EMAP-Wetlands: A sampling design with global application

The U.S. Environmental Protection Agency (EPA) initiated the Environmental Monitoring and Assessment Program (EMAP) in 1988. The wetland component (EMAP-Wetlands) is designed to provide quantitative assessments of the current status and long-term trends in the ecological condition of wetland resources. EMAP-Wetlands will develop a wetland monitoring network and will identify and evaluate indicators that describe and quantify wetland condition. The EMAP-Wetlands network will represent a probability sample of the total wetland resource. The EMAP sample is based on a triangular grid of approximately 12,600 sample points in the conterminous U.S. The triangular grid adequately samples wetland resources that are common and uniformly distributed in a region, such as the prairie pothole wetlands of the Midwest. However, the design is flexible and allows the base grid density to be increased to adequately sample wetland resources, such as the coastal wetlands of the Gulf of Mexico, which are distributed linearly along the coast. The Gulf sample network required a 49-fold increase in base grid density. EMAP-Wetlands aggregates the 56 U.S. Fish and Wildlife Service's (FWS) National Wetland Inventory (NWI) categories (Cowardin et al. 1979) into 12 functionally similar groups (Leibowitz et al. 1991). Both the EMAP sample design and aggregated wetland classes are suitable for global inventory and assessment of wetlands.The research described in this report has been funded by the U.S. Environmental Protection Agency. This document has been prepared at the EPA Environmental Research Laboratory in Corvallis, OR, through contract No. 68-C8-0006 to Man Tech Environmental Technology, Inc. This paper has been subjected to the Agency's peer and administrative review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Reproductive and developmental responses in the self-fertilizing fish,Rivulus marmoratus,induced by the plasticizer,di-n-butylphthalate

Synopsis Specialized life-history attributes of the cyprinodontiform fish, Rivulus marmoratus, allow continuous life cycle testing to reveal effects of chemicals or environmental stresses upon fertilization, fecundity, egg viability, embryonic development, sex ratios, frequency of growth or skeletal anomalies, as well as other biological markers. This study reports responses in fecundity, viability of embryos, and skeletal anomalies during and after exposure of parental fish to the plasticizer, di-n-butylphthalate (DBP). Skeletal anomalies among offspring were classified as mild, moderate, or severe compared with non-deformed normal offspring. The frequency of skeletal anomalies increased from 4% (all categories combined) in controls, to 10% and 19% of the offspring from adults exposed to 1 and 2 mg I^-1 DBP, respectively. DBP treatment was conducted over a 21 week interval, followed by a 9 week post-treatment observation interval. During post-treatment, frequency of skeletal anomalies decreased to less than 5% in all groups. Contributions No. 610, Environmental Research Laboratory, Gulf Breeze, Florida 32561 U.S.A. The information in this document has been funded wholly by the U.S. Environmental Protection Agency, and has been subjected to the Agency's peer and administrative review. Mention of commercial products or trade names does not constitute the Agency's endorsement or recommendation for use.     

Species-specific effects of live roots and shoot litter on soil decomposer abundances do not forecast plant litter-nitrogen uptake

Plant species produce litter of varying quality and differ in the quality and quantity of compounds they release from live roots, which both can induce different decomposer growth in the soil. To test whether differences in decomposer growth can forecast the amount of N species acquire from plant litter, as suggested by theory, we grew individuals of three grassland plants—Holcus lanatus, Plantago lanceolata and Lotus corniculatus—in soils into which ¹⁵N-labelled litter of either Holcus, Plantago or Lotus was added. We measured the effects of live roots and litter of each species on soil microbes and their protozoan and nematode feeders, and to link decomposer growth and plant nutrient uptake, we measured the amount of N taken up by plants from the added litter. We hypothesised that those species that induce the highest growth of microbes, and especially that of microbial feeders, will also take up the highest amount of N from the litter. We found, however, that although numbers of bacterial-feeding Protozoa and nematodes were on average lower after addition of Holcus than Plantago or Lotus litter, N uptake was higher from Holcus litter. Further, although the effects on Protozoa and bacterial- and fungal-feeding nematodes did not differ between the live plants, litter-N uptake differed, with Holcus being the most efficient compared to Plantago and Lotus. Hence, although microbes and their feeders unquestionably control N mineralization in the soil, and their growth differs among plant species, these differences cannot predict differences in litter-N uptake among plant species. A likely reason is that for nutrient uptake, other species-specific plant traits, such as litter chemistry, root proliferation ability and competitiveness for soil N, override in significance the species-specific ability of plants to induce decomposer growth.     

