Distribution of spore-positive and spore-negative nodules ofAlnus incana ssp.rugosa in Maine,USA

The distribution of spore-positive (sp+) and spore-negative (sp−) root nodules ofAlnus incana ssp.rugosa (DuRoi) Clausen (speckled alder) was examined at 29 sites with a wide range of environmental conditions in Maine, USA. These included: pH 3.4 to 7.0, soil texture ranging from coarse gravel to clay to organic soils, elevation from 3 to 591 m and latitude 43 to 47°N. Habitat types included disturbed areas, streamsides, swamps and old fields. Sp (−) nodules were substantially more common, making up 76% of all nodules, whereas only 24% were sp (+). Sp (−) nodules often occurred in pure stands and predominated at disturbed sites with mineral soils at the surface and in old fields and swamps with pH>4.0 Sp (+) nodules were nearly always found in mixture with sp (−) nodules. They occurred primarily at streamside and lakeshore sites where they made up 40% of the nodules and at sites with pH<4.0 regardless of habitat type. It is suggested that sp (−) strains ofFrankia may be maintained at a site by saprophytic growth in soil and thus nodulate newly established hosts, whereas sp (+) strains may be maintained primarily by spore production within nodules and thus depend on extended presence of the host.     

Early colonization of red alder and Douglas fir by ectomycorrhizal fungi and Frankia in soils from the Oregon coast range

The potential for mycorrhizal formation and Frankia nodulation were studied in soils from six sites in the Pacific Northwest. The sites included young and old alder stands, a 1-year-old conifer clear-cut, a young conifer plantation, and rotation-aged and old-growth conifer stands. A bioassay procedure was used with both red alder and Douglas fir seedlings as hosts. After 6 weeks growth, seedlings of both hosts were harvested every 3 weeks for 21 weeks and numbers of nodules and ectomycorrhizal types estimated. Nodules formed on red alder and ectomycorrhizae formed on both alder and Douglas fir in soil from all sites. Nodulation potential was highest in soil from the alder stands and the conifer plantation. Seven morphologically distinct ectomycorrhizal types were recovered on Douglas fir and five on alder. Only Thelephora terrestris, a broad-host-range mycobiont, formed mycorrhizae on both hosts. New ectomycorrhizal types formed on both hosts throughout the bioassay. Ectomycorrhizal colonization of alder was greatest in the alder and clear-cut soils. Low ectomycorrhizal colonization on alder was found in soils from sites where conifers were actively growing. Ectomycorrhizal colonization of Douglas fir was highest in the young alder and conifer plantation soils and was low in the rotation-aged conifer soil. The highest diversity of ectomycorrhizal types was found on alder in the conifer clear-cut soil and on Douglas fir in the rotation-aged conifer soil. Effects of host specificity, nodulation and mycorrhiza-forming potential and nodule-mycorrhiza interactions on seedling establishment are discussed in relation to seral stage dynamics and attributes of pioneer ectomycorrhizal fungal species.     

Distribution of spore-positive and spore-negative nodules in stands ofAlnus glutinosa andAlnus incana in Finland

Summary The distribution of spore positive (Sp⁺) and spore negative (Sp⁻) nodules on the two native alder species (A. incana andA. glutinosa) in Finland was investigated. Nodules were collected throughout the country from different ecosystems (forests, swamps, lake- sea- and riversides, old pastures and fields as well as from alder plantations). OnA. incana Sp⁺ nodules predominated, whereas onA. glutinosa the vast majority of the nodules were of the Sp⁻ type. Sp⁺ nodules onA. glutinosa were found only at sites where the two alder species grew close together. This distribution pattern indicates an association of nodule type with alder species, the reasons for which are discussed. Indications of saprophytic growth in the Sp⁻ strain were also found.     

Distribution ofFrankia in soils from forest and afforestation sites in northern Sweden

Summary The presence in soil ofFrankia, capable of forming nitrogen-fixing root nodules onAlnus incana (L.) Moench, was investigated. Intact soil cores from forested as well as disturbed sites were sampled and both alder-rich and alder-free sites were included in the study. Surface-sterilized alder seeds were sown in the soil cores which were kept in sterile culture tubes in a growth chamber. Root nodules with nitrogenase activity developed in soil cores from all sites studied. Thus, infective and effectiveFrankia was present in all of the soils sampled, even from sites free from actinorhizal plants and irrespective of pH and nitrogen content of the soils.     

