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Pioneer mosses are among the dominant vegetation in the early stages of xeric successions. Recent climate warming may have a significant effect on the productivity of these mosses, thereby affecting successional processes. In this study, we investigated the effects of temperature changes on the productivity of Racomitrium japonicum, a pioneer moss species commonly found on open ground in Japan. We examined the microclimate (moss temperature and water content) of a natural R. japonicum stand in Higashi-Hiroshima City, western Japan, and related them to the climate records of the weather station to create a model for estimating microclimate from past climatic data. We also examined the effects of environmental factors (light, temperature, and water) on photosynthesis in the laboratory to construct a production model. Using these models, we estimated the net primary production (NPP) over the last 10 years (2009-2018) based on the climatic data (air temperature and precipitation) recorded at the weather station of Higashi-Hiroshima City. The estimated NPP showed negative values in summer, which indicated that respiratory carbon loss exceeded photosynthetic carbon gain. In contrast, NPP was positive in the spring and winter seasons throughout the 10 years. Autumn NPP varied widely, showing both positive and negative values. The annual NPP also showed considerable year-to-year variations. Additionally, we examined the effects of temperature conditions on NPP assuming annual temperature changes of 0 °C (present temperature), + 1 °C, and + 2 °C. The results indicated that NPP decreased with increasing temperature, except in the winter season. The findings of this study suggest that climate warming has a large impact on the NPP of R. japonicum; however, the impact can be both positive and negative depending on the season. The results also suggest that future climate warming is likely to decrease NPP on an annual basis.

The 11th Symposium on Polar Science/Ordinary sessions: [OB] Polar Biology, Poster presentations, Mon. 16 Nov. - Fri. 18 Dec.

The Japanese mud snail Batillaria attramentaria, a common gastropod in northeastern Asia, often predominates in isolated or degraded intertidal flat ecosystems in Japan and in other countries where it has invaded as an alien species. To evaluate the effects of B. attramentaria on carbon flow in intertidal flat ecosystems, we estimated the annual respiration of B. attramentaria from field surveys and laboratory experiments. The densities of the snails, as determined at an intertidal flat of the Seto Inland Sea, western Japan, were 235–485 individuals m−2. Temperature and snail size strongly affected their respiration rates, as determined by measuring their CO2 emission rates using an open-flow infrared gas analyzer method. The respiration rates were higher in the submerged condition than in the air-exposed condition. Based on the size structure of the natural population, laboratory experiment results, and environmental factors in the field (temperature and duration of the ebb/flood tide), we estimated the respiration in spring, summer, and autumn, respectively, as 1.9, 2.4, and 4.0 g C m−2. The total amount of carbon mineralized annually by the respiration of B. attramentaria exceeds 10% of that mineralized through sediment respiration. Based on these data and respiration/ingestion ratios in previous reports, we conclude that B. attramentaria has a significant impact on the carbon flows in intertidal flat ecosystems.

Rapid glacial retreat in the High Arctic causes the expansion of new habitats, but the successional trajectories of soil microbial communities are not fully understood. We examined microbial succession along a chronosequence twice with a 10-year interval in a High Arctic glacier foreland. Soil samples were collected from five study sites with different ages and phospholipid fatty acids analysis was conducted to investigate the microbial biomass and community structure. Microbial biomass did not differ significantly between the two sampling times but tended to increase with the chronosequence and showed a significant correlation with soil carbon (C) and nitrogen (N) content. Microbial community structure clearly differed along the chronosequence and was correlated with C and N content. The largest shift in community structure over 10 years was observed in the newly exposed sites after deglaciation. The accumulation of soil organic matter was regarded as an important determinant both of microbial biomass and community structure over the successional period. In contrast, the initial microbial community on the newly exposed soil changed rapidly even in the High Arctic, suggesting that some key soil processes such as C and N cycling can also shift within the relatively short period after rapid glacial retreat.

