Measurements of CO₂ flux were made by the eddy correlation method over a sub-arctic black spruce forest in interior Alaska. Observed CO₂ budget were sinks of -531~-247 and -219~0 g CO₂ m^-2 year^-1 during 2003 and 2004, respectively. The broad range is caused by uncertainty regarding assessment of the nocturnal fluxes. The sequestration of CO₂ during 2004 was limited by high temperature, drought or low light intensity conditions. The net CO₂ flux is in a delicate balance between two large terms, which would shift from sink to source due to global warming.

A spatially-distributed model of net ecosystem production (NEP) was run over western Oregon for the period 2001-2003 at the 1 km spatial resolution and daily temporal resolution.  Inputs included MODIS-based FPAR, Landsat-based land cover and disturbance history, and distributed meteorology. Resulting NEP showed sensitivity to 1) areas of recent disturbance, such as a large forest fire in 2002, 2) areas of intensive management for timber production, 3) topographically-driven climatic gradients, and 4) interannual variation in climate. Validation measurements included a network of field plots and a chronosequence study.

The influence of nitrogen fertilizing on carbon accumulation and decomposition in arable soils of different fertility – gray forest soil and chernozem was investigated in greenhouse experiment with corn. Growing of plants without N application on rich chernozem favored the considerable (about 1% of С_org) C growth, and on poor gray forest soil contributed to C decrease. Soil organic matter (SOM) decomposition in both soils under unfertilized plants was the same. N usage on gray forest soil resulted in increase of C accumulation due to the substantial increase of C input with roots of fertilized plants and as organic matter active phase of this soil was stable against decomposition under N. N application on chernozem in reverse significantly increased SOM decomposition and affected plant productivity to a lesser degree. Thus, N fertilizing favors C sink in arable soils of low fertility and can reduce soil C accumulation in arable soils of high fertility.

Carbon enters ecosystems through a single process, photosynthesis, and nearly all is returned to the atmosphere through respiration, some 50-80% of which occurs below-ground. Soil (belowground) respiration integrates CO₂ derived from C that has resided in the ecosystem for periods of differing duration, ranging from relatively recent photosynthetic products that fuel root metabolism, to CO₂ derived from decomposition of plant and soil organic matter that may be decades to centuries old.  A comparison of the radiocarbon content of CO₂ respired by roots, microbes, and soils with the record of radiocarbon in atmospheric CO₂ allows direct estimation of the mean age of C being respired [Trumbore 2000; Wang et al. 2000, Cisneros Dozal et al. 2005; Borken et al. 2005]. 

The magnitude and spatial pattern of the emissions of CO₂, CH₄ and N₂O from China’s terrestrial ecosystems are poorly understood. In this study, we have used a coupled biogeochemistry model in conjunction with remote-sensing and field data to quantify spatial and temporal patterns of CO₂, CH₄ and N₂O fluxes in the terrestrial ecosystems of China since 1980. We have documented the patterns of land-use change across China from 1980 to present and quantified the consequences of land transformations on productivity in natural and managed ecosystems. We also examine how the fluxes of CO₂, CH₄ and N₂O have changed as a result of multiple stresses and interactions among those stresses including land-use change, climate variability, atmospheric composition (carbon dioxide and tropospheric ozone), precipitation chemistry (nitrogen composition), and fire frequency through using factorial simulation experiments with the coupled biogeochemistry model. The estimates of CO₂, CH₄ and N₂O emissions from the terrestrial ecosystems of China are evaluated through comparisons with the results of field studies within China.

We measured components of ecosystem respiration and biomass from wood, foliage and roots in two stands in an old-growth hemlock-northern hardwood forest. Respiration was measured by the chamber method and upscaled to the stand level. Wood production was calculated from the increase in tree size. Foliage biomass was measured from litterfall. Root production was measured from in-growth root cores. Based on the measurements of respiration and biomass we calculated gross primary production (GPP) and net ecosystem production (NEP). The annual GPP was estimated as 1144 and 1089 g C m² y^-1 in the hardwood and hemlock stands, respectively. GPP was partitioned into 131, 115, 270, 168, 257, 203 g C m² y^-1 of wood, foliage, and root respiration, and wood, foliage, and root production, respectively, in the hardwood stand, and 206, 72, 155, 190, 139, 327 g C m² y^-1 of wood, foliage, and root respiration, and wood, foliage, and root production, respectively, in the hemlock stand. The percentage of GPP allocated to wood, foliage and roots for growth and respiration was 20%, 23%, and 57%, respectively, for the hardwood stand, and 31%, 14%, and 55%, respectively, for the hemlock stand. The ratio of net primary production (NPP)/GPP was 30% in the hardwood stand and 33% in the hemlock stand.

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.

For more than 1000 years, the forests in mountainous areas of Japan have been distinguished by excessive harvesting and litter collection. Revegetation of these areas over the past 130 years has resulted in the current forest coverage. However, the forest soils are immature and contain very little organic carbon. Therefore, the past human impact likely affects the present carbon cycle and CO₂ efflux at the forest floor. It is important to estimate the carbon cycle and CO₂ efflux at the forest floor in such a heavily affected ecosystem to discuss the relationship between the carbon cycle and land use management. Therefore, we measured the CO₂ efflux at the forest floor in a deciduous forest heavily affected by human activities in Japan and estimated the annual rate.

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.

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.