adjacent orchard soil

After removal of the above-ground plant debris three different soil layers were taken from a typical coniferous forest and its adjacent orchard in Numata City, Japan. The potentials of soil CH₄ uptake at two initial CH₄ concentrations were studied under aerobic conditions in the laboratory, along with inhibition of soil CH₄ oxidation by urea-N or KNO₃-N addition. Due to long-term N inputs, the CH₄ uptake of the upper mineral layer of the orchard soil was 25.4% and 87.7% lower than that of the surface forest soil at 2.4 and 12.6 l l^–1 CH₄, respectively. Methane uptake of the forest soil decreased with increasing soil depths at two CH₄ levels. However, maximal CH₄-consuming activity occurred in the 9- to 23-cm depth of the orchard soil at 12.6 l l^–1 methane. Nitrogen additions in the form of KNO₃ or urea at the rate of 200 g N g^–1 soil substantially reduced soil CH₄ uptake in the upper and sub-surface mineral layers at both sites, except that the addition of KNO₃-N had no apparent inhibitory effect on the CH₄ uptake in the 9- to 23-cm depth of the orchard soil. A strong inhibitory effect of NO₃^– addition on the CH₄ uptake, in contrast to NH₄⁺, occurred in the surface forest soil. The use of KNO₃-N, as compared to urea or urea plus a nitrification inhibitor (dicyandiamide), resulted in a lower potential to cause inhibition of CH₄ oxidation in the 0- to 23-cm depth of the orchard soil.     

Methane oxidation in a temperate coniferous forest soil: effects of inorganic N

Methane oxidation rates were measured in soils obtained from a coniferous forest in northern England. The effects of depth and added K⁺ (K₂SO₄), NH₄⁺ ((NH₄)₂SO₄) and NO₃⁻ (KNO₃) on potential CH₄ oxidation were investigated in a series of laboratory incubations. The humus (H) layer soil showed much greater CH₄ oxidation rates than the other soil layers, with maximal rates of 53 and 226 ng CH₄ gdw⁻¹ h⁻¹ when incubated with initial 10 and 1000 μl CH₄ l⁻¹, respectively. Additions of the solutes K⁺, NH₄⁺ and NO₃⁻ showed differing degrees of inhibition on CH₄ oxidation, which varied with the initial CH₄ concentration, the ion added, and the ion concentration. In general, inhibition by the ions was slightly greater for incubations with an initial concentration of 1000 μl CH₄ l⁻¹ than for 10 μl CH₄ l⁻¹ under otherwise identical conditions. For K⁺ and NH₄⁺ treatments, inhibitory rates were usually less than 15%, but at high K⁺ and NH₄⁺ concentrations inhibition could reach 50%, the inhibitory effects of NH₄⁺ were consistently slightly greater than those of K⁺ at the same concentration. In marked contrast to NH₄⁺, NO₃⁻ showed a very strong inhibitory effect. Added NO₃⁻ and NO₂⁻ produced via added NO₃⁻ reduction in anaerobic ‘microsites’ are probably toxic to CH₄-oxidizing bacteria. These results, together with those from other reports, suggest that NO₃⁻ may have a greater importance in the inhibition of CH₄ oxidation in forest soils than that attributed to NH₄⁺ and needs to be investigated in a wide range of soil types from various forests.     

Decomposition rates and feeding activities of soil fauna in deciduous forest soils in relation to soil chemical parameters following liming and fertilization