Solfatara fields, areas surrounding fumaroles (volcanic vents) near the hot springs or volcanoes, are characterized by severe environmental conditions such as low soil pH and high aluminum contents. Fimbristylis dichotoma subsp. podocarpa is an endangered plant distributed in solfatara fields of Kyushu, western Japan. This species is known to form stands in sites closed to fumaroles where another solfatara plant Miscanthus sinensis do not colonize. We conducted field survey and culture experiments to test the hypothesis that F. dichotoma has higher tolerance to low pH and high aluminum conditions than M. sinensis, which corresponds to the distribution pattern of the two species. In the study site of Myoban Hot Spring, Oita Prefecture, rhizosphere soils of F. dichotoma showed lower pH and higher aluminum contents than those of M. sinensis. The culture experiment showed that germination of F. dichotoma was not inhibited even at pH 2, whereas significant decline in germination (%) was observed in M. sinensis. However, because of the low germination (%) of F. dichotoma, the values of the two species were similar at pH 2. In the pot culture, seedling growth of M. sinensis was suppressed at the aluminum concentrations tested (400 mg AlCl3 L−1). Conversely, no significant decline in the seedling growth was observed in F. dichotoma at the same aluminum levels. Considering soil conditions in the field, we concluded that that the difference in the tolerance to aluminum between the two species played a significant role in determining their distribution pattern.

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.

Arctic terrestrial ecosystems are extremely vulnerable to climate change. A major concern is how the carbon balance of these ecosystems will respond to climate change. In this study, we constructed a simple ecological process-based model to assess how the carbon balance will be altered by ongoing climate change in High Arctic tundra ecosystems using in situ observations of carbon cycle processes. In particular, we simulated stand-level photosynthesis, root respiration, heterotrophic respiration, and hence net ecosystem production (NEP) of a plant community dominated by vascular plants and mosses. Analyses were carried out for current and future temperature and precipitation conditions. Our results showed that the tundra ecosystem was a CO2 sink (NEP of 2.3–18.9 gC m−2 growing season−1) under present temperature conditions. Under rising temperature (2–6 °C), carbon gain is significantly reduced, but a few days’ extension of the foliage period caused by their higher temperatures compensated for the negative effect of temperature on NEP. Precipitation is the major environmental factor driving photosynthetic productivity of mosses, but it had a minor influence on community-level NEP. However, NEP decreased by a maximum 15.3 gC m−2 growing season−1 under a 30-day prolongation of the moss-growing season, suggesting that growing season extension had a negative effect on ecosystem carbon gain, because of poorer light conditions in autumn. Because the growing season creates a weak CO2 sink at present, lengthening of the snow-free season coupled with rising temperature could seriously affect the future carbon balance of this Arctic tundra ecosystem.

Moss tundra that accumulates a thick peat layer is one of the most important ecosystems in the High Arctic, Svalbard. The importance of this ecosystem for carbon sequestration was estimated from the apparent rates of carbon accumulation based on the 14C age and amount of peat in the active layer. The study site at Stuphallet, Brogger Peninsula, northwestern Svalbard was covered with a thick peat layer dominated by moss species such as Calliergon richardsonii, Paludella squarrosa, Tomenthypnum nitens, and Warnstorfia exannulata. The average thickness of the active layer (brown moss and peat) was approximately 28 cm in 1 August 2011. The calibrated (cal) age of peat from the bottom of the active layer (20–30 cm below the peatland surface) ranged from 81 to 701 cal yr BP (median value of 2σ range). Based on the total carbon (4.5–9.2 kg C m−2), the apparent rate of carbon accumulation in the active layer was 9.0–19.2 (g C m−2 yr−1), which is similar to or greater than the net ecosystem production or net primary production reported for other vegetation types in this area. Our data suggest that moss tundra plays an important role in carbon sequestration in this area.

Mud shrimps, Upogebia spp., are major constituents of macrobenthic communities in tidal flats in Japan. The impact of Upogebia yokoyai on carbon flow on tidal flats was examined by comparing CO2 emission rates from plots with and without burrows in the Kurose River estuary, Japan. In situ CO2 emission rates from plots with burrows were significantly higher than from those without. Laboratory measurements using sediment core samples that excluded respiration of macrobenthic organisms showed similar trends. Although there were no significant differences in grain size distribution, water content, or ignition loss between the sediment cores with and without burrows, oxidation–reduction potential was significantly higher in sediment cores with burrows. Analysis of phospholipid fatty acids (PLFA) indicated that microbial biomass and community structure did not differ significantly between cores with and without burrows. However, microbial respiration activity, as indicated by CO2 emission rates per total PLFA content, was significantly higher in sediment cores with burrows than in those without. Our results indicate that burrows of U. yokoyai change the physicochemical conditions and increase microbial activity in the sediment, significantly affecting carbon flow in the tidal flat.

