大橋 瑞江

To clarify soil respiration (soil CO2 efflux, R-s) characteristics in a subtropical evergreen broad-leaved natural forest in Yambaru, Okinawa, Japan, we examined spatiotemporal variation in R-s and its determining factors. We then compared yearly R-s with the value in other forests. The spatial variation in R-s (coefficient of variation [CV] = 38.9%) was not significantly related to temperature or soil water content but was evidently dependent on ground surface litter coverage. R-s was greater in summer (ca. 7-10 mu mol m(-2) s(-1)), and its seasonal variation was exponentially related to soil temperature (Q(10) = 2.16). As a function of soil temperature, we estimated a yearly mean stand-scale R-s of 5.17 mu mol m(-2) s(-1), and a total carbon efflux from the soil of 1959 g C m(-2) year(-1) for 2014. Despite showing similar seasonal patterns as those in temporal forests, the R-s in this ecosystem is very high throughout the year, and the yearly value is much higher for natural mature forests. A mass balance approach suggests that the large amount of belowground carbon allocation of plants contributed to the high CO2 emissions from the soils.

Abstract. Dissolved organic matter (DOM) degradation in freshwater rivers and streams plays a major role in the global carbon cycle. However, little is known about how the source and composition of riverine DOM contribute to the production of greenhouse gases, especially in high-latitude areas with a large proportion of carbon-rich peatlands. Here, we conducted for the first time the combination of molecular-level characterization of terrestrially derived DOM and the potential carbon dioxide (CO2) production measurements in pristine subarctic rivers of Finnish Lapland. 21-day incubation studies were conducted with water samples taken from two rivers differing in DOM content during spring and fall 2018. The changes in the DOM concentration and molecular composition, as well as the CO2 production, were measured. The DOM molecular characterization was carried out using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Our results demonstrate efficient mineralization of dissolved organic carbon (DOC) into CO2 in mineral soil associated clearwater river during the incubation, while significantly lower CO2 production per DOC was observed in the brown-water river surrounded by peatlands. The limited degradability in the brown-water river was caused by a large number of terrestrial and aromatic compounds (i.e., highly unsaturated and phenolic compounds, condensed aromatics, and polyphenolics) from surrounding peatlands. In the clearwater river, the percentage of formulas assigned to aliphatics decreased over the incubation, indicating microbial utilization of biolabile DOM. This study highlights the importance of energy-rich, biolabile molecular compounds and the contribution of clearwater systems in the DOM degradation dynamics of subarctic catchments.

Tree resistance to uprooting can be estimated as the critical turning moment in tree-pulling experiments. The depth at the center point of rotation (Dcp) in tree-pulling experiments is measured as an indicator of below-ground traits and is related to this critical turning moment. However, few researchers have investigated the relationship between the Dcp and maximum root depth. Our objective in this study was to clarify whether the Dcp in tree-pulling experiments can be estimated as the maximum root depth of Pinus thunbergii Parl. in sandy soils. We also estimated which position of displacement of the center of rotation (Cp) can be applied as the Dcp. We conducted tree-pulling experiments, and compared the Dcp obtained from images with the measured maximum root depth. We found significant positive correlations between the Dcp and maximum root depth. The Cp displacement concentrated immediately below the stem when the maximum critical turning moment was reached. This position should be measured as the Dcp, which is related to the maximum root depth. We found that the Dcp can serve as a parameter, preventing the need for uprooting, when tree-pulling experiments are performed to obtain an important below-ground trait for understanding the critical turning moment.

Three-dimensional (3D) root system architecture (RSA) is a predominant factor in anchorage failure in trees. Only a few studies have used 3D laser scanners to evaluate RSA, but they do not check the accuracy of measurements. 3D laser scanners can quickly obtain RSA data, but the data are collected as a point cloud with a large number of points representing surfaces. The point cloud data must be converted into a set of interconnected axes and segments to compute the root system traits. The purposes of this study were: (i) to propose a new method for easily obtaining root point data as 3D coordinates and root diameters from point cloud data acquired by 3D laser scanner measurement; and (ii) to compare the accuracy of the data from main roots with intensive manual measurement. We scanned the excavated root systems of two Pinus thunbergii Parl. trees using a 3D laser scanner and neuTube software, which was developed for reconstructing the neuronal structure, to convert the point cloud data into root point data for reconstructing RSA. The reconstruction and traits of the RSA calculated from point cloud data were similar in accuracy to intensive manual measurements. Roots larger than 7 mm in diameter were accurately measured by the 3D laser scanner measurement. In the proposed method, the root point data were connected as a frustum of cones, so the reconstructed RSAs were simpler than the 3D root surfaces. However, the frustum of cones still showed the main coarse root segments correctly. We concluded that the proposed method could be applied to reconstruct the RSA and calculate traits using point cloud data of the root system, on the condition that it was possible to model both the stump and ovality of root sections.

© 2020 IAWF. Forest fires can change the quality of dissolved organic matter (DOM) in soils, and consequently have a great influence on biogeochemical cycles in forest ecosystems. However, little information is available regarding the effects of fire on the chemical composition of DOM in boreal forest soils. To clarify these effects, the molecular composition of soil DOM was compared between recently-burned and long-unburned boreal forests (6 and 156 years since the last fire, respectively) in Finnish Lapland. Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that there were no significant differences in species, average molecular weight or the number of molecular compounds detected between the recently-burned and long-unburned forests. However, the number of compounds with condensed aromatic structures tended to be larger in the recently-burned forest, whereas the numbers of proteins and carbohydrates not shared between the two forests were significantly smaller. Lignin-like molecules accounted for most of the total molecular species in both forests. Our results suggest that fire not only generated several species of dissolved black carbon, but also caused burned plant residues, which supplied diverse lignin-like molecules in the recently-burned forest soils and led to the number of molecular species being comparable to that in the long-unburned forest soils.

