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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 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.

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.

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.

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

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 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.

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.

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 response patterns of net photosynthesis to moisture level of mosses in xeric habitats were compared with those in mesic habitats, in order to determine whether the former species are better adapted to the xeric condition with regard to carbon gain.