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In the past few decades, moso bamboo (Phyllostachys pubescens) forests in Japan have rapidly expanded, and moso bamboo is now invading nearby native forests. In this study, we assessed the effects of moso bamboo invasion on the soil microbial community and activity in warm temperate forests in western Japan. We sampled soil, measured soil microbial respiration, and used phospholipid fatty acid (PLFA) analysis to examine changes in microbial community composition. We found that the invasion of bamboo into the native secondary forest of Japan can cause changes to some soil properties. We also observed a significant difference in soil microbial community composition between the bamboo and native forests. The ratio of bacterial PLFA to fungal PLFA was significantly higher after bamboo invasion, while bacterial PLFA contents were significantly lower in the organic layer. Soil microbial respiration rates significantly decreased in the organic layer, and significantly increased in the mineral layer. Microbial respiration activity, as indicated by soil microbial respiration rates per total PLFA content, decreased in the organic layer but increased in the mineral layer after bamboo invasion. These results indicate that bamboo invasion significantly affects associated soil microbial communities and decomposition patterns of soil organic matter.

We conducted an open-top chamber experiment for 3 years to examine the effect of elevated CO2 and temperature on soil respiration in experimental stands of Quercus glauca, an evergreen tree species common in the warm temperate zone of Japan. Seedlings of Q. glauca were planted in open-top chambers and treated with factorial combinations of ambient and elevated (ambient × 1.4, ambient × 1.8) CO2 concentrations and ambient and elevated (+3°C) air temperatures. Elevated CO2 significantly increased the total soil respiration rate (P

Sphagnum palustre L. is one of the few Sphagnum species distributed in the warm-temperate zone. To elucidate the mechanisms that enable S. palustre to maintain its productivity under warm climatic conditions, we examined the temperature conditions and photosynthetic characteristics of this species in a lowland wetland in western Japan. Moss temperatures during the daytime were much lower than the air temperature, particularly during summer. The optimum temperature for the net photosynthetic rate was approximately 20°C, irrespective of the season, but summer and autumn samples maintained high rates at higher temperatures as well. The net photosynthetic rate at near light saturation was much higher during summer–autumn than during spring–winter. A model estimation in which net production was calculated from the photosynthetic characteristics and microclimatic data showed that both the low temperature of the moss colony and the seasonal shift in photosynthetic characteristics are among the mechanisms that enable this species to maintain its productivity under warm climatic conditions.

The polar willow (Salix polaris), predominant in the late successional stage in deglaciated areas of Ny-Alesund, Svalbard, is rarely found in the early stage, when purple saxifrage (Saxifraga oppositifolia) dominates. To elucidate the pattern and the mechanism of successional change from the Saxifraga stage to the Salix stage, we examined the distribution pattern, size structure and habitat conditions of a colonizing Salix population in the seral stage where Salix was invading Saxifraga-dominated sites. The present distribution pattern and aerial photographs taken in the past suggest that Salix colonization at this site commenced within the last 70 years. We found 115 Salix individuals (22 male, 13 female and 80 unknown) in a 30 m ¥ 30 m quadrat on the seral stage. Although the largest individual had a size of 2000 cm2 (length ¥ maximum width), the majority (84%) of individuals were smaller than 100 cm2. The seedling size distribution, as inferred from the leaf scar number, indicated that annual recruitment was slight. Of the individuals observed about 75% had colonized bare ground; only four individuals grew within Saxifraga colonies. No significant difference was found in soil characteristics (water content, and carbon and nitrogen concentrations) between the seral stage and the earlier stage prior to colonization by Salix. These results suggest that difficulties in seed production, germination and/or seedling establishment of Salix, rather than soil formation by preceding species (Saxifraga), limits the early-stage colonization by Salix.

The hypotheses that carbon and nitrogen availability limit microbial activity, and that the key factors limiting microbes vary along the successional gradient were tested in a High Arctic glacier foreland. We examined the responses of the respiration rate and the phospholipid fatty acid content to the addition of carbon and/or nitrogen. Soil samples were collected from the early stage and late stage of primary succession in the foreland of a glacier near Ny-Ålesund, Svalbard. The addition of both carbon (glucose) and nitrogen (ammonium nitrate) engendered an increase in the microbial respiration rate in the early stage of succession. In contrast, the addition of either carbon or nitrogen did not increase the microbial respiration rate. In the late stage of succession the addition of carbon alone, as well as the addition of both carbon and nitrogen, increased the microbial respiration rate. However, neither the addition of carbon nor the addition of nitrogen affected the total phospholipid fatty acid content (an index of microbial biomass) for any soil within 15 days of incubation at 10 ° C. An increase in the respiration rate was therefore attributed to changes in the physiological activities of the microbial community, such as enzymatic activity. Our study suggests that microbial respiration was limited by the low availability of both carbon and nitrogen in the early stage of succession. Thereafter, nitrogen limitation is mitigated.

