Net Carbon Storage Research Articles

Subtropical plantations are large carbon sinks: Evidence from two monoculture plantations in South China

Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration ( R h). In comparisons of R h determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO 2 efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO 2 flux in trenched plots ( R h-t) was significantly lower than in tree-girdled plots ( R h-g) in both plantations. The estimates of R h-t and R h-g, expressed as a percentage of total soil respiration, were 58 ± 4% and 74 ± 6%, respectively, for A. crassicarpa, and 64 ± 3% and 78 ± 5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO 2 efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual R h (mean of the annual R h-t and R h-g) and net primary production (NPP) were 470 ± 25 and 800 ± 118 g C m −2 yr −1, respectively, for A. crassicarpa, and 420 ± 35 and 2380 ± 187 g C m −2 yr −2, respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330 ± 76 C m −2 yr −1 for A. crassicarpa and 1960 ± 178 g C m −2 yr −1 for E. urophylla.

ABIOTIC REGULATION OF INVESTMENT IN SEXUAL VERSUS VEGETATIVE REPRODUCTION IN THE CLONAL KELP LAMINARIA SINCLAIRII (LAMINARIALES, PHAEOPHYCEAE)1.

Clonal kelp taxa may reproduce both sexually and vegetatively resulting in a potential trade-off in the allocation of acquired carbon and nitrogen resources. Such trade-offs may dictate a different response of clonal kelps to varying environmental conditions relative to aclonal kelp taxa. Laboratory temperature and nutrient manipulation experiments demonstrated that investment in sexual and vegetative reproduction in Laminaria sinclairii (Harv. ex Hook. f. et Harv.) Farl., C. L. Anderson et D. C. Eaton was regulated by different abiotic factors. Sorus production (investment in sexual reproduction) and blade growth were significantly higher at 12°C compared to 17°C, regardless of nutrient concentration. Net carbon storage and depletion in rhizomes were observed in the low- and high-temperature treatments, respectively, suggesting that carbon stores were not responsible for increased growth. Rhizome elongation (investment in vegetative reproduction), on the other hand, was significantly higher in 12 μM NO3- than in 2 μM NO3- , irrespective of temperature. This increase in rhizome growth was concurrent with elevated rhizome percent tissue nitrogen levels also observed in treatments with higher nutrients, again indicating a growth response to treatment independent of previous nutrient stores. These results suggest that regulation of growth and investment in sexual reproduction in L. sinclairii is similar to that in aclonal kelps (i.e., warmer temperatures result in decreased reproductive output). Additionally, depletion of carbon and nitrogen from rhizomes in suboptimal conditions confirms the role of clonal kelp rhizomes in carbon and nutrient storage.

China's terrestrial carbon balance: Contributions from multiple global change factors

[1] The magnitude, spatial, and temporal patterns of the terrestrial carbon sink and the underlying mechanisms remain uncertain and need to be investigated. China is important in determining the global carbon balance in terms of both carbon emission and carbon uptake. Of particular importance to climate-change policy and carbon management is the ability to evaluate the relative contributions of multiple environmental factors to net carbon source and sink in China's terrestrial ecosystems. Here the effects of multiple environmental factors (climate, atmospheric CO2, ozone pollution, nitrogen deposition, nitrogen fertilizer application, and land cover/land use change) on net carbon balance in terrestrial ecosystems of China for the period 1961–2005 were modeled with newly developed, detailed historical information of these changes. For this period, results from two models indicated a mean land sink of 0.21 Pg C per year, with a multimodel range from 0.18 to 0.24 Pg C per year. The models' results are consistent with field observations and national inventory data and provide insights into the biogeochemical mechanisms responsible for the carbon sink in China's land ecosystems. In the simulations, nitrogen deposition and fertilizer applications together accounted for 61 percent of the net carbon storage in China's land ecosystems in recent decades, with atmospheric CO2 increases and land use also functioning to stimulate carbon storage. The size of the modeled carbon sink over the period 1961–2005 was reduced by both ozone pollution and climate change. The modeled carbon sink in response to per unit nitrogen deposition shows a leveling off or a decline in some areas in recent years, although the nitrogen input levels have continued to increase.

Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors

By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands.

