Lucidophyllous (evergreen broad-leaved) forests are the dominant forests in human-dominated subtropical/warm-temperate regions in East Asia. Biometric-based estimates of net primary production (NPP) were conducted in a secondary lucidophyllous forest on Mt. Kinka (35°26′ N, 136°47′ E) near the northern limit of their distribution in central Japan for three years, including the masting event. The forest stand mainly consists of Castanopsis cuspidata (Thunb.) Schottky and Cleyera japonica Thunb. in the canopy and subtree layers, respectively. In 2018, the total NPP of the masting year was 14.53 ± 2.03 ton ha−1 yr−1, including woody NPP (above: 2.63 ± 0.35 ton ha−1 yr−1; below: 0.57 ± 0.08 ton ha−1 yr−1), foliage NPP (4.07 ± 0.23 ton ha−1 yr−1), reproductive NPP (4.81 ± 0.77 ton ha−1 yr−1), and fine root production (Pfr) (2.46 ± 1.84 ton ha−1 yr−1). Pfr and belowground production comprised 16.9% and 20.9%, respectively, of the total NPP. The nut production of C. cuspidata in 2018 (4.31 ± 0.75 ton ha−1 yr−1) was significantly higher than that in 2017 (0.77 ± 0.13 ton ha−1 yr−1) and 2019 (0.23 ± 0.06 ton ha−1 yr−1). No significant change was observed for the three years of foliage NPP and total NPP without Pfr. However, the woody NPP in 2018 (3.20 ± 0.43) was lower than in 2017 (5.37 ± 0.33 ton ha−1 yr−1) and 2019 (4.71 ± 0.38 ton ha−1 yr−1). This suggests that nut production in the masting years compensated by decreasing woody production in the Castanopsis forest.

Amendment by biochar made by thermal degradation of biomass is expected to enhance carbon sequestration through stimulating carbon assimilation by plants. We clarified the effect of biochar amendment on the photosynthesis of trees in forest ecosystems. Biochar was applied to young oak trees (Quercus serrata) in temperate deciduous forest at rates of 0, 5, 10 and 20 Mg ha−1 in four plots (C0, C5, C10, and C20). The variation in photosynthetic parameters (the maximum photosynthetic rate: Pmax, maximum carboxylation rate: Vcmax and the potential rate of electron transport: Jmax) and leaf traits (the stomatal conductance: gc, leaf mass per area (LMA) and leaf nutrient concentrations) were examined every month during the growing seasons for 3 years. Pmax generally increased in C5 and C10 and did not increase in C20. Similarly, Vcmax and Jmax increased in C5 and C10 and correlated significantly positively with Pmax, suggesting that biochar amendment basically increased the photosynthetic rate through improvements in physiological activities but that there was a maximum useful dosage. We also found that gc, LMA and leaf nutrient (N, Mg, and S) showed significant positive correlations with Pmax, indicating that an increase in photosynthetic rates would be supported by these leaf traits. However, stimulation of photosynthesis became smaller year by year, indicating that the effects of biochar amendment faded gradually. We concluded that biochar amendment basically improved the photosynthesis of oak trees in the forest through the change of all gc, LMA and leaf nutrient concentrations but declined yearly.

Few studies have evaluated the application of biochar to forest ecosystems and their responses under field conditions. We manually spread grounded biochar on the forest floor, at rates of 0 (control), 5, and 10 Mg ha−1 (C0, C5 and C10, respectively), of an oak forest in central Japan to test the effects of biochar on tree growth and productivity. The relative growth rate of the diameter at breast height (dbh) of canopy oak trees (dbh > 20 cm) significantly increased in C10 compared with that of the control (C0), but not in C5, in the second to third years after application. Despite the increasing growth rate of canopy trees, foliage production (NPPF) and woody production (NPPW) did not respond to biochar application. Conversely, the production of reproductive organs (NPPR, mainly oak acorns) increased in line with the biochar application rate gradients (1.04 ± 0.09 Mg ha−1 yr−1 in C0, 1.30 ± 0.08 Mg ha−1 yr−1 in C5, and 1.47 ± 0.13 Mg ha−1 yr−1 in C10). Since the contribution of NPPR to total NPP was fairly small, there were no significant differences in total NPP (=NPPW + NPPF + NPPR) for C5 (14.57 ± 0.20 Mg ha−1 yr−1) or C10 (16.11 ± 0.73 Mg ha−1 yr−1) compared with the control (15.07 ± 0.48 Mg ha−1 yr−1).

Abstract

We aimed to clarify the individual and interactive effects of temperature increase during snow‐free seasons and snow depth change (increase/decrease) on litter decomposition and microbial community in cool‐temperate semi‐natural grassland. We conducted a 2‐year in situ composite warming experiment comprising temperature increase (ca. 2°C) using infrared heaters during snow‐free seasons and manual snow depth manipulation (±50% in snow depth) in Japanese grassland. Changes in litter mass remaining and litter carbon‐to‐nitrogen ratio (C/N ratio) were assessed by litter bag methods. Microbial biomass and community structure were determined by phospholipid fatty acid analysis. Litter decomposition constant (k) was low in the plots with temperature increase during snow‐free seasons (0.56) and with less snow cover (0.57), but combining these two treatments resulted in acceleration of decomposition (k = 0.70); probably, decreased decomposition in the cold climate of early spring resulting from advanced snow melting was compensated for by higher temperature. Differences in mass loss among the treatments were well explained by litter C/N, microbial biomass and microbial community structure. The plots with a high mass loss showed lower litter C/N ratio, larger microbial biomass and different microbial community structure comparing to the plots with low mass loss. Our results showed the complex responses of litter decomposition to summer and winter climate change and combination of less snow cover and summer warming seemed to accelerate the decomposition in cool‐temperate semi‐natural grassland.