The solfatara field is a unique ecosystem characterized by harsh conditions such as acidic soils. We examined the respiration rate and phospholipid fatty acid (PLFA) content of solfatara soils and their responses to carbon and nitrogen addition to determine whether soil microbial respiration and biomass in a solfatara field are limited by substrate availability. Soil samples were collected from locations along a transect across a solfatara field in Oita Prefecture, Japan. The soil in the central part of the solfatara field was highly acidic (pH 2.4) and contained low amounts of carbon and nitrogen. Low basal respiration rates were detected in these soil samples. Measurements of substrate-induced respiration (SIR) and PLFA contents suggested that it was partly attributable to low microbial biomass. Addition of a carbon source (glucose) to the solfatara soil engendered a marked increase in the microbial respiration rate, whereas the nitrogen source (ammonium nitrate) application had no marked effect. Addition of both carbon and nitrogen caused a nearly eightfold increase in the microbial respiration rate and a threefold increase in the total PLFA contents. These results suggest that some acidophilic and/or acid-tolerant microorganisms exist in solfatara soil, but that their respiration and biomass are limited by low substrate availability.

A pot culture experiment was conducted to examine the effects of arbuscular mycorrhizal (AM) fungi and soil developmental stages on the growth and nutrient absorption of pioneer plants growing in the early stage of primary succession on Mt. Fuji. Four herbaceous plants, Polygonum cuspidatum (Polygonaceae), Miscanthus oligostachyus (Gramineae), Aster ageratoides var. ovatus (Compositae), and Hedysarum vicioides (Leguminosae), were grown from seed in soils collected from two different successional stages, bare ground and an herbaceous plant community. Spores of indigenous AM fungi collected from the herbaceous plant community were used as inoculum. The initial colonizer P. cuspidatum showed very low levels of AM colonization (

We conducted field and culture experiments to study the effects of arbuscular mycorrhizal (AM) fungi on the establishment of the alien plant Oenothera laciniata (Onagraceae) in a coastal sand dune in Japan. We examined the distribution of plants, AM fungal colonization of their roots, and fungal spore density in the soil of a coastal sand dune at Keinomatsubara, Hyogo Prefecture, western Japan. Of the nine dominant plant species at the study site, six species, including O. laciniata, were heavily colonized by AM fungi. The spore density tended to decrease from inland toward the shoreline, but there were no significant relationships between the level of AM fungal colonization and spore density. Seedlings of O. laciniata inoculated with AM fungi, as well as uninoculated seedlings, were transplanted to the study site. No significant difference in survival rates was detected between the two groups of seedlings. We also examined the effects of AM infection and nutrient (N and P) application on plant g...

As part of a study on soil carbon flow in forest ecosystems, the biomass of fine roots (≪2.0 mm in diameter) and root-associated fungi, including ectomycorrhizal fungi, were estimated in the summer season in 1998 at a Pinus densiflora (Japanese red pine) stand in western Japan. Fine roots of pine were classified into three categories: class I roots (0.5–2.0 mm in diameter), long class II roots (long roots with diameter ≪0.5 mm; IIL), and short class II roots (short roots with diameter ≪0.5 mm; IIS). Total biomass of fine roots (I + IIL + IIS) at this stand was estimated to be 91.0 g m−2, about 23% of which was class II roots (IIL + IIS). Ergosterol, which is a component of fungal membranes, was analyzed to estimate the biomass of root-associated fungi in roots. In the upper soil layers (from the surface to 13.4 cm in depth), ergosterol contents in the class I, IIL and IIS roots were in the ranges 43.1–82.2, 126.1–196.3 and 271.2–321.0 µg g−1 root DW, respectively. The ergosterol content was converted to fungal biomass using the median (minimum–maximum) value of ergosterol concentration reported for ectomycorrhizal fungi. Root-associated fungal biomass in this stand was estimated to be 2.0 (0.5–9.6) g m−2. The data suggest the biomass of ectomycorrhizal fungi in the P. densiflora stand is small compared with that in other forest ecosystems.