 This study investigated the influence of liming and P/K fertilization on the feeding activities of soil fauna and leaf litter decomposition rates in deciduous forest soils. The parameters examined were correlated to soil chemical characteristics. In 1994, we established a field experiment with six plots in an oak-beech forest and added different amounts of dolomite, partly combined with P/K fertilization. Two years thereafter a bait-lamina test was used to examine the feeding activity of soil fauna and a minicontainer test to study beech-leaf decomposition. In 1996, the feeding activity in the Ah horizon was lower in the plots left untreated in 1994 than in the plots which had been fertilized in 1994. The highest feeding activity was found in the treatment with 6 t dolomite ha^–1 plus P/K. In all plots, the feeding activity decreased with increasing soil depth. The decomposition rates varied from 0.49% to 0.78% week^–1 in the period April–October 1996. In 1996, the plots treated with 6 t dolomite ha^–1 had the highest decomposition rates and differed significantly from those treated with 9 t or 15 t dolomite ha^–1. No significant differences were found between the untreated plots and those treated with 9 t or 15 t dolomite ha^–1. These results were confirmed by those obtained in 1997. The C/N ratio of litter also decreased, mostly in the treatment with 6 t dolomite ha^–1. Feeding activities in the Ah horizon correlated positively with pH and concentrations of mobile Ca, Mg, K, and negatively with concentrations of mobile Al and heavy metals. We concluded that an increased supply of mobile nutrients and a decrease in mobile Al and heavy metals in these forest soils, as well as a balanced ratio between macro- and micronutrients, led to increased biological activity. Received: 26 June 1998     

Short- and long-term effects of nitrogen fertilization on methane oxidation in three Swedish forest soils

 Under normal conditions, CH₄, one of the most important greenhouse gases, is subject to biological oxidation in forest soils. However, this process can be negatively affected by N amendment. The reported experiment was conducted in order to study the short- and long-term effects of N amendment on CH₄ oxidation in pine (Pinus sylvestris L.) forest soils. Soil samples were taken from three experimental sites, two of which had been amended with N once, over 20 years earlier, while the third had been amended 3 weeks earlier. The soil samples were incubated fresh at 15  °C at ambient CH₄ concentrations (ca. 1.8 ppmv CH₄). The variation in CH₄-turnover rates was high within the treatments: CH₄ was produced [up to 22.6 pmol CH₄ g dry wt. soil^–1 h^–1] in samples from the recently amended site, whereas it was consumed at high rates (up to 431 pmol CH₄ g dry wt. soil^–1 h^–1) in samples from the plot that had received the highest N amendment 27 years before sampling. Although no significant differences were found between N treatments, in the oldest plots there was a correlation between consumption of atmospheric CH₄ and the total C content at a depth of 7.5–15 cm in the mineral soil (r ²=0.74). This indicates that in the long-term, increased C retention in forest soils following N amendment could lead to increased CH₄ oxidation. Received: 3 September 1997     

Water-soluble Al inhibits methane oxidation at atmospheric concentration levels in Japanese forest soil

The effect of aluminium on methane oxidation was examined from incubation experiments involving the addition of several concentrations of Al solution (0.1, 0.2, 0.5, 1, 3 and 5 mM) to two soil samples that possessed different CH₄ oxidation potential. Atmospheric CH₄ oxidation activity was inhibited by the addition of as little as 0.1 mM Al solution (approximately 0.5 μg of Al per gram dry weight soil) to a forest soil that contained low water-soluble Al and possessed a high CH₄ oxidation potential. Our results indicate that Al inhibition of CH₄ oxidation activity is concentration-dependant after a certain time and the inhibition increases gradually over time until at least 96 h have elapsed. We also found that relatively small amounts of Al additions, such as 10-20 μg per gram dry weight of soil, halved the CH₄ oxidation rate compared to the control, regardless of the original CH₄ oxidation potential of the soil. Since the Al concentrations used in our experiment are often observed in forest soils, we can assume that Al acts as an important inhibitor of CH₄ oxidation in forest soils under natural conditions. The sharp falls and a continuous decrease in CH₄ oxidation rate in other forest samples with the addition of deionized water implies that the water-soluble Al contained in soils contributes to the inhibition of CH₄ oxidation rate. This result suggests that precipitation causes a relatively prolonged inhibition of CH₄ oxidation in soils containing a high concentration of water-soluble Al.     