The significance of aquatic lateral carbon (C) export in mangrove ecosystems highlights the extensive contribution of aquatic pathways to the net ecosystem carbon budget. However, few studies have investigated lateral fluxes of dissolved organic carbon (DOC) and inorganic carbon (DIC), partly due to methodological difficulty. Therefore, we evaluated area-based lateral C fluxes in a small mangrove estuary that only had one exit for water exchange to the coast. We sampled water from the mouth of the creek and integrated discharge and consecutive concentration of mangrove-derived C (ΔC). Then, we estimated the area-normalized C fluxes based on the inundated mangrove area. DIC and DOC concentrations at the river mouth increased during ebb tide during both summer and winter. We quantified the ΔC in the estuary using a two-component conservative mixing model of freshwater and seawater. DIC and DOC proportions of ΔC concentrations at the river mouth during ebb tide was between 34% and 56% in the winter and 26% and 42% in the summer, respectively. DIC and DOC fluxes from the estuary were estimated to be 1.36 g C m−2 d−1 and 0.20 g C m−2 d−1 in the winter and 3.35 g C m−2 d−1 and 0.86 g C m−2 d−1 in the summer, respectively. Based on our method, daily fluxes are mangrove area-based DIC and DOC lateral exports that can be directly incorporated into the mangrove carbon budget.

© 2019, Coastal and Estuarine Research Federation. To clarify the effects of crab burrows on variation in sediment CO2 flux in mangrove forest, we measured the traits of crab burrows (density and entrance area size) and the CO2 flux rate from sediment surfaces, in areas with and without burrows, in a subtropical mangrove forest on Ishigaki Island, southwestern Japan. Burrow density and entrance area showed significant differences among seasons (warm, middle, and cool) and mangrove zones (upper-, middle-, and downstream), which may have depended on crab phenology, life cycle, and species composition. The sediment CO2 flux rate was significantly higher at plots with crab burrows (B+) than at those without burrows (B−) in each zone and season. However, standardized sediment CO2 flux rate by burrow surface area at B+ plots did not differ significantly from that at B− plots. In addition, there were no significant differences in sediment temperature and sediment water content between the two types of plots. Moreover, the level of microbial respiration differed significantly between sediments collected from the deep part and those collected from either the ground surface part or burrow walls. These results suggest that crab burrows increase sediment CO2 flux from the mangrove forest floor by increasing the sediment–atmosphere interface area, thereby inducing a change to aerobic conditions in the sediments around burrows. Therefore, the seasonal and spatial effect of crab burrows on the forest floor should be considered when evaluating sediment CO2 flux and examining the role of the mangrove ecosystem as a carbon sink.

© 2019, © 2019 Japanese Society of Soil Science and Plant Nutrition. The role of biochar in the mitigation of CO2 emissions has been extensively studied in agricultural soils but is not well understood in Japanese forest soils, especially in relation to CO2 emissions from applied biochar and native soil C (i.e., the priming effect; PE). We hypothesized that the type of biochar and/or the application method (mixed or sprinkled) affect the direction and magnitude of PE in forest soil, and in particular, negative PE can be achieved relatively easily if biochar produced under higher temperature conditions were sprinkled on the soil surface. To test our hypothesis, we measured CO2 emissions from biochar-amended brown forest soil in Japan and examined its PE by conducting a medium-term (~4 months) incubation study. As substrates, we used plain straw from the C4 grass Miscanthus sinensis (SU) and two qualities of biochar produced from it at either 300°C (BC300) or 800°C (BC800) and compared two application methods: mixed into or sprinkled onto the soil. BC800 had a greater C content and C:N ratio as well a lower volatile matter content and higher nonvolatile matter content than BC300

Humic substances (HS) are the primary constituents of dissolved organic matter (DOM) and play pivotal roles in aquatic systems. Optical indices of DOM, such as specific UV absorbance (SUVA254), the fluorescence index (FI) and biological index (BIX), have gained wide interest because of their ease of use. In this study, we explored the relationship between HS and the indices in the Trat River Basin (eastern Thailand) from headwaters to the river mouth through the distinct dry and rainy seasons to examine whether changes in index values reflect variability in the relative contribution of HS to DOM, or %HS. The results show that %HS and the indices did not exhibit significant linear relationships (FI and BIX, P &gt
0.05), or the relationships changed seasonally (SUVA254). However, analyzing the indices versus %HS did show clear DOM composition changes by season with more humic-like or terrestrial material in the rainy season. Relationships between DOM and dissolved iron (dFe) concentrations were also explored. Separating the relationships of DOM versus dFe into HS versus dFe and non-HS versus dFe provides us the opportunity to better understand which fraction contributes more to dFe mobilization. The results indicate stronger positive linear relationships between HS and dFe concentrations independent of river tributary. Overall, this study highlights the importance of quantifying HS for the study of DOM dynamics or compositional changes along a river transect as well as for DOM-induced iron mobilization.