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R trench) and in a control plot (R control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO2 m−2 h−1) to August (840–1150 mg CO2 m−2 h−1) and then decreased during autumn (200–650 mg CO2 m−2 h−1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R r) and heterotrophic respiration rate (R h) were estimated from R control, R trench, and R D. We estimated that the contribution of R r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between Rh and soil temperature, whereas R r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R r and R h.

Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200–400 µmol·m–2·s–1, which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m–2. A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Key words: arctic semi-desert, climate change, net ecosystem production (NEP), net primary production (NPP), Salix polaris, photosynthesis.

The bambooPhyllostachys bambusoides has been widely planted on riverbanks in Japan to protect against erosion. Recently, unmanagedP. bambusoides stands with high culm density are spreading along the banks of rivers. In order to study the impact of the bamboo stands on riparian ecosystems, the relations between bamboo stand structure, light conditions and plant communities under the canopy were examined. The study sites were set in bamboo stands with various culm densities in the middle of the Yahagi River in Toyota, Aichi Prefecture. There was a close relationship between canopy coverage and relative photon flux density (RPFD) in the bamboo stands. RPFD showed a highly negative relationship with total culm density, whereas no significant relation was observed between the basal area of bamboo and RPFD. The total number of plant species in the bamboo stands increased with decreasing culm density. Only a small number of tree saplings were observed in the stands with the highest culm densities, while several species of forest floor herbs were found in the stands with lower culm densities. A number of invasive and annual plants colonized the thinned stand. We suggest that moderate thinning and clearing of dead culms are needed to maintain biological diversity in the bamboo stands on riverbanks.

Saxifraga oppositifolia is morphologically variable, and many scientists recognize two morphs; the Prostrate form (P-form) and Cushion form (C-form). In order to investigate the adaptation of the d...

As a part of the study on soil carbon flow in a deglaciated area in Ny-Alesund, Svalbard (79°N), we estimated the contribution of the belowground respiration of vascular plants to total soil respiration in August 1996. Four study sites were set up along a primary successional series, ranging from newly deglaciated moraine to older moraine with well-developed vegetation cover. Respiratory activity of the belowground parts (roots + belowground stems) of three dominant species, Salix polaris, Saxifraga oppositifolia and Luzula confusa, was determined under laboratory conditions. The respiratory activity and the Q10 value of the respiration were higher in S. polaris than in the other two species. Total soil respiration rates measured in the field varied widely. The areas with dense vegetation cover tended to show high respiration rates. Belowground respiration of vascular plants was estimated based on the respiratory activity and biomass of the belowground parts at each study site. The contribution to the belowground respiration to total soil respiration was negligible in the early stages of succession. On the other hand, the respiration of the belowground parts contributed to a significant proportion (?29%) of the total soil respiration in the latter stages of succession.

In order to clarify the role of micro-organisms in the carbon cycle of the boreal forest ecosystem, the vertical distribution of soil carbon, soil microbial biomass and respiratory activity was studied in a black spruce forest near Candle Lake in Saskatchewan, Canada. The total amount of carbon contained in moss and soil layers (to the depth of 50 cm beneath the mineral soil surface) was 7.2 kg m−2, about 47% of which was in the L and FH horizons of the soil. Soil microbial biomass per dry weight of soil was largest in the L horizon, while the biomass per ground area was largest in the FH horizon. Soil respiration rate, measured using a portable infrared gas analyzer, was highest in the FH horizon, exceeding 50% of the total soil respiration. Low but significant CO2 emission was detected even in deeper soil horizon (E horizon). We also examined the respiration rate of cut roots and the effect of root excision on respiration. The contribution of root respiration to total soil respiration, calculated from root biomass and respiration rate of cut roots, was about 54%. The amount of carbon evolved through microbial respiration during the snow-free season (June–October) was estimated as 221 g C m−2. Micro-organisms in the L horizon showed high respiratory activity as compared with those in deeper soil horizons.