Methane oxidation in boreal forest soils: kinetics and sensitivity to pH and ammonium

In soil incubation experiments we examined if there are differences in the kinetic parameters of atmospheric methane (CH₄) oxidation in soils of upland forests and forested peatlands. All soils showed net uptake of atmospheric CH₄. One of the upland forests included also managed (clear-cut with or without previous liming or N-fertilization) study plots. The CH₄ oxidation in the forested peat soil had a higher K_m (510 μl l⁻¹) and V_max (6.2 nmol CH₄ cm⁻³ h⁻¹) than the upland forest soils (K_m from 5 to 18 μl l⁻¹ and V_max from 0.15 to 1.7 nmol CH₄ cm⁻³ h⁻¹). The forest managements did not affect the K_m-values. At atmospheric CH₄ concentration, the upland forest soils had a higher CH₄ oxidation activity than the forested peat soil; at high CH₄ concentrations the reverse was true. Most of the soils oxidised CH₄ in the studied pH range from 3 to 7.5. The pH optimum for CH₄ oxidation varied from 4 to 7.5. Some of the soils had a pH optimum for CH₄ oxidation that was above their natural pH. The CH₄ oxidation in the upland forest soils and in the peat soil did not differ in their sensitivities to (NH₄)₂SO₄ or K₂SO₄ (used as a non-ammonium salt control). Inhibition of CH₄ oxidation by (NH₄)₂SO₄ resulted mainly from a general salt effect (osmotic stress) though NH₄⁺ did have some additional inhibitory properties. Both salts were better inhibitors of CH₄ oxidation than respiration. The differences in the CH₄ oxidation kinetics in the forested peat soil and in the upland forest soils reveal that there are differences in the physiologies of the CH₄ oxidisers in these soils.     

Methane concentrations and methanotrophic community structure influence the response of soil methane oxidation to nitrogen content in a temperate forest

Methane oxidation in forest soils removes atmospheric CH₄. Many studies have determined methane uptake rates and their controlling variables, yet the microorganisms involved have rarely been assessed simultaneously over the longer term. We measured methane uptake rates and the community structure of methanotrophic bacteria in temperate forest soil (sandy clay loam) on a monthly basis for two years in South Korea. Methane uptake rates at the field site did not show any seasonal patterns, and net uptake occurred throughout both years. In situ uptake rates and uptake potentials determined in the laboratory were 2.92 ± 4.07 mg CH₄ m⁻² day⁻¹ and 51.6 ± 45.8 ng CH₄ g⁻¹ soil day⁻¹, respectively. Contrary to results from other studies, in situ oxidation rates were positively correlated with soil nitrate concentrations. Short-term experimental nitrate addition (0.20-1.95 μg N g⁻¹ soil) significantly stimulated oxidation rates under low methane concentrations (1.7-2.0 ppmv CH₄), but significantly inhibited oxidation under high methane concentrations (300 ppmv CH₄). We analyzed the community structures of methanotrophic bacteria using a DNA-based fingerprinting method (T-RFLP). Type II methanotrophs dominated under low methane concentrations while Type I methanotrophs dominated under high methane concentrations. Nitrogen addition selectively inhibited Type I methanotrophic bacteria. Overall, the results of this study indicate that the effects of inorganic N on methane uptake depend on methane concentrations and that such a response is related to the dissimilar activation or inhibition of different types of methanotrophic bacteria.     