Assessing the adaptability of the actinorhizal symbiosis in the face of environmental change

Human activity, and in particular industrial activity, has altered natural environments. Here we present an experimental approach adapted to study the actinorhizal symbiosis in alder trees and shrubs submitted to abiotic stress. We measured the impact of exogenous nitrogen on the establishment of the alder symbiosis with Frankia sp., and its primary function; nitrogen fixation. Results showed our version of the growth pouch method was functional, and corroborated the gradual inhibition of symbiosis in the presence of increasing exogenous nitrogen concentrations. In mountain alder (Alnus viridis ssp. crispa) there was a gradual and suppressive effect of nitrogen on the relative number or root nodules, while in black alder (Alnus glutinosa) results suggested a threshold effect at 45 ppm N. Shoot to root biomass ratios were increased in the presence of the microsymbiont, and this effect was generally maintained even in the presence of heavy metals (As, Se or V). Alders and the actinorhizal symbiosis were not heavily affected by the presence of heavy metals, confirming potential applications in soil rehabilitation, however the distribution of metals in plant tissues sometimes changed when high levels of metals were present. A. glutinosa plants exposed to high levels of As significantly increased the allocation of As to roots (≈90%), while those exposed to high levels of Se rose their aerial tissue Se allocation to roughly 86%. A. glutinosa plants exposed to high V levels did not change behavior: V was in all cases preferentially accumulated in underground tissues (≥90%). Our results detail the use of a high-throughput approach to study the plasticity of the actinorhizal symbiosis in the presence of fluctuating nitrogen and metal conditions. These methods are transposable to numerous actinorhizal studies in both fundamental and applied research.     

Symbiont nitrogenase,alder growth,and soil nitrate response to phosphorus addition in alder (Alnus incana ssp. rugosa) wetlands of the Adirondack Mountains,New York State,USA

Speckled alder (Alnus incana ssp. rugosa) is a characteristic species of scrub-shrub 1-type wetlands, the second most common wetland type in major watersheds of the Adirondack Mountains in New York State. Speckled alder is an actinorhizal nitrogen fixer that relies heavily on N₂ over soil N and fixes substantial amounts of nitrogen in wetlands, resulting in little vegetation processing of anthropogenic N between alder-shrub wetlands and streams. Phosphorus (P) is an element that limits nitrogen fixation and plant growth. However, studies testing this hypothesis in the field, especially for actinorhizal plants, are very few. The objectives of this study were to evaluate the potential limitation of N fixation and growth in speckled alder by P, and to determine interactions between P fertilization and nitrate levels in riparian alder stands in a region that receives elevated N in atmospheric deposition. P fertilization significantly increased specific nitrogenase activity during the seasonal peak in early August. Nitrate concentrations were greater in reference plots compared to treatment plots, and phosphate concentrations were lower in reference plots compared to treatment plots over a period of 6 weeks in the growing season. There was a significant twig and foliar biomass response to P fertilization in the second year after fertilization, but no significant change in individual biomass or relative numbers of different sized nodules. Response of nitrogen fixation to P appears limited to a brief but significant increase in specific activity of nitrogenase late in the growing season, but P stimulated growth of above ground tissues 1 year following fertilizer application, and decreased resin-captured nitrate beneath riparian speckled alder. These results suggest that growth of alder and growth or activity of soil microbes, rather than nitrogen fixation, is P limited in riparian wetlands dominated by speckled alder, and that P controls nitrate leaching in these near-stream systems.     

兰坪铅锌尾矿区豆科根瘤菌遗传多样性ARDRA分析

通过16S rDNA扩增产物限制性片段长度多态性分析(ARDRA),对兰坪铅锌尾矿区豆科植物根瘤菌的遗传多样性进行了研究。采用限制性内切酶Hae Ⅲ、Hind Ⅲ、Hinf Ⅰ和Taq Ⅰ对16S rDNA扩增产物进行了酶切分型,根据ARDRA酶切图谱的不同,进行树状聚类。结果表明:49株根瘤菌在40%的相似水平上按氮含量不同及铅锌含量的采集地不同分别聚为OTU1、OTU2和OTU33个群,说明根瘤菌的遗传多样性及分布与土壤中的氮含量和铅锌含量有关。代表菌株的16S rDNA测序结果分析表明,它们在系统发育树上属于Rhizobium sp.、Sinorhizobium sp.和Bradyrhizobium sp.3个系统发育分支,进一步说明兰坪铅锌尾矿区豆科植物根瘤菌多样性较丰富。     