© 2019 Elsevier B.V. Tree root diameter and root distribution are crucial factors for root reinforcement in forest soils and can be estimated using nondestructive ground-penetrating radar (GPR). However, no studies on estimating root reinforcement have been performed using GPR. The aim of this study was to evaluate root reinforcement using GPR in thinned and unthinned stands of Cryptomeria japonica in Andisols. Roots in each stand were detected using a 900 MHz GPR and the diameter and horizontal distribution of roots were estimated. Roots were also excavated to compare their GPR estimates. The relationships between root diameter and tensile force were established through field pullout tests. Finally, root reinforcements in each stand were estimated using the recently proposed root bundle model (RBM). There were no significant differences in the diameter frequency distribution of roots estimated between thinned and unthinned stands, determined using either the GPR or excavation methods. The detection frequency of the number of roots >5 mm in diameter using GPR was 27.2%, but it increased to 58.7% for roots >10 mm. The waveform indexes, determined using the sum of time intervals between zero crossings (ΣT) of all reflection waveforms of GPR, had a significant linear relationship with the diameters of excavated roots, indicating that waveform index could be used to estimate root diameter using the GPR index in these stands. Furthermore, the relationship between the root tensile force (F) and- root diameter (d) was estimated as F = 15.69 d1.75 (R2 = 0.87). The root reinforcements at the center of gaps between individual trees were estimated to be 23.4–32.9 kPa in the thinned stand and 8.8–23.9 kPa in the unthinned stand using GPR. These values ranged from 31.9% to 170.7% of those obtained by using the excavation method. There were no significant differences in root reinforcement between thinned and unthinned stands, regardless of the method used. This study revealed that GPR, together with diameter-tensile force relationships, can nondestructively estimate root reinforcement in managed forests. This protocol can be applied to manage forests to evaluate the effects of management on belowground roots.

© 2019, Springer Nature Switzerland AG. Aims: Root phenology patterns in tropical regions are poorly understood because limited data are available. Using the root scanner method, the aims of this study were to clarify 1) the temporal phenology of root production and decomposition, 2) the spatial variability of the root phenology, and 3) the contribution of different root diameter classes to root production and decomposition. Methods: Image acquisition was conducted monthly from April 2014 to May 2015 at five sites in a Bornean tropical rainforest. The projected area and length of root production and decomposition were derived manually from images using image-processing software and were grouped into 0.5-mm-diameter intervals. Results: The spatial distribution of root production and decomposition differed among the sites. Monthly projected root length indicated that the number and timing of peak root production and decomposition differed with each site. A substantial proportion of root production and decomposition was dominated by very fine roots (<0.5 mm diameter). Conclusions: The scanner method was useful to monitor the root phenology at the root system scale though the scanner images cover only a portion of the root systems of mature trees. Different patterns of root phenology among the sites might be associated with the high diversity and the indistinct seasonality of the Bornean tropical rainforest.

© 2019, Springer Nature Switzerland AG. Aims: Tropical forests contribute significantly to the stability of global carbon (C) balance; however, little is known about root litter decomposition in tropical rainforests. In this study, we aimed to (1) characterise the effect of soil depth, root diameter and soil organisms on root litter decomposition and (2) estimate the contribution of root decomposition to soil carbon dioxide (CO 2 ) efflux in a tropical rainforest in Malaysian Borneo. Methods: We incubated soil chambers with fine and coarse root litterbags at varying soil depths. Soil chambers were covered with nets of different mesh sizes, and CO 2 efflux was monitored from the top of each soil chamber during the incubation. Results: Our results showed that coarse roots decomposed faster than fine roots. There was no impact of soil depth, but soil animals and fungi had a significant impact on coarse root decomposition from 398 days after the start of the experiment. Soil CO 2 efflux increased linearly with C loss from root decomposition, indicating that 40% of the CO 2 efflux originates from root litter. Conclusions: The variation in root decomposition rates suggests the possible role of root litter in soil C storage and emission in a tropical rainforest.

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Main conclusion: We developed simple algorithms for reconstructing tree root system architecture using only the root point coordinate and diameter, which can be systematically obtained without digging up the root systems. Root system architecture (RSA) is strongly related to various root functions of the tree. The aim of this study was to develop a three-dimensional (3D) RSA model using systematically obtained information on root locations and root diameters at the locations. We excavated root systems of Cryptomeria japonica and systematically obtained XYZ coordinates and root diameters using a 10-cm grid. We clarified the patterns of the root point connections and developed a reconstructed root system model. We found that the root diameters farther from the stump centre are smaller. Additionally, we found that the root lengths of the segments running between the base and the connected root point were smaller than those of other root segments, and the inner angle between the base and the stump and between the base and the connected root point was narrower than for the other pairs. The new RSA model developed according to these results had average accuracies of 0.64 and 0.80 for estimates of total volume and length, respectively. The developed model can estimate 3D RSA using only root point data, which can be obtained without digging up root systems. This suggests a wide applicability of this model in root function evaluation.