施用铵态氮对森林土壤硝态氮和铵态氮的影响

对取自武夷山的红壤、黄壤、黄壤性草甸土分别在对照(CK,N 0 mg/kg)、低氮(LN,N 50 mg/kg)、高氮(HN,N 100 mg/kg)3种氮(N)水平处理下开展培养实验,研究施加NH4+-N对森林土壤N转化的短期影响.结果表明,添加NH4+-N可显著(p＜0.05)降低土壤NO3--N含量4.5％～25.7％,但LN与HN处理差异不显著,NO3--N降低可能与NO3--N反硝化和异氧还原有关;然而,黄壤性草甸土NO3--N没有降低.与培养前比较,在第56天红壤NO3--N含量显著增加5倍左右;桐木关黄壤增加40％左右,而黄冈山25 km黄壤仅在CK处理下增加16％,但是黄壤性草甸土显著降低;结果显示LN与HN处理土壤NO3--N含量变化幅度小于CK.与CK相比,LN和HN处理红壤NH4+-N分别显著(p＜0.05)升高24.1％ ～ 96.5％和68.7％～114.1％,且随培养进行没有累积,可能与微生物固N有关;桐木关NH4+-N分别升高17.6％ ～ 39.6％和37.6％～95.8％ (p＜0.05),LN处理黄冈山25 km黄壤NH4+-N只有第7天升高17.8％ (p＜0.05),HN处理第7、14、28、42天显著升高17.5％～48.6％(p＜0.05).LN处理黄壤性草甸土的NH4+-N在前3周显著降低11.6％～28.5％ (p＜0.01); HN处理在第7天和14天分别降低10.8％(p＜0.01)和7.5％,但是在第28～56天显著增加17.6％～20.4％(p=0.002).随着培养进行,CK处理红壤NH4+-N逐渐降低,桐木关黄壤、黄冈山25 km黄壤和黄壤性草甸土升高;LN和HN处理黄壤和黄壤性草甸土NH4+-N逐渐升高.可见,不同海拔土壤类型对NH4+-N添加响应存在差异.     

Methane uptake in salt-affected soils shows low sensitivity to salt addition

Methane oxidation in aerated soils is a significant sink for atmospheric methane (CH₄). Salt-affected soils are extensively present and constitute about 7% of total land surface. However, our knowledge about CH₄ turnover between the atmosphere and the saline soils is very limited. In order to evaluate the potential of CH₄ consumption in saline soils, CH₄ fluxes were measured in intact cores of the slightly (ECe = 3.2 mS cm⁻¹), moderately (ECe = 7.1 mS cm⁻¹) and extremely (ECe = 50.7 mS cm⁻¹ and 112.6 mS cm⁻¹) saline soils from the Yellow River Delta, China. CH₄ uptake of cores from the slightly saline soil ranged from 14 to 24 μg CH₄-C m⁻² h⁻¹, comparable to those in the non-saline forest soils with similar texture. CH₄ uptake of cores from the moderately saline soil was only about 6% of that in the slightly saline soil. CH₄ uptake was too low to be measurable in the extremely saline soil. Compared with the non-saline soil, CH₄ uptake in the saline soils was much less sensitive to salt, suggesting the higher salt-tolerance of CH₄ oxidizers in the saline soil. The result also indicated an underestimate in CH₄ uptake for the naturally-occurring saline soils by adding salt to non-saline soils. These results should be useful to study the global CH₄ budget and to explore the physiological and ecological characteristics of methanotrophic bacteria in the salt-affected soils.     

Effect of nutrients and liming on changes in pH,redox potential,and uptake of iron and manganese by wetland rice in iron-toxic soil

In a greenhouse experiment, the nutrients NPK, NPK + lime, K, and Mn were applied to an iron-toxic soil (Typic Haplastulf). Soil pH and dry matter production were increased and Eh and available Fe in the soil were decreased. Though liming the soil decreased available Fe and Mn and increased pH to the greatest extent, the highest dry matter production was obtained with NPK application. NPK + lime produced a smaller yield than NPK without lime. Though the application of K or Mn alone produced much less dry matter than NPK or NPK + lime, no symptoms of Fe toxicity were observed. We conclude that Fe toxicity can be reduced with a balanced use of fertilizers (NPK or NPK + lime) and its occurrence was mostly due to nutrient stress.     