To study the relationship between vegetation development and changes in the soil microbial community during primary succession in a volcanic desert, we examined successional changes in microbial respiration, biomass, and community structure in a volcanic desert on Mount Fuji, Japan. Soil samples were collected from six successional stages, including isolated island-like plant communities. We measured microbial respiration and performed phospholipid fatty acid (PLFA) analysis, denaturing gradient gel electrophoresis (DGGE) analysis, and community-level physiological profile (CLPP) analysis using Biolog microplates. Microbial biomass (total PLFA content) increased during plant succession and was positively correlated with soil properties including soil water and soil organic matter (SOM) contents. The microbial respiration rate per unit biomass decreased during succession. Nonmetric multidimensional scaling based on the PLFA, DGGE, and CLPP analyses showed a substantial shift in microbial community structure as a result of initial colonization by the pioneer herb Polygonum cuspidatum and subsequent colonization by Larix kaempferi into central areas of island-like communities. These shifts in microbial community structure probably reflect differences in SOM quality. Microbial succession in the volcanic desert of Mt. Fuji was initially strongly affected by colonization of the pioneer herbaceous plant (P. cuspidatum) associated with substantial changes in the soil environment. Subsequent changes in vegetation, including the invasion of shrubs such as L. kaempferi, also affected the microbial community structure.

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 distribution of organic carbon and its relationship to vegetation development were examined on a glacier foreland near Ny-Alesund, Svalbard (79°N). In a 0.72-km 2 area, we established 43 study plots on three line transects along primary succession from recently deglaciated area to old well-vegetated area. At each plot, we measured the type and percent coverage of vegetation types. The organic carbon content of vegetation, organic soil, and mineral soil samples was determined based on their organic carbon concentration and bulk density. Cluster analysis based on vegetation coverage revealed five types of ground surfaces representing variations in the amounts and allocation patterns of organic carbon. In the later stages of succession, 7%–24% and 31%–40% of organic carbon was contained in the organic and deeper soil layers, respectively. Organic carbon storage in the later stages of succession ranged from 1.1 – 7.9 kg C m −2 . A larger amount of organic carbon, including ancient carbon in a raised beach deposit, was expected to be contained in much deeper soil layers. These results suggest that both vegetation development and geological history affect ecosystem carbon storage and that a non-negligible amount of organic carbon is distributed in this High Arctic glacier foreland.

To quantify organic matter mineralization at estuarine intertidal flats, we measured in situ sediment respiration rates using an infrared gas analyzer in estuarine sandy intertidal flats located in the northwestern Seto Inland Sea, Japan. In situ sediment respiration rates showed spatial and seasonal variations, and the mean of the rates is 38.8 mg CO2-C m−2 h−1 in summer. In situ sediment respiration rates changed significantly with sediment temperature at the study sites (r 2 = 0.70, p

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.

Summary •We examined the photosynthetic characteristics and net primary production of biological soil crusts to evaluate their contribution to the carbon cycle in the High Arctic glacier foreland. •Biological soil crust samples were collected from a deglaciated area in Ny-Alesund, Svalbard, Norway. Net photosynthetic rates (Pn) and dark respiration rates (R) of biological soil crusts were determined using CO2 gas exchange rates. We examined the effects of moisture conditions, temperature and photon flux density on Pn and R, and estimated the net primary production by a model based on the relationships between abiotic factors and Pn and R. •The maximum Pn value occurred at 50% of the maximum water-holding capacity. Pn decreased with increasing temperature and dropped below zero at high temperatures (c. > 13°C). The estimated net primary production of the biological soil crust was greater than the net primary production of other vegetation when based on ground surface area, during the early stage of primary succession. Model simulation showed that the net primary production of the biological soil crust decreased with increasing temperature. •These results suggest that biological soil crust productivity plays an important role in the carbon cycle during the early stage of succession of the High Arctic glacier foreland, and is susceptible to temperature increases from global warming.