Acetylene reduction in conifer logs during early stages of decomposition

Acetylene reduction was examined periodically for as long as 68 months in the outer and inner bark, sapwood, and heartwood of decaying logs of western hemlock [Tsuga heterophylla (Raf.) Sarg.] western redcedar (Thuja plicata D. Don), Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], and Pacific silver fir (Abies amabilis Dougl. ex Forbes) in the western Oregon Cascade Mountains. Tissues from freshly cut logs from sound trees were unable to reduce acetylene. However, after 18 months of decomposition, acetylene reduction was found in all log tissues except heartwood. Over the 68-month study period, no significant relationship between reduction rate and tissue moisture was found. Acetylene reduction rates differed significantly among tissues, log species, and time of exposure to decomposers. Although acetylene reduction generally showed a steady increase with time, tissues of some species showed a more complex, nonlinear pattern of change. Although the amount of nitrogen fixed is low compared to the total present in decaying logs, it might be an important source of readily available nitrogen for the microbiota responsible for decomposition.Paper 2587, Forest Research Laboratory, Oregon State University, Corvallis.Paper 2587, Forest Research Laboratory, Oregon State University, Corvallis.     

Nitrification and nitrate reductase activity along a secondary successional gradient

The control of nitrification was studied in a secondary successional gradient on Nantucket Island, MA. It was hypothesized that 1) variability in nitrification along the gradient is controlled by litter primary and secondary chemistry, and 2) differences in nitrate availability along the gradient are reflected in potential nitrate assimilation rates in plant tissue. Nitrification varied significantly (p<0.05) by successional stage in all study sites, generally increasing with successional age. The ratio of nitrification to total N mineralization did not vary significantly between successional stages, suggesting substrate limitation of nitrification. Litter terpenoid resin concentration was a significant predictor (p<0.05) of nitrification rate, but soil %C, %N, and water content also contributed significantly to a stepwise regression model predicting nitrification. Nitrate reductase activity (NRA), an index of potential nitrate assimilation, was measured in an assay species (Schizachyrium scoparium). Although there was no significant correlation with nitrification, NRA was significantly (p<0.05) negatively correlated with soil ammonium concentration along the successional gradient at one site, suggesting that plants preferentially utilized ammonium in this system.     

Potential Nitrification as an Indicator of Preferential Uptake of Ammonium or Nitrate by Plants in an Oak Woodland Understorey

The preferences of some woodland understorey species for ammoniumand nitrate were investigated by measuring the potential nitrification(conversion of ammonium to nitrate) in the rhizosphere comparedwith the bulk soil. Less acid-tolerant species, which usuallyprefer nitrate or a mixture of ammonium and nitrate in hydroponicculture, should have a higher potential nitrification in therhizosphere compared to the bulk soil due to a low uptake ofammonium (since ammonium is relatively immobile). Acid-tolerantspecies should have a high uptake of ammonium and thereby loweror equal potential nitrification in the rhizosphere comparedto the bulk soil. The hypothesis was tested in a field investigationof five understorey herb species, Deschampsia flexuosa, Convallariamajalis, Poa nemoralis, Geum urbanum andAegopodium podagrariaperformed in oak forests in southern Sweden. Overall, the twoless acid-tolerant species, Geum urbanum and Aegopodium podagraria,had high potential nitrification in the rhizosphere comparedto the bulk soil (indicating a relatively low uptake of ammonium),whilst the acid tolerant species, Deschampsia flexuosa andConvallariamajalis , had approximately equal potential nitrification inthe rhizosphere compared to the bulk soil (indicating a relativelyhigh uptake of ammonium). In the case of Poa nemoralis, a specieswhich grows in both acid and less acid soils, we found the potentialnitrification in the rhizosphere and in the bulk soil to besimilar at low inorganic nitrogen concentrations, but the difference(rhizosphere > bulk) increased when nitrification in thebulk soil was enhanced (i.e. when the nitrogen availabilityincreased). The potential nitrification in the bulk soil variedbetween 0 and 16 nmol g^-1h^-1and was positively correlated withpH. When species occurred at the same site, the potential nitrificationin the bulk soil tended to be lower for the acid tolerant species.Despite a large variation in potential nitrification, the methodoffers a possibility of measuring the preference of plants forammonium/nitrate in a soil system, under natural conditions.Copyright 2000 Annals of Botany Company Ammonium uptake, nitrate uptake, nitrogen preference, potential nitrification, rhizosphere, Deschampsia flexuosa, Convallaria majalis, Poa nemoralis, Geum urbanum, Aegopodium podagraria     

