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Steven C Wofsy - One of the best experts on this subject based on the ideXlab platform.
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dynamics of canopy stomatal conductance transpiration and evaporation in a Temperate Deciduous Forest validated by carbonyl sulfide uptake
Biogeosciences, 2016Co-Authors: R Wehr, William J Munger, Roisin Commane, Barry J Mcmanus, David D Nelson, Mark S Zahniser, Scott R Saleska, Steven C WofsyAbstract:Abstract. Stomatal conductance influences both photosynthesis and transpiration, thereby coupling the carbon and water cycles and affecting surface–atmosphere energy exchange. The environmental response of stomatal conductance has been measured mainly on the leaf scale, and theoretical canopy models are relied on to upscale stomatal conductance for application in terrestrial ecosystem models and climate prediction. Here we estimate stomatal conductance and associated transpiration in a Temperate Deciduous Forest directly on the canopy scale via two independent approaches: (i) from heat and water vapor exchange and (ii) from carbonyl sulfide (OCS) uptake. We use the eddy covariance method to measure the net ecosystem–atmosphere exchange of OCS, and we use a flux-gradient approach to separate canopy OCS uptake from soil OCS uptake. We find that the seasonal and diurnal patterns of canopy stomatal conductance obtained by the two approaches agree (to within ±6 % diurnally), validating both methods. Canopy stomatal conductance increases linearly with above-canopy light intensity (in contrast to the leaf scale, where stomatal conductance shows declining marginal increases) and otherwise depends only on the diffuse light fraction, the canopy-average leaf-to-air water vapor gradient, and the total leaf area. Based on stomatal conductance, we partition evapotranspiration (ET) and find that evaporation increases from 0 to 40 % of ET as the growing season progresses, driven primarily by rising soil temperature and secondarily by rainfall. Counterintuitively, evaporation peaks at the time of year when the soil is dry and the air is moist. Our method of ET partitioning avoids concerns about mismatched scales or measurement types because both ET and transpiration are derived from eddy covariance data. Neither of the two ecosystem models tested predicts the observed dynamics of evaporation or transpiration, indicating that ET partitioning such as that provided here is needed to further model development and improve our understanding of carbon and water cycling.
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site level evaluation of satellite based global terrestrial gross primary production and net primary production monitoring
Global Change Biology, 2005Co-Authors: David P Turner, Steven C Wofsy, William D Ritts, Warren B Cohen, Thomas K Maeirsperger, Stith T Gower, Al A Kirschbaum, S W Running, Maosheng Zhao, Allison L DunnAbstract:Operational monitoring of global terrestrial gross primary production (GPP) and net primary production (NPP) is now underway using imagery from the satellite-borne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Evaluation of MODIS GPP and NPP products will require site-level studies across a range of biomes, with close attention to numerous scaling issues that must be addressed to link ground measurements to the satellite-based carbon flux estimates. Here, we report results of a study aimed at evaluating MODIS NPP/GPP products at six sites varying widely in climate, land use, and vegetation physiognomy. Comparisons were made for twenty-five 1km 2 cells at each site, with 8-day averages for GPP and an annual value for NPP. The validation data layers were made with a combination of ground measurements, relatively high resolution satellite data (Landsat Enhanced Thematic Mapper Plus at � 30m resolution), and process-based modeling. There was strong seasonality in the MODIS GPP at all sites, and mean NPP ranged from 80gCm � 2 yr � 1 at an arctic tundra site to 550gCm � 2 yr � 1 at a Temperate Deciduous Forest site. There was not a consistent over- or underprediction of NPP across sites relative to the validation estimates. The closest agreements in NPP and GPP were at the Temperate Deciduous Forest, arctic tundra, and boreal Forest sites. There was moderate underestimation in the MODIS products at the agricultural field site, and strong overestimation at the desert grassland and at the dry coniferous Forest sites. Analyses of specific inputs to the MODIS NPP/ GPP algorithm ‐ notably the fraction of photosynthetically active radiation absorbed by the vegetation canopy, the maximum light use efficiency (LUE), and the climate data ‐ revealed the causes of the over- and underestimates. Suggestions for algorithm improvement include selectively altering values for maximum LUE (based on observations at eddy covariance flux towers) and parameters regulating autotrophic respiration.
