Net Ecosystem Carbon Balance Research Articles

Maize carbon dynamics are driven by soil erosion state and plant phenology rather than nitrogen fertilization form

Carbon (C) stored in soils represents the largest C pool of terrestrial ecosystems and consequently plays a crucial role in the global C cycle. So far, it is widely unclear to what extent different land uses and land use change influence soil C storage. The hummocky ground moraine landscape of northeastern Germany is characterized by distinct small-scale soil heterogeneity on the one hand, and intensive energy crop cultivation on the other. Both factors are assumed to significantly influence gaseous C exchange; as such, they likely drive soil organic carbon (SOC) stock dynamics in terrestrial agricultural ecosystems. To date, it is not clear to what extent N fertilization forms, which are associated with energy crop cultivation (e.g., application of biogas fermentation residues) and soil type relative to soil erosion state, influence soil C dynamics, nor is it clear whether one of these factors is more important than the other. To investigate the influence of soil erosion state and N fertilization form on soil C dynamics, we present dynamic and seasonal net ecosystem carbon balances (NECB) as a proxy for changes in soil organic carbon stocks. Measurements were conducted for maize (Zea mays L.) at five sites in the “CarboZALF-D” experimental field during the 2011 growing season. Measurement sites represent different soil erosion states (non-eroded Albic Luvisols, extremely eroded Calcaric Regosols and depositional Endogleyic Colluvic Regosols) and N fertilization forms (100% mineral fertilizer, 50% mineral and 50% organic fertilizer, and 100% organic fertilizer). Fertilization treatments were established on the Albic Luvisol. Net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) were measured every four weeks using a dynamic flow-through non-steady-state closed manual chamber system. Gap filling was performed based on empirical temperature and PAR dependency functions and was used to derive daily NEE values. In parallel, daily above-ground biomass production (NPPshoot) was estimated using a logistic growth equation, fitted on periodic biomass samples. Finally, C dynamics were calculated as the balance of daily NEE and NPPshoot based on the initial C input due to organic fertilization. Resulting NECB varied from pronounced soil C losses at the Endogleyic Colluvic Regosol (592g C m−2) to soil C gains at the Calcaric Regosol (−124g C m−2). Minor to modest C losses were observed for the Albic Luvisol. Compared to N fertilization forms, soil erosion states generally had a stronger impact on derived NECB. However, interannual variations in plant phenology and interactions between soil erosion states and fertilization forms might result in different NECB values over multiple years. Hence, long-term measurements of different fertilization treatments on characteristic soil landscape elements are needed.

Fire-regime variability impacts forest carbon dynamics for centuries to millennia

Abstract. Wildfire is a dominant disturbance agent in forest ecosystems, shaping important biogeochemical processes including net carbon (C) balance. Long-term monitoring and chronosequence studies highlight a resilience of biogeochemical properties to large, stand-replacing, high-severity fire events. In contrast, the consequences of repeated fires or temporal variability in a fire regime (e.g., the characteristic timing or severity of fire) are largely unknown, yet theory suggests that such variability could strongly influence forest C trajectories (i.e., future states or directions) for millennia. Here we combine a 4500-year paleoecological record of fire activity with ecosystem modeling to investigate how fire-regime variability impacts soil C and net ecosystem carbon balance. We found that C trajectories in a paleo-informed scenario differed significantly from an equilibrium scenario (with a constant fire return interval), largely due to variability in the timing and severity of past fires. Paleo-informed scenarios contained multi-century periods of positive and negative net ecosystem C balance, with magnitudes significantly larger than observed under the equilibrium scenario. Further, this variability created legacies in soil C trajectories that lasted for millennia. Our results imply that fire-regime variability is a major driver of C trajectories in stand-replacing fire regimes. Predicting carbon balance in these systems, therefore, will depend strongly on the ability of ecosystem models to represent a realistic range of fire-regime variability over the past several centