A land surface model (Biosphere-Atmosphere Interaction Model Ver.2: BAIM2) can estimate not only the energy fluxes, but also the carbon dioxide flux between terrestrial ecosystems and the atmosphere. The photosynthesis processes for C₃ and C₄ plants are adopted in the model. The carbon storage of vegetation is divided into five components (leaves, trunk, root, litter, and soil), and the carbon exchanges among the components of vegetation and the atmosphere are estimated in each time step of the on-line model integration. The values of morphological parameters using in the model are derived from the carbon storage values of the components, and the phenological changes of vegetation are reproduced by the model. The BAIM2 was incorporated into a spectral general circulation model, and was connected on-line to the atmospheric model. Using this climate model, an experimental control time integration was performed under the actual global vegetation condition. After the control time integration, the vegetation types of Southeast Asia were changed to the C₄ grass, and the vegetation change impact integration was performed. The results of the impact experiment were compared with the results of the control. In the Indochina Peninsula area, by the vegetation change from the tropical seasonal forest to the C₄ grass, year mean values of the NPP generally increased, and those of the NEP also increased. On the other hand, in the maritime continent area, by the change from the tropical rain forest to the C₄ grass, the NPP values generally decreased, and the NEP values also decreased. It was considered that the differences of phenological changes of vegetation in these areas and the differences of climatic impact of vegetation changes induced the different change phenomena of the carbon cycles. There is a possibility that the influences of the vegetation changes (deforestation) on the carbon cycles are different in the area where the original vegetation types are different.

Measurements of net ecosystem CO₂ exchange using continental tower flux networks provide a critical constraint in models of regional and global carbon budgets. Uncertainty exists in these measurements due to the effects of complex terrain and vegetation gradients. Using an array of seven towers distributed across a mountain landscape, we estimated that a significant error exists in the five-year record of measured net ecosystem CO₂ exchange. The error was due to the previously ignored influence of advective CO₂ fluxes. When this error was rectified by explicit consideration of the advective flux components, the forest was predicted to exhibit a 38% higher potential for carbon sequestration than previously thought.

Leaf and branch biomass productivity of plant communities have been little studied in northern Mexico. Global warming concerns are prompting research dealing with biomass production and carbon sequestration by plant communities. Biomass components and productivity are key pieces of information for running several carbon models. In this research, we developed information on leaf and branch biomass productivity of sixteen different plant communities encompassing native pine, oak, shrub, and exotic pine forests. We established sampling plots, measured dasometric features of trees, and collected leaf and branch biomass for periods of 7 to 21 days during 2004 in Nuevo Leon, Mexico. Results indicate that leaf and branch productivity is on the average 3.70 Mg ha^-1 y^-1 (±0.98 Mg ha^-1 y^-1) with only two plant communities (intermittent riverine Tamaulipan matorral and upland planted Cupressus spp communities) surpassing 7 Mg ha^-1 y^-1. The exotic pine species (P. nelsoni, P. pinceana, and P. cembroides) planted in proceeding trials produced less than 3 Mg ha^-1 y^-1. The statistical analysis of this information showed large spatial and temporal variations. The former was explained by microsite and plant density. The last source of variation was partially dependent on climate fluctuations and the natural annual productivity cycle. Further research is required to understand the fate of leaf and branch on soils.

Annual changes in soil carbon stock are considered of the abandoned managed agricultural lands that were under natural regrowth over the territory of Russia within the period 1990-2002. Total area of abandoned agricultural land is 21,6 millions ha. The projections of changes in the carbon stock have been made for the period from present to 2010. The ROTHC model was employed in the investigation of carbon dynamics in soils. The territory of Russia was subdivided into 40 regions. The average basic soil and climatic parameters, as well as the annual input of organic matter into soils due to natural succession were estimated for each region. Average annual net-emission over the territory of abandoned lands was 2,1 ± 1,8 Tg C/yr in 1990-1999. CO₂ removal from the atmosphere by soils was 5,2 ± 2,8 Tg C/yr on average in 2000-2002. A total increase in carbon stock of the abandoned lands over the country can be as high as 153 Tg C (that corresponds to the removal of 561 Tg of CO₂ from the atmosphere) in 2010. Central regions of the European part of Russia, south of East Siberia and the Far East will have the highest intensity of carbon sequestration.