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fluxes of nitrogen oxides over a Temperate Deciduous Forest
Journal of Geophysical Research, 2004Co-Authors: Cassandra Volpe Horii, William J Munger, David D Nelson, Mark S Zahniser, Steven C Wofsy, Barry J McmanusAbstract:[1] Eddy covariance flux measurements of NO, NO2, and O3 were obtained above the mixed Deciduous canopy at Harvard Forest in central Massachusetts from April to November 2000. Net deposition of NOx was observed throughout the measurement period, with average velocity of ∼0.2 cm s−1. At night, NO2 is deposited at a rate that depends nonlinearly on NO2 concentration and cannot be explained by N2O5 hydrolysis, suggesting HONO formation by heterogeneous disproportionation of NO2. During the day, photochemically driven NOx fluxes conform to the predicted behavior based on gradients of light and eddy diffusivity through the canopy, with residual net flux attributable to both stomatal and nonstomatal processes. The results were consistent with a compensation point for NO2 near 1.5 nmol mol−1. These results were confirmed by independent evidence from NO, NO2, and O3 profiles acquired at the site over several years. If the rate of NOx deposition observed at this site in April through November continues during the winter, it would have a larger potential impact on tropospheric chemistry because mixing depths are shallow and chemical NOx oxidation is slow during winter; the impact at night is important for the same reasons. The results contradict widely used parameterizations of NO2 deposition that both overestimate stomatal uptake and do not allow for surface uptake when stomates are closed.
Hiroshi Takeda - One of the best experts on this subject based on the ideXlab platform.
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Microfungus communities of Japanese beech logs at different stages of decay in a cool Temperate Deciduous Forest
Canadian Journal of Forest Research, 2009Co-Authors: Yu Fukasawa, Takashi Osono, Hiroshi TakedaAbstract:Fallen logs of Japanese beech (Fagus crenata Blume) at various stages of decomposition were sampled from a cool Temperate Deciduous Forest in Japan and studied for differences in the associated microfungus communities. Wood samples were directly plated onto each of two different media for the identification of fungal species. Approximately 1500 isolations were made, which represent 96 species of filamentous microfungi, consisting of 16 zygomycetes and 80 anamorphic ascomycetes. The number of species per log (α-diversity) increased with log decomposition, while dissimilarity of species composition among logs (β-diversity) showed a unimodal response with the optimum at the intermediate decay stage. The water content and nitrogen concentration of the wood were positively correlated, while the lignocellulose index and relative density were negatively correlated with α-diversity. Stepwise regression models suggested that lignocellulose index was the single most important determinant of variation in α-diversity...
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above and belowground biomass and net primary production in a cool Temperate Deciduous Forest in relation to topographical changes in soil nitrogen
Forest Ecology and Management, 2004Co-Authors: Ryunosuke Tateno, Takuo Hishi, Hiroshi TakedaAbstract:Abstract Patterns in above- and belowground allocation of biomass and net primary production (NPP) along a topographic and soil N availability gradient were measured in a cool-Temperate Deciduous Forest in central Japan. In this study site, soil N availability changed along the topographic sequence and decreased up the slope. Total NPP ranged from 8.8 to 14.1 t ha−1 and showed no trends along the topographic sequence, while the percentage of belowground NPP to total NPP ranged from 15.2 to 55.1% and increased up the slope. The aboveground NPP ranged from 5.6 to 8.6 t ha−1 and decreased up the slope. Belowground NPP ranged from 1.5 to 7.7 t ha−1 and increased up the slope. Fine root production contributed to this trend. Allocation to structural components in the lower slope exceeded that on upper slope positions, whereas higher allocation to fine roots on the upper slope may result in higher annual belowground litterfall. Our results suggest that differences in the carbon allocation pattern of plants between structural and litter components may be a driving force to create variations in Forest structure and nutrient cycling along the topographic sequence.
