We partitioned the components of CO₂ flux by the chamber approaches for a 45-year-old larch forest in northern Japan. In 2003, annual soil-CO₂ efflux was averaged to 9.59 tC ha^-1, heterotrophic respiration was about 5.47 tC ha^-1 that accounted about 57% of the soil-CO₂ efflux, net annual CO₂ exchange of understory vegetation was about -0.39 tC ha^-1, annual aboveground woody tissue respiration was bout 0.75 tC ha^-1, and annual photosynthesis and respiration of the canopy was about -12.75 and 1.15 tC ha^-1, respectively. Annual GPP, NPP, NEP and ecosystem respiration for this forest was estimated to be about 13.49, 7.16, 2.04 and 11.45 tC ha^-1, respectively. The contribution of canopy respiration, aboveground woody respiration, root respiration and heterotrophic respiration to GPP was about 8.1%, 5.6%, 30.6% and 40.5%, respectively.

The contribution of roots to the annual CO₂ emission from gray forest and soddy podzolic soils measured in the field experiments under crops and native vegetation varied in the wide range from 10 to 58% of CO₂ emission from the soil by mean value of 33%. The contribution of roots to the CO₂ emission from soil surface calculated for growth season for all the ecosystems studied was equal to 44%. In agroecosystems the contribution of roots was strongly related to the length of crops growth. CO₂ emission during dormant periods of the year was greatly controlled by the decomposition of surface litter and detritus in the soil than by respiration of roots and soil microorganisms.

The stable isotope composition of atmospheric CO₂ is being monitored in five AmeriFlux sites (four forests and one grassland) by collecting air samples inside and above canopies at weekly intervals. Measurements of concentration, d¹³C and d¹⁸O of atmospheric CO₂ have continuously been made from 100-ml flask samples since 2001. These measurements, in concert with eddy covariance flux measurements, provide mechanistic insights relating observed isotope changes and the controls over carbon sequestration and loss on seasonal and interannual bases. Data and a brief project description are available via the Internet at: http://ecophys.biology.utah.edu/Research/DOE_TCP/index.html.

Carbon balance of cultivated soil (loamy Phaeozems) under fallow was compared with that of soils abandoned 1, 5, 10, and 25 years converted naturally to permanent grassland (Moscow region, Russia). Carbon inflow or net primary production (NPP) was calculated as the sum of the above and below ground productivity of grassland ecosystems. The total C outflow was equal to the annual CO₂ fluxes from the soils and was estimated as CO₂ emission measured by the closed chamber method. Carbon balance (CB) was defined as the difference between respiration of heterotrophs and NPP. Botanical survey clearly showed that the vegetation of abandoned agricultural lands changed to permanent grasslands after 5 years of abandonment. Carbon inflow increased from 97 g C·m-2·yr^-1 in the arable soils to 1100 g C·m-2·yr^-1 in the 10-yr grassland. Total annual carbon losses from soils as CO₂ amounted to 347-845 g C·m-2·yr^-1. Heterotrophic respiration varied from 272 g C·m-2·yr^-1 in cultivated soil to 411 g C·m-2·yr^-1 in 25-yr grassland. Our estimations showed that 5, 10, and 25 yr grasslands act as carbon sink and their C balance constituted -217 g C·m-2·yr^-1, -778 g C·m-2·yr^-1 and -473 g C·m-2·y^-1, respectively. Arable soils under the fallow act as CO₂ source (CB = +175 g C·m-2·yr^-1). Carbon balance of the one-year grassland was close to zero. Hence, after 5 years abandonment former arable lands converted to permanent grasslands become a stable C sink.

Accurate estimations of the land biotic O₂/CO₂ exchange ratios are required to allow quantification of the land/ocean carbon sink partitioning from atmospheric measurements of both O₂ and CO₂ concentrations.

This study shows atmospheric O₂ and CO₂ mixing ratios as well as their diurnal cycles over a three day period in May 2005 from flask samples collected at 3 different heights (1, 4 and 12m) in an  undisturbed forest in central Germany. An average O₂/CO₂ ratio of 0.99 was estimated with very little variation between the three different heights. In addition, the “night time” average value of atmospheric O₂/CO₂ ratio did not show any significant difference from the average “daytime” value.