© 2019 by the authors. Rainwater interacts with tree canopies in forest ecosystems, which greatly influence its quality. However, little information is available regarding how tree canopies influence dissolved organic matter (DOM) in rainwater. To examine this, we collected bulk deposition (rainfall) and throughfall in a conifer (Chamaecyparis obtusa) plantation, western Japan, during a rain event, and analyzed their DOM molecular compositions using ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry. The dissolved organic carbon flux and the number of DOM molecular species detected were approximately seven times and three times higher in throughfall than in rainfall, respectively. We found that the average proportion of molecular species shared between five sample replicates was larger in throughfall (69%) than in rainfall (50%). Nonmetric multidimensional scaling revealed that the molecular species were significantly differentiated between throughfall and rainfall, and the dissimilarity among the replicates was much smaller in throughfall. This indicates that the quality of DOM in rainwater became spatially homogeneous due to contact with tree canopies. The number of lignin-like molecules was larger than those of any other biomolecular compounds in throughfall and seven times larger than in rainfall, suggesting that many of plant-derived DOM molecules were dissolved into rainwater.

© 2018 by the authors. Research highlights: Estimates of fine root production using ingrowth cores are strongly influenced by decomposed roots in the cores during the incubation period and should be accounted for when calculating fine root production (FRP). Background and Objectives: The ingrowth core method is often used to estimate fine root production; however, decomposed roots are often overlooked in estimates of FRP. Uncertainty remains on how long ingrowth cores should be installed and how FRP should be calculated in tropical forests. Here, we aimed to estimate FRP by taking decomposed fine roots into consideration. Specifically, we compared FRP estimates at different sampling intervals and using different calculation methods in a tropical rainforest in Borneo. Materials and Methods: Ingrowth cores were installed with root litter bags and collected after 3, 6, 12 and 24 months. FRP was estimated based on (1) the difference in biomass at different sampling times (differential method) and (2) sampled biomass at just one sampling time (simple method). Results: Using the differential method, FRP was estimated at 447.4 ± 67.4 g m -2 year -1 after 12 months, with decomposed fine roots accounting for 25% of FRP. Using the simple method, FRP was slightly higher than that in the differential method after 12 months (516.3 ± 45.0 g m -2 year -1 ). FRP estimates for both calculation methods using data obtained in the first half of the year were much higher than those using data after 12-months of installation, because of the rapid increase in fine root biomass and necromass after installation. Conclusions: Therefore, FRP estimates vary with the timing of sampling, calculation method and presence of decomposed roots. Overall, the ratio of net primary production (NPP) of fine roots to total NPP in this study was higher than that previously reported in the Neotropics, indicating high belowground carbon allocation in this forest.

<p>In recent ethological studies, the behaviors and interactions of animals have been recorded by digital video cameras and webcams, which provide high functionality at reasonable cost. However, extracting the behavioral data from these videos is a laborious and time-consuming manual task. We recently proposed a novel method for tracking unmarked multiple honeybees in a flat arena, and developed a prototype software named "K-Track". The K-Track algorithm successfully resolved nearly 90% of cases involving overlapped or interacted insects, but failed when such events happened near an edge of a circular arena, which is commonly employed in experiments. In the present study, we improved our K-Track algorithm by comparing the interaction trajectories obtained from forward and backward playing of video episodes. If the tracking results differed between the forward and backward episodes, the trajectory with lower maximum moving distance per frame is chosen. Based on this concept, we developed a new software, "K-Track-kai", and compared the performances of K-Track and K-Track-kai in honeybee tracking experiments. In the cases of 6 and 16 honeybees, K-Track-kai improved the tracking accuracy from 91.7% to 96.4% and from 94.4% to 96.7%, respectively.</p>

© 2018 Elsevier B.V. The extent of damage to Pinus thunbergii trees in coastal forests resulting from the tsunami caused by the Great East Japan Earthquake in 2011 differed depending on the local environment. The height (H) of P. thunbergii was generally limited in stands closer to the coastline and these trees could fail due to the force of the tsunami. The resistance forces of coastal forests to tsunamis are expressed as critical turning moments and measured by tree-pulling experiments. However, few studies have focused on the differences in the critical turning moment between stands with locally different environmental conditions among P. thunbergii coastal forests. We determined the differences in the critical turning moments of P. thunbergii in two contrasting sites having different distances from the coastline. We also estimated the tolerance of P. thunbergii in the two sites against loading from tsunami. Two experimental plots, sea-side and land-side, in a coastal P. thunbergii forest were established with different depths of the water table belowground and wind forces. In both plots, the aboveground traits, including the diameter at breast height (DBH), and H × DBH2 of P. thunbergii, were positively correlated with the critical turning moments. In particular, when P. thunbergii had the same H × DBH2 between the plots, there were no differences in the critical turning moments. This result suggested that P. thunbergii at the sea-side had acclimated for 50 years to their environment by changing shallow tap roots for shallower belowground water and developing horizontal roots for strong winds. The depth of the center point of rotation was significantly deeper and was positively correlated with moments in the land-side plot, suggesting changes from a tap root system to a plate root system in the sea-side plot with a shallower water table. The estimated loading from the tsunami with a 2 m wave height was over the critical turning moments for both plots. P. thunbergii trees at the sea-side plot could be more susceptible to overturning by lower-height waves than at the land-side plot because of differences in aboveground traits of H × DBH. We propose that the practical management of coastal forests is to create an embankment by raising the ground level to develop tree growth with capable of enhanced resilience to tsunamis.