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comparison of litter decomposing ability among diverse fungi in a cool Temperate Deciduous Forest in japan
Mycologia, 2002Co-Authors: Takashi Osono, Hiroshi TakedaAbstract:The litter decomposing ability of 79 fungal isolates (41 genera, 60 species) was assessed with the pure culture decomposition test. The isolates were collected qualitatively in a cool Temperate Deciduous Forest in Japan during a 21-mo period. Loss of original weight of sterilized litter ranged from 0.1% to 57.6%. Six isolates in the Basidiomycota caused high weight losses ranging from 15.1% to 57.6%. Fourteen isolates in Xylaria and Geniculosporium (the Xylariaceae and its anamorph) also caused high weight losses ranging from 4.0% to 14.4%. Other isolates in the Ascomycota and associated anamorphs and in the Zygomycota caused low weight losses on mean. Six fungi in the Basidiomycota, and all in the Xylariaceae showed a bleaching activity of the litter and caused lignin and carbohydrate decomposition. Mean lignin/weight loss ratios (L/W) and lignin/carbohydrate loss ratios (L/C), were 0.9 and 0.7 for the Basidiomycota and 0.7 and 0.4 for the Xylariaceae, respectively. Significant differences were found in ...
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comparison of litter decomposing ability among diverse fungi in a cool Temperate Deciduous Forest in japan
Mycologia, 2002Co-Authors: Takashi Osono, Hiroshi TakedaAbstract:The litter decomposing ability of 79 fungal isolates (41 genera, 60 species) was assessed with the pure culture decomposition test. The isolates were collected qualitatively in a cool Temperate Deciduous Forest in Japan during a 21-mo period. Loss of original weight of sterilized litter ranged from 0.1% to 57.6%. Six isolates in the Basidiomycota caused high weight losses ranging from 15.1% to 57.6%. Fourteen isolates in Xylaria and Geniculosporium (the Xylariaceae and its anamorph) also caused high weight losses ranging from 4.0% to 14.4%. Other isolates in the Ascomycota and associated anamorphs and in the Zygomycota caused low weight losses on mean. Six fungi in the Basidiomycota, and all in the Xylariaceae showed a bleaching activity of the litter and caused lignin and carbohydrate decomposition. Mean lignin/weight loss ratios (L/W) and lignin/carbohydrate loss ratios (L/C), were 0.9 and 0.7 for the Basidiomycota and 0.7 and 0.4 for the Xylariaceae, respectively. Significant differences were found in L/W and L/C between the two groups when the result of Xylaria sp. that showed marked delignification was excluded. These differences in lignin and carbohydrate utilization patterns are discussed in relation to the structural and the chemical properties of the decomposed litter and to the implications for organic chemical changes during litter decomposition processes.
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organic chemical and nutrient dynamics in decomposing beech leaf litter in relation to fungal ingrowth and succession during 3 year decomposition processes in a cool Temperate Deciduous Forest in japan
Ecological Research, 2001Co-Authors: Takashi Osono, Hiroshi TakedaAbstract:Decomposition processes of beech leaf litter were studied over a 3-year period in a cool Temperate Deciduous Forest in Japan. Organic chemical and nutrient dynamics, fungal biomass and succession were followed on upper (Moder) and lower (Mull) of a Forest slope. Litter decomposition rates were similar between the sites. Nutrient dynamics of the decomposing litter was categorized into two types: weight changes in nitrogen and phosphorus showed two phases, the immobilization (0–21 months) and the mobilization phase (21–35 months), while those in potassium, calcium and magnesium showed only the mobilization phase. The rate of loss of organic chemical constituents was lignin < holocellulose < soluble carbohydrate < polyphenol in order. The changes in lignocellulose index (LCI), the ratio of holocellulose in lignin and holocellulose, were significantly correlated to the changes in nitrogen and phosphorus concentrations during the decomposition. During the immobilization phase, increase in total fungal biomass contributed to the immobilization of nitrogen and phosphorus. The percentage of clamp-bearing fungal biomass (biomass of the Basidiomycota) to total fungal biomass increased as the decomposition proceeded and was significantly correlated to LCI. Two species in the xylariaceous Ascomycota were dominantly isolated by the surface sterilization method from decomposing litter collected in the 11th month. The organic chemical, nitrogen and phosphorus dynamics during the decomposition were suggested to be related to the ingrowth, substrate utilization and succession of the Xylariaceae and the Basidiomycota. Twenty-one species in the other Ascomycota and the Zygomycota isolated by the washing method were classified into three groups based on their occurrence patterns: primary saprophytes, litter inhabitants and secondary sugar fungi. These species showed different responses to LCI and soluble carbohydrate concentration of the litter between the groups.