In a temperate deciduous forest in Japan situated complex terrain, net ecosystem CO₂ exchange (NEE) was estimated using micro-meteorological method, and net ecosystem products (NEP) was estimated by measures of major carbon pools and fluxes using biometric and chamber methods. In this study we evaluate the threshold value of u* for interpolation in case stability was high using estimated NEP acquired by biometric method. And the function which relate temperature to FCO₂ for interpolation was evaluated by the data acquired using automated chamber for soil, CWD, trunk and foliage CO₂ exchanges. Averaged net uptake of CO₂ measured by eddy covariance method from 1999 to 2002 was 3.4 tC yr^-1 ha^-1 without compensation of nighttime underreport. Increase of live under and above ground biomass from 1994 to 1999 was 1.56 tC yr^-1 ha^-1. U* threshold values based on biometric and chamber NEP were respectively 0.28 and 0.35 m sec^-1

A long-term observation of CO₂ exchange was conducted above a broadleaved deciduous forest in Sapporo, northern Japan. The CO₂ exchange was measured using the eddy covariance method with closed-path gas analyzer and we obtained net ecosystem production (NEP). We estimated a carbon budget using a simple empirical model. In this model, ecosystem respiration (RE) and gross primary production (GPP) were parameterized by soil temperature and photosynthetically active radiation (PAR) respectively. The annual NEP derived from an equation “NEP = GPP -RE” ranged from 237 to 431 g C m^-2 year^-1 for 4 years (2000 - 2003).

Concentrations of ²²²Rn, CO₂, N₂O and CH₄ were measured in a cold-temperate northern Japanese grassland soil during 1996 to compare the fluxes of CO₂, N₂O and CH₄ calculated by the ²²²Rn method and the static chamber method and to estimate the source strengths of CO₂ and N₂O in the soil using the ²²²Rn method. The ²²²Rn fluxes ranged from 890 to 3400 dpm/m²/h and the average was 1570±310 dpm/m²/h on sandy soil (50% sand). The results of CO₂, N₂O and CH₄ flux-measurements by the ²²²Rn method were in agreement with those by the static chamber method within the observed range of error. The vertical profiles of soil source strengths of CO₂ and N₂O were also calculated from the concentration gradients of ²²²Rn, CO₂ and N₂O to investigate seasonal changes in the soil production rates of CO₂ and N₂O. The production rates of CO₂ and N₂O varied significantly by season, averaging 1650±450 mgC/m³/h and 19±3.2 µgN/m³/h, respectively. These seasonal changes in the source strengths of CO₂ and N₂O in the surface soil corresponded with changes in fluxes of CO₂ and N₂O from the soil.

Progress in determining CO₂ sources, sinks, and their response to environmental forcing will rely on utilization of more extensive and intensive CO₂ and related observations including those from satellite remote sensing.  Full exploitation of new observations will require new modeling and analysis techniques, especially those that can use information at finer spatial and temporal scales than has traditionally been employed in “top-down” carbon flux studies.  We report on a modeling effort to reduce uncertainty in carbon cycle processes that create the so-called missing terrestrial sink of atmospheric CO₂ using transport fields derived from NASA’s GEOS-4 meteorological assimilation analyses.  Our overall objective is to improve characterization of CO₂ source/sink processes globally with improved formulations for atmospheric transport, terrestrial uptake and release, biomass and fossil fuel burning, and observational data analysis.  We show results from an advanced biosphere model (SiB3) constrained by remote sensing data and coupled to the global transport model to produce distributions of CO₂ fluxes and concentrations that are consistent with actual meteorological variability.  Use of analyzed meteorological data allows comparison to observations on a wide range of temporal and spatial scales.  Here we compare with local-to-global data for hourly to annual CO₂ simulation.  The results will help to prepare for the use of satellite CO₂ and other data in a multi-disciplinary carbon data assimilation system for analysis and prediction of carbon cycle changes and carbon/climate interactions.

Model simulations indicated that Canada’s forests and wetlands acted as a carbon (C) sink of 112 Tg C
yr^-1 averaged during 1901-1998. Wetlands was a crucial contributor to this sink (50 Tg C yr^-1). Disturbance history determined the decadal temporal pattern of C balance. Nondisturbance factors enhanced C accumulations in Canada’s forests and wetlands in the last century. The enhancement of each nondisturbance factor on C uptake changed temporally.