To evaluate the deforestation and forestation effects on the carbon and water cycles, micrometeorological and hydrological observations were conducted in a conifer-broadleaf mixed forest in northernmost Japan in the series of these activities.  The clear-cutting of trees changed the carbon balance of the ecosystem to the net source in the plant-growing period, although the undergrowth, Sasa bamboos, still keeps large biomass after the tree-cutting and the half-hourly flux indicate carbon sequestration in the daytime. Strip-cutting of Sasa bamboos and planting of the larch saplings did not cause the distinct change in the emission rate. On the other hand, the evapotranspiration rate recovered to the same level with that in the mixed forest within 2 years after the clear-cutting. We attributed the increase in the evapotranspiration rate partly to the acclimation in the transpiration capacity of Sasa bamboos.

Understanding the energy/H₂O/CO₂ exchange processes is very important for evaluating the roles of tropical rain forest in climate change. The sensible heat, latent heat, and CO₂ fluxes above a tropical rain forest in Peninsular Malaysia were measured using the eddy covariance method for the year 2003. The diurnal patterns of energy, H₂O and CO₂ flux were investigated using a multi-layer model that considered patchy stomatal closure. Both bimodal and homogeneous stomatal opening distributions were simulated, and the results indicated that the observed negative relationship between CO₂ absorption under light-saturated conditions and vapor pressure deficit were not sufficiently explained by stomatal closure alone, for homogeneous stomatal opening distributions. For bimodal stomatal opening distributions, however, a greater depression in canopy photosynthesis was found with increased atmospheric vapor pressure deficit. These results strongly suggested that the depression in canopy photosynthesis was caused not only by stomatal closure limitation but also by the patchy (bimodal) stomatal behavior response to the increased atmospheric vapor pressure deficit. Thus, the midday depression in canopy photosynthesis was mainly caused by patchy (bimodal) stomatal closure.

We examined CO₂ flux over an alpine meadow on the northeastern Tibetan Plateau to elucidate how temperature controls the carbon dynamics. The CO₂ flux was measured in a Kobresia meadow at an elevation of 3200m above sea level from 2002 to 2004 using the eddy covariance technique. The alpine meadow was a weak sink of atmospheric CO₂ with net ecosystem production (NEP) of 193 g C m^-2 yr^-1 for 2004, which was about twice of that for the other two years. Both the low ecosystem respiration (ER) and high gross primary production (GPP) contributed the high NEP in 2004. The annual GPP was 34g Cm^-2 and 105 g C m^-2 higher in 2004 than 2003 and 2002, respectively. The lowest GPP of 2002 was clearly due to the low GPP in the autumn season when remarkably high air and soil temperature were recorded. The low ER in 2004 was due to mainly the small ER in the summer period when temperature was much lower than other years. In 2004, the growing season was estimated to be about two weeks longer than the other two years. The advance of growing season in 2004 corresponded well to the temperature elevation in the spring season. Further analysis showed that the day/night difference in soil temperatures was positively correlated to the daily net ecosystem CO₂ exchange. The study suggests that temperature environment plays the major role in the annual variation of NEP in the alpine meadow ecosystem.

The mixing ratio and the surface-atmosphere exchange of carbon dioxide have been monitored at different elevations on a tall tower in West Hungary (Hegyhátsál, 46^o57'N, 16^o39'E, 248 m asl) since 1994 and 1997, respectively. The vertical mixing ratio profile measurements along the 115 m tall tower has been completed with occasional aircraft measurements up to 3000 m above the ground. The poster presents the Hungarian tall tower site and the temporal variation of carbon dioxide observed here. We discuss the region of influence determining the mixing ratio variability, the so-called concentration footprint, as well as that of the flux measurements. Methodological problems caused by the elevated monitoring levels, and their solutions, are also given. The environmental factors governing the net ecosystem exchange (NEE) of the vegetation are analyzed by means of a process oriented ecosystem simulation model. It might be used to estimate the future behavior of the region as the climate is changing. On the basis of the measurements at Hegyhátsál a boundary layer model has been developed which can give rough surface-atmosphere carbon dioxide flux estimate for sites where only surface mixing ratio monitoring is available.

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.

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.