Chuankuan Wang - One of the best experts on this subject based on the ideXlab platform.
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Measuring Vegetation Phenology with Near-Surface Remote Sensing in a Temperate Deciduous Forest: Effects of Sensor Type and Deployment
Remote Sensing, 2019Co-Authors: Xingchang Wang, Chuankuan WangAbstract:Near-surface remote sensing is an effective tool for in situ monitoring of canopy phenology, but the uncertainties involved in sensor-types and their deployments are rarely explored. We comprehensively compared three types of sensor (i.e., digital camera, spectroradiometer, and routine radiometer) at different inclination- and azimuth-angles in monitoring canopy phenology of a Temperate Deciduous Forest in Northeast China for three years. The results showed that the greater contribution of understory advanced the middle of spring (MOS) for large inclination-angle of camera and spectroradiometer. The length of growing season estimated by camera from the east direction extended 11 d than that from the north direction in 2015 due to the spatial heterogeneity, but there was no significant difference in 2016 and 2018.The difference infield of view of sensors caused the MOS and the middle of fall, estimated by camera, to lag a week behind those by spectroradiometer and routine radiometer. Overall, the effect of azimuth-angle was greater than that of inclination-angle or sensor-type. Our assessments of the sensor types and their deployments are critical for the long-term accurate monitoring of phenology at the site scale and the regional/global-integration of canopy phenology data.
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Autumn phenology of a Temperate Deciduous Forest: Validation of remote sensing approach with decadal leaf-litterfall measurements
Agricultural and Forest Meteorology, 2019Co-Authors: Fan Liu, Xingchang Wang, Chuankuan WangAbstract:Abstract Autumn (i.e., leaf-fall) phenology plays an important role in regulating the canopy duration and is often monitored using near-surface and satellite remote sensing techniques, but the measurements have rarely been validated by the ground observation. The objectives of this study were to: (1) evaluate the performance of radiometer-based broadband vegetation index (VIB) and Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation index (VIM) in monitoring the autumn phenology of a Chinese Temperate Deciduous Forest with decadal (2008 – 2018) leaf-litterfall measurements, and (2) explore the feasibility of using VIB to validate the VIM products for monitoring the autumn phenology. We found that the seasonal and interannual trends of both VIB and VIM agreed well with those of the leaf-litterfall (correlation coefficients r > 0.93). The broadband normalized difference vegetation index (NDVIB) best tracked the interannual variation in the end-of-season (EOS) among the six metrics of the VIB investigated, while the MODIS enhanced vegetation index (EVIM) did so among the six metrics of the VIM, with the corresponding determination coefficient (R2) of 0.66 and 0.44 with the EOS estimated by the leaf-litterfall. The EOS estimated by VIB and VIM was 0 – 11 d earlier than that by the leaf-litterfall. Comparing the six metrics of VIM with the corresponding ones of VIB, the EOS derived from the NDVI had the closest correlation with each other (R2 = 0.67). Conclusively, our study validated the remote-sensed leaf-fall phenology with decadal ground measurements, and suggested that radiometer and MODIS could effectively track the autumn phenology in Temperate Deciduous Forests and the leaf-litterfall collection could be used as a complementary approach.
Shohei Murayama - One of the best experts on this subject based on the ideXlab platform.