We report long-term continuous phenological and sky images taken by time-lapse cameras through the Phenological Eyes Network (http://www.pheno-eye.org. Accessed 29 May 2018) in various ecosystems from the Arctic to the tropics. Phenological images are useful in recording the year-to-year variability in the timing of flowering, leaf-flush, leaf-coloring, and leaf-fall and detecting the characteristics of phenological patterns and timing sensitivity among species and ecosystems. They can also help interpret variations in carbon, water, and heat cycling in terrestrial ecosystems, and be used to obtain ground-truth data for the validation of satellite-observed products. Sky images are useful in continuously recording atmospheric conditions and obtaining ground-truth data for the validation of cloud contamination and atmospheric noise present in satellite remote-sensing data. We have taken sky, forest canopy, forest floor, and shoot images of a range of tree species and landscapes, using time-lapse cameras installed on forest floors, towers, and rooftops. In total, 84 time-lapse cameras at 29 sites have taken 8 million images since 1999. Our images provide (1) long-term, continuous detailed records of plant phenology that are more quantitative than in situ visual phenological observations of index trees
(2) basic information to explain the responsiveness, vulnerability, and resilience of ecosystem canopies and their functions and services to changes in climate
and (3) ground-truthing for the validation of satellite remote-sensing observations.

The chamber method with plant clipping has been widely used for measuring soil respiration (SR) in grassland ecosystems. However, plant clipping may cause overestimation of SR by changing the environmental factors and injuring the plants. To solve these problems, we developed a new non-destructive method using multiple-microchambers (3 cm diameter, 8 cm height), which enables measurement of SR without plant clipping by installing chambers into gaps among the grasses. The new method was compared with the conventional method at various flow rates in vitro to assess the accuracy of SR measurement. The new method overestimated the SR rate
however, the ratio of overestimation to the conventional method was constant for each flow rate. These ratios fitted the logarithmic curve, indicating the potential for correction of the SR rate measured by the new method using the logarithmic equation. The corrected SR rate obtained by the new method was equal to the rate by the conventional method. This suggests that accurate measurement of SR in grassland ecosystems is possible using the multiple-microchambers method. We then compared the non-destructive method and the destructive method in situ on summer season and found that the destructive method overestimated SR rate in the grassland ecosystem by about 276% on average. There were two possible reasons for this overestimation
first, the clipping treatment may change environmental conditions such as soil temperature and soil water content, and second, it may directly increase plant respiration.

Secondary lucidophyllous forest is one of the dominant forests in human-dominated subtropical/warm-temperate regions in East Asia. There were few direct monitoring techniques to elucidate the following hypotheses: (a) self-thinning may govern the stand development process and (b) wood production decline can be observed during secondary succession in a lucidophyllous forest. We conducted a long-term study at a permanent plot in central Japan, since 1989. The forest consists mainly of Castanopsis cuspidata in a canopy layer, Cleyera japonica, and Eurya japonica in a subtree layer. During the 28-year period, the basal area of the stand significantly increased due to the growth of C. cuspidata, from 29.18 +/- 1.84 (87.8% of total) to 38.71 +/- 2.22 m(2) ha(-1) (91.9%), while the stem density of C. cuspidata significantly decreased from 666 +/- 13 to 404 +/- 10 stems ha(-1) in proportion to accumulating biomass (117.8 to 166.6 ton ha(-1)). The annual woody net primary production ranged from 2.40 +/- 0.13 to 3.93 +/- 0.33 ton ha(-1) year(-1) as a nearly 70-year-old forest. There was no age-related decline of woody net primary production (NPP) was found during secondary succession, and the growth of individual tree still increased when the self-thinning process governed the stand.

Dissolved organic carbon (DOC) plays an important role in C cycling in forest ecosystems. Here we measured the concentrations and fluxes of DOC in a cool-temperate broad-leaved deciduous forest (Takayama Forest) to quantify the contribution of DOC from different forest water flux conditions. Mean DOC concentration during the growing season increased in the sequence from bulk precipitation (2.98 +/- 0.45 mg L-1), throughfall above dwarf bamboo (6.84 +/- 0.45 mg L-1), throughfall below dwarf bamboo (7.08 +/- 0.42 mg L-1), stemflow (15.05 +/- 0.98 mg L-1), and litter leachate (21.33 +/- 1.01 mg L-1). Litter leachate DOC concentration, being high in spring and autumn, which was fairly correlated with the amount of litterfall of bamboo and trees. In stemflow, the DOC concentration was high during early summer and gradually decreased, in addition, it also showed dramatic variation among different plant species. Litter leachate (72.5%) accounted for most of the DOC input to the soil during the growing season (311.5 kg C ha(-1) 7 months(-1)), while stemflow (1.6%) contributed the least. A great quantity of precipitation at the study site was associated with a subsequent high atmospheric contribution of DOC flux (8.6%), which was more than half of throughfall (16.5%). The high input of DOC to the soil and andisol soil characteristics at the Takayama Forest suggest that the DOC fluxes are vital to the soil carbon sequestration. Therefore, DOC fluxes should be taken into account when the carbon balance is assessed at forest ecosystems.