Study of terrestrial carbon flux by eddy covariance method in revegetated manganese mine spoil dump at Gumgaon, India

The micrometeorological technique of eddy covariance is a powerful tool for characterizing the carbon (C) budget of terrestrial ecosystems. Eddy covariance method was used for estimating Net Ecosystem Exchange (NEE) of carbon dioxide between atmosphere and revegetated manganese mine spoil dump at Gumgaon, India. In this paper, we analyzed the diel CO2 flux pattern and its response to various physical environmental conditions. The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes. Study of diel pattern of CO2 flux showed that carbon uptake was dependent on sunlight. Effect of temperature and latent heat on the CO2 flux showed that rate of CO2 uptake increased proportionally, but later declined due to various factors like stomatal response, high evaporative demand, circadian rhythm and/or a combination of all three. Net ecosystem production of revegetated land was found to be 28.196 KgC/ha/day whereas average net carbon release by the ecosystem, through respiration was observed to be 5.433 KgC/ha/day. Thus, quantifying net carbon (C) storage in degraded land is a necessary step in the validation of carbon sequestration estimates and in assessing the possible role of these ecosystems in offsetting adverse impacts of fossil fuel emissions.

Short- and long-term effects of thinning and prescribed fire on carbon stocks in ponderosa pine stands in northern Arizona

Euro–American logging practices, intensive grazing, and fire suppression have increased the amount of carbon that is stored in ponderosa pine (Pinus ponderosa Dougl. Ex Laws) forests in the southwestern United States. Current stand conditions leave these forests prone to high-intensity wildfire, which releases a pulse of carbon emissions and shifts carbon storage from live trees to standing dead trees and woody debris. Thinning and prescribed burning are commonly used to reduce the risk of intense wildfire, but also reduce on-site carbon stocks and release carbon to the atmosphere. This study quantified the impact of thinning on the carbon budgets of five ponderosa pine stands in northern Arizona, including the fossil fuels consumed during logging operations. We used the pre- and post-treatment data on carbon stocks and the Fire and Fuels Extension to the Forest Vegetation Simulator (FEE–FVS) to simulate the long-term effects of intense wildfire, thinning, and repeated prescribed burning on stand carbon storage.The mean total pre-treatment carbon stock, including above-ground live and dead trees, below-ground live and dead trees, and surface fuels across five sites was 74.58Mg C ha−1 and the post-treatment mean was 50.65Mg C ha−1 in the first post-treatment year. The mean total carbon release from slash burning, fossil fuels, and logs removed was 21.92Mg C ha−1. FEE–FVS simulations showed that thinning increased the mean canopy base height, decreased the mean crown bulk density, and increased the mean crowning index, and thus reduced the risk of high-intensity wildfire at all sites. Untreated stands that incurred wildfire once within the next 100 years or once within the next 50 years had greater mean net carbon storage after 100 years compared to treated stands that experienced prescribed fire every 10 years or every 20 years. Treated stands released greater amounts of carbon overall due to repeated prescribed fires, slash burning, and 100% of harvested logs being counted as carbon emissions because they were used for short-lived products. However, after 100 years treated stands stored more carbon in live trees and less carbon in dead trees and surface fuels than untreated stands burned by intense wildfire. The long-term net carbon storage of treated stands was similar or greater than untreated wildfire-burned stands only when a distinction was made between carbon stored in live and dead trees, carbon in logs was stored in long-lived products, and energy in logging slash substituted for fossil fuels.

Interactions between nitrogen deposition, land cover conversion, and climate change determine the contemporary carbon balance of Europe