Distribution of spore-positive and spore-negative nodules ofMyrica gale in Maine,USA

The distribution of spore-positive and spore-negative root nodules ofMyrica gale L. was investigated at 34 sites throughout Maine. the sites represented a wide range of environmental conditions, including soils from organic to sand, soil pH from 3.1 to 6.4, elevations from 3 to 529 m, and average number of frost-free days per year from 80 to 162. Habitats included peatlands, streamsides and lakeshores. Spore(−) nodules dominated with 61% of the nodules examined sp(−) and 39% sp(+). Two sites were 100% sp(+), 7 sites were 100% sp(−) and the remaining 25 sites had varying proportions of both types. Overall, sp(+) and mixed sites dominated in the southern interior and coastal regions, areas with lower elevations and longer growing seasons. Spore(−) sites were located primarily in northern and western Maine, areas with higher elevations and shorter growing seasons. In all habitats occurrence of spore(+) modules was positively correlated with the average number of frost-free days per year (r=0.57 for peatlands, r=0.71 for lakeshores and streamsides). In addition, at the 21 lakeshore and streamside sites occurrence of sp(+) nodules was also positively correlated with percent organic matter in the soil (r=0.56) and negatively correlated with pH (r=−0.60). Within mixed sites sp(+) and sp(−) nodules were distribated randomly and were often closely intermingled.     

Nodulation potential of soils from red alder stands covering a wide age range

Red alder (Alnus rubra Bong.) stands in the Pacific Northwest are the common first stage in succession following disturbance. These stands are highly productive and contribute a large amount of N to the soils as a result of their N₂-fixing symbiosis with Frankia. As these alder stands age, the soils not only increase in total N, but concentrations of NO^– ₃ increase and pH decreases as a result of nitrification. The objective of this study was to determine how the nodulation capacity of Frankia varies as red alder stands age and if differences in nodulation capacity are related to changes in soil properties. Nodulation capacity was determined by a red alder seedling bioassay for soils from red alder stands in the Oregon coast range covering a wide range of ages. Six chronosequences were sampled, each containing a young, an intermediate, and an older alder stand. Soil total N, total C, NO^– ₃, NH⁺ ₄, and pH were measured on the same soil samples. These factors as well as alder stand characteristics were compared with nodulation capacity in an attempt to identify soil characteristics typical in developing alder stands that most strongly affect nodulation capacity. Soil pH and NO^– ₃ concentration were highly correlated with nodulation capacity and with each other. Cluster analysis of the sites using these two variables identified two groups with distinctly different nodulation capacities. The cluster with the higher nodulation capacity was lower in NO^– ₃ and higher in pH than the other cluster, which included the majority of sites. There was substantial overlap in the age ranges for the two clusters and there was no significant correlation between age and nodulation capacity. Thus nodulation capacity appears to be most closely related to soil properties than to stand age.     

Dynamics of leaf minerals,bdleaf area,and biomass from hardwoods intensively grown on a peat bog

Summary Water willow and grey alder were grown on a raised sphagnum bog in central Sweden. The stands were intensively treated by daily irrigation and fertilization during the growing period in order to improve site fertility. After a 2-year establishment period high production rates were achieved in willow stands, 0.8 kg stem dry weight m^–2 year^–1 on current plus one (C+1) year old shoots. In these stands the canopy was closed with a leaf area index (LAI) that peaked at approximately 7. The canopy in the alder stand did not close during the initial 3 years of growth and the measured production rate was relatively low, at approximately 0.4 kg dry weight m^–2 year ^–1 in the last year. The leaf nitrogen content was 3%–4% of dry weight during the summer and the other studied mineral elements were in almost optimal proportion to nitrogen. This was considered to be an effect of the intensive fertilization regime. Above-ground production close to maximum yield was attained in the prevailing conditions of soil, climate and biomass partitioning.     

