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.

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.

Better quantification of atmosphere-ecosystem exchange of the isotopologues of CO₂ could substantially improve our ability to probe under­lying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of the isotopic composition of exchange fluxes has been limited by measure­ment difficulties. Quantum cascade (QC) lasers are a new generation of infrared light sources that offer increased stability and power for absorption spectroscopy applications (including the measurement of isotope ratios in atmospheric CO₂) and promise substantial improvements over existing instruments: smaller size, increased robustness, and most significantly for remote or long-term field deployments, no need for cryogenic cooling of laser or detectors. 

The Carbon Cycle Data Assimilation System (CCDAS) infers values of the parameters controlling the function of a process model of the terrestrial biosphere using various observations. An obvious restriction of this approach is the limitation by the dynamics of the underlying process model. Careful study of the model-data mismatch and analysis of residuals can alert us to the presence of systematic errors which then candidate processes to extend the terrestrial biosphere model and the assimilation system. In a previous study, Rayner et al. [2005] noticed systematic underestimate of carbon release events in the tropics. The most likely explanation for this was the absence of any model of biomass burning in the biosphere model used in that study. Here, we extend CCDAS to infer the spatial and temporal patterns of biomass burning in the period 1979-1999. In a first attempt we include some flux components to account for missing processes. This so-called weak constraint form avoids biasing the inferences since the underlying model is no longer forced to match data without necessary processes. Also the magnitudes of the extra inferred fluxes quantify the missing processes.

Soil respiration is derived from heterotrophic (decomposition of soil organic matter) and autotrophic (root/rhizosphere respiration) sources, but there is considerable uncertainty about what factors control variations in their relative contributions in space and time. We took advantage of a unique whole-ecosystem radiocarbon label in a temperate forest to partition soil respiration into three sources: (1) recently photosynthesized carbon (C), which dominates root and rhizosphere respiration; (2) leaf litter decomposition and (3) decomposition of root litter and soil organic matter >1-2 years old. Heterotrophic sources and specifically leaf litter decomposition were large contributors to total soil respiration during the growing season. Relative contributions from leaf litter decomposition ranged from a low of ~1 ±3% of total soil respiration (6 ±3 mg C m^-2 hr^-1) when leaf litter was extremely dry, to a high of 42 ±16% (96 ±38 mg C m^-2 hr^-1). Total soil respiration fluxes varied with the strength of the leaf litter decomposition source, indicating that moisture-dependent changes in litter decomposition drive variability in total soil respiration fluxes. Root/rhizosphere respiration accounted for 16 ±10% to 64 ±22% of total soil respiration, with highest relative contributions coinciding with low overall soil respiration fluxes. In contrast to leaf litter decomposition, root respiration fluxes did not exhibit marked temporal variation ranging from 34 ±14 to 40 ±16 mg C m^-2 hr^-1 at different times in the growing season with a single exception (88 ±35 mg C m^-2 hr^-1). Radiocarbon signatures of root respired CO₂ changed markedly between early and late spring (March vs. May), suggesting a switch from stored nonstructural carbohydrate sources to more recent photosynthetic products.

Stand-replacing crown fires in boreal spruce forests initiate a vegetation succession from forbs to deciduous trees to coniferous trees. Soils are warmest during the first decades and cool throughout the succession as shading by trees and cover with bryophytes and plant litter increase. It was postulated that the initially warmer soil temperatures enhance decomposition of soil organic matter (SOM) by microorganisms, and that decomposition would release similar amounts of CO₂ as combustion during fire [Auclair and Carter, 1993].

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).

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.