Laboratory experiments and field measurements were conducted to examine the effect of tide on the organic carbon mineralization rate in sediments under aerobic conditions of an intertidal estuary. Core samples of surface sediments were collected from an intertidal estuary of the Kurose River, Hiroshima, Japan. To mimic low and high tide in the intertidal estuary, organic carbon mineralization rates in the samples were measured in the laboratory under both air-exposed and submerged conditions. Mineralization rates under air-exposed conditions were two to five times higher than those under submerged conditions. Field measurements of the rate of CO2 emission from the sediment surface revealed a rapid increase in the rate as the sea level fell during ebb tide. The estimated amount of daily organic carbon mineralization assuming a constantly submerged condition was 30% less than that estimated when considering the semi-diurnal fluctuation in sea level. These results indicate that tide has a marked impact on the organic carbon mineralization rate in sediments under aerobic conditions on an intertidal estuary, and tidal effects need to be considered when the amount of mineralized organic carbon is estimated.

Raised beach deposits are widespread on the north-western coast of Spitsbergen, Svalbard. To elucidate the importance of these deposits in an ecosystem carbon cycle, we measured the concentrations of organic carbon and adenosine 5-triphosphate (ATP; an index of living microbial biomass) in a raised beach deposit found under terrestrial vegetation in Ny-Alesund. A shell in the deposit found at a depth of ca. 20 cm below the ground surface had a (not calibrated) 14C age of 11080 _ 140 yr BP, whereas soil organic carbon in the same deposit showed an older 14C age (22380 _ 90 yr BP). Organic carbon concentration in the layer of 20–40 cm belowground was about 1–2%, which was comparable to those in shallower mineral soil layers. Results of ATP analyses suggested that low but non-negligible amounts of microorganisms existed in the deposit. The proportion of biomass carbon to soil organic carbon tended to decrease with increasing depth, suggesting that organic carbon in the deep layer was less available to microorganisms than that in the shallow layers.

Salix gracilistyla is one of the dominant plants in the riparian vegetation of the upper-middle reaches of rivers in western Japan. This species colonizes mainly sandy habitats, where soil nutrient levels are low, but shows high potential for production. We hypothesized that S.␣gracilistyla uses nutrients conservatively within stands, showing a high resorption efficiency during leaf senescence. To test this hypothesis, we examined seasonal changes in nitrogen (N) and phosphorus (P) concentrations in aboveground organs of S. gracilistyla stands on a fluvial bar in the Ohtagawa River, western Japan. The concentrations in leaves decreased from April to May as leaves expanded. Thereafter, the concentrations showed little fluctuation until September. They declined considerably in autumn, possibly owing to nutrient resorption. We converted the nutrient concentrations in each organ to nutrient amounts per stand area on the basis of the biomass of each organ. The resorption efficiency of N and P in leaves during senescence were estimated to be 44 and 46%, respectively. Annual net increments of N and P in aboveground organs, calculated by adding the amounts in inflorescences and leaf litter to the annual increments in perennial organs, were estimated to be 9.9 g and 0.83 g m−2 year−1, respectively. The amounts released in leaf litter were 6.7 g N and 0.44 g P m−2. These values are comparable to or larger than those of other deciduous trees. We conclude that S. gracilistyla stands acquire large amounts of nutrients and release a large proportion in leaf litter.

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.

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.

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'N, 82°45'W). 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.

The fruticose lichen Cetrariella delisei is among the dominant lichen species in the deglaciated High Arctic areas of Svalbard. As part of a study of carbon cycling in the High Arctic, we aimed to estimate the primary production of lichen in a deglaciated area in Ny-Alesund, Svalbard (79° N), by examining the effects of abiotic factors on the net photosynthesis (Pn) and dark respiration (R) rates of C. delisei. Experiments were conducted in the snow-free season of 2000 using an open-fl ow gas exchange system with an infrared gas analyser. Positive photosynthetic activities were observed on rainy days or soon after rainfall when the thallus water content was high, whereas photosynthetic activities dropped below the detectable limit on clear days because of the low thallus water content. Under a suffi ciently high thallus water content and close to light saturation, Pn was nearly constant over a wide temperature range of 4 - 20 °C, while R increased with increasing temperature. We constructed a model for estimating the net primary production (NPP) of lichen based on the relationships between abiotic factors and the CO2 exchange rate. The mean, minimum and maximum NPP values in the snow-free season, estimated using meteorological data obtained from 1995–2003, were 5.1, 1.0 and 8.4 g dry wt. m–2 snow-free season–1, respectively. These results suggest that NPP is highly variable and the contribution of lichen to carbon input is small compared with that of vascular plants and mosses in the study site.