Distribution of roots and root nodules and biomass allocation in young intensively managed grey alder stands on a peat bog

Development of below-ground biomass and biomass allocation were studied in two different stands of young grey alder stands growing on a peat bog. Both stands were given the same fertilization and irrigation treatment. The roots were investigated from 1) open plastic tubes enclosing the complete root systems in 1982, and 2) root cores 1984–86. Coarse roots (diameter>1 mm) were mainly found close to the trunk of the trees while fine roots (≤1 mm) were more evenly distributed in the stands. Root nodules were intermediate in distribution. The root systems were shallow, with more than 90% of the biomass in the uppermost 9–10 cm of the soil, probably because of low oxygen availability in the peat soil. The biomass allocation to the above-ground parts increased during the study period.     

N2 fixing alder (Alnus viridis spp. fruticosa) effects on soil properties across a secondary successional chronosequence in interior Alaska

Green alder (Alnus viridis ssp. fruticosa) is a dominant understory shrub during secondary successional development of upland forests throughout interior Alaska, where it contributes substantially to the nitrogen (N) economy through atmospheric N₂ fixation. Across a replicated 200+ year old vegetation chronosequence, we tested the hypotheses that green alder has strong effects on soil chemical properties, and that ecosystem-level N inputs via N₂ fixation decrease with secondary successional stand development. Across early-, mid-, and late-successional stands, alder created islands of elevated soil N and carbon (C), depleted soil phosphorus (P), and more acidic soils. These effects translated to the stand-level in response to alder stem density. Although neither N₂ fixation nor nodule biomass differed among stand types, increases in alder densities with successional time translated to increasing N inputs. Estimates of annual N inputs by A. viridis averaged across the upland chronosequence (6.6 ± 1.2 kg N ha^?1 year^?1) are substantially less than inputs during early succession by Alnus tenuifolia growing along Alaskan floodplains. However, late-succession upland forests, where densities of A. viridis are highest, may persist for centuries, depending on fire return interval. This pattern of prolonged N inputs to late successional forests contradicts established theory predicting declines in N₂-fixation rates and N₂-fixer abundance as stands age.     

An ineffective strain type of Frankia in the soil of natural stands of Alnus glutinosa (L.) Gaertner

An ineffective strain type of Frankia of unknown strain composition, coded AgI-WD1 was discovered in the soil of wet dune slacks where A. glutinosa was the dominant tree species. Strain type AgI-WD1 was recognized by the development of slow growing root nodules on A. glutinosa testplants inoculated with soil suspensions. Microscopical examination of these nodules showed extremely reduced development of vesicles, normal development of intracellular clusters of hyphae and absence of sporangia. The stability of characteristics of this strain type such as the expression of root nodule symbiosis and ineffectivity of symbiontic N-fixation was demonstrated through ‘subculture’ of ineffective root nodules in successive hydrocultures of A. glutinosa. The nodulation process also differed from normal effective root nodules by the occurrence of resistance to strain type AgI-WD1 among part of the half-siblings of A. glutinosa used in the nodulation tests. Strain type AgI-WD1 was detected in the soil of different dune slacks which are inundated for a large part of the year and in a nearby peatbog covered with alder. The contribution of this strain type to soil populations of Frankia was demonstrated by nodulation potentials that were up to 500 times higher than that of the concurrent effective strain type AgSp^-. The distribution of strain type AgI-WD1 appeared to be restricted to sites with water-logged soil conditions. Nodulation experiments pointed to potentials for competitive interactions between effective and ineffective strain thpes, especially to a density dependent reduction of nodule type AgI-WD1 by strain type AgSp^-. The impact of competitive interactions is also affected by host trees that are resistant to AgI-WD1. The occurrence of resistance in the study areas was suggested by resistance among seedlings of a local seedbatch (±70% of the half-siblings) and by the absence of ineffective root nodules at site VD7-1, despite a high nodulation potential of the soil population of strain type AgI-WD1.     

ASPECTS OF THE MYCORRHIZAL ECOLOGY OF PRAIRIE DROPSEED,SPOROBOLUS HETEROLEPIS (POACEAE)