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Key message: Use of ground-penetrating radar (GPR) can non-destructively estimate diameter and distribution of coarse roots in Cryptomeria japonica in weathered granite soils under field conditions. Abstract: Ground-penetrating radar (GPR) has been used as an assessment tool for non-destructive detection of tree root biomass, but few studies have estimated root diameter under forest field conditions. The aim of this study was to clarify whether coarse root diameter of C. japonica in weathered granite soils can be estimated using GPR in a forest. Roots of mature C. japonica were scanned using a 900 MHz GPR antenna before being excavated. The diameter and distribution of excavated roots were compared with those identified by GPR, and the relationships between the diameter and waveform indices in radar profiles were also examined. The detection frequency of the number of roots larger than 5 mm in diameter was 47.7%. Limiting factors affecting root detection using GPR in forest field conditions were small root diameter, increasing root depth, and number of adjacent roots. Only one waveform index, using the sum of time intervals between zero crossings (ΣT, ns) of all reflection waveforms of GPR within the range from the first break time at the root top to the delay point time at the root bottom, had a significant relationship with excavated root diameters. A linear regression model was constructed to estimate root diameter using ΣT, and a significant positive relationship in diameter between GPR-estimated and excavated roots was confirmed. The results in this study indicate that the diameter and distribution of C. japonica coarse roots under forest field conditions could be estimated using GPR and this technique could contribute to future evaluation of slope stability by evaluating tree roots under vulnerable soils, such as weathered granite.

© 2018, Springer International Publishing AG, part of Springer Nature. The original version of this article unfortunately contained a mistake. Table 3 was published erroneously. This Table has now been corrected.

© 2018, Springer International Publishing AG, part of Springer Nature. Aims: The different root systems of Pinus thunbergii observed after the tsunami in 2011 were possibly influenced by different groundwater levels before the tsunami. The aims of this study were to quantify the tap and horizontal root structure and evaluate their relationship with the above-ground parts under different groundwater levels in a coastal P. thunbergii forest. Methods: Two plots, sea- and land-side, with different groundwater levels, in a P. thunbergii stand, were established, and the entire root-systems of three select trees each were harvested to evaluate the biomass, lengths, and cross-sectional areas of the tap and horizontal roots. Results: In the sea-side plot, which had a shallower groundwater level, plate root systems with thicker and longer horizontal roots, but fewer tap roots were observed, whereas tap root systems were well developed in the land-side plots, where the groundwater level was deeper. The root-to- shoot ratio was significantly higher in the sea-side plot than in the land-side plot. Conclusion: We confirmed that quantitative contrasting root systems of P. thunbergii develop under different groundwater levels and higher biomass allocation to horizontal roots occur under shallower groundwater depths, emphasizing the need for management practices that promote the development of tap root systems to enhance resistance to tsunamis.

© 2017 IEEE. In recent studies, researchers can easily record the behaviors of animals by digital video cameras, which provide high functionality at reasonable cost. However, it is a laborious and time-consuming manual task for them to extract the useful behavioral data from these videos. We recently proposed a tracking method for unmarked multiple honeybees in a flat arena, named the 'K-Track' algorithm. The algorithm can successfully identify and track nearly 90% of interaction cases of targets. In this study, we proposed an improved method for the existing K-Track algorithm by tracking results using backward-play movie. If the tracking results differed between the forward and backward episodes, one of them had probably resulted from correct tracking. Therefore, by comparing the forward and backward trajectories of the same interaction, we assumed that there is the potential for an increase in tracking accuracy. In the experiments, K-Track using backward movies successfully tracked four out of five situations that was failed by original K-Track and we confirmed that the method has the potential of improved tracking accuracy.

© 2018 The Japanese Forest Society. To investigate the contribution of soil animals to the cesium-137 (137Cs) concentration change in the course of the litter decomposition process, we conducted litter bag experiments in forest sites located about 50 km northwest from the Fukushima Dai-ichi Nuclear Power Plant. To control the influence of soil animals of different size, two different mesh sizes of litter bags (fine and coarse mesh) were used. Litter bags were placed in three different types of forests: (1) broad-leaved forest, (2) Japanese red pine mixed broad-leaved, and (3) Japanese cedar plantation, for the period from November 2012 to April 2014. Through the whole period, litter was decomposed to 60–70% from the initial dry weight. We found no significant difference between the mesh sizes. The litter 137Cs concentration and the relative 137Cs amount in each sampling time from initial 137Cs amount (relative 137Cs amount) in broad-leaved and mixed broad-leaved forests increased from the initial. In both forest types, 137Cs concentration in coarse mesh showed higher than the fine mesh. In cedar plantation, relative 137Cs amount in both mesh sizes did not differ from the initial value. We assumed that enhancement of the activity of microbes by the mesofauna contributed to an increase in the amount of 137Cs in the litter. Although we could not deny the effect of mesh size of the litter bag, the activity of soil organism could be one of the factors that lead to an incremental increase of the 137Cs amount in the litter layer.

© The Author(s) 2018. Clarifying the dynamics of fine roots is critical to understanding carbon and nutrient cycling in forest ecosystems. An optical scanner can potentially be used in studying fine-root dynamics in forest ecosystems. The present study examined image analysis procedures suitable for an optical scanner having a large (210 mm × 297 mm) root-viewing window. We proposed a protocol for analyzing whole soil images obtained by an optical scanner that cover depths of 0–210 mm. We tested our protocol using six observers with different experience in studying roots. The observers obtained data from the manual digitization of sequential soil images recorded for a Bornean tropical forest according to the protocol. Additionally, the study examined the potential tradeoff between the soil image size and accuracy of estimates of fine-root dynamics in a simple exercise. The six observers learned the protocol and obtained similar temporal patterns of fine-root growth and biomass with error of 10–20% regardless of their experience. However, there were large errors in decomposition owing to the low visibility of decomposed fine roots. The simple exercise revealed that a smaller root-viewing window (smaller than 60% of the original window) produces patterns of fine-root dynamics that are different from those for the original window size. The study showed the high applicability of our image analysis approach for whole soil images taken by optical scanners in estimating the fine-root dynamics of forest ecosystems.