This paper reports seasonal data regarding leaf litter for 14 deciduous broad-leaved species and one evergreen coniferous species as well as leaf area index (LAI) data for the 14 deciduous broad-leaved species in a cool-temperate deciduous broad-leaved forest in Japan. The seasonal leaf biomass of various tree species is important for accurately evaluating ecosystem functions such as photosynthesis and evapotranspiration under climate change. However, there is a lack of freely available, long-term data. We collected litterfall every 1 to 4 weeks from September or October to November or December each year from 2005 to 2014 in Takayama, Japan (36A degrees 08'46aEuro(3)N, 137A degrees 25'23aEuro(3)E, 1420 m a.s.l.). After sorting the litter into leaves (according to species categories), stems + branches, and "other", we dried and weighed the litter groups. We also collected seasonal leaf data (number of leaves and leaf length and width) for each broad-leaved species, which we recorded every 1 to 4 weeks from April or May to October or November using multiple target shoots. To estimate the LAI in autumn for each deciduous broad-leaved species, we used a semi-empirical model of the vertical integration of leaf dry mass per unit leaf area. To estimate the LAI in spring and summer, we used the relationship between the LAI in autumn and the seasonal leaf data. Our data provide input, calibration, and validation parameters for determining LAI based on satellite remote-sensing observations or radiative transfer models and for use in ecosystem models.

The structural complexity, especially canopy and gap structure, of old-growth forests affects the spatial variation of soil respiration (Rs). Without considering this variation, the upscaling of Rs from field measurements to the forest site will be biased. The present study examined responses of Rs to soil temperature (Ts) and water content (W) in canopy and gap areas, developed the best fit model of Rs and used the unique spatial patterns of Rs and crown closure to upscale chamber measurements to the site scale in an old-growth beech-oak forest. Rs increased with an increase in Ts in both gap and canopy areas, but the effect of W on Rs was different between the two areas. The generalized linear model (GLM) analysis identified that an empirical model of Rs with the coupling of Ts and W was better than an exponential model of Rs with only Ts. Moreover, because of different responses of Rs to W between canopy and gap areas, it was necessary to estimate Rs in these areas separately. Consequently, combining the spatial patterns of Rs and the crown closure could allow upscaling of Rs from chamber-based measurements to the whole site in the present study.

We measured the CO2 flux from sediment surfaces (soil respiration in the pedosphere to the atmosphere) in a mangrove forest using an improved automatic open/close chamber (AOCC) method. Soil respiration rates and environmental factors were continuously measured from 4 to 8 July, 2013, in a mangrove dominated by Bruguiera gymnorrhiza. Variation in respiration rate did not exhibit a clear correlation with soil temperature. However, tidal effects were related to variation in soil temperature and may also have contributed to variation in respiration rate. High respiration rates were detected immediately before submergence or after exposure, due to the physical effects of tidal variation. Respiration rates during the period of exposure were lower than those in terrestrial ecosystems, likely due to three factors unique to mangrove forests: soil respiration measurements generally do not include root respiration, organic matter decomposition is restricted to a shallow anaerobic area, and some mineralized carbon is lost as dissolved inorganic carbon. Respiration rates during submergence were half of those measured during exposed conditions, suggesting that previous studies overestimated annual soil respiration. Therefore, measuring soil respiration rates during both exposed and submerged conditions using the AOCC method provides a much more accurate understanding of carbon dynamics in the pedosphere of mangrove forests.

To clarify the effects of long-term warming on ecosystem matter cycling, we conducted an in situ 7-year experimental warming (2009-2015) using infrared heaters in a cool temperate semi-natural grassland in Japan. We measured plant aboveground biomass, soil total C and N, soil inorganic N (NH4 (+)-N and NO3 (-)-N), and soil microbial biomass for 7 years (2009-2015). We also measured heterotrophic respiration for 2 years (2013-2014) and assessed net N mineralization and nitrification in 2015. We found that warming immediately increased plant aboveground biomass, but this effect ceased in 2013. However, the soil microbial biomass was continuously depressed by warming. Soil inorganic N concentrations in warmed plots substantially increased in the later years of the experiment (2013-2015) and the potential net N mineralization rate was also higher than in the earlier years. In contrast, heterotrophic respiration decreased with warming in 2013-2014. Our observations indicate that long-term warming has a contrasting effect on plants and soil microbes. In addition, the warming could have different effects on subterranean C and N cycling. To enhance the accuracy of estimation of future climate change, it is essential to continuously observe the warming effects on ecosystems and to focus on the change in subterranean C and N cycling.

We examined two hypotheses based on laboratory amendment experiments: (1) that development of the soil microbial community on volcanic deserts was regulated by substrate limitation; and (2) that the type and the extent of substrate limitation would change along the succession gradient. Soils were collected from the early (Stage B) and the late (Stage F) stages of primary succession of a subalpine volcanic desert on Mt. Fuji and they were amended with three carbon (C) sources (glucose, cellulose, or lignin), inorganic nitrogen (N), or phosphorus (P) sources alone or in a mixture. Respiration rates were monitored for 25 days and changes in microbial biomass and community structure were examined using the content and composition of phospholipid fatty acids. For both soils, the magnitude of the microbial response differed depending on the type of C source and it decreased in the following order reflecting the availability to microorganisms: glucose > cellulose > lignin. For Stage B soil, although any single amendment did not affect the microbial properties, combined amendment of C (glucose) and N increased microbial respiration and biomass and shifted the microbial community structure. In contrast, microbial properties in Stage F soils responded positively to single amendments of C source. Our results suggest that the microbial community in the early stage of succession is primarily limited by simultaneous shortage of C and N sources but the quality of the C source becomes more important in the late successional stages, which have large, but recalcitrant, organic matter pools in the soil. (C) 2016 Elsevier Masson SAS. All rights reserved.

We evaluated the uncertainty in the estimation of year-to-year variability in the timing of leaf fall detected by the analysis of red, green and blue (RGB) values extracted from daily phenological images in a deciduous broad-leaved forest in Japan. We examined (1) the spatial distribution of individual tree species within a 1-ha permanent plot and the spatio-temporal variability of leaf litter of various species for 8 years; and (2) the relationship between the year-to-year variability of leaf fall detected by leaf litter and that detected by phenological images of various species. Uncertainties were caused by (1) the heterogeneous distribution of each species within the whole forest community; (2) the year-to-year variability of the timing of leaf fall among species; and (3) differences in leaf colouring and leaf fall patterns among species. Our results indicate the importance of integrating RGB analysis of each species and of the whole canopy on the basis of spatial locations of individuals and proportions of tree species within a forest to reduce uncertainty. (C) 2015 Elsevier B.V. All rights reserved.

Soil respiration (R (s) ) is a key component in the estimation of the net ecosystem production (NEP) of old-growth forests, which are generally thought to have ceased carbon accumulation. The objectives of the present study were to characterize the spatial and temporal patterns of R (s) , and to identify the determinants of the spatial and temporal variability of R (s,) using general linear mixed models (GLMM), in an old-growth beech-oak forest. GLMM analyses identified monthly effect as a significant explanatory variable for temporal variation, as well as gap/canopy and soil water content (SWC) as explanatory variables for spatial variation, in R (s) . The complexity of vertical structure in the forest was reflected in the spatial pattern of R (s) , which was higher in canopy areas than in gap areas during the growing season, except in November. This spatial pattern was not affected by soil temperature. Moreover, SWC did not differ between gap and canopy areas, although SWC partially explained the spatial heterogeneity in R (s) . The carbon:nitrogen ratios of soil organic matter in canopy areas were significantly higher than those in gap areas. Fine root biomass was 1.7-fold greater in canopy areas than in gap areas, likely because of the higher R (s) in canopy areas, and root respiration made a much large contribution to R (s) than heterotrophic respiration. The different patterns of fine root biomass between gap and canopy areas mainly control the spatial heterogeneity in R (s) ; thus, it is worth considering the gap/canopy variability in R (s) when evaluating annual efflux in old-growth forests.

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 C-14 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 2s 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. (C) 2015 Elsevier B.V. and NIPR. All rights reserved.

成熟林における17年間での森林群落の構造的変化とバイオマスの時間変動を調べるために,白山の東斜面に位置する冷温帯落葉広葉樹林に1haの永久方形区を設置して,1995年と2012年に毎木調査を行った。この森林はブナとミズナラが優占しており,2012年調査時の最大DBHはそれぞれ,100.3cmと194.7cmに達した。17年間で,DBHが5cm以上の樹木密度は1haあたり908本から940本に増加したが,9本の林冠木の枯死が見られた。この林冠木の枯死のために,17年間でギャップは拡大し,さらにM-w図から見ると高木層と亜高木層での森林構造の変化が認められた。森林のバイオマスは1995年には537.8t ha^<-1>で,2012年には536.7t ha^<-1>であった。巨大なミズナラ林冠木の存在のために,この森林のバイオマスは日本国内で過去に報告された成熟ブナ林のどの値よりも大きかった。巨大なミズナラ林冠木の枯死で失われたバイオマス(73.7t ha^<-1>)は,ブナの成長によって補償されたために,17年間でバイオマスはほとんど変化しなかった。このブナ-ミズナラ成熟林は,ミズナラ林冠木の枯死に伴うギャップ拡大とブナの成長というように森林動態から見ると非平衡状態にあるが,森林バイオマスは定常状態に達していると考えられる。

To assess soil microbial response to global warming in cool temperate semi-natural grassland, we conducted an in situ warming experiment in grassland located in the mountains of central Japan. Five pairs of plots (control and warmed) of Zoysia japonica were established. For each pair of plots, one was warmed by ca. 2 A degrees C using infrared heaters during the growing seasons of 2009-2011. Above-ground biomass of Z. japonica was estimated using the modified point-frame method. Soil organic matter contents, soil total carbon and nitrogen contents, as well as inorganic nitrogen (ammonium and nitrate) contents were determined from soil samples. Total phospholipid fatty acid (PLFA) contents and PLFA compositions were determined and used as indices for total microbial biomass and community structure, respectively. Analyses showed that the warming increased the above-ground biomass of Z. japonica significantly. Soil organic matter and soil total nitrogen contents were significantly decreased, while soil ammonium content was significantly increased in the warmed plots. Soil microbial biomass (especially fungal biomass) was lower in the warmed plots, probably reflecting higher temperature, lower soil water content, and/or depletion in available nutrients. The significant decrease in fungal biomass, in combination with our PLFA composition data, suggests that the soil microbial community structure shifted from a fungal-dominated to a bacteria-dominated one, causing changes in community-level physiological activity.

Soil organic layer samples of two different forest types were observed using compact MRI to visualize internal structure and clarify physical properties of forest soil. Soil pores and organic materials were distinguished by differences in proton mobility and visualized with a spatial resolution of 234 A mu m. Soil pore ratios and water mobility were calculated by image processing, and their differences between the two forest soils were detected. Our results suggest that compact MRI has potential for non-destructive analysis of soil physical properties and is expected to have significant applications in ecological studies.

Long-term continuous phenological observation of cherry tree blooming is an important and challenging task in the evaluation of year-to-year weather and climate changes in spring in Japan. Here, (1) we performed daily field observations with a time-lapse digital camera in a deciduous broad-leaved forest in Japan from January 2004 to December 2013; and (2) we detected year-to-year variations in the blooming phenology of Prunus sargentii by visual inspection of the images and by image analysis. We found that (1) the red digital numbers (i.e., the digital intensity values of the red pixels; DNR) extracted from the time-lapse digital camera images tended to peak in full bloom; and (2) the green excess index (GET) (based on the red, green, and blue digital numbers) tended to be lowest in full bloom. These results indicate that DNR and GEI are useful for detecting the timing of full bloom in P. sargentii.

Livestock dung provides an important direct pathway by which carbon and nutrients enter soils in pasture ecosystems and affects carbon and nitrogen cycling indirectly through changes in soil and plant properties. Here, we quantify dung deposition, decomposition, and the effects of dung on soil and plants in a Zoysia japonica grassland in Japan. We determined (1) the distribution of dung, (2) the mass loss rate of dung and the amount of carbon respired as CO2, and (3) changes in soil properties and aboveground biomass of Z. japonica. Dung deposition was 4.0-9.7 g C and 0.4-1.0 g N m(-2) year(-1) and distributed patchily (Morishita's I (delta) &gt; 1). Most (71 %) of the carbon in dung deposited in June was lost within a single grazing period by aerobic decomposition, more than mass loss rate of Z. japonica litter in the first year (about 50 %), suggesting that grazing and defecation can accelerate carbon cycling compared with the typical litterfall-decomposition regime. Nitrogen in dung mass entered the soil as ammonium nitrogen and was nitrified. The spatiotemporal distribution of these processes corresponded to that of stimulated Z. japonica growth. These results suggested that dung deposition significantly affected the inorganic nitrogen status of soil and, therefore, the growth of Z. japonica. However, these effects were very restricted temporally (July-August) and spatially (within 10 cm from dung edge). Thus, such spatiotemporally restricted effects combined with the patchy distribution of dung may contribute to the heterogeneous structure of pasture ecosystems.

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.

Trenching (Tr), root biomass regression (RR), and root excising (RE) methods were used to estimate the contribution of root (RR) and heterotrophic (HR) respiration to soil respiration (SR) in a cool-temperate deciduous forest in central Japan. The contribution ratios of RR to SR were 23 % (-16 to 46 %), 11 % (-19 to 61 %), and 115 % (20 to 393 %), as estimated by the Tr, RR, and RE methods, respectively. The contribution ratio showed clear seasonal variation with high values in summer for the Tr method, while they were undetectable for the RR and RE methods because of some methodological problems. These results suggest the Tr method is the best of the three methods used to estimate the contribution ratio of RR and HR to SR in the forest. Annual SR, RR, and HR rates, estimated by the Tr method, were 479, 369, 110 gC m(-2) year(-1), respectively. The seasonal variation of SR was mainly influenced by HR (77 %) throughout the year, while the influence of RR on SR was strongest in summer (46 %). This effect occurred because RR (Q (10) = 7.5) is more sensitive to temperature than HR (Q (10) = 3.2). Also, the contribution of fine RR to total RR was higher than that of coarse RR because of high respiratory activity (Q (10) and R (10)) as well as the large biomass of fine roots. These results suggest that each component of SR responds differently to the same environmental factors and their relative influence on SR changes across the seasons.

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.

土壌呼吸に対する土壌生物呼吸の寄与率の季節および年変化と，それらの変化が森林生態系の炭素収支に与える影響を明らかにするために，呼吸量・土壌温度・土壌水分量の関係と約3年間の土壌生物呼吸の寄与率の季節および年変化を推定した。土壌生物呼吸はトレンチ法を用いて土壌呼吸から分離し，2009年11月から2012年9月まで土壌表面からのCO₂放出速度を土壌温度，体積土壌含水率とともに測定した。また，トレンチ法の問題点である枯死根の分解にともなうCO₂放出を，従来法よりも正確に考慮するため，これらの季節および年変化をルートバッグ法と2つの分解モデルを用いて推定した。<br> その結果，土壌温度や土壌水分量に対して土壌呼吸と土壌生物呼吸は異なる応答を示した。土壌温度の上昇にともない各呼吸量は上昇し，その応答性は土壌呼吸よりも土壌生物呼吸の方が低かった。一方，土壌水分量の上昇に伴い，土壌呼吸は増加したのに対して，土壌生物呼吸は減少した。したがって，土壌生物呼吸の寄与率は土壌温度及び土壌水分量が上昇するのにともない減少した。これらの結果は，土壌温度と土壌水分量の両方が同時に変化する野外環境において，呼吸量や寄与率が複雑に変動することを示唆している。<br> 本研究において土壌生物呼吸の年寄与率は2010年，2011年ともに62%であったが，この寄与率は大きな季節変化（60～100%）を示した。これらの季節変化を考慮しなかった場合，推定される2010年の土壌生物呼吸量は1.50から2.51 kg CO₂ m^-2 yr^-1で変動し，この値は季節変化を考慮した場合（1.56 kg CO₂ m^-2 yr^-1）の96～161%の値となった。また，土壌生物呼吸の寄与率の推定に土壌水分量を考慮しなかった場合，年寄与率は80%となった。この値から推定された土壌生物呼吸量は2.01 kg CO₂ m^-2 yr^-1となり，土壌水分量を考慮した場合の128%の値となった。一方，寄与率の年変化は非常に小さく，推定される土壌生物呼吸量に大きな影響はなかった。したがって，森林生態系においてより正確な土壌生物呼吸量や森林の炭素収支を明らかにするためには，土壌生物呼吸の寄与率が明確な季節性を示すこと，そして土壌温度だけでなく土壌水分量による影響を強く受けていることを考慮することが重要である。

The aim of this study is to clarify changes in the ecosystem carbon cycle in response to predicted global warming in various ecosystems including semi-natural grassland. To clarify responses of the whole ecosystem to warming in a semi-natural cool-temperate grassland, we conducted an in situ warming experiment and examined plant growth and CO₂ flux responses. Five pairs (control and warmed plots) of Zoysia japonica plots were established. Warmed plots were warmed using infrared heaters from June to November 2009. Once a month, aboveground biomass (AGB) of Z. japonica was estimated using the point frame method. Net ecosystem production (NEP) and ecosystem respiration (Re) were determined from CO₂ flux measured using the closed chamber method. Each month, relationships were obtained between photosynthetic photon flux density (PPFD) and NEP (PPFD-NEP curve) and soil temperature (ST) and Re (ST-Re curve). Monthly cumulative NEP, Re, and gross primary production (GPP, sum of NEP and Re) were calculated using these relationships and continuously recorded PPFD and ST data. Although there were some mechanical problems when using infrared heaters, the soil temperature in the warmed plots where infrared heaters worked well was an average of 2.3°C higher than the control plots. This suggests the heating method using infrared heaters is applicable to grassland ecosystems. AGB in the warmed plots tended to be higher (by a maximum of 70%) than in the control plots throughout the experimental period, suggesting that experimental warming affected the phenology and extended the growth period of Z. japonica. Initial slope and light compensation point of PPFD-NEP curve were significantly affected by the warming. Monthly cumulative GPP in the warmed plots tended to be higher (by a maximum of 32%) than in the control plots. This is partly explained by the increased biomass and changed photosynthetic characteristics in the warmed plots. Although not all parameters of the ST-Re curve were affected by warming, monthly cumulative Re in the warmed plots tended to be higher (by a maximum of 35%) than in the control plots. As a result, monthly cumulative NEP in the warmed plots tended to be higher than in the control plots, especially in July (approximately 70% higher) and October (approximately 100% higher). These results suggest that experimental warming affected the carbon cycle in semi-natural cool-temperate grassland by changing the phenology and photosynthetic characteristics of Z. japonica. To promote a better understanding of whole ecosystem responses to predicted warming, a longer term experiment and more detailed descriptions of carbon dynamics including the belowground part of the ecosystem are needed.

暖温帯常緑広葉樹林における土壌加温に対する微生物群集の反応

Polar willow (Salix polaris Wahlenb.), a mycorrhizal dwarf shrub, colonizes recently deglaciated areas in the High Arctic, Svalbard. To clarify successional changes in ECM fungi associated with S. polaris after glacier retreat, we examined the diversity and density of ECM fungi in culture and field conditions. Plant and soil samples were collected from three sites of different successional stages in the deglaciated area of Austre Broggerbreen, near Ny-lesund, Svalbard. The successional stages were early stage with newly exposed bare ground (site I), transient stage with scattered colonization of Salix (sites IIa and IIb), and late stage with well-developed vegetation (site III). No ECM colonization on Salix was observed in soils collected from bare ground in early and transient stages (sites I and IIa). However, most Salix individuals showed ECM colonization in soils collected from sites close to Salix colonies in transient and late stages (sites IIb and III). Based on molecular analyses and operational taxonomic unit (OTU: &gt; 95% ITS sequence similarity) delimitations, we identified 15 OTUs/species in eight genera. The dominant OTU/species of ECM fungi identified in the transient and late stages was Geopora sp.1 and Cenococcum sp.1, respectively. In the culture experiment, ECM diversity was greater in late stage (eight OTUs/species) than in transient stage (three OTUs/species). This pattern was consistent with field observations, i.e., late-stage sites contained more OTUs/species of ECM fungi. These results indicate that species diversity of ECM fungi increases and the dominant species changes with the progress of succession after glacier retreat in the High Arctic.

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 CO(2) 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. &gt; 13 degrees 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.

IPCC(2007)の予測によると、今世紀末の地球表面温度の上昇は北極地域が最も著しいとされている。北極陸上生態系には、樹木を欠き、矮性の低木や草本、あるいは蘚苔類や地衣類によって優占されているツンドラ生態系が広がっている。ツンドラ生態系では、維管束植物に比べて非維管束植物の種数は多くなる傾向があり、ある地域では植物の種組成の7割以上を非維管束植物が占めることが知られている。本発表では、寒冷な地においても高い多様性を維持し、ツンドラ生態系の主要な構成要素となっている、非維管束植物の光合成生産におよぼす温度の影響について紹介する。<br>ノルウェー・スピッツベルゲン島、ニーオルスンにある東ブレッガー氷河後退域に優占する、カギハイゴケ、トゲエイランタイ、および藻類や地衣類等から成り、地表面に"かさぶた"状の構造体をつくるバイオロジカルソイルクラスト（以下、クラスト）の光合成特性を調査した。その結果、水分が供給されている際の最大光合成速度は、カギハイゴケ>トゲエイランタイ>クラストとなった。純光合成速度の至適温度は、カギハイゴケが最も高く、トゲエイランタイとクラストは低かった。温度上昇が光合成生産に与える影響を、モデルを用いて推定したところ、いずれの植物も純生産量は減少したが、その度合いは著しく異なり、温度上昇の影響は植物によって異なることが示唆された。