Vesicular-arbuscular mycorrhizal (VAM) fungal colonization of prairie dropseed and rhizosphere spore abundance were sampled seasonally at two sites in Illinois. At Goose Lake Prairie (GLP), Gaussian ordination of 49 vegetation stands, using plant cover data for 40 species, assigned stands x-vector values and ordered them along a soil moisture-nutrient gradient. Prairie dropseed cover data plotted over ordered stands yielded a significant Gaussian curve across a relatively narrow gradient segment. In contrast, colonization and spore abundance had significant negative linear correlations with stand x-vector values that decreased from the drier, low-nutrient portion of the gradient to the wetter, high-nutrient sector. Variation in spore abundance suggested that no VAM fungal species responded to environmental gradient conditions in a manner similar to that of prairie dropseed. The differential responses of host and VAM mycobionts across the gradient suggest that their respective success may be partially independently determined or limited by different parameters. Also, the generally ubiquitous VAM fungal distributions suggest that the host may be more sensitive to gradient conditions than its mycobiont associates. Colonization and spore abundance at GLP were significantly negatively correlated with available Ca and Mg, and pH. Spore abundance was significantly positively correlated with available K. Neither colonization nor spore abundance were significantly correlated with available P, total N, or organic matter. Seasonally, patterns of VAM colonization and rhizosphere spore abundance varied, having significant positive correlations at GLP and Weston Cemetery Prairie (WCP) in some seasons but not others. In general, colonization levels were highest in fall 1983 for GLP and fall 1984 for WCP. For 1984, increasing colonization was observed from spring (WCP) or summer (GLP) to fall.     

In situ estimates of annual net nitrogen mineralization and nitrification in a subarctic watershed

Summary Annual estimates of surface soil nitrogen transformations were determined using an in situ method in four different subarctic vegetation types within a watershed in southwestern Alaska. The net nitrogen mineralization estimates were 22.5, 0.5, 4.7, and 2.7 kg-N ha^-1 yr^-1 for the alder, dry tundra, moist tundra, and white spruce sites, respectively. Only the soil from the alder site showed net nitrification (about 10 kg-N ha^-1 yr^-1). Annual inogranic nitrogen flux from the overlying organic layer to the mineral soil was almost seven times greater than net N production in the surface mineral soil in the alder site, indicating that the alder forest floor is potentially a substantial source for plant-available N. Rates of mobilization of N from the surface organic layers of the other sites were similar to net N production rates in surface mineral soils. In situ rates of N transformations showed a similar trend among sites as did laboratory estimates conducted in a previous study, suggesting a strong substrate control of N transformations in these soils.     

Defense characteristics of seral deciduous broad-leaved tree seedlings grown under differing levels of CO2 and nitrogen

Mixed broad-leaved forests are abundantly populated by several kinds of herbivore species in northern Japan. The life of herbivores depends strongly on the quality of food leaves. Leaf quality is changing with increasing atmospheric CO₂ and nitrogen deposition. Four seral species of deciduous broad-leaved tree seedlings (alder, birch, oak and maple) were raised in all four combinations of two levels of CO₂ and two levels of nutrient, to examine foliar defense traits. To evaluate the relative defense capacity of the four tree species, we used wild silkworms (Erisan; a generalist herbivore) as a bioassay material. Except with alder, the survival rate and longevity (ML₅₀) of the silkworms were least when they were fed with leaves of seedlings raised under high CO₂ and infertile soil conditions, and longest on a diet of leaves grown in ambient CO₂ and fertile soil, especially in birch and maple. The longevity of Erisan decreased in the order birch, oak, and maple. The longevity of Erisan fed with alder leaves was independent of CO₂ levels and was longer on alder seedlings grown in infertile soil conditions. Alder is an actinorhizal plant that can fix atmospheric nitrogen in root nodules formed by the actinomycetes Frankia sp. The activity of symbiotic microbes would have been enhanced by the greater amount of photosynthates received from the host plants at high CO₂, improving the food quality for the silkworms. It was concluded that in all but alder, leaf chemical traits, especially C/N ratio, affect the ML₅₀ of Erisan larvae.     