Spatial pattern of soil nitrogen availability and its relationship to stand structure in a coniferous-broadleaved mixed forest with a dense dwarf bamboo understory in northern Japan

Natural disturbances create spatial patterns of the ecosystem processes and functions in natural forests. However, how dynamics and the spatial structure of forests relate to soil nitrogen dynamics is not well understood. We examined the spatial relationship between the distributions of canopy and understory species, and soil nitrogen dynamics in a natural coniferous-broadleaved mixed forest with a dense understory of Sasa dwarf bamboo in northern Japan. The O horizon was thick where coniferous litter predominated, and it was thin where broadleaved litter predominated. The soil water content was low in areas with a thick O horizon and a high abundance of coniferous trees. The soil nitrate content was low where the soil water content was low, and the soil nitrate content increased linearly with increasing net nitrification potential. These results suggest that the soil nitrate content under the coniferous canopy was lower because of the low nitrification potential of soil microbes in soils with low water contents. The soil nitrate content and nitrification potential were higher in the canopy gap than under the canopy. Our results suggest that forest structure, specifically the thickness of the forest floor, significantly affects the spatial pattern of the soil water content, thereby creating a spatial pattern of soil nitrogen availability at a relatively small scale with flat topography. The higher nitrification potential under the canopy gap could pose a long-term risk of nitrate leaching because of the suppression of the natural regeneration of canopy species by dense Sasa dwarf bamboo in this forest ecosystem.     

Experimental removal and addition of leaf litter inputs reduces nitrate production and loss in a lowland tropical forest

Environmental perturbations such as changes in land use, climate, and atmospheric carbon dioxide concentrations may alter organic matter inputs to surface soils. While the carbon (C) cycle response to such perturbations has received considerable attention, potential responses of the soil nitrogen (N) cycle to changing organic matter inputs have been less well characterized. Changing litter inputs to surface to soils may alter the soil N cycle directly, by controlling N substrate availability, or indirectly, via interactions with soil C biogeochemistry. We investigated soil N-cycling responses to a leaf litter manipulation in a lowland tropical forest using isotopic and molecular techniques. Both removing and doubling leaf litter inputs decreased the size of the soil nitrate pool, gross nitrification rates, and the relative abundance of ammonia-oxidizing microorganisms. Gross nitrification rates were correlated with the relative abundance of ammonia-oxidizing archaea, and shifts in the N-cycling microbial community composition correlated with concurrent changes in edaphic properties, notably pH and C:N ratios. These results highlight the importance of understanding coupled biogeochemical cycles in global change scenarios and suggest that environmental perturbations that alter organic matter inputs in tropical forests could reduce inorganic N losses to surface waters and the atmosphere by limiting nitrate production.     

香樟凋落叶分解对辣椒及土壤氮营养的限制作用

香樟(Cinnamomum camphora)凋落叶分解能够明显干扰受体植物的生长、生殖、光合生理和活性氧代谢。该研究继续采用盆栽试验,探讨了不同量[0(对照)、25、50和100g]的香樟凋落叶添加到土壤(10kg/盆)中对受体植物辣椒(Capsicum annuum)及其土壤氮营养状况的影响,外源氮(尿素)输入对凋落叶分解的交互作用,以及凋落叶分解效应的产生是否因为其较高的C/N比而导致微生物争氮。结果显示:(1)各剂量(25~100g/盆)凋落叶处理下,辣椒幼苗硝态氮、可溶性蛋白和全氮含量均在至少2个月内大幅显著降低。(2)土壤硝态氮与辣椒硝态氮、全氮间均具有极显著的协同下降趋势;土壤微生物生物量氮则在总体上高于对照,而土壤全氮和铵态氮的响应较小。(3)施氮不仅使辣椒各氮组分和土壤硝态氮含量整体提升,还使凋落叶分解在这些指标上的抑制作用显著减弱。(4)香樟凋落叶的初始C/N为125.61±4.89,其在土壤中分解48~137d后的C/N始终远高于Hodge假说指出的可导致微生物争氮的临界值,但经过分解120d和135d的凋落叶添加到土壤中并不抑制辣椒的生长。研究认为,香樟凋落叶分解初期可能释放了不利于土壤硝化过程的物质,造成土壤硝态氮匮乏,以致受体植物的氮素吸收和积累减少,而凋落叶较高的C/N比及土壤微生物争氮并非主导因素。     