Dimethyl sulphoxide (DMSO) and dimethyl sulphide (DMS) as inhibitors of methane oxidation in forest soil

Dimethyl sulphoxide (DMSO) at 14 mM inhibits CH₄ oxidation in forest soil, but the inhibition mechanism is unknown. When soil slurries are incubated in gas tight flasks, there is a lag of about 45 h before DMSO inhibits CH₄ oxidation. We tried to determine if some metabolic compound derived from DMSO, as a result of microbial activity, is responsible for the inhibition. Dimethyl sulphide (DMS) accumulated in the sealed flasks up to 5-83 μl l⁻¹ in the headspace during a 2-week period. DMS at 1 μl l⁻¹ in the headspace (0.64 μM in soil-water slurry) had a negligible effect on CH₄ oxidation but 50 μl l⁻¹ DMS (32 μM) inhibited CH₄ oxidation completely. However, the inhibition by DMSO was already evident after 45 h, when DMS concentrations were generally non-inhibiting (0.1-0.7 μl l⁻¹). DMSO was also shown to inhibit CH₄ oxidation when the DMS produced was continuously removed. Results suggest that the production of DMS from DMSO makes a minor contribution to the inhibition of CH₄ oxidation by DMSO with incubation times relevant in CH₄ oxidation studies.     

Aluminum complexation suppresses citrate uptake by acid forest soil microorganisms

Organo-mineral interactions have been hypothesized to play a major role in biogeochemical cycling and pedogenesis in some forest soils. These processes are likely to be controlled to some extent by their persistence in soil, however, the factors regulating their bioavailability remain poorly understood. Therefore, we investigated the microbial utilization of ¹⁴C-labeled citrate in glass bead filled bioreactors containing a biofilm developed from an inoculum from an acid forest soil. The removal of Al-citrate in the bioreactors was negligible compared to the rate of citrate removal in the absence of Al. There was no evidence that in the short-term the microbial community adapted to increase the utilization of Al-citrate. In bioreactors filled with a Picea abies forest soil (Haplic Arenosol) the rates of citrate utilization were always slightly higher than that of Al-citrate. We conclude that complexation of citrate by metals such as Al may have a significant effect on their role in soil biogeochemical cycles.     

Consequences of nitrogen fertilization on soil methane consumption in a productive temperate deciduous forest

To investigate the consequences of long-term N additions on soil CH₄ dynamics, we measured in situ CH₄ uptake rates, soil profiles and kinetics parameters during the growing season in a temperate deciduous forest in northwestern Pennsylvania (Allegheny College Bousson Environmental Forest). Measurements were made in control and adjacent plots amended with 100 kg N ha^–1 year^–1 for 8 years. We found that the in situ consumption rates were 0.19±0.02 (mean±SE) for the control and 0.12±0.01 mg CH₄–C m^–2 h^–1 for the N treatment, indicating that consumption had been reduced by 35% after 8 years of N amendments. Despite the large difference in rates of consumption, there were no differences in the CH₄ concentration profiles between the control and N-amended plots. Laboratory incubations of CH₄ consumption throughout the soil column (organic horizon and mineral soil depths) showed that rates were greatest in the organic horizon of both control and N-amended soils, although consumption was reduced by 42% in the N-amended plot. However, the rate in the organic horizon was only about 50% the rate measured in organic horizons at other temperate forests. The apparent K_m [K_m(app)] value in the organic horizon of the control plot was fourfold less than the K_m(app) value in the organic horizon of another temperate forest, but similar to the K_m(app) values in adjacent plots amended with N for a decade. Unlike results for other temperate forests, K_m(app) values at Bousson generally did not decrease with soil depth. These results indicate that N cycling strongly controls the CH₄-consuming community, and suggest that alterations of the N cycle due to N deposition or addition may alter rates and the location of CH₄ consumption by soils, even in soils with high N content and cycling rates.     

The effect of earthworms and liming on soil microbial communities

The effect of liming and earthworms on the composition and function of soil microbial communities was investigated in an upland soil from the UK in order to understand interactions between the biotic and abiotic components of soil systems. A factorial experiment was established using soils from the Sourhope Farm, near Kelso, with lime or no lime added, with or without earthworms added and a combined treatment of both lime and earthworm additions. The soils were incubated and destructively sampled after 180 days. Measurements of soil microbial biomass, dehydrogenase activity, phenotypic structure (by phospholipid fatty acid analysis (PLFA) and responses to four carbon substrates (d-glucose, l-arginine, α-ketoglutaric acid, α-cyclodextrin) were determined. Statistically significant results were limited to the litter layers, with no significant observations in either the H or Ah horizons. There were significant decreases in the soil microbial biomass and microbial activity in the litter layers caused by the addition of earthworms; liming reduced microbial biomass only. The addition of earthworms caused a significant difference in the PLFA principle component analysis (PCA) profile, as did liming. For the PLFA PCA profile, earthworm plus lime treatment was indistinguishable from the liming result. Addition of earthworms significantly suppressed the response to glucose; this effect was removed by liming. This indicates that liming may significantly alter the ecological interactions between earthworms and the microbial community.     