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O 2 :CO 2 exchange ratios observed in a cool Temperate Deciduous Forest ecosystem of central Japan
Tellus B: Chemical and Physical Meteorology, 2013Co-Authors: Shigeyuki Ishidoya, Nobuko Saigusa, Shohei Murayama, Hiroaki Kondo, Chikako Takamura, Daisuke Goto, Shinji Morimoto, Nobuyuki Aoki, Shuji Aoki, Takakiyo NakazawaAbstract:Detailed observations of O 2 :CO 2 exchange ratios were conducted in a cool Temperate Deciduous Forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11±0.01 and 1.02±0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O 2 /N 2 ratio and the CO 2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87±0.02) than in the nighttime (1.03±0.02) with a daily mean value of 0.94±0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a one-box canopy O 2 /CO 2 budget model simulation of net turbulent O 2 and CO 2 fluxes between the atmosphere and the Forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O 2 and CO 2 fluxes depend sensitively on the Forest ecosystem processes. Keywords: O 2 :CO 2 exchange ratio, Forest ecosystem, atmospheric O 2 /N 2 ratio, continuous measurements (Published: 4 December 2013) Citation: Tellus B 2013, 65 , 21120, http://dx.doi.org/10.3402/tellusb.v65i0.21120
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Seasonal variations of atmospheric CO2, δ13C, and δ18O at a cool Temperate Deciduous Forest in Japan: Influence of Asian monsoon
Journal of Geophysical Research, 2010Co-Authors: Shohei Murayama, Nobuko Saigusa, Susumu Yamamoto, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, C. Takamura, Hiroyasu Kondo, T. Usami, Masayuki KondoAbstract:[1] Atmospheric CO2 concentration and its isotopes have been measured at the Takayama site in central Japan since 1994, together with δ18O in precipitation since 2002, to examine their temporal variations in a cool-Temperate Deciduous Forest environment strongly influenced by the Asian monsoon. The CO2 concentration and δ13C at the observational site show prominent seasonal variations accompanied by a secular trend, suggesting that the average seasonal cycle is caused mainly by a seasonal-dependent CO2 exchange with C3 plants. However, the variation in summer is found to be related to CO2 exchange with a significantly heavier δ13C signal compared to the other seasons, indicating some influence at the Takayama site of atmospheric transport of CO2 impacted by exchange with C4 plants from upstream regions. Compared with CO2 and δ13C, δ18O measurements in atmospheric CO2 are scattered, showing no clear seasonal variation. From late spring to early fall, significant year-to-year differences in the variation of δ18O are observed, with low and high values associated with rainy and sunny summer conditions, respectively. Comparisons with data from other northern midlatitude sites suggest that the rapid decrease of δ18O seen at Takayama in the early summer of a rainy summer year is characteristic of the Asian monsoon region. On the other hand, the characteristic increase in δ18O observed from winter to spring is likely caused by long-range transport of air with enriched δ18O.
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Temporal variations of atmospheric CO2 concentration in a Temperate Deciduous Forest in central Japan
Tellus B: Chemical and Physical Meteorology, 2003Co-Authors: Shohei Murayama, Nobuko Saigusa, Susumu Yamamoto, Hiroaki Kondo, Douglas Chan, Yozo EguchiAbstract:In order to examine the temporal variation of the atmospheric CO 2 concentration in a Temperate Deciduous Forest, and its relationship with meteorological conditions, continuous measurements of CO 2 and meteorological parameters have been made since 1993 on a tower at Takayama in the central part of Japan. In addition to an average secular increase in atmospheric CO 2 of 1.8 ppm yr −1 , diurnal variation with a maximum during the night-time to early morning and a minimum in the afternoon is observed from late spring to early fall; the diurnal cycle is not so clearly observed in the remaining seasons of the year. A concentration difference between above and below the canopy, and its diurnal variation, can also be seen clearly in summer. Daily mean concentration data show a prominent seasonal cycle. The maximum and the minimum of the seasonal cycle occur in April and from mid August to mid September, respectively. Day-to-day changes in the diurnal cycle of CO 2 are highly dependent on the day-to-day variations in meteorological conditions. However, CO 2 variations on longer time scales (>10 d) appear to be linearly related to changes in respiration. At Takayama, variations in the 10-d standard deviation of daily mean CO 2 data and 10-d averaged respiration show distinct relationships with soil temperature during spring and fall seasons. In spring, respiration has a stronger exponential dependence on soil temperature than in fall. Interestingly, in summer when soil temperature becomes greater than about 15 °C, biological respiration becomes more variable and independent of the soil temperature. Thus, at the Takayama site, the Q 10 relationship is seasonally dependent, and does not represent well the biological respiration process when the soil temperature rises above 15 °C. DOI: 10.1034/j.1600-0889.2003.00061.x