THE INFLUENCE AND COMPARISON OF INDIVIDUAL FOREST TREES ON SOIL PROPERTIES AND POSSIBLE INHIBITION OF NITRIFICATION DUE TO INTACT VEGETATION

Soil properties were found to vary with increasing distance from tree trunks of individuals of the same species, and different species were found to vary in their effects on soil properties. The differences in pH and mineral concentration at different distances from the trunk were often statistically significant even under the same tree. When all species are considered, iron had the least variability at different distances from the trunks of all minerals investigated, followed by potassium. Nitrate nitrogen had the greatest overall variability at different distances from the trunks. Ammonium nitrogen in the soil was always considerably higher than nitrate nitrogen when compared at each distance from the trunk under each species. Low amounts of nitrate nitrogen could not have been due to its uptake by the intact vegetation, because the soil samples were taken before the active growth period. It seems possible that the variable tree litter under different species plays an important role in controlling the soil pH, nitrification, and mineralization. Thus, it appears that in a climax community different dominating species, by developing variable physio-ecological niches, can determine the variable undergrowth vegetation under them.     

Original Articles: Differential Influence of Plant Species on Soil Nitrogen Transformations Within Moist Meadow Alpine Tundra

Plant species can influence nitrogen (N) cycling indirectly through the feedbacks of litter quality and quantity on soil N transformation rates. The goal of this research was to focus on small-scale (within-community) variation in soil N cycling associated with two community dominants of the moist meadow alpine tundra. Within this community, the small-scale patchiness of the two most abundant species (Acomastylis rossii and Deschampsia caespitosa) provides natural variation in species cover within a relatively similar microclimate, thus enabling estimation of the effects of plant species on soil N transformation rates. Monthly rates of soil N transformations were dependent on small-scale variation in both soil microclimate and species cover. The relative importance of species cover compared with soil microclimate increased for months 2 and 3 of the 3-month growing season. Growing-season net N mineralization rates were over ten times greater and nitrification rates were four times greater in Deschampsia patches than in Acomastylis patches. Variability in litter quality [carbon:nitrogen (C:N) and phenolic:N], litter quantity (aboveground and fine-root production), and soil quality (C:N) was associated with three principal components. Variability between the species in litter quality and fine-root production explained 31% of the variation in net N mineralization rates and 36% of net nitrification rates. Site variability across the landscape in aboveground production and soil C:N explained 33% of the variation in net N mineralization rates and 21% of net nitrification rates. Within the moist meadow community, the high spatial variability in soil N transformation rates was associated with differences in the dominant species' litter quality and fine-root production. Deschampsia-dominated patches consistently had greater soil N transformation rates than did Acomastylis-dominated patches across the landscape, despite site variability in soil moisture, soil C:N, and aboveground production. Plant species appear to be an important control of soil N transformation in the alpine tundra, and consequently may influence plant community structure and ecosystem function.     

Effects of understory removal, N fertilization, and litter layer removal on soil N cycling in a 13-year-old white spruce plantation infested with Canada bluejoint grass

Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter, partially decomposed litter and humus on the soil surface) and mineral soil (0–10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer 2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg⁻¹ day⁻¹ in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been limited by NH₄ ⁺ availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated litter layer on soil N cycling and the implications for forest management.     

Responses of Nitrification and Ammonia-Oxidizing Bacteria to Reciprocal Transfers of Soil between Adjacent Coniferous Forest and Meadow Vegetation in the Cascade Mountains of Oregon

Despite the critical position of nitrification in N cycling in coniferous forest soils of western North America, little information exists on the composition of ammonia-oxidizing bacteria (AOB) in these soils, or their response to treatments that promote or reduce nitrification. To this end, an experiment was conducted in which a set of soil cores was reciprocally transplanted between adjacent forest (low nitrification potential) and meadow (high nitrification potential) environments, at two high-elevation (~1500 m) sites in the H.J. Andrews Experimental Forest located in the Cascade Mountains of Oregon. Half of the cores were placed in screened PVC pipe (closed) to prevent new root colonization, large litter debris inputs, and animal disturbance; the other cores were placed in open mesh bags. A duplicate set of open and closed soil cores was not transferred between sites and was incubated in place. Over the 2-year experiment, net nitrification increased in both open and closed cores transferred from forest to meadow, and to a lesser extent in cores remaining in the forest. In three of four forest soil treatments, net nitrification increases were accompanied by increases in nitrification potential rates (NPR) and 10- to 100-fold increases in AOB populations. In open cores remaining in the forests, however, increases in net nitrification were not accompanied by significant increases in either NPR or AOB populations. Although some meadow soil treatments reduced both net nitrification and nitrification potential rates, significant changes were not detected in most probable number (MPN)-based estimates of AOB population densities. Terminal restriction fragment profiles (T-RFs) of a PCR-amplified 491-bp fragment of the ammonia monooxygenase subunit A gene (amoA) changed significantly in response to some soil treatments, and treatment effects differed among locations and between years. A T-RF previously shown to be a specific biomarker of Nitrosospira cluster 4 (Alu390) was widespread and dominant in the majority of soil samples. Despite some treatments causing substantial increases in AOB population densities and nitrification potential rates, nitrosomonads remained undetectable, and the nitrosospirad AOB community composition did not change radically following treatment.     