Annual carbon fluxes via soil and root respiration were estimated in a cool-temperate deciduous forest to evaluate the importance of root respiration in the forest's overall carbon balance. Total soil respiration rates were measured during the snow-free season in 2000 and 2001 using an open-flow gas-exchange system with an infrared gas analyzer. To determine the annual carbon emission from the soil, we constructed a polynomial multiple-regression model that included two variables (soil temperature and soil water content) and that used hourly data for soil respiration rates. To estimate root respiration, we used data on the seasonal changes in the contribution of root respiration to the soil respiration rate that were determined in a previous study. The annual root respiration rate was estimated to be 4.8 t C ha−1 year−1, which corresponds to 45% of the annual total soil respiration (10.6 t C ha−1 year−1). Thus, root respiration contributed about half of the total annual soil respiration in the cool-temperate forest. The importance of root respiration in determining a forest's carbon balance is discussed in relation to data on net ecosystem production by the same forest.

Winter CO2 emissions from soil and snow-covered surfaces can represent a significant fraction of the annual carbon cycle in cool-temperate broad-leaved deciduous forests. The sources of this CO2 production are, however, poorly understood. To clarify the role of saprophytic microorganisms in the carbon cycle during the winter (December‐April), mass loss rates of organic substrates(leaflitterand cellulosesheets),andmicrobialactivity andfungalbiomassin thelitterlayerofacool-temperatebroadleaved deciduous forest in Japan were investigated. The mass loss rate of leaves reached 13%, which accounted for 26% of the annual mass loss. Microbial respiration in the leaf litter, measured in the laboratory, was detected even at � 2 8C. The ergosterol content(anindicatoroffungalbiomass)ofthecellulosesheetsincreasedsignificantlyinthesnow-coveredseason.Sevengeneraof fungi including Varicosporium elodeae, Epicoccum purpurascens and Cylindrocarpon destructans were isolated from leaf litter collected from under snow cover. Microbial respiration during the winter was estimated based on the relationships between the amount of leaf litter available, the temperature dependency of microbial respiration and the temperature in the litter layer. The microorganisms in the litter layer emitted 31 gCO2-C m � 2 , which accounts for 38% of the total CO2 eff lux during the winter. These results suggest that through soil respiration, microorganisms in the litter layer play an important role in the carbon cycle during the winter. # 2005 Elsevier B.V. All rights reserved.

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...

The Arctic terrestrial ecosystem is thought to be extremely susceptible to climate change. However, because of the diverse responses of ecosystem components to change, an overall response of the ecosystem carbon cycle to climate change is still hard to predict. In this review, we focus on several recent studies conducted to clarify the pattern of the carbon cycle on the deglaciated area of Ny-Alesund, Svalbard in the high Arctic. Vegetation cover and soil carbon pools tended to increase with the progress of succession. However, even in the latter stages of succession, the size of the soil carbon pool was much smaller than those reported for the low Arctic tundra. Cryptogams contributed the major proportion of phytomass in the later stages. However, because of water limitation, their net primary production was smaller than that of the vascular plants. The compartment model that incorporated major carbon pools and flows suggested that the ecosystem of the later stages is likely to be a net sink of carbon at least for the summer season. Based on the eco-physiological characteristics of the major ecosystem components, we suggest several possible scenarios of future changes in the ecosystem carbon cycle.