Abstract. European ecosystems are thought to take up large amounts of carbon, but neither the rate nor the contributions of the underlying processes are well known. In the second half of the 20th century, carbon dioxide concentrations have risen by more that 100 ppm, atmospheric nitrogen deposition has more than doubled, and European mean temperatures were increasing by 0.02 °C yr−1. The extents of forest and grasslands have increased with the respective rates of 5800 km2 yr−1 and 1100 km2 yr−1 as agricultural land has been abandoned at a rate of 7000 km2 yr−1. In this study, we analyze the responses of European land ecosystems to the aforementioned environmental changes using results from four process-based ecosystem models: BIOME-BGC, JULES, ORCHIDEE, and O-CN. The models suggest that European ecosystems sequester carbon at a rate of 56 TgC yr−1 (mean of four models for 1951–2000) with strong interannual variability (±88 TgC yr−1, average across models) and substantial inter-model uncertainty (±39 TgC yr−1). Decadal budgets suggest that there has been a continuous increase in the mean net carbon storage of ecosystems from 85 TgC yr−1 in 1980s to 108 TgC yr−1 in 1990s, and to 114 TgC yr−1 in 2000–2007. The physiological effect of rising CO2 in combination with nitrogen deposition and forest re-growth have been identified as the important explanatory factors for this net carbon storage. Changes in the growth of woody vegetation are suggested as an important contributor to the European carbon sink. Simulated ecosystem responses were more consistent for the two models accounting for terrestrial carbon-nitrogen dynamics than for the two models which only accounted for carbon cycling and the effects of land cover change. Studies of the interactions of carbon-nitrogen dynamics with land use changes are needed to further improve the quantitative understanding of the driving forces of the European land carbon balance.

Diurnal and seasonal variation in methane emissions in a northern Canadian peatland measured by eddy covariance

AbstractEddy covariance measurements of methane (CH4) net flux were made in a boreal fen, typical of the most abundant peatlands in western Canada during May–September 2007. The objectives of this study were to determine: (i) the magnitude of diurnal and seasonal variation in CH4 net flux, (ii) the relationship between the temporally varying flux rates and associated changes in controlling biotic and abiotic factors, and (iii) the contribution of CH4 emission to the ecosystem growing season carbon budget. There was significant diurnal variation in CH4 emission during the peak of the growing season that was strongly correlated with associated changes in solar radiation, latent heat flux, air temperature and ecosystem conductance to water vapor. During days 181–215, nighttime average CH4 efflux was only 47% of the average midday values. The peak value for daily average CH4 emission rate was approximately 80 nmol m−2 s−1 (4.6 mg CH4 m−2 h−1), and seasonal variation in CH4 flux was strongly correlated with changes in soil temperature. Integrated over the entire measurement period [days 144–269 (late May–late September)], the total CH4 emission was 3.2 g CH4 m−2, which was quite low relative to other wetland ecosystems and to the simultaneous high rate of ecosystem net CO2 sequestration that was measured (18.1 mol CO2 m−2 or 217 g C m−2). We estimate that the negative radiative forcing (cooling) associated with net carbon storage over the life of the peatland (approximately 2200 years) was at least twice the value of positive radiative forcing (warming) caused by net CH4 emission over the last 50 years.

Can ocean iron fertilization mitigate ocean acidification?

Ocean iron fertilization has been proposed as a method to mitigate an- thropogenic climate change, and there is continued commercial interest in using iron fertilization to generate carbon credits. It has been further speculated that ocean iron fertilization could help mitigate ocean acidification. Here, using a global ocean car- bon cycle model, we performed idealized ocean iron fertilization simulations to place an upper bound on the effect of iron fertilization on atmospheric CO2 and ocean acidification. Under the IPCC A2 CO2 emission scenario, at year 2100 the model simulates an atmospheric CO2 concentration of 965 ppm with the mean surface ocean pH 0.44 units less than its pre-industrial value of 8.18. A globally sustained ocean iron fertilization could not diminish CO2 concentrations below 833 ppm or reduce the mean surface ocean pH change to less than 0.38 units. This maximum of 0.06 unit mitigation in surface pH change by the end of this century is achieved at the cost of storing more anthropogenic CO2 in the ocean interior, furthering acidifying the deep- ocean. If the amount of net carbon storage in the deep ocean by iron fertilization produces an equivalent amount of emission credits, ocean iron fertilization further acidifies the deep ocean without conferring any chemical benefit to the surface ocean.

