Three techniques for separation of total CO₂ efflux from soil into root and microbial respiration were compared: component integration, root exclusion and pulse labelling of shoots in ¹⁴CO₂ atmosphere. The contribution of rhizosphere to total CO₂ efflux from soil varied from 19 to 49% (including root respiration amounted to 9-32%). The share of non-rhizosphere respiration was 51-80%. The results obtained by component integration and root exclusion techniques were similar. Rhizosphere respiration estimated by pulse labelling were less as estimated by two non-isotopic methods.

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.

The paper presents new estimates of live biomass (phytomass) and net primary production (NPP) of Russian forests for 1993 and 2003. These indicators are estimated based on forest inventory data and a specially developed semi-empirical modeling system. The latter contains regional models of growth by major forest forming species, multi-dimensional models of phytomass and models of biological production. It is shown that the fractional structure of forest phytomass substantially differs from previous estimates that indicated significant temporal trends of the share of aboveground wood (AGW), green part (GP) and belowground (BG) phytomass. The total forest NPP (of 307 g C m^-2yr^-1 for 2003) is substantially higher than previously reported. These changes may be attributed to climatic change which was dramatic over the last four decades, particularly in Asian Russia.

The development of agriculture responding to increasing demand for food raises the question of the role of cultivated land in relation to carbon sources and sinks, their spatial patterns and temporal variability.

During photosynthesis, atmospheric carbon sequestration goes on at the expense of formation and accumulation of organic substance, and an inverse process (carbon emission in the atmosphere) takes place during decomposition and oxidation of this organic substance. On land, in non-swamp ecosystems, these processes are balanced as a whole both under climax forms and interchange of: 1) periods of active oxidation of organic substance under influence of disturbing factors (more often, fires), and 2) periods of active formation of organic substance in the process of regeneration successions.

In this study, we developed an integrated modeling system to simulate dynamics of a stable carbon isotope of CO₂, moisture, energy, and momentum between boreal ecosystems and the atmosphere as well as their diffusion processes through the whole convective boundary layer (CBL), using remotely sensed surface parameters to characterize the surface heterogeneity, and the marine boundary layer matrix data to represent the CBL top condition. Model validation and primary results in boreal ecosystems were presented in this paper.

A process model was used to simulate changes in the carbon fluxes and stocks at a site that was transformed a grassland to a plantation at Qian Yanzhou. The total carbon storage of the zonal vegetation (evergreen broadleaf forest) was simulated and taken as the saturated carbon storage value of that site. The simulated vegetation density and soil organic carbon (SOC) were compared with the observed. The simulates indicate that after 20 years planting of the needle leaf forests (Pinus Massoniana, Cunninghamia lanceolata and Pinus elliottii ect) on ex-grassland, the net carbon storage increase in the plantation was 8.03 kg C/m²，in which the vegetation carbon storage increased 8.5334 kg C/m² and the soil carbon storage decreased 0.518 kg C/m². The total carbon storage of 20 years plantation is 58.6％ of the saturated value. The study also shows that between 0 and 7 years of land use change the soil carbon was decreased and between 7 and 20 years it was predicted to increase slowly.

Mechanistic explanations for the downward excursion in d¹⁸O of atmospheric CO₂ observed during the mid-1990s and the generally large interannnual variability characteristic of this isotopologue are lacking. We hypothesize that the excursion and related variations in d¹⁸O of atmospheric CO₂ may be linked to global-scale variations in cloud cover. However, very little is known about the influence of clouds on biosphere-atmosphere CO¹⁸O exchanges. Recent work has demonstrated the influence of boundary layer clouds on canopy photosynthesis through increases in the diffuse radiation fraction and relative humidity, combined with decreases in leaf temperature. In concert, these alterations tend to increase canopy photosynthesis and conductance, which should also increase CO¹⁸O isofluxes. However, photosynthetic CO¹⁸O isofluxes also depend critically on the d¹⁸O of leafwater, and enhanced cloudiness typically decreases the d¹⁸O of leafwater by enhancing relative humidity and water vapor exchange across stomata. Thus, the net impact of differing cloud regimes on biosphere-atmosphere CO¹⁸O exchanges is difficult to predict. Preliminary simulations suggest a large impact of diffuse radiation on canopy photosynthesis by increasing the flux from shade leaves. The impact of this effect on biosphere-atmosphere CO¹⁸O exchanges is diluted somewhat by the lower enrichment in leafwater d¹⁸O on cloudy days with high diffuse radiation fractions. Our results suggest that these effects are very dependent on LAI and photosynthetic pathway (C₃ or C₄).