We examined soil microbial activities, i.e., biomass, respiration rate, and temperature dependence of the respiration on a glacier foreland in Ny-Alesund, Svalbard, Norway. We collected soil samples from 4 study sites that were set up along a primary succession (Site 1, the youngest, to Site 4, the oldest). Microbial biomass measured with the SIR method increased with successional age (55 to 724μg Cbiomass g−1 soil d.w. from Site 1 to Site 4). The microbial respiration rate of the soil was measured in a laboratory with an open-flow infrared gas-analyzer system, changing the temperature from 2° to 20°C at 3–4° intervals. The microbial respiration rate increased exponentially with the temperature at all sites. The temperature dependence (Q10) of the microbial respiration rate ranged from 2.2 to 4.1. The microbial respiration rates at a given temperature increased with succession as a step change (0.48, 0.43, 1.26, and 1.29μg C g−1soil h−1 at 8°C from Site 1 to Site 4, respectively). However, the su...

Soil respiration rates were measured in a successional glacier foreland in Ny-_lesund, Svalbard, and the amount of CO2 efflux during the plant-growing season was estimated using a simple regression model. Three study sites (Site 1, Site 2 and Site 3) were set up along with the primary succession in the deglaciated area of East Br_gger glacier in Ny-_lesund, Svalbard, Norway (79‹N 12‹E). Another study site, Site RB, was set up on a riverbed in the Bay River between Site 2 and Site 3. Soil respiration (SR), air temperature at 10 cm height (AT), soil surface temperature (SST) and soil temperature at 1 cm depth (ST) were measured at the four study sites with an open-airflow system using an infra-red gas analyzer from July to August, 1995. The mean soil respiration rate varied among the four sites: 6.2, 44, 63 and 3.7 mg CO2 m-2 h-1 at Site 1, Site 2, Site 3 and Site RB, respectively. These differences in the soil respiration rate among the four sites corresponded with the soil organic amount, microbial biomass, and root biomass. The soil respiration rate showed the best correlation with AT at Site 1, Site 2 and Site RB, and with ST at Site 3. The cumulative amount of CO2 efflux calculated using correlation equations obtained from the above relationships between SR and AT or ST was 5.8, 46, 69 and 3.3 g CO2 m-2 at Site 1, Site 2, Site 3 and Site RB, respectively, for two months (from July to August, 1995). These values were extremely low compared to those of warmer ecosystems, such as low-arctic tundra, temperate mixed forests, and tropical moist forests.

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.

We examined the response of the temperature coefficient (Q10) for soil respiration rate to changes in environmental temperature through a laboratory incubation experiment. Soil samples were collected from three climatic areas: arctic (Svalbard, Norway), temperate (Tsukuba, Japan) and tropical (Pasoh, Malaysia). The arctic and temperate soils were incubated at 8 °C (control), 12 °C (4 °C warming) and 16 °C (8 °C warming) for 17 days. The tropical soil was incubated at 16 °C (8 °C cooling), 24 °C (control) and 32 °C (8 °C warming). Before and after the incubation experiment, the temperature dependence of soil microbial respiration was measured using an open-airflow method with IRGA by changing the temperature in a water bath. The initial Q10 before the incubation experiment was larger in the soils from higher latitudes: 3.4 in the arctic soil, 2.9 in the temperate soil, and 2.1 in the tropical soil. The response of the microbial respiration rate to change in temperature differed among the three soil types. The temperature dependence of respiration rate in the arctic soil did not change in response to warming by 4 and 8 °C with a Q10 of about 3. On the other hand, the Q10 in the temperate soil decreased with increasing incubation temperature: from 2.8 in soils incubated at 8 °C to 2.5 at 12 °C and 2.0 at 16 °C. In the tropical soil, the Q10 was not changed even by the 8 °C warming with a value of 2.1, whereas the Q10 was increased from 2.1 to 2.7 by the 8 °C cooling. These results suggest that the response of microbial respiration to climatic warming may differ between soils from different latitudes.