Greenhouse Gas Emissions Calculator for Grain and Biofuel Farming Systems

Opportunities for farmers to participate in greenhouse gas (GHG) credit markets require that growers, students, extension educators, offset aggregators, and other stakeholders understand the impact of agricultural practices on GHG emissions. The Farming Systems Greenhouse Gas Emissions Calculator, a web‐based tool linked to the SOCRATES soil carbon process model, provides a simple introduction to the concepts and magnitudes of gas emissions associated with crop management. Users choose a county of interest on an introductory screen and are taken to the input/output window, where they choose crops, yields, tillage practices, or nitrogen fertilizer rates. Default values are provided based on convention and county averages. Outputs include major contributors of greenhouse gases in field crops: soil carbon change, nitrous oxide (N2O) emission, fuel use, and fertilizer. We contrast conventional tillage and no‐till in a corn–soybean–wheat (Zea mays L.–Glycine max (L.) Merr.–Triticum aestivum L.) rotation and compare continuous corn fertilized at 101 and 134 kg N ha−1 yr−1. In corn years, N2O was the dominant GHG, due to high fertilizer requirements for corn. No‐till management reduced greenhouse gas emissions by 50% due to net soil carbon storage. Continuous corn fertilized at 101 kg N ha−1 yr−1 emitted 1.25 Mg CO2 equivalents ha−1 yr−1 compared with 1.42 Mg CO2 equivalents ha−1 yr−1 at 134 kg N ha−1 yr−1, providing a 12% GHG savings. The calculator demonstrates how cropping systems and management choices affect greenhouse gas emissions in field crops.

Carbon and nitrogen balances for six shrublands across Europe

Shrublands constitute significant and important parts of European landscapes providing a large number of important ecosystem services. Biogeochemical cycles in these ecosystems have gained little attention relative to forests and grassland systems, but data on such cycles are required for developing and testing ecosystem models. As climate change progresses, the potential feedback from terrestrial ecosystems to the atmosphere through changes in carbon stocks, carbon sequestration, and general knowledge on biogeochemical cycles becomes increasingly important. Here we present carbon and nitrogen balances of six shrublands along a climatic gradient across the European continent. The aim of the study was to provide a basis for assessing the range and variability in carbon storage in European shrublands. Across the sites the net carbon storage in the systems ranged from 1,163 g C m−2 to 18,546 g C m−2, and the systems ranged from being net sinks (126 g C m−2 a−1) to being net sources (−536 g C m−2 a−1) of carbon with the largest storage and sink of carbon at wet and cold climatic conditions. The soil carbon store dominates the carbon budget at all sites and in particular at the site with a cold and wet climate where soil C constitutes 95% of the total carbon in the ecosystem. Respiration of carbon from the soil organic matter pool dominated the carbon loss at all sites while carbon loss from aboveground litter decomposition appeared less important. Total belowground carbon allocation was more than 5 times aboveground litterfall carbon which is significantly greater than the factor of 2 reported in a global analysis of forest data. Nitrogen storage was also dominated by the soil pools generally showing small losses except when atmospheric N input was high. The study shows that in the future a climate‐driven land cover change between grasslands and shrublands in Europe will likely lead to increased ecosystem C where shrublands are promoted and less where grasses are promoted. However, it also emphasizes that if feedbacks on the global carbon cycle are to be predicted it is critically important to quantify and understand belowground carbon allocation and processes as well as soil carbon pools, particularly on wet organic soils, rather than plant functional change as the soil stores dominate the overall budget and fluxes of carbon.

Modeling the effects of alternative management strategies on forest carbon in the Nothofagus forests of Tierra del Fuego, Chile

The impact of forest management activities on the ability of forest ecosystems to sequester and store atmospheric carbon is of increasing scientific and social concern. The nature of these impacts varies among forest ecosystems, and spatially and temporally explicit ecosystem models are useful for quantifying the impacts of a number of alternative management regimes for the same forest landscape. The LANDIS-II forest dynamics simulation model is used to quantify changes to the live overstory and coarse woody debris pools under several forest management scenarios in a high-latitude South American forest landscape dominated by two species of southern beech, Nothofagus betuloides and N. pumilio. Both harvest type (clearcutting vs. partial overstory retention) and rotation length (100 years vs. 200 years) were significant predictors of carbon storage in the simulation models. The prompt regeneration of harvest units greatly enhanced carbon storage in clearcutting scenarios. The woody debris pool was particularly sensitive to both harvest type and rotation length, with large decreases noted under short rotation clearcutting. The roles of extended rotations and partial overstory retention are noted for enhancing net carbon storage on the forest landscape.