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gross primary production and net ecosystem exchange of a cool Temperate Deciduous Forest estimated by the eddy covariance method
Agricultural and Forest Meteorology, 2002Co-Authors: Nobuko Saigusa, Susumu Yamamoto, Shohei Murayama, Hiroaki Kondo, Noboru NishimuraAbstract:Abstract An eddy covariance measurement system was installed to measure long-term turbulent fluxes of heat, water vapor, and CO2 over a cool-Temperate Deciduous Forest in the central part of Japan. Previous to a long-term measurement, a comparison of flux measurements using open- and closed-path type infrared gas analyzers was conducted for CO2 and water vapor. The closure of the energy budget over the Forest was also examined to test the validity of the flux measurements. Using a whole year data from 25 July 1998 to 24 July 1999, the relation between the night-time air temperature and the night-time CO2 flux over the Forest (ecosystem respiration) was investigated. The results suggest that the night-time CO2 flux was significantly influenced by the vertical air temperature gradient over the canopy. The night-time CO2 flux increased exponentially with the temperature when the stability was nearly neutral, while it was insensitive to the temperature under stable conditions. Daily values of the net ecosystem exchange (NEE) and the gross primary production (GPP) of the Forest were estimated, and they were parameterized as a function of the air temperature and the absorbed photosynthetic active radiation (APAR). The results show a clear seasonal change in GPP caused by changes in the light-use efficiency and the maximum rate of carbon fixation of the canopy with LAI. The estimated NEE based on the parameterization agrees well with the observed NEE during the observational period.
Nobuko Saigusa - One of the best experts on this subject based on the ideXlab platform.
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O 2 :CO 2 exchange ratios observed in a cool Temperate Deciduous Forest ecosystem of central Japan
Tellus B: Chemical and Physical Meteorology, 2013Co-Authors: Shigeyuki Ishidoya, Nobuko Saigusa, Shohei Murayama, Hiroaki Kondo, Chikako Takamura, Daisuke Goto, Shinji Morimoto, Nobuyuki Aoki, Shuji Aoki, Takakiyo NakazawaAbstract:Detailed observations of O 2 :CO 2 exchange ratios were conducted in a cool Temperate Deciduous Forest located in central Japan. The exchange ratios of soil respiration and net assimilation were found to be 1.11±0.01 and 1.02±0.03 from soil chamber and branch bag measurements, respectively. Continuous measurements of the atmospheric O 2 /N 2 ratio and the CO 2 concentration, made inside the canopy during a summer season, indicated that the average exchange ratio was lower in the daytime (0.87±0.02) than in the nighttime (1.03±0.02) with a daily mean value of 0.94±0.01. The observed average daytime and nighttime exchange ratios were nearly consistent with the corresponding values obtained from a one-box canopy O 2 /CO 2 budget model simulation of net turbulent O 2 and CO 2 fluxes between the atmosphere and the Forest ecosystem. Our results suggest that the daily mean exchange ratios of the net turbulent O 2 and CO 2 fluxes depend sensitively on the Forest ecosystem processes. Keywords: O 2 :CO 2 exchange ratio, Forest ecosystem, atmospheric O 2 /N 2 ratio, continuous measurements (Published: 4 December 2013) Citation: Tellus B 2013, 65 , 21120, http://dx.doi.org/10.3402/tellusb.v65i0.21120
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Seasonal variations of atmospheric CO2, δ13C, and δ18O at a cool Temperate Deciduous Forest in Japan: Influence of Asian monsoon
Journal of Geophysical Research, 2010Co-Authors: Shohei Murayama, Nobuko Saigusa, Susumu Yamamoto, Shinji Morimoto, Shuji Aoki, Takakiyo Nakazawa, C. Takamura, Hiroyasu Kondo, T. Usami, Masayuki KondoAbstract:[1] Atmospheric CO2 concentration and its isotopes have been measured at the Takayama site in central Japan since 1994, together with δ18O in precipitation since 2002, to examine their temporal variations in a cool-Temperate Deciduous Forest environment strongly influenced by the Asian monsoon. The CO2 concentration and δ13C at the observational site show prominent seasonal variations accompanied by a secular trend, suggesting that the average seasonal cycle is caused mainly by a seasonal-dependent CO2 exchange with C3 plants. However, the variation in summer is found to be related to CO2 exchange with a significantly heavier δ13C signal compared to the other seasons, indicating some influence at the Takayama site of atmospheric transport of CO2 impacted by exchange with C4 plants from upstream regions. Compared with CO2 and δ13C, δ18O measurements in atmospheric CO2 are scattered, showing no clear seasonal variation. From late spring to early fall, significant year-to-year differences in the variation of δ18O are observed, with low and high values associated with rainy and sunny summer conditions, respectively. Comparisons with data from other northern midlatitude sites suggest that the rapid decrease of δ18O seen at Takayama in the early summer of a rainy summer year is characteristic of the Asian monsoon region. On the other hand, the characteristic increase in δ18O observed from winter to spring is likely caused by long-range transport of air with enriched δ18O.