The shrubby willow Salix gracilistyla Miq. is one of the dominant plants in the riparian vegetation of the upper-middle reaches of rivers in Japan and has been used in river restoration practice in Japan. In this study, we measured the biomass and production of a S. gracilistyla stand on a fluvial bar in the Ohtagawa River, Hiroshima Prefecture. Allometric relationships between the stem diameter and the dry weights of plants were determined every month from May to October and in December 2000. To determine the thickening growth, we measured the diameters at ground level of randomly selected shoots. From May to October, the stem diameter at ground level increased by 30%, showing considerable thickening growth. The aboveground biomass, estimated from the stem diameter by using the allometric relationship, increased from May (0.9 kg m-2) to September (2.2 kg mm-2) and decreased thereafter because of leaf shedding. In September, leaf and current branch biomass reached 0.6 and 0.3 kg mm-2 respectively. The biomass increment of old branches and stems from May to December was 0.4 kg mm-2. The underground biomass determined by digging in the following February was 1.6 kg mm-2. The aboveground production of S. gracilistyla was estimated to be 1.3 kg mm-2 yr-1. This value is comparable to those of other pioneer trees and temperate forests. Our results suggest that S. gracilistyla has a high potential for production despite its small aboveground biomass.

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.

As part of the study on carbon cycling in a deglaciated area in the High Arctic, Ny-Alesund, Svalbard (79°N), we examined the effects of abiotic factors on the net photosynthesis and dark respirati...

The effects of rainfall events on soil CO2 fluxes were examined in a cool temperate Quercus/Betula forest in Japan. The soil CO2 fluxes were measured using an open-flow gas exchange system with an infrared gas analyzer in the snow-free season from August 1999 to November 2000. Soil CO2 flux showed no significant diurnal trend on days without rain. In contrast, rainfall events caused a significant increase in soil CO2 flux. To determine the effect of rainfall events and to evaluate more precisely the daily and annual soil carbon flux, we constructed a multiple polynomial regression model that included two variables, soil temperature and soil water content, using the soil CO2 flux data recorded on sunny days. Daily soil carbon fluxes on sunny days calculated by the model were almost the same as those determined by the field measurements. On the contrary, the fluxes measured on rainy days were significantly higher than those calculated daily from the soil carbon fluxes by the model. Annual soil carbon fluxes in 1999 and 2000 were estimated using models that both do and do not take rainfall effects into consideration. The result indicates that post-rainfall increases in soil CO2 flux represent approximately 16–21% of the annual soil carbon flux in this cool temperate deciduous forest.

The effects of climatic factors, especially those of temperature, on the carbon balance of the moss Sanionia uncinata were examined on King George Island in the maritime Antarctic. Net photosynthesis (P n ) and dark respiration rates of two colonies (A and B) were measured with a portable infrared gas analyzer. Colony A showed small P n compared with its dark respiration rates throughout the growing season. Colony B showed much higher net photosynthetic rates, but the dark respiration rates of the two colonies did not differ significantly. Net photosynthetic rate determined at light saturation was almost constant over a wide temperature range, from 5° to 15°C, while the dark respiration was strongly affected by temperature. To assess the impact of warming on the carbon balance of the moss, cumulative carbon gain of the moss was calculated using a simulation model for the main part of the growing season. The results suggest that climatic warming may cause a reduction of carbon gain in some relatively photosynthetically inactive moss colonies.

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.

A field survey and a pot culture experiment were conducted to examine the effects of nutrients (N and P) and arbuscular mycorrhizal (AM) fungi on the growth of Salix gracilistyla, a pioneer plant in riparian habitats. The plants growing in the field were colonized by AM and/or ectomycorrhizal fungi. However, the direct effect of AM colonization on seedling growth was not detected in the pot culture experiment. In contrast, N application significantly promoted plant growth, suggesting that the growth of S. gracilistyla seedlings is largely limited by the availability of N in the field.

Microbial biomass in arctic soil was examined in relation to a primary succession on arctic deglaciated moraines in Ny-Alesund, Svalbard (79°N, 12°E). Soil samples at four study sites representing different successional stages were collected at every 1cm depth from the soil surface to 3cm depth in early August 1995. Microbial biomass was measured with a substrate-induced respiration procedure. The microbial biomass was highest at the soil surface (0-1cm depth) in all successional stages, and decreased to a negligible amount at 3cm depth. Mean microbial biomass in 0-2cm layer increased from 0.06mgCg^ soil d. w. in the youngest site to 1.03mgC g^ soil d. w. in the oldest site, which is comparable to ecosystems in warmer regions. Throughout all successional stages, there was positive high correlation between soil carbon or nitrogen content and microbial biomass.

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.