Co-amelioration of red soil acidity and fertility with pig manure rather than liming

Lime (calcium oxide), animal manure and crop straw soil treatments have been shown to ameliorate soil acidity, yet their effectiveness at concurrently enhancing soil fertility status and improving crop yields is less well understood. In this study, an acidic nutrient deficient red soil (Ferralic Cambisol) received these treatments at various dosage rates (% of DW soil) in pot experiments with maize plants. Lime was applied at four dosage rates (0.05%, 0.10%, 0.15% and 0.20%), pig manure at three rates (0.50%, 1.00% and 1.50%), maize straw or milk vetch at two rates (0.50% and 1.00%) and combinations of lime (0.10% or 0.15%) with maize straw (0.50%) and/or pig manure (0.50%). Soils treated with and without chemical fertilizers were also included as controls. Measurements of soil pH, exchangeable acidity, plant available nutrients and maize shoot biomass were recorded. Maize shoot biomass increased by 4.7–7.6 times under pig manure treatments, 1.1–1.6 times under milk vetch, 0.4–1.5 times under lime and 1.1–6.2 times under combination treatments, compared with the control. Soil pH increased by 0.5–0.9 units under lime, by 0.2–0.4 units under pig manure and by 0.7 pH units under the combination treatment relative to the control. Variance partitioning analysis showed that on an individual basis, soil acidity amelioration (pH, exchangeable H⁺ and Al³⁺) or nutrient input (C, N, P, K, Ca, Mg, Zn) explained only 4.3% and 5.6% of improved maize growth, respectively. Whereas, their interaction explained 85.9% of the variation. We also report that the over-application of pig manure could lead to P saturation and negative impacts on aquatic systems in the wider environment. Therefore, we recommend a combination of lime, pig manure and straw provides an optimal solution for addressing soil acidity and limiting P saturation in acid soils.     

Effects of liming on survival and reproduction of two potentially invasive earthworm species in a northern forest Podzol

During the last several decades, colonization of soil by exotic earthworms and their effects on soil properties and biodiversity have been reported in forests of North America. In some northern hardwood stands, acid soils or harsh climate may have prevented earthworm colonization. However, climatic change and the increasing use of liming to restore the vigor of declining sugar maple (Acer saccharum Marsh.) stands, situated on base-poor soils in USA and Canada, could make many of these sites more suitable for earthworm colonization. We tested survival and reproduction of two exotic earthworm species (Lumbricus terrestris and Amynthas hawayanus) in unlimed and limed soils at the northern limit of the northern hardwood forest distribution in Canada. Improving soil parameters of base-poor, acidic soils by liming positively influenced activity, survivability and reproductive output of L. terrestris in this northern hardwood forest. In contrast, the high mortality and low vigor of L. terrestris observed in the unlimed plots show that soils in this area with a pH of 4.3 are not favorable to this species. Our results suggest that A. hawayanus was very active prior to winter at both soil pHs, but was not able to complete its life cycle during one year at this latitude. Both earthworm species significantly reduced organic C and total N, and increased the C/N ratio of the forest floor. Given that forest liming activities are increasing in proximity to human activities, there is high probability that some earthworm species, such as L. terrestris, will invade limed northern hardwood forests in the next decades, with possible consequences for soil organic matter turnover, nutrient cycling and forest biodiversity and dynamics.     