© 2017, The Ecological Society of Japan. The aggressive expansion of Moso bamboo (Phyllostachys pubescens) forest into adjacent ecosystems which might alter the carbon balance replacement, has been noted recently in East Asian countries such as Taiwan. Moso bamboo has a biennial growth cycle that causes significant inter-annual variations in net primary productivity (NPP) and net ecosystem productivity (NEP). To our knowledge, only one study has investigated NPP covering biennial cycles in a Moso bamboo forest. Therefore, the aim of the present study was to clarify the NPP and NEP in a Moso bamboo forest in Taiwan by considering above- and below-ground processes over a 4-year experimental period. The estimated NPP and NEP showed considerable inter-annual variations (coefficient of variation of 39 and 79%, respectively). Averaged over the 4 years, the NPP and NEP were 8.86 ± 3.46 and 4.32 ± 3.35 Mg C ha−1 year−1, respectively, which were within the ranges (6.53–14.36 and 3.59–7.98 Mg C ha−1 year−1, respectively) reported for Moso bamboo forests in East Asian countries. A global comparison of NPP and NEP among forest ecosystems using data from published literature indicated that the estimated NPP and NEP in the present study, as well as those in Moso bamboo forests from East Asian countries, were within the upper range of the values reported for other forest ecosystem. The results indicate that Moso bamboo forests may have high potential as a carbon sink among forests ecosystems.

© 2017, The Ecological Society of Japan. The correct name of the first author should be ‘Meng-Ying Lin’, and not ‘Meng-Yin Lin’ as given in the original publication of the article.

© 2017 Elsevier B.V. Ants and termites are highly abundant in tropical forest soil, but their role in soil CO2 emission is poorly understood. Our goal in this study was to determine the CO2 emission from nests of ants and termites in a tropical rainforest in Sarawak (Borneo), Malaysia. The study was conducted in Lambir Hills National Park, Miri. We located nests of ants and termites and measured CO2 emission from the nests and from the surrounding control soils. Soil temperature and moisture content were also recorded at the nests and control soil locations. The ants and termites were identified to genera (and to species in many cases) and their body mass was determined. In total, we found 113 nests of 36 ant species and 20 nests of 10 termite species. CO2 emission from ant and termite nests was significantly higher than that from the surrounding soils, suggesting ant and termite nests are hot spots of CO2 emission from the soil. Because of nesting activities, soil moisture content was significantly lower in ant nests compared to that of the control soils. The effect of soil temperature and moisture content on nest CO2 emission was less clear when compared to emission from the surrounding control soils. Significant differences in nest CO2 emission were observed between different ant species, which could be partly attributable to differences in body mass.

© 2017 The Author(s). Dissolved organic matter (DOM) strongly affects water quality within boreal forest ecosystems. However, how the quality of DOM itself changes spatially is not well understood. In this study, to examine how the diversity of DOM molecules varies in water moving through a boreal forest, the number of DOM molecules in different water samples, i.e., rainwater, throughfall, soil water, groundwater, and stream water was determined using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in Norway spruce and Scots pine stands in eastern Finland during May and June 2010. The number of molecular compounds identified by FT-ICR MS (molecular diversity) ranged from 865 to 2,194, revealing large DOM molecular diversity in the water samples. Additionally, some of the molecular compounds were shared between different water samples. The DOM molecular diversity linearly correlated with the number of low-biodegradable molecules, such as, lignin-like molecules (lignins), but not with dissolved organic carbon concentration. The number of lignins shared between different sampling locations was larger than that of any other biomolecular class. Our results suggest that low-biodegradable molecules, especially lignins, regulate spatial variations in DOM molecular diversity in boreal forests.

© 2016 Elsevier B.V. The sodium (Na) respiration hypothesis (SER) states that low Na availability limits the activity and density of soil organisms and therefore plays an important role in decomposition processes of tropical forest soils. Support for this hypothesis was found in several studies reporting higher decomposition rates attributed to higher densities of macro-invertebrates after sodium chloride (NaCl) additions. However, it was also suggested that high doses of NaCl might make organic material unpalatable or even toxic for microbes. Most of these studies were conducted in inland tropical rainforests, where atmospheric deposition of Na is low compared to coastal areas and therefore Na limitation may be more severe. We assessed how treating standardized organic material with different NaCl concentrations affects decomposition rates in a coastal primary rainforest on the island of Borneo. For this purpose, we established a multi-factorial short-term (7 days) decomposition experiment in which we incubated cotton cloths (standard organic material). The cloths were treated with 0%, 0.5%, 1%. 2.5% or 5% NaCl solutions and either provided access for all soil decomposer communities (no mesh) or excluded macro-invertebrates >2 mm (metal mesh). The cloths were placed in the mineral soil and on top of the litter layer. We found higher decomposition in the mineral soil compared to the top of the litter layer. Decomposition rates of cloths treated with 5% NaCl were significantly higher compared to all other cloths, which provides first evidence that the SER might also hold for coastal systems. In addition, we found higher decomposition for the meshed than the non-meshed cloths suggesting that macro-invertebrates either “grazed” on the smaller invertebrates/microbes or that the smaller soil fauna was more efficient in exploiting NaCl when macro-invertebrates were absent. Overall our findings suggest that Na may also control the activity of soil organisms in coastal tropical forest ecosystems.

© 2016 Elsevier Ltd The nuclear accidents at Chernobyl and Fukushima released large amounts of 137 Cs radionuclides into the atmosphere which spread over large forest areas. We compared the 137 Cs concentration distribution in different parts of two coniferous forest ecosystems (needle litter, stems and at different depths in the soil) over short and long term periods in Finland and Japan. We also estimated the change in 137 Cs activity concentrations in needle and soil between 1995 and 2013 in Southern Finland based on the back-calculated 137 Cs activity concentrations. We hypothesized that if the 137 Cs activity concentrations measured in 1995 and 2013 showed a similar decline in concentration, the 137 Cs activity concentration in the ecosystem was already stable in 1995. But if not, the 137 Cs activity concentrations were still changing in 2013. Our results showed that the vertical distribution of the 137 Cs fallout in the soil was similar in Hyytiälä and Fukushima. The highest 137 Cs concentrations were observed in the uppermost surface layers of the soil, and they decreased exponentially deeper in the soil. We also observed that 137 Cs activity concentrations estimated from the samples in 1995 and 2013 in Finland showed different behavior in the surface soil layers compared to the deep soil layer. These results suggested that the 137 Cs nuclei were still mobile in the surface soil layers 27 years after the accident. Our results further indicated that, in the aboveground parts of the trees, the 137 Cs concentrations were much closer to steady-state when compared to those of the surface soil layers based on the estimated declining rates of 137 Cs concentration activity in needles which were similar in 1995 and 2013. Despite its mobility and active role in the metabolism of trees, the 137 Cs remains in the structure of the trees for decades, and there is not much exchange of 137 Cs between the heartwood and surface layers of the stem.

© 2016 Elsevier B.V. Wood CO2 efflux (Rwood) is an important carbon cycling process in forest ecosystems and is less understood in Bornean tropical rainforests compared with that in Neotropics, which have differing biotic and abiotic characteristics. Bornean tropical rainforests have particularly higher aboveground biomass because of high stand densities of tall emergent trees, and no regular seasonal dry period. These properties may reflect specific Rwood variation and higher annual Rwood at the ecosystem scale (annual-Rwood) in Borneo. Hence, in this study, we investigated factors that affect inter-individual variation in chamber-based Rwood on stem surfaces at breast height (chamber-Rwood) and estimated Rwood at the ecosystem scale (ecosystem-Rwood) in a Bornean tropical rainforest. Subsequently, we examined temporal variation in ecosystem-Rwood with environmental factors, estimated annual-Rwood, and then evaluated the effects of large trees on ecosystem-Rwood. Stem growth rates were the most significant predictor of inter-individual variation in chamber-Rwood during all five measurement periods between 2012 and 2014. Accordingly, stem growth rates allowed accurate estimates of ecosystem-Rwood, although chamber-Rwood varied with diameter at breast height (DBH) and tree species in some measurement campaigns. Ecosystem-Rwood decreased with soil moisture. Considering the inter-individual and temporal variation, annual-Rwood was estimated at 7.06 ± 2.09 MgC ha-1 year-1. This value was comparable to those determined in Neotropical forests, even though aboveground biomass in the present study site was approximately twice of those in Neotropical sites. Large trees with DBH >70 cm comprised 38% of aboveground biomass but accounted for only 23% of ecosystem-Rwood because of the small portion of woody tissue surface area of the large trees. These data indicate that the stand density of large trees can considerably affect aboveground biomass but exert less influence on variation in ecosystem-Rwood among various forests.

© 2015, Springer-Verlag Berlin Heidelberg. Key message: The estimates of fine root production by net sheet method were not affected by the net material or the aperture size, but flexible nets are preferable to avoid an underestimation. Abstract: The estimation of the fine root production is important for understanding the mechanisms of carbon cycling in ecosystems. The recently developed net sheet method allows the measurement of fine root production in forest ecosystems. The simplicity of this innovative technique reduces labor costs and causes little soil disturbance during installation. However, the protocols and methods are still poorly developed; for example, the effects of net material, mesh aperture size and firmness on the results remain unknown. Therefore, we measured the number and dry mass of fine roots grown through net sheets in forest soils to determine the effect of the net quality and type (polyamide, polyethylene, polyethylene terephthalate, stainless steel), mesh aperture size (2 and 4 mm) and firmness (firm and flexible) on the results. The study was conducted in managed and unmanaged Japanese cedar forests in Japan and in a mixed dipterocarp forest in Malaysia. No effect of net material or mesh aperture size on the number of roots grown through the net sheets or on root production was observed. A smaller number of roots grew through the firm type of nets than that of the flexible nets in the managed Japanese cedar and mixed dipterocarp forests. These results suggest that fine root production is not affected by the material of the net sheets or the mesh aperture size, but flexible nets are preferable to avoid an underestimation of fine root production.

© The Author(s) 2016. The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 emitted 1.2 × 1016 Bq of cesium-137 (137 Cs) into the surrounding environment. Radioactive substances, including 137 Cs, were deposited onto forested areas in the northeastern region of Japan. 137 Cs is easily adsorbed onto clay minerals in the soil; thus, a major portion of 137 Cs can be transported as eroding soil and particulate organic matter in water discharge. Dissolved 137 Cs can be taken up by microbes, algae, and plants in soil and aquatic systems. Eventually, 137 Cs is introduced into insects, worms, fishes, and birds through the food web. To clarify the mechanisms of dispersion and export of 137 Cs, within and from a forested ecosystem, we conducted intensive monitoring on the 137 Cs movement and storage in a forested headwater catchment in an area approximately 50 km from the Nuclear Power Plant. Two major pathways of 137 Cs transport are as follows: (1) by moving water via dissolved and particulate or colloidal forms and (2) by dispersion through the food web in the forest-stream ecological continuum. The 137 Cs concentrations of stream waters were monitored. Various aquatic and terrestrial organisms were periodically sampled to measure their 137 Cs concentrations. The results indicate that the major form of exported 137 Cs is via suspended matter. Particulate organic matter may be the most important carrier of 137 Cs. High water flows generated by a storm event accelerated the transportation of 137 Cs from forested catchments. Estimation of 137 Cs export from the forested catchments requires precise evaluation of the high water flow during storm events. The results also suggested that because the biggest pool of 137 Cs in the forested ecosystem is the accumulated litter and detritus, 137 Cs dispersion is quicker through the detritus food chain than through the grazing food chain.