We used phospholipid fatty acid (PLFA) analysis to examine the relation of microbial biomass and community composition to vegetation zonation on a coastal sand dune. Soil samples were collected along 3 line transects established from the shoreline to the inland bush. Total PLFA content and PLFA composition of soils were used as indices of total microbial biomass and community composition, respectively. The microbial biomass was much higher in the inland Vitex rotundifolia zone than in the seaside plots. The microbial community composition also differed among the vegetation zones, with a higher contribution of fungal biomarkers in the inland plots. The microbial biomass increased significantly with increasing soil organic matter (SOM) content, but was not correlated with soil salinity. These results suggest that microbial biomass in the coastal sand dune was controlled primarily by the accumulation of SOM. The microbial community composition also changed with SOM content in the seaside plots, but SOM had little effect in the inland plots. These results suggest that the factors limiting the microbial community composition differed with location on the dune.

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. (c) 2006 Elsevier Masson SAS. All rights reserved.

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.

土壌微生物は有機物分解や無機化を通して土壌生成に重要な役割を果たしており、その質や量（バイオマスや群集構造、活性）は、土壌が未発達な一次遷移初期においても重要であると考えられる。氷河後退後に一次遷移が見られる高緯度北極域では、植生や土壌理化学性の変化に関して多数の報告があるが、土壌微生物相の遷移についての情報は少ない。本研究では北極エルズミア島オーブロヤー湾周辺（N80˚50'，W82˚45'）の氷河後退域において、一次遷移の進行に伴う微生物相の変化を明らかにすることを目的とした。微生物のバイオマス及び群集構造の解析には、リン脂質脂肪酸分析を用いた。この方法は、微生物の細胞膜成分であるリン脂質由来の脂肪酸を分析する方法であり、特定の微生物グループの指標となる脂肪酸を定性・定量することで、量的な情報と同時に質的な情報が得られるという利点がある。<br> 2004年7月に、オーブロヤー湾周辺の生成年代が異なるモレーン上に、計5つのプロット（最新期、新期、中期、古期、最古期）を設置した。モレーンの生成年代は250年程度から25000–35000年程度と推定されている。各プロットにつき5箇所から、鉱質土層の0–0.5，0.5–2.0，2.0–5.0 cmを採取した。土壌は真空乾燥させて日本に持ち帰った後、リン脂質脂肪酸分析に供した。<br> 微生物バイオマスの指標である全脂肪酸量は、新期–最古期の4プロットに比べて最新期で著しく少なかったが、新期–最古期間での変化は小さく、むしろ同一プロット内の植生の異なる地点間で大きな違いが認められた。群集構造の指標の1つである糸状菌/バクテリアバイオマス比も採取地点の植生及び深度によって大きく異なった。これらの違いについて、モレーンの生成年代や植生、土壌中C・N量などと関連付けて議論する。

スバールバル諸島・ニーオールスンには、氷河後退域のツンドラ生態系が広がっており、氷河後退時期や微地形などの違いにより植生のモザイク状分布が認められる。生態系機能は植生タイプと密接に関係しており、ツンドラ生態系の広域的な炭素固定機能評価の第一段階として、一次遷移に伴う土壌の発達プロセスと植生構造との関係を明らかにすることを目的とした。<br> 2003年の8月に東ブレッガー氷河の先端から海岸まで約3kmのライントランセクトを5本設定し、各トランセクト上に200m間隔で調査プロット（各4m²) を設置した。各プロットにおいて、植生調査として藻類の被度と、コケ・地衣植物及び維管束植物のリストと被度、土壌調査として地表面の礫被度、動物の糞被度、土壌深度、土壌水分量、pHの測定を行った。さらに各調査プロットの複数の地点で深さ別の土壌サンプリングを行い土壌中の全炭素量と全窒素量を測定した。<br> 調査を行った全64プロットにおいて維管束植物は43種出現した。維管束植物の出現しない場所を除いた51プロットの組成からTWINSPANにより植生タイプを区分した結果、Salix polarisとOxilia digynaを指標種として、両種が出現しないプロット（氾濫源と若い氷河後退域）と両種の出現するプロット（古い氷河後退域）の大きく二つのグループに分けられた。一次遷移の初期段階である、前者のグループでは礫被度は80％以上で、土壌深度は浅くpHは8以上のアルカリ性を示した。このグループのプロットでは植物の被度は極端に少ないが、コケや地衣類とほぼ同時に一次遷移のごく初期段階から維管束植物のSaxifraga oppositifolia が侵入することが確認された。一次遷移が進行した後者のグループでは土壌深度は10cmを超える場合もあり、pHもほぼ中性であった。このグループのプロットでは維管束植物のSalix polarisとコケ植物のSanionia uncinataが優占する群落が広がっているが、地形的要因によって、Dryas octopetala群落などのいくつかの植生タイプが区分された。