Increased Litter Build Up and Soil Organic Matter Stabilization in a Poplar Plantation After 6 Years of Atmospheric CO2 Enrichment (FACE): Final Results of POP-EuroFACE Compared to Other Forest FACE Experiments

Free air CO2 enrichment (FACE) experiments in aggrading temperate forests and plantations have been initiated to test whether temperate forest ecosystems act as sinks for anthropogenic emissions of CO2. These FACE experiments have demonstrated increases in net primary production and carbon (C) storage in forest vegetation due to increased atmospheric CO2 concentrations. However, the fate of this extra biomass in the forest floor or mineral soil is less clear. After 6 years of FACE treatment in a short-rotation poplar plantation, we observed an additional sink of 32 g C m−2 y−1 in the forest floor. Mineral soil C content increased equally under ambient and increased CO2 treatment during the 6-year experiment. However, during the first half of the experiment the increase in soil C was suppressed under FACE due to a priming effect, that is, the additional labile C increased the mineralization of older SOM, whereas during the second half of the experiment the increase in soil C was larger under FACE. An additional sink of 54 g C m−2 y−1 in the top 10 cm of the mineral soil was created under FACE during the second half of the experiment. Although, this FACE effect was not significant due to a combination of soil spatial variability and the low number of replicates that are inherent to the present generation of forest stand FACE experiments. Physical fractionation by wet sieving revealed an increase in the C and nitrogen (N) content of macro-aggregates due to FACE. Further fractionation by density showed that FACE increased C and N contents of the light iPOM and mineral associated intra-macro-aggregate fractions. Isolation of micro-aggregates from macro-aggregates and subsequent fractionation by density revealed that FACE increased C and N contents of the light iPOM, C content of the fine iPOM and C and N contents of the mineral associated intra-micro-aggregate fractions. From this we infer that the amount of stabilized C and N increased under FACE treatment. We compared our data with published results of other forest FACE experiments and infer that the type of vegetation and soil base saturation, as a proxy for bioturbation, are important factors related to the size of the additional C sinks of the forest floor–soil system under FACE.

The effects of a thinning treatment on carbon stocks in a northern Arizona ponderosa pine forest

Vast areas of ponderosa pine ( Pinus ponderosa Dougl. ex Laws.) forest in the western United States have become unnaturally dense because of relatively recent land management practices that include fire suppression and livestock grazing. In many areas, thinning treatments can re-establish the natural ecological processes and help restore ecosystem structure and function. Precipitous global climate change has focused attention on the carbon storage in forests. An unintended consequence of fire suppression has been the increased storage of carbon in ponderosa stands. Thinning treatments reduce standing carbon stocks while releasing carbon through the combustion of fuel in logging machinery, burning slash, and the decay of logging slash and wood products. These reductions and releases of stored carbon must be compared to the risk of catastrophic fire burning through the stand and releasing large quantities of carbon to the atmosphere to more fully understand the costs and benefits – in carbon terms – of forest restoration strategies. This study examines the effect of a restoration thinning treatment on the carbon stock of a ponderosa pine forest. The total pre-treatment above-ground carbon stock was 48,880 kg C ha −1 and the post-treatment stand had 36,420 kg C ha −1. The carbon stock in trees across the stand ranged from 28,560 to 67,560 kg C ha −1 pre-treatment and from 11,970 to 55,510 kg C ha −1 post-treatment. 8240 kg C ha −1 was removed from the site and sold to the wholesale firewood market (plot values ranged from 4890 to 12,310 kg C ha −1), 91 kg C ha −1 was released from the combustion of fuel in harvesting operations and trucking, and the processing of the firewood required carbon released 33 kg C ha −1. The burning of slash piled on site released 4140 kg C ha −1 (plot values ranged from 2920 to 6900 kg C ha −1). We estimated that in a stand-replacing fire, the treated stand would release 2410 kg C ha −1 less to the atmosphere than the untreated stand. However, the thinning treatment resulted in stand structural changes that make the stand less likely to support a crown fire and therefore more likely to avoid the carbon releases associated with crown fires, even under extreme fire conditions. On balance, the thinning treatment released 3114 kg C ha −1. If the wood removed from the site had been used in longer-lasting products, the thinning could have resulted in net carbon storage on the order of 3351 kg C ha −1.