© 2015 Elsevier Ltd. Since the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011, large areas of the forests around Fukushima have become highly contaminated by radioactive nuclides. To predict the future dynamics of radioactive cesium (137Cs) in the forest catchment, it is important to measure each component of its movement within the forest. Two years after the accident, we estimated the annual transportation of 137Cs from the forest canopy to the floor by litterfall, throughfall and stemflow. Seasonal variations in 137Cs transportation and differences between forests types were also determined. The total amount of 137Cs transported from the canopy to the floor in two deciduous and cedar plantation forests ranged between 3.9 and 11.0 kBq m-2 year-1. We also observed that 137Cs transportation with litterfall increased in the defoliation period, simply because of the increased amount of litterfall. 137Cs transportation with throughfall and stemflow increased in the rainy season, and 137Cs flux by litterfall was higher in cedar plantation compared with that of mixed deciduous forest, while the opposite result was obtained for stemflow.

© 2014 The Authors. Many ant species construct subterranean nests. The presence of their nests may explain soil respiration "hot spots", an important factor in the high CO2 efflux from tropical forests. However, no studies have directly measured CO2 efflux from ant nests. We established 61 experimental plots containing 13 subterranean ant species to evaluate the CO2 efflux from subterranean ant nests in a tropical seasonal forest, Thailand. We examined differences in nest CO2 efflux among ant species. We determined the effects of environmental factors on nest CO2 efflux and calculated an index of nest structure. The mean CO2 efflux from nests was significantly higher than those from the surrounding soil in the wet and dry seasons. The CO2 efflux was species-specific, showing significant differences among the 13 ant species. The soil moisture content significantly affected nest CO2 efflux, but there was no clear relationship between nest CO2 efflux and nest soil temperature. The diameter of the nest entrance hole affected CO2 efflux. However, there was no significant difference in CO2 efflux rates between single-hole and multiple-hole nests. Our results suggest that in a tropical forest ecosystem the increase in CO2 efflux from subterranean ant nests is caused by species-specific activity of ants, the nest soil environment, and nest structure.

Earthworms are important soil macrofauna inhabiting almost all ecosystems. Their biomass is large and their burrowing and ingestion of soils alters soil physicochemical properties. Because of their large biomass, earthworms are regarded as an indicator of "soil heath". However, primarily because the difficulties in quantifying their behavior, the extent of their impact on soil material flow dynamics and soil health is poorly understood. Image data, with the aid of image processing tools, are a powerful tool in quantifying the movements of objects. Image data sets are often very large and time-consuming to analyze, especially when continuously recorded and manually processed. We aimed to develop a system to quantify earthworm movement from video recordings. Our newly developed program successfully tracked the two-dimensional positions of three separate parts of the earthworm and simultaneously output the change in its body length. From the output data, we calculated the velocity of the earthworm's movement. Our program processed the image data three times faster than the manual tracking system. To date, there are no existing systems to quantify earthworm activity from continuously recorded image data. The system developed in this study will reduce input time by a factor of three compared with manual data entry and will reduce errors involved in quantifying large data sets. Furthermore, it will provide more reliable measured values, although the program is still a prototype that needs further testing and improvement. Combined with other techniques, such as measuring metabolic gas emissions from earthworm bodies, this program could provide continuous observations of earthworm behavior in response to environmental variables under laboratory conditions. In the future, this standardized method will be applied to other animals, and the quantified earthworm movement will be incorporated into models of soil material flow dynamics or behavior in response to chemical substances present in the soil. © 2014 Kodama et al.

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ~40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux.

Difficult access to 40-m-tall emergent trees in tropical rainforests has resulted in a lack of data related to vertical variations in wood CO2 efflux, even though significant variations in wood CO2 efflux are an important source of errors when estimating whole-tree total wood CO2 efflux. This study aimed to clarify vertical variations in wood CO2 efflux for emergent trees and to document the impact of the variations on the whole-tree estimates of stem and branch CO2 efflux. First, we measured wood CO2 efflux and factors related to tree morphology and environment for seven live emergent trees of two dipterocarp species at four to seven heights of up to ~40 m for each tree using ladders and a crane. No systematic tendencies in vertical variations were observed for all the trees. Wood CO2 efflux was not affected by stem and air temperature, stem diameter, stem height or stem growth. The ratios of wood CO2 efflux at the treetop to that at breast height were larger in emergent trees with relatively smaller diameters at breast height. Second, we compared whole-tree stem CO2 efflux estimates using vertical measurements with those based on solely breast height measurements. We found similar whole-tree stem CO2 efflux estimates regardless of the patterns of vertical variations in CO2 efflux because the surface area in the canopy, where wood CO2 efflux often differed from that at breast height, was very small compared with that at low stem heights, resulting in little effect of the vertical variations on the estimate. Additionally, whole-tree branch CO2 efflux estimates using measured wood CO2 efflux in the canopy were considerably different from those measured using only breast height measurements. Uncertainties in wood CO2 efflux in the canopy did not cause any bias in stem CO2 efflux scaling, but affected branch CO2 efflux. © 2014 The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The honeybee waggle dance communicates the location of profitable food sources, usually with a certain degree of error in the directional information ranging from 10-15° at the lower margin. We simulated one-day colonial foraging to address the biological significance of information error in the waggle dance. When the error was 30° or larger, the waggle dance was not beneficial. If the error was 15°, the waggle dance was beneficial when the food sources were scarce. When the error was 10° or smaller, the waggle dance was beneficial under all the conditions tested. Our simulation also showed that precise information (0-5° error) yielded great success in finding feeders, but also caused failures at finding new feeders, i.e., a high-risk high-return strategy. The observation that actual bees perform the waggle dance with an error of 10-15° might reflect, at least in part, the maintenance of a successful yet risky foraging trade-off.