Litter decomposition and nitrogen mineralization of soils in subtropical plantation forests of southern China,with special attention to comparisons between legumes and non-legumes

Litter decomposition and nitrogen mineralization were investigated in subtropical plantation forests in southern China. The CO₂ –C release from incubated litter and the forest floor of Acacia mangium, Acacia auriculaeformis, Eucalyptus citriodora, Pinus elliotii and Schima superba stands were used to estimate relative rates of litter decomposition. Decomposition was not positively correlated with litter nitrogen. E. citridora litter decomposed most rapidly and A. mangium litter most slowly, both with and without the addition of exotic nitrogen. Aerobic incubation and intact soil core incubation at 30 °C over a period of 30 days were used to assess nitrogen mineralization of six forest soils. Although there were differences in results obtained using the two methods, patterns between legume and non-legume species were the same regardless of method. All soils had pH values below 4.5, but this did not prevent nitrification. The dominant form of mineral nitrogen was nitrate for legume species and ammonium for non-legume species. The nitrogen mineralization potential was highest for soils in which legumes were growing.     

Environmental conditions in high mountain lakes containing toxic benthic cyanobacteria

In glacial lakes on an alpine pasture in Switzerland, benthic cyanobacteria produced microcystin, a cyclic hepatotoxic heptapeptide. The cyanobacteria formed dense mats on sediments and submerged stones. The mats consisted mainly of Oscillatoria limosa, Phormidium konstantinosum (= Oscillatoria tenuis) and Tychonema granulatum (= Oscillatoria granulata). In order to characterize the ecological conditions of these cyanobacteria, nutrient concentrations were determined, and an automatic data acquisition station was installed in one of the lakes. It continuously recorded air temperature, global irradiance, precipitation, atmospheric pressure, wind speed and direction; as well as temperature, pH, oxygen content and conductivity of the lake water. The nutrient situation in the lakes was mainly influenced by the erosion of the gneissic catchment by glacial meltwater and by precipitation. In the glacial lakes, the concentrations of calcium, iron, magnesium, sodium and sulphate increased throughout the summer season. Conductivity values of 4–110 μS cm^-1 represent generally low nutrient concentrations. Nevertheless, iron concentrations of up to 20 μM occurred. Biomass, expressed as protein concentration, as well as the microcystin content of the cyanobacterial mats varied within one season and between different years (1994 and 1995). In one cyanobacterial mat community, biomass and microcystin concentrations were highest at the same time, in an other one the microcystin content was maximal three weeks after the highest biomass concentration was reached. Our observations suggest that biomass and toxin production in the mats were strongly influenced by mechanical stress, temporary desiccation and high irradiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biological inhibition of soil nitrification by forest tree species affects Nitrobacter populations

Some temperate tree species are associated with very low soil nitrification rates, with important implications for forest N dynamics, presumably due to their potential for biological nitrification inhibition (BNI). However, evidence for BNI in forest ecosystems is scarce so far and the nitrifier groups controlled by BNI-tree species have not been identified. Here, we evaluated how some tree species can control soil nitrification by providing direct evidence of BNI and identifying the nitrifier group(s) affected. First, by comparing 28 year-old monocultures of several tree species, we showed that nitrification rates correlated strongly with the abundance of the nitrite oxidizers Nitrobacter (50- to 1000-fold changes between tree monocultures) and only weakly with the abundance of ammonia oxidizing archaea (AOA). Second, using reciprocal transplantation of soil cores between low and high nitrification stands, we demonstrated that nitrification changed 16 months after transplantation and was correlated with changes in the abundance of Nitrobacter, not AOA. Third, extracts of litter or soil collected from the low nitrification stands of Picea abies and Abies nordmanniana inhibited the growth of Nitrobacter hamburgensis X14. Our results provide for the first time direct evidence of BNI by tree species directly affecting the abundance of Nitrobacter.     