The annual legumeKummerowia striata often predominates in river floodplains forming a large population, but it is rare in gravelly areas adjacent to it. In order to clarify the factors limiting the distribution ofK. striata, its distribution pattern, germination and survival of seeds sown artificially were studied in the floodplain of the Ohta River. There was a positive correlation between the cover value ofK. striata and the percentage of fine particles (

In order to evaluate the importance of growth of mosses in controlling evaporative water loss, the evaporation rates of some subalpine moss species of various growth forms were compared with each other. The growth forms of the xerophytic species examined were large cushion and compact mat, while those of the mesophytic species in the coniferous forest floor were smooth mat, weft and tall turf. The evaporation rate per moss dry weight (Ew) was much smaller in the xerophytic species than in the mesophytic species. However, the evaporation rate per basal area of moss colony (Ea) was not necessarily smaller in the xerophytic species. The relation between Ea and dry weight per basal area of the colony (Wa) had a close correlation with the growth form. It was concluded that the difference in the evaporation rate per weight between the exerophytic species and the mesophytic species was largely due to the difference in Wa, and that the growth forms of the xerophytic species were suitable for increasing Wa without increasing surface roughness.

To study the effects of river flooding on vesicular-arbuscular mycorrhizae (VAM), VAM infection of plants was examined at a fluvial bar in the middle reach of the Ohta River in Hiroshima Prefecture, Japan. Among 23 plant species belonging to 11 families collected in spring and early summer 1993, 17 species showed VAM with arbuscules. The relation between VAM infection and plants' growth stages was investigated in the annual legume Kummerowia striata. VAM infection was observed early in seedlings that had few leaves. Prolonged flooding in the 1993 summer season severely destroyed the vegetation in the study site. However, most of the plants survived the flooding, and those which germinated afterward showed VAM infection. Spores of VAM fungi were found not only in the soils of areas with good vegetation cover but also in the soils of gravelly areas without vegetation. However, spore density and infection level tended to be lower in severely eroded sites.

Nitrogen-fixing (acetylene-reducing) activity of intact saplings ofAlnus maximowiczii was measured under natural conditions in the subalpine zone of Mt Fuji. The nitrogen-fixing activity was detected from the middle of June when expansion of leaves had just begun to the end of October when the shedding of leaves was almost completed. Diurnal changes in the activity were almost parallel with those of ground temperature. The measured nitrogen-fixing activity was related to ground temperature and total leaf area. Using this relation, annual nitrogen fixation was estimated from the data of ground temperature and leaf area measured in the field. The amount of annual nitrogen fixation was almost the same as that of nitrogen used for annual growth. It was concluded that nitrogen fixation by nodules made a considerable contribution to the nitrogen economy in the saplings ofA. maximowiczii.

Studies on terrestrial ecosystems in the high Arctic region have focused on the response of these ecosystems to global environmental change and their carbon sequestration capacity in relation to ecosystem function. We report here our study of the photosynthetic characteristics and biomass distribution of the dominant vascular plant species, Salix polaris, Dryas octopetala and Saxifraga oppositifolia, in the high Arctic tundra ecosystem at Ny-Alesund, Svalbard (78.5 degrees N, 11.5 degrees E). We also estimated net primary production (NPP) along both the successional gradient created by the proglacial chronosequence and the topographical gradient. The light-saturated photosynthesis rate (A (max)) differed among the species, with approximately 124.1 nmol CO(2) g(-1)leaf s(-1) for Sal. polaris, 57.8 for D. octopetala and 24.4 for Sax. oppositifolia, and was highly correlated with the leaf nitrogen (N) content for all three species. The photosynthetic N use efficiency was the highest in Sal. polaris and lowest in Sax. oppositifolia. Distributions of Sal. polaris and D. octopetala were restricted to the area where soil nutrient availability was high, while Sax. oppositifolia was able to establish at the front of a glacier, where nutrient availability is low, but tended to be dominated by other vascular plants in high nutrient areas. The NPP reflected the photosynthetic capacity and biomass distribution in that it increased with the successional status; the contribution of Sal. polaris reached as high as 12-fold that of Sax. oppositifolia.

The distributions of carbon, nitrogen and phosphorus in a moss community-soil system developed on a naked region in Rundvagskollane (69050'S, 39009'E), East Antarctica, were investigated in order to analyze the flow of matter in an Antarctic terrestrial ecosystem. 1) The moss community was formed from many moss blocks of different sizes and was composed ofBryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb.,Ceratodon purpureus (Hedw.) Brid. andGrimmia lawiana J. H. Willis. The surface of the community was covered with cyanobacteria. 2) It was estimated that nitrogen fixed by cyanobacteria flowed from these organisms to the moss and that little nitrogen was transported within the moss body. 3) A large amount of phosphorus existed in the soil. The moss community had a high phosphorus content although the amount itself was relatively little due to the small phytomass. 4) It seems that absorption of phosphorus from soil is difficult for moss, because of the paucity of water necessary for the movement of phosphorus and the suppressed growth of moss due to the arid conditions.