传统农业生态系统中桤木改良土壤效应研究综述

桤木(Alnus nepalensis)是一种重要的非豆科固氮植物,广泛分布于喜马拉雅山脉东部地区。在东南亚地区的传统农业生态系统中,多用桤木作为休耕树种,或将其与农作物间作。桤木根瘤固氮量随季节和年龄而变化,在桤木-小豆蔻(Elettaria cardamomum)系统中15年达到高峰(155 kg·hm^-2);桤木通过共生固氮对系统产生的氮增加量在纯桤木林中7年达到高峰(117 kg·hm^-2)。桤木与农作物间作可显著提高农作物的产量,桤木-小豆蔻立地上小豆蔻的经济产量是在森林-小豆蔻立地上的2.2倍。桤木休闲地的休闲效果明显好于自然休闲地,其地上部分生物量在休闲6年后是自然休闲地的4倍,N蓄积量是自然休闲地的3倍,P、K蓄积量是自然休闲地的2倍。桤木根系特征似乎最适合混农林系统,其细根生物量(FRB)集中于土壤剖面上层10 cm范围内,在此范围内,FRB在“树+农作物”间作条件下比在“只有树”条件下高5%;在两种立地条件下,60%以上的细根都分布于树干周围0.5 m内,大部分木质根(直径>0.5 mm)都分布于土壤上层0~10 cm处,长度都不超过1 m。桤木可加速系统的养分循环。桤木凋落物降解速率比非固氮植物快,并且与其它植物凋落物混合后的降解速率与自身凋落物降解速率一样快。在传统刀耕火种系统中,用桤木替代自然林休闲在3~6年内即可恢复土壤肥力,改善土壤理化性质,显著缩短休闲周期。该文综述了近30年来桤木在传统农业生态系统中改良土壤效应的研究成果,以提高人们对桤木的生态作用的重视程度,使人们更好地将桤木利用到农业生态系统中,达到发展山区农业和保护生态环境双赢的目的。     

Functional Diversity of Culturable Bacterial Communities in the Rhizosphere in Relation to Fine-root and Soil Parameters in Alder Stands on Forest, Abandoned Agricultural, and Oil-shale Mining Areas

Grey alder (Alnus incana) and black alder (Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil-shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil–root interface and in the bulk soil in relation to fine-root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community-level physiological profiles (CLPP) of culturable bacteria in soil–root interface and bulk soil samples. CLPP were summarized as AWCD (average well color development, OD 48 h⁻¹) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil–root interface. The soil–root interface/bulk soil ratio of AWCD was estimated. Substrate-induced respiration (SIR) and basal respiration (BAS) of bulk soil samples were measured and metabolic quotient (Q = BAS/SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g⁻¹ and from 0.12 to 0.51, respectively. Short-root morphological studies were carried out by WinRHIZO^TM Pro 2003b; mean specific root area (SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m² kg⁻¹, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil–root interface and bulk soil were found for the young alder stands on oil-shale mining spoil and on abandoned agricultural land. Soil–root interface/bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency (FOE) was negatively correlated with soil–root interface/bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short-root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder-species-related differences were revealed.     

桤柏混交林根系的研究

研究了桤柏混交林和柏木纯林的根系组成、根系形态特征和根量分布,并比较了这两种林型根系的生物量、生产力和氮元素在根库中的积累与分布规律。结果表明,不同物种、同一物种在不同林型中根系的重量、组成、形态和分布有较大差异。在桤柏混交林中,桤木根系分布线,侧根发达,细根相对比例少;柏木根系分布较深,在不同土层分布较均匀,吸收根和细根相对含量较高。与混交林相比,柏木纯林根系主要集中在０￣４０ｃｍ土层中,吸收根     

Changes in nitrogen and base cation concentrations in soil water due to the tree cutting in a wetland alder forest in the Kushiro Wetland, northern Japan

As part of the Kushiro Wetland Restoration Project, we evaluated the effect of the tree-cutting (February 2003) on soil water chemistry for 3 years in an alder (Alnus japonica) shrubland on the peat soil in the Kushiro Wetland, the largest wetland in Japan. The alder stand was divided into two types; low stature and high stature stands, mean heights being 1.5 and 2.6 m, respectively. The treatment plot with tree cutting and the reference plot measuring 25 m × 25 m each were established in both stands, and a soil incubation experiment was also conducted by trenching the root zone of wetland vegetation in the treatment plots in both stands in the summer of 2004. The tree cutting did not substantially increase the concentrations of ammonium ion (NH₄ ⁺) and nitrate ion (NO₃ ⁻) in the soil water, although a gradual and slight increase of NO₃ ⁻ concentration was found after the tree-cutting only in the high stature stand (<10 μmol/l). This increase in the NO₃ ⁻ concentration in the high stature stand was probably due to the rhizosphere oxidation of wetland herbaceous vegetation, and was accompanied by the increase of Ca²⁺ concentration. The soil incubation experiment showed no significant change of the nitrogen concentration, suggesting that inorganic nitrogen was immobilized and NO₃ ⁻ was denitrified intensively in this wetland peat soil. The results of this study suggested that this wetland ecosystem had a high potential to stabilize the soil water chemistry.