Nitrogen cycling in an Antarctic ecosystem. 1. Biological nitrogen fixation in the vicinity of Syowa Station

As part of the studies of the nitrogen flows in the Antarctic terrestrial ecosystems, nitrogen-fixing activities of moss communities, algae and lichens, collected in various ice-free areas near Syowa Station, East Antarctica, were measured by the acetylene reduction method. Moss communities which grew on the sand at dry habitats had dense cover of cyanobacteria and showed high nitrogen-fixing activities, while those at wet habitats near streams showed weak or no activity. Folious colonies of Nostoc sp. Showed significant activities. Some colonies of Chlorophyceae Prasiola crispa had weak activities which were probably due to associating cyanobacteria. No activity was detected for lichen species tested. The results suggest that nitrogen fixation by cyanobacteria, especially those epiphytic on mosses, plays an important role in the nitrogen budgets of terrestrial ecosystems developed in dry ice-free areas near Syowa Station

Relationships between vegetation types and soil properties along a topographical gradient on the northern coast of the Brgger Peninsula, Svalbard

Vegetation patterns in the high Arctic vary not only with proglacial chronosequence but also with a topographical gradient on older deglaciated areas which are covered by mature vegetation. A preliminary survey of local scale vegetation patterns along a topographical gradient with special reference to soil properties was conducted on the northern coast of the Brgger Peninsula, Svalbard in the high Arctic. Three community types of vascular plants were distinguished by common dominants: Cardamine type, Salix type and Oxyria/Luzula type. Each community type was comprised of different habitat types. The Cardamine type was restricted to near the bottom of depressions, where there was high soil water content. The Oxyria/Luzula type was characterized by habitats belonging to upper slopes to ridges, having high gravel content soils. On the other hand, the habitat preference of the Salix type, which had higher vegetation cover and biomass of vascular plants compared to the other two types, was not clear. The core habitat of fertile/undisturbed area, as described by the centrifugal community organization model, might be dominated by Salix polaris in this area. The other species had a refugium from interspecific competition in their preferred peripheral habitats such as exposed ridge or wetland

The methane flux along topographical gradients on a glacier foreland in the High Arctic, Ny-Alesund, Svalbard

In order to examine the relationship between the methane (CH_4) flux and soil factors and vegetation in High Arctic tundra, we investigated the CH_4 flux along topographical gradients on a glacier foreland in Ny-Alesund, Svalbard (79°N, 12°E). The CH4 flux rates varied widely among sites even within the same vegetation type, ranging from positive (emission) to negative (absorption) values. High CH_4 emission rates were detected on ridges and in sites with a low soil water content, but there was no significant relationship between CH_4 flux rates and soil factors including soil moisture, pH, soil carbon and nitrogen content. Mean values of CH_4 emission and CH_4 absorption were 0.30±0.33 mg m^(-2) h^(-1) (n=12) and 0.11±0.06 mg m^(-2) h^(-1) (n=11), respectively. These findings suggest that the study area is a small source of CH_4 with a mean flux of 0.11 mg CH_4 m^(-2) h^(-1) (0.083 mg C m^(-2) h^(-1)). It was concluded that carbon flux derived from CH_4 accounts for an extremely small proportion of the total carbon flux from soil in this area

Characterization of soil microflora on a successional glacier foreland in the high Arctic on Ellesmere Island, Nunavut, Canada using phospholipid fatty acid analysis

We investigated soil microbial biomass and community structure along a primary successional gradient after deglaciation in the high Arctic, at Ellesmere Island, Nunavut, Canada(80°50\u27N, 82°45\u27W). Soil samples were collected from five glacial moraines(M1 to M5) with different developmental periods. Time since the recession of glaciers at M1, M3, and M5 was estimated to be 300, 9000, and over 17000 years, respectively. Soil samples from five points in each moraine were subjected to phospholipid fatty acid(PLFA) analysis. Total PLFA content(an index of microbial biomass) in M1 was significantly lower than those in older moraines(M2-M5), whereas the content remained at an almost constant level from M2 to M5. Significant differences in PLFA composition(an index of microbial community structure) were also observed between M1 and older moraines(M2-M5); the proportion of straight chain saturated fatty acids in M1 was higher than those in older moraines(M2-M5), whereas those of branched fatty acids and unsaturated fatty acids in M1 were lower than those in older moraines(M2-M5). These results suggest that changes of microflora occurred in the early phase of succession after deglaciation and became stable thereafter. Microbial biomass had a positive correlation with soil carbon and nitrogen contents over the successional chronosequence, suggesting that development of soil microflora was affected in part by organic matter accumulation

Successional changes in mycorrhizal type in the pioneer plant communities of a subalpine volcanic desert on Mt. Fuji, Japan

Isolated island-like plant communities dominated by the perennial herb Polygonum cuspidatum are typical pioneer vegetation in the subalpine volcanic deserts of Japan. To study the relationship between mycorrhizal associations and plant community development, we conducted a survey of the mycorrhizal status of plants in subalpine island communities in a volcanic desert on Mt. Fuji. Roots of 45 native species, belonging to 23 families, were collected from island communities at 3 different successional stages: (I) pioneer communities dominated by P. cuspidatum, (II) mixed communities of herbs and grass, and (III) mixed communities of herbs and shrubs. Arbuscular mycorrhiza (AM) was the predominant mycorrhizal type in the early stages of community successions (I and II). P. cuspidatum, which had previously been reported as a non-mycorrhizal species, formed AM at the study site. In the later stage (III), 5 mycorrhizal types, AM, ecto-, ericoid, arbutoid and orchid mycorrhizal, were observed. Seven woody species had two types of mycorrhizas (AM and ectomycorrhiza). High spore densities of AM fungi were observed in the soil of the island communities, whereas few spores were observed in bare ground without vegetation cover. The average colonization levels of the AM fungi were within a wide range of 0.1 to 72%, independent of successional progress. These data show that marked increases in mycorrhizal types occur during the succession of island communities, although AM is the predominant mycorrhizal type throughout the successional process

Causes of long-term changes in organic pollution of a river system with increasing population : a case study in the Kurosegawa River, Higashi-Hiroshima, Hiroshima

The Kurosegawa River, a polluted small river, flows through Higashi-Hiroshima, Hiroshima, where the population has increased steadily within the last decade. In order to clarify the impact of urbanization on the quality of the river water, changes in the state of organic pollution were studied in relation to population, construction of sewers and septic tanks in a recent 13-year period (1989-2001). Improvement in water quality (as indicated by BOD) was observed in the central area of the city, possibly as a result of the co11struction of sewers and septic tanks. In contrast, the BOD tended to increase in the lower reaches of the river. The pollutant flow analysis indicated that inflow of pollutant from a sewage treatment plant contributed to a significant proportion of the load. A simulation suggested that, with increasing population and sewage water, the BOD in the lower reaches of the river would be higher in the future because of the increase in the load from the plant. Based on the pollutant flow analysis, some solutions for reducing organic pollution are suggested.本研究の一部は学園都市づくり交流会議の地域課題研究事業の補助を受けて行われたものである

Decomposition and ergosterol content of the moss Hylocomium splendens litter under various climatic conditions

We examined the differences in the decomposition rate and fungal biomass in the litter of Hylocomium splendens among forests under different climatic conditions. The samples were collected from one boreal forest in Canada, three subalpine forests on Mt. Fuji and one cool temperate forest on Mt. Tsurugi, Shikoku in Japan. The decomposition rate in the cool temperate forest was much faster than those in the boreal and subalpine forests. Ergosterol, which is a component of fungal cell membranes, was used as an indicator of fungal biomass. Ergosterol was detected not only from brown moss litter but also from green shoots of the moss. In spite of the faster decomposition rate, ergosterol content of the moss litter of the cool temperate forest was about one half of those of the boreal and subalpine forests. The results suggest that the relationship between fungal biomass and decomposition rate differs significantly among forest types

Periphyton contribution to nitrogen dynamics in the discharge from a wastewater treatment plant

To evaluate the importance of periphyton to nitrogen dynamics in the discharge from wastewater treatment plants (WWTPs), we examined changes in total and inorganic nitrogen content downstream from a WWTP on the Kurose River in Hiroshima Prefecture, Japan. At 0.7 km downstream of the WWTP (point A), NH4+-N was the dominant form of inorganic nitrogen, but concentrations decreased rapidly to 5 km downstream (point B). In contrast, no significant change in the [NO2– + NO3–]-N concentration was observed between the two points. Total nitrogen (TN) load decreased significantly between the two points, suggesting that sorption and/or denitrification occurred in the river channel. Potential rates of nitrogen sorption and transformation by periphyton were determined in a laboratory experiment in which changes in the nitrogen content of river water were examined in an acrylic chamber with periphyton. Nitrification and nitrogen removal occurred mainly in the periphyton. The contributions of periphyton activity to TN and NH4+-N decrease in the field, as estimated from the results of the laboratory experiments, were 6%–18% and 23%–72%, respectively. These results suggest that periphyton plays an important role in decreasing NH4+-N concentration in the discharge from wastewater treatment plants

The impact of sika deer on a secondary forest and resident life in a mountainous area of the Chugoku District: Present status and residents’ awareness

中国地方の中山間地域を対象に，野外調査と地域住民に対するアンケート調査を行い，二次林と住民生活に対するシカ被害の現状とそれを引き起こした要因について考察した。東広島市福富町を調査対象地域とし，ヒノキの大径木と広葉樹が混生する二次林で植生調査を行った。調査区内の14種180本の樹木のうち，3.3%に角研ぎ跡，7.2％に食痕が認められ, 角研ぎに関してはヒノキ，摂食に関してはリョウブに有意な嗜好性が認められた。林床の植被率は低く，不嗜好性植物のアセビが優占していた。シカ被害に関するアンケートでは，「農業被害」が最も多く，この10 ～ 20年で目撃や被害が増加しているという回答が大半を占めた。自由記述では，以前は山の手入れを行っていたが，近年は手が入らなくなったというコメントが多かった。山に入らなくなった理由としては，生活様式の変化のほか，マツ枯れによってマツタケがとれなくなったことをあげる回答者が多かった。以上から，森林利用の停止によってシカの住処となる放置林が増加したが，林内に餌植物が少ないため，人家近くにシカが出現し被害をもたらしていると推測された。To investigate the impact of sika deer (Cervus nippon) on the forest ecosystem and resident life in a mountainous area of the Chugoku District, we conducted a vegetation survey and an awareness questionnaire survey. The study area was located in Fukutomi-Cho, Higashi-Hiroshima, Hiroshima Prefecture. We set a study plot in a secondary forest composed mainly of Chamaecyparis obtusa and broadleaf trees and recorded the damage by sika deer (herbivory and fraying) on each tree within the plot. There were 180 individual trees belonging to 14 species in the study plot, about 3.3% of which had fraying scars and 7.2% had feeding scars. The analysis indicated that sika deer had a significant preference for C. obtusa as fraying trees and Clethra barbinervis as food. Plant coverage of the forest floor was small and dominated by Pieris japonica, which is known to be unpalatable to deer. The awareness questionnaire survey revealed that the most common damage by sika deer was crop damage. The survey also indicated that the residents felt that sightings of and damage by sika deer had increased in the last 10–20 years. The residents noted that they had managed their forests for various purposes but stopped the management partly due to lifestyle changes and prevalence of pine wilt disease, which caused a significant decline in matsutake mushrooms. The results suggest that the increase of unmanaged forests provided sika deer with their habitat, and that the deer moved from the overgrazed forests to human habitation in search of food

Temporal and spatial fluctuations of populations of the freshwater snail Kawanina (Semisulcospira libertina) in streams: A survey using the “Kawanina trap”

カワニナを個体サイズや底質に関わらず採取できるトラップを作成し，それを用いて広島県東広島市を流れる二つの小河川を対象に，カワニナ個体群の時空間的変動に及ぼす環境要因について検討を行った。半自然河川の角脇川にトラップを仕掛け，5月～ 11月の経時変化を調べたところ，採取された個体数は期間を通じ地点により大きく異なっていた。この差は，水温や流速，BOD，pH では説明できず，河床材料との関係も明瞭ではなかったが，礫質の地点では個体数変動が少なく，殻径3mm未満の稚貝が多く捕獲された。コンクリート三面護岸化された半尾川では，角脇川に比べ非常に少数のカワニナしか捕獲されず，稚貝も1匹しか捕獲されなかったため，ほとんど繁殖が行われていないと考えられた。カワニナの生息に適した環境を評価するためには，個体サイズを考慮した調査を行うことが重要であり，本調査で用いたようなトラップは有効な手段となりうると思われる。This study aimed to elucidate the environmental factors that determine spatiotemporal fluctuations of populations of the freshwater snail Kawanina (Semisulcospira libertina) in two streams in Higashi-Hiroshima City based on a field survey using a trap designed for sampling regardless of the individual snail size or sediment. The changes from May to November in the semi-natural stream Kadowakigawa were investigated, and the number of individual snails captured by traps varied greatly depending on the site throughout the period. Differences in the numbers of captured snails could not be explained by differences in water temperature, water flow, BOD, pH, or riverbed materials between sites. However, the number of snails tended to be stable, and small individuals (< 3 mm) were frequently captured in the site with a stony riverbed. In the Hannogawa, a concrete-lined stream, only a very small number of Kawanina were captured by the trap compared to the Kadowakigawa, and only one young snail was captured by the trap during the investigation period, so the snail reproduction in this stream was considered to be unsuccessful. Quantitative studies considering the size structure of the population are important in assessing the suitability of a stream for the habitat of the snail. The “Kawanina trap” can be a useful tool for such research