Plant functional traits and soil carbon sequestration in contrasting biomes

Plant functional traits control a variety of terrestrial ecosystem processes, including soil carbon storage which is a key component of the global carbon cycle. Plant traits regulate net soil carbon storage by controlling carbon assimilation, its transfer and storage in belowground biomass, and its release from soil through respiration, fire and leaching. However, our mechanistic understanding of these processes is incomplete. Here, we present a mechanistic framework, based on the plant traits that drive soil carbon inputs and outputs, for understanding how alteration of vegetation composition will affect soil carbon sequestration under global changes. First, we show direct and indirect plant trait effects on soil carbon input and output through autotrophs and heterotrophs, and through modification of abiotic conditions, which need to be considered to determine the local carbon sequestration potential. Second, we explore how the composition of key plant traits and soil biota related to carbon input, release and storage prevail in different biomes across the globe, and address the biome-specific mechanisms by which plant trait composition may impact on soil carbon sequestration. We propose that a trait-based approach will help to develop strategies to preserve and promote carbon sequestration.

Effects of tropospheric ozone pollution on net primary productivity and carbon storage in terrestrial ecosystems of China

We investigated the potential effects of elevated ozone (O3) along with climate variability, increasing CO2, and land use change on net primary productivity (NPP) and carbon storage in China's terrestrial ecosystems for the period 1961–2000 with a process‐based Dynamic Land Ecosystem Model (DLEM) forced by the gridded data of historical tropospheric O3 and other environmental factors. The simulated results showed that elevated O3 could result in a mean 4.5% reduction in NPP and 0.9% reduction in total carbon storage nationwide from 1961 to 2000. The reduction of carbon storage varied from 0.1 Tg C to 312 Tg C (a decreased rate ranging from 0.2% to 6.9%) among plant functional types. The effects of tropospheric O3 on NPP were strongest in east‐central China. Significant reductions in NPP occurred in northeastern and central China where a large proportion of cropland is distributed. The O3 effects on carbon fluxes and storage are dependent upon other environmental factors. Therefore direct and indirect effects of O3, as well as interactive effects with other environmental factors, should be taken into account in order to accurately assess the regional carbon budget in China. The results showed that the adverse influences of increasing O3 concentration across China on NPP could be an important disturbance factor on carbon storage in the near future, and the improvement of air quality in China could enhance the capability of China's terrestrial ecosystems to sequester more atmospheric CO2. Our estimation of O3 impacts on NPP and carbon storage in China, however, must be used with caution because of the limitation of historical tropospheric O3 data and other uncertainties associated with model parameters and field experiments.

Influence of ozone pollution and climate variability on net primary productivity and carbon storage in China's grassland ecosystems from 1961 to 2000

Our simulations with the Dynamic Land Ecosystem Model (DLEM) indicate that the combined effect of ozone, climate, carbon dioxide and land use have caused China's grasslands to act as a weak carbon sink during 1961–2000. This combined effect on national grassland net primary productivity (NPP) and carbon storage was small, but changes in annual NPP and total carbon storage across China's grasslands showed substantial spatial variation, with the maximum total carbon uptake reduction of more than 400 g m −2 in some places of northeastern China. The grasslands in the central northeastern China were more sensitive and vulnerable to elevated ozone pollution than other regions. The combined effect excluding ozone could potentially lead to an increase of 14 Tg C in annual NPP and 0.11 Pg C in total carbon storage for the same time period. This implies that improvement in air quality could significantly increase productivity and carbon storage in China's grassland ecosystems.

Carbon storage and flux for alpine tundra ecosystems in Changbai Mountains, Northeast China

This paper examined the carbon storage and flux of vegetation-litter-soil in alpine tundra ecosystems in Changbai Mountains, Approximately 17251 t∙a^(-1) of carbon was yearly stored in the vegetation and 15043.1 t∙a^(-1) of carbon flew into soil by litters. The vegetation-litter-soil ecosystem stored 452624 t∙a^(-1) of carbon, which was the important CO2 sink. The net carbon storage was currently 3146 t∙a^(-1) vegetation-litter-soil ecosystem.