A computer program that tracks animal behavior, thereby revealing various features and mechanisms of social animals, is a powerful tool in ethological research. Because honeybee colonies are populated by thousands of bees, individuals co-exist in high physical densities and are difficult to track unless specifically tagged, which can affect behavior. In addition, honeybees react to light and recordings must be made under special red-light conditions, which the eyes of bees perceive as darkness. The resulting video images are scarcely distinguishable. We have developed a new algorithm, K-Track, for tracking numerous bees in a flat laboratory arena. Our program implements three main processes: (A) The object (bee's) region is detected by simple threshold processing on gray scale images, (B) Individuals are identified by size, shape and spatiotemporal positional changes, and (C) Centers of mass of identified individuals are connected through all movie frames to yield individual behavioral trajectories. The tracking performance of our software was evaluated on movies of mobile multi-artificial agents and of 16 bees walking around a circular arena. K-Track accurately traced the trajectories of both artificial agents and bees. In the latter case, K-track outperformed Ctrax, well-known software for tracking multiple animals. To investigate interaction events in detail, we manually identified five interaction categories; 'crossing', 'touching', 'passing', 'overlapping' and 'waiting', and examined the extent to which the models accurately identified these categories from bee's interactions. All 7 identified failures occurred near a wall at the outer edge of the arena. Finally, K-Track and Ctrax successfully tracked 77 and 60 of 84 recorded interactive events, respectively. K-Track identified multiple bees on a flat surface and tracked their speed changes and encounters with other bees, with good performance. © 2014 Kimura et al.

© 2014, Springer International Publishing Switzerland. Aim: In this study, we clarify the effect of short-term drought treatment on the spatial variation of soil CO2 efflux in a forest, and to interpret the changes in soil CO2 efflux caused by root activities.Methods: Experimental plots (15 m radius) were established around six emergent trees and a drought treatment was conducted for three of the six plots. Soil CO2 efflux was measured along with environmental factors and root biomass, respiration and production in each plot.Results: Soil CO2 efflux at 0.5 m of the emergent trees was nearly three times higher than at 5 and 10 m away from the trees. Root respiration and biomass had no correlation with the spatial variation. Soil water content decreased by nearly 30 % during the drought treatment, although soil CO2 efflux was unchanged between drought and control plots.Background: Our previous studies documented how soil CO2 efflux, one of the main carbon pathways in forest ecosystems, is affected by soil moisture and forest structure in an aseasonal tropical rainforest in Borneo, Malaysia.Conclusions: Our result suggests a strong spatial variation exists in soil CO2 efflux around emergent trees, but short-term severe drought has little effect on it.

Tree root respiration is an important component of the carbon balance in forest ecosystems; however, it is not clear whether root preparation treatments (such as excising and washing) affect root respiration measurements. Here, we aimed to compare the respiration rates of roots subjected to different treatments (i.e., washing with water vs. brushing without water, and excising vs. not excising) for 17-month-old seedlings of Cryptomeria japonica. Immediately after sampling an entire root system, the root respiration rate was measured on a mass basis using a closed static chamber system equipped with an infrared gas analyzer. We found that the respiration rates for roots that were excised 10-20 times were significantly higher than those for roots that were not excised. There was no significant difference in the root respiration rates between washing and brushing treatments. Our results indicate that large numbers of excisions (>10 times) could lead to bias in the measured changes in specific root respiration rates, and imply that differences between washing and brushing treatments do not affect the specific root respiration rate. We conclude that potential variation in recorded root respiration rates could be minimized by standardizing the root preparation technique, which should involve rapidly removing all loose soil and limiting the extent of root excision. © 2012 The Japanese Forest Society and Springer.

To clarify characteristics of carbon (C) allocation in a Bornean tropical rainforest without dry seasons, gross primary production (GPP) and C allocation, i.e., above-ground net primary production (ANPP), aboveground plant respiration (APR), and total below-ground carbon flux (TBCF) for the forest were examined and compared with those from Amazonian tropical rainforests with dry seasons. GPP (30.61 MgC ha-1 year-1, eddy covariance measurements; 34.40 MgC ha-1 year-1, biometric measurements) was comparable to those for Amazonian rainforests. ANPP (6.76 MgC ha-1 year-1) was comparable to, and APR (8.01 MgC ha-1 year-1) was slightly lower than, their respective values for Amazonian rainforests, even though aboveground biomass was greater at our site. TBCF (19.63 MgC ha-1 year-1) was higher than those for Amazonian forests. The comparable ANPP and higher TBCF were unexpected, since higher water availability would suggest less fine root competition for water, giving higher ANPP and lower TBCF to GPP. Low nutrient availability may explain the comparable ANPP and higher TBCF. These data show that there are variations in C allocation patterns among mature tropical rainforests, and the variations cannot be explained solely by differences in soil water availability. © 2012 The Botanical Society of Japan and Springer Japan.