Enchytraeid and nematode numbers in urban,polluted Scots pine (Pinus sylvestris) stands in relation to other soil biological parameters

Summary We examined the number of enchytraeids and nematodes in the mor humus layer of polluted Scots pine (Pinus sylvestris L.) stands, located on a sulphur gradient from 1.2 to 2.8 mg g^-1 in mor humus and up to a distance of 40 km from the centre of Oulu, an industrialized city in northern Finland, in autumn 1989 and spring 1990. The number of enchytraeids, dominated by one species, Cognettia sphagnetorum, showed a clear positive correlation with the soil respiration rate and the diversity and production of mycorrhizal fungi, and all these were negatively related with S and N concentrations in the soil, as measured in 1987 and 1988. This negative correlation may have been caused by an alteration in food supply of enchytraeids, owing to changes in litter quality and the amount and species composition of fungi and mycorrhizae. Nematode numbers showed a positive correlation with the activity of dehydrogenase enzymes mineral N, and soil pH. The feeding characteristics of nematodes as a group need further study. The numbers of both enchytraeids and nematodes were higher in the autumn than in the spring and in the case of nematodes this variation was related to soil moisture.The work was carried out in the Department of Botany, University of Oulu, Linnanmaa, SF-90570 Oulu, Finland, and in Forestry Canada, Petawawa National Forestry Institute, Chalk River, Ontario, K0J 1J0, Canada     

Microfungi in coniferous forest soils treated with lime or wood ash

Summary Microfungal species composition was studied in coniferous forest soils which had been treated with lime or wood ash. The pH increased by about 2.5 units at the highest rate of application. Fungi were isolated 4–5 years after the treatments using a soil washing technique. At one site, Öringe, clear differences in species composition due to liming were found. Penicillium spinulosum, Oidiodendron cf. truncatum, Mortierella spp., and two sterile taxa decreased in abundance in limed areas, while Geomyces pannorum, Penicillium cf. brevicompactum, Trichoderma polysporum, and Trichosporiella sporotrichioides increased in isolation frequency. At another site, Torrmyra, the effect of liming was less pronounced, although the pH changes due to the treatments were larger compared to the Öringe site. However, T. polysporum increased, while a sterile taxon decreased in abundance in lime- and wood ash-treated plots. The changes in microfungal species composition after liming were similar to those found earlier in urea-treated soils, and opposite to those found in artifically acidified or ammonium nitrate-fertilized soils.     

Nitrogen mineralization in relation to site history and soil properties for a range of Australian forest soils

Rates of N mineralization were measured in 27 forest soils encompassing a wide range of forest types and management treatments in south-east Australia. Undisturbed soil columns were incubated at 20°C for 68 days at near field-capacity water content, and N mineralization was measured in 5-cm depth increments to 30 cm. The soils represented three primary profile forms: gradational, uniform and duplex. They were sampled beneath mature native Eucalyptus sp. forest and from plantations of Pinus radiata of varying age (<1 to 37 years). Several sites had been fertilized, irrigated, or intercropped with lupins. The soils ranged greatly in total soil N concentrations, C:N ratios, total P, and sand, silt, and clay contents. Net N mineralization for individual soil profiles (0–30 cm depth) varied from 2.0 to 66.6 kg ha^-1 over 68 days, with soils from individual depths mineralizing from <0 (immobilization) to 19.3 kg ha^-1 per 5 cm soil depth. Only 0.1–3.1% of the total N present at 0–30 cm in depth was mineralized during the incubation, and both the amount and the percentage of total N mineralized decreased with increasing soil depth. N fertilization, addition of slash residues, or intercropping with lupins in the years prior to sampling increased N mineralization. Several years of irrigation of a sandy soil reduced levels of total N and C, and lowered rates of N mineralization. Considuring all soil depths, the simple linear correlations between soil parameters (C, N, P, C:N, C:P, N:P, coarse sand, fine sand, silt, clay) and N mineralization rates were generally low (r<0.53), but these improved for total N (r=0.82) and organic C (r=0.79) when the soils were grouped into primary profile forms. Prediction of field N-mineralization rates was complicated by the poor correlations between soil properties and N mineralization, and temporal changes in the pools of labile organic-N substrates in the field.