The disappearance of relict permafrost in boreal north America: Effects on peatland carbon storage and fluxes

AbstractBoreal peatlands in Canada have harbored relict permafrost since the Little Ice Age due to the strong insulating properties of peat. Ongoing climate change has triggered widespread degradation of localized permafrost in peatlands across continental Canada. Here, we explore the influence of differing permafrost regimes (bogs with no surface permafrost, localized permafrost features with surface permafrost, and internal lawns representing areas of permafrost degradation) on rates of peat accumulation at the southernmost limit of permafrost in continental Canada. Net organic matter accumulation generally was greater in unfrozen bogs and internal lawns than in the permafrost landforms, suggesting that surface permafrost inhibits peat accumulation and that degradation of surface permafrost stimulates net carbon storage in peatlands. To determine whether differences in substrate quality across permafrost regimes control trace gas emissions to the atmosphere, we used a reciprocal transplant study to experimentally evaluate environmental versus substrate controls on carbon emissions from bog, internal lawn, and permafrost peat. Emissions of CO2 were highest from peat incubated in the localized permafrost feature, suggesting that slow organic matter accumulation rates are due, at least in part, to rapid decomposition in surface permafrost peat. Emissions of CH4 were greatest from peat incubated in the internal lawn, regardless of peat type. Localized permafrost features in peatlands represent relict surface permafrost in disequilibrium with the current climate of boreal North America, and therefore are extremely sensitive to ongoing and future climate change. Our results suggest that the loss of surface permafrost in peatlands increases net carbon storage as peat, though in terms of radiative forcing, increased CH4 emissions to the atmosphere will partially or even completely offset this enhanced peatland carbon sink for at least 70 years following permafrost degradation.

Full accounting of the greenhouse gas (CO 2, N 2O, CH 4) budget of nine European grassland sites

The full greenhouse gas balance of nine contrasted grassland sites covering a major climatic gradient over Europe was measured during two complete years. The sites include a wide range of management regimes (rotational grazing, continuous grazing and mowing), the three main types of managed grasslands across Europe (sown, intensive permanent and semi-natural grassland) and contrasted nitrogen fertilizer supplies. At all sites, the net ecosystem exchange (NEE) of CO 2 was assessed using the eddy covariance technique. N 2O emissions were monitored using various techniques (GC-cuvette systems, automated chambers and tunable diode laser) and CH 4 emissions resulting from enteric fermentation of the grazing cattle were measured in situ at four sites using the SF 6 tracer method. Averaged over the two measurement years, net ecosystem exchange (NEE) results show that the nine grassland plots displayed a net sink for atmospheric CO 2 of −240 ± 70 g C m −2 year −1 (mean ± confidence interval at p > 0.95). Because of organic C exports (from cut and removed herbage) being usually greater than C imports (from manure spreading), the average C storage (net biome productivity, NBP) in the grassland plots was estimated at −104 ± 73 g C m −2 year −1, that is 43% of the atmospheric CO 2 sink. On average of the 2 years, the grassland plots displayed annual N 2O and CH 4 (from enteric fermentation by grazing cattle) emissions, in CO 2-C equivalents, of 14 ± 4.7 and 32 ± 6.8 g CO 2-C equiv. m −2 year −1, respectively. Hence, when expressed in CO 2-C equivalents, emissions of N 2O and CH 4 resulted in a 19% offset of the NEE sink activity. An attributed GHG balance has been calculated by subtracting from the NBP: (i) N 2O and CH 4 emissions occurring within the grassland plot and (ii) off-site emissions of CO 2 and CH 4 as a result of the digestion and enteric fermentation by cattle of the cut herbage. On average of the nine sites, the attributed GHG balance was not significantly different from zero (−85 ± 77 g CO 2-C equiv. m −2 year −1). The net exchanges by the grassland ecosystems of CO 2 and of GHG were highly correlated with the difference in carbon used by grazing versus cutting, indicating that cut grasslands have a greater on-site sink activity than grazed grasslands. However, the net biome productivity was significantly correlated to the total C used by grazing and cutting, indicating that, on average, net carbon storage declines with herbage utilisation for herbivores.