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Temporal variations of atmospheric CO2 concentration in a Temperate Deciduous Forest in central Japan
Tellus B: Chemical and Physical Meteorology, 2003Co-Authors: Shohei Murayama, Nobuko Saigusa, Susumu Yamamoto, Hiroaki Kondo, Douglas Chan, Yozo EguchiAbstract:In order to examine the temporal variation of the atmospheric CO 2 concentration in a Temperate Deciduous Forest, and its relationship with meteorological conditions, continuous measurements of CO 2 and meteorological parameters have been made since 1993 on a tower at Takayama in the central part of Japan. In addition to an average secular increase in atmospheric CO 2 of 1.8 ppm yr −1 , diurnal variation with a maximum during the night-time to early morning and a minimum in the afternoon is observed from late spring to early fall; the diurnal cycle is not so clearly observed in the remaining seasons of the year. A concentration difference between above and below the canopy, and its diurnal variation, can also be seen clearly in summer. Daily mean concentration data show a prominent seasonal cycle. The maximum and the minimum of the seasonal cycle occur in April and from mid August to mid September, respectively. Day-to-day changes in the diurnal cycle of CO 2 are highly dependent on the day-to-day variations in meteorological conditions. However, CO 2 variations on longer time scales (>10 d) appear to be linearly related to changes in respiration. At Takayama, variations in the 10-d standard deviation of daily mean CO 2 data and 10-d averaged respiration show distinct relationships with soil temperature during spring and fall seasons. In spring, respiration has a stronger exponential dependence on soil temperature than in fall. Interestingly, in summer when soil temperature becomes greater than about 15 °C, biological respiration becomes more variable and independent of the soil temperature. Thus, at the Takayama site, the Q 10 relationship is seasonally dependent, and does not represent well the biological respiration process when the soil temperature rises above 15 °C. DOI: 10.1034/j.1600-0889.2003.00061.x
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gross primary production and net ecosystem exchange of a cool Temperate Deciduous Forest estimated by the eddy covariance method
Agricultural and Forest Meteorology, 2002Co-Authors: Nobuko Saigusa, Susumu Yamamoto, Shohei Murayama, Hiroaki Kondo, Noboru NishimuraAbstract:Abstract An eddy covariance measurement system was installed to measure long-term turbulent fluxes of heat, water vapor, and CO2 over a cool-Temperate Deciduous Forest in the central part of Japan. Previous to a long-term measurement, a comparison of flux measurements using open- and closed-path type infrared gas analyzers was conducted for CO2 and water vapor. The closure of the energy budget over the Forest was also examined to test the validity of the flux measurements. Using a whole year data from 25 July 1998 to 24 July 1999, the relation between the night-time air temperature and the night-time CO2 flux over the Forest (ecosystem respiration) was investigated. The results suggest that the night-time CO2 flux was significantly influenced by the vertical air temperature gradient over the canopy. The night-time CO2 flux increased exponentially with the temperature when the stability was nearly neutral, while it was insensitive to the temperature under stable conditions. Daily values of the net ecosystem exchange (NEE) and the gross primary production (GPP) of the Forest were estimated, and they were parameterized as a function of the air temperature and the absorbed photosynthetic active radiation (APAR). The results show a clear seasonal change in GPP caused by changes in the light-use efficiency and the maximum rate of carbon fixation of the canopy with LAI. The estimated NEE based on the parameterization agrees well with the observed NEE during the observational period.