The effect of an intermittent water-table gradient on soil and xylem nitrate in cotton

Summary Cotton (Gossypium hirsutum cv Deltapine 61) was grown in a sloping plot of soil in the field to examine the effect of a gradient of water-table depth on soil nitrate availability and plant uptake during two periods of the growing season. Before the water-table was imposed NO₃ was less concentrated at the lower end of the sloping plot. This was attributed to slow denitrification at microsites within the soil at the lower end which was wetter than further up the plot. At flooding NO₃ disappeared only slowly due to a carbon substrate limitation to denitrification in the soil. This loss occurred primarily in areas where the water-table was high and oxygen concentration in the soil solution was low. Plant NO₃ uptake, assessed by measuring the concentration in the xylem, parallelled the distribution of NO₃ in the soil solution. Under high water-tables xylem NO₃ levels fell but it was not possible to say whether this was due to impaired root function or to the reduced concentration of NO₃ observed in the soil solution. At intermediate water-table depths where soil NO₃ availability remained high xylem NO₃ concentration fell relative to the well drained control plants, suggesting that flooding had damaged the root system.Manufactured by Merck. Mention of commerical names does not imply endorsement by either CSIRO or USDA.     

Soil nitrogen turnover in proximal and distal stem areas of European beech trees

In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in the top 15 cm soil in proximal (defined as 1 m² around beech stems) and distal stem areas. Laboratory incubations and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification, and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal and distal areas. In the in situ incubations the average ratio of nitrification/ammonification was 0.85 in proximal and 0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m^-2 90 day^-1 in both areas. Mineralized nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification. Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the high nitrogen input by stemflow rather than to soil nitrogen turnover. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrification and nitrogen accumulation in the early stages of primary succession on Mt. Fuji

The relationship between nitrification potential and nitrogen accumulation was studied in an early successional sere on Mt. Fuji. Soil organic nitrogen accumulated with the invasion ofPolygonum cuspidatum and successively withMiscanthus oligostachyus and other species. Laboratory incubation experiments showed a higher nitrification potential at theM. oligostachyus state. The numbers of nitrifying bacteria increased with the progress of succession. No significant difference in nitrate reductase activity was found between pioneer and succeeding species. The soil solution at theM. oligostachyus stage contained a lower level of nitrate than rainwater, while that of the bare ground and theP. cuspidatum stage contained a higher nitrate level than rainwater. It was concluded that the high nitrate levels in the soil solution of the bare ground and theP. cuspidatum stage were due to lower nitrate-absorbing activity, leading to loss of nitrogen with precipitation, while the lower nitrate levels at theM. oligostachyus stage when higher nitrification activity occurred were due to higher nitrate-absorbing activity, preventing net loss of nitrogen from the ecosystem.     

Diversity of arbuscular mycorrhizal fungi along a sand dune stabilization gradient: A case study at Praia da Joaquina, Ilha de Santa Catarina, South Brazil

Species diversity of arbuscular mycorrhizal fungi (AMF) was assessed along a dune stabilization gradient (embryonic dune, foredune and fixed dune) at Praia da Joaquina, Ilha de Santa Catarina. The dunes were chosen as a case study to assess whether diversity and mycorrhizal inoculum potential (MIP) increase along the gradient. Ten soil samples were collected from each stage and pooled, and then six 100-g soil sub-samples were taken to identify and enumerate spores. Twelve AMF species were detected, and all three families in Glomales were represented. Gigasporaceae species dominated the embryonic dune, while Glomaceae species dominated the fixed dune. Total spore numbers and richness increased as the dunes became more stabilized. However, indices of Margalef, Simpson and Shannon reached maximal values at different stages, suggesting that species abundance was different among stages. In both embryonic and fixed dunes, species abundance data fit the broken stick model, while in the foredune the log series model best described the data. The MIP followed spore numbers and increased along the gradient, suggesting that spores are important in initiating root colonization in this system. Relationships between edaphic factors and functional roles of Glomales families as determinants of AMF distribution are discussed. This document was subjected to peer and administrative reviews of the U.S. EPA at the National Health and Environmental Effects Research Laboratory, Western Ecology Division, and was approved for publication. Mention of trade names or commercial products in this paper does not constitute endorsement or recommendation of use.