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.

Some infrared CO₂ sensors, such as GMD20 and GMT222 (VAISALA), are widely used for soil CO₂ efflux measurements despite the fact they have a slow response rate. The output signal is delayed both from diffusion processes in the sample cell and internal averaging calculations necessary for stable data output. For accurate estimations of CO₂ efflux, we therefore need to know the actual increase in CO₂ concentration in a chamber without composite delays. To parameterize these delays, we conducted laboratory experiments to determine the response characteristics of sensors under diffusion and flow-through conditions. Next, we developed a backward calculation method for estimation of the actual CO₂ concentration increase using the delayed sensor output (BCDC: Backward calculation for delay compensation). The results showed that the slow response of sensors caused large estimation errors in CO₂ efflux measurements. In the case of GMT222, a 10% underestimation was suggested when the soil CO₂ efflux was calculated with non-corrected data using a nonlinear regression method with sampling intervals of 300 seconds. Thus, correction of the sensor response with a backward estimation might be effective. We also calculated and evaluated the CO₂ efflux from a forest floor in a deciduous forest employing the BCDC method.

Seasonal variations in nocturnal aboveground forest level respiration were measured using static, automated foliage and stem chambers in the Yamashiro Experimental Forest (YEF), a broadleaved secondary forest in Kyoto, Japan. The growth component of the respiration during the growing season equaled 12% of the total annual aboveground nocturnal forest level respiration in the YEF. These findings suggest that growth respiration is an important component of total respiration in similar forests.

The first objective of this paper is to make the link between the seasonality of fine root dynamics and soil respiration in a ponderosa pine (Pinus ponderosa P. & C. Lawson) plantation located in the Sierra Nevada of California. The second objective is to better understand how canopy photosynthesis influences fine root initiation, growth and mortality in this ecosystem. We compared CO₂ flux measurements (NEE, soil CO₂ efflux) with aboveground and belowground root dynamics. Soil respiration was measured in a control and a trenched plot to separate heterotrophic and autotrophic soil respiration.

The forests of Siberia represent one of the last natural frontiers in the world. Nearly 65% of Siberia's forests grow in areas with permafrost and Larch forests are dominated here. According to our estimates, carbon stocks in the soils of permafrost forest and tundra ecosystems of Yakutia amount to 17 Gt (altogether 126 Mha of forest area and 37 Mha of tundra).  It is about 25% of total carbon stock in forest soils of the Russian Federation. This carbon has been accumulated during centuries, and rapid climate change may release its huge amount for relatively short period, thus enhancing rather source than sink role of Russia. The total stock of terrestrial phytomass carbon of forests, tundra and meadows of Yakutia is 2.2-4.5 Gt C, including 0.053 Gt C of tundra and meadows.

Pressure fluctuations at the earth’s surface are caused by a variety of atmospheric phenomena. Examples include low frequency barometric pressure variations, high frequency atmospheric turbulence, atmospheric gravity waves, and quasi-static pressure fields created as wind blows over or around topographic features, like buildings, hills, wind breaks, etc. These naturally occurring pressure fields cause air to move in and out of soils, snowpacks, and other permeable media. Consequently, the uptake or release of trace gases from soils and snowpacks is a combination of molecular diffusion and advective flows caused by surface pressure fluctuations. Such pressure forcing has been found to influence the exchange rate of many trace gases from the underlying substrate to the atmosphere. Given the importance of these trace gases to understanding biogeochemical cycling and global change, it is crucial to quantify (as much as possible) any impact these advective flows can have on gas transport within soils and snowpacks. 

Dynamics of organic matter in agricultural soils attract significant interest because of strong impact on global climate. Steppe ecosystems are considered as having high potential to preserve global carbon and are located mainly in arid and semiarid areas with annual precipitation smaller than 400 mm. Steppe ecosystems of the wheat belt in Kazakhstan have annual precipitation 250 to 350 mm. Here is our attempt to evaluate whether microbial quotients could be applied to evaluate the potential of soil to act as sink for CO₂.

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.

Annual and seasonal dynamics of total soil respiration (TSR) of sandy Albeluvisols and clay Phaeozems under forest, grassland, and arable were studied in situ (Russia, Moscow Region). Measurements of soil CO₂ emission were carried out by closed chamber method from November 1997 through October 2003 weekly. The highest mean TSR (806+86 g C·m^-2·yr^-1) was observed for sandy Albeluvisols under grassland. It significantly exceeded the annual CO₂ fluxes from soils of other ecosystems (P< 0.1). The lowest value of mean annual TSR was observed for arable clay Phaeozems (361+55 g C·m^-2·yr^-1). It was reliably lower than in soils of the other cenoses (P<0.5). No significant differences were found between annual amounts of CO₂ emitted from Albeluvisols under forest and Phaeozems under forest and grassland. The interannual variability of TSR caused by the difference of weather conditions was 30% on average and ranged from 25-26% (forest and grassland ecosystems on Albeluvisols) to 37% (agroecosystem on Phaeozems). We found that TSR in natural ecosystems positively correlated with the total annual precipitation and sum of precipitation for the spring season (R=0.73-0.90, P<0.1). The share of the cold period (November-April) to the annual CO₂ flux was substantial and averaged 22-25% and 17% for natural and agricultural ecosystems, respectively. Therefore, emission of CO₂ during the cold period was an essential part of the annual CO₂ fluxes from soils of sub-boreal zone, which should be taken into account while calculating the carbon budget for the whole year.  

In 2003 a Nordic Centre of Excellence on Ecosystem Carbon Exchange and Its Interactions with the Climate System, NECC, was initiated. The center comprises practically all eddy covariance flux sites (ca. 25) in the Nordic countries which, represents wetlands, coniferous and deciduous forests, ‘Kyoto’ forests, lakes, agricultural sites and one urban site. The forest sites cover a range of age classes and management practices, and long-term sites with more than 8-10 years of continuous flux data. The center has also access to a flux aircraft for regional assessments and involves high precision CO₂ and CH₄ measurements in high towers. A synthesis of the current sink/source strength of CO₂ and CH₄ of the different ecosystems is in preparation and will be presented. Analysis of long-term data from a few sites and how it relates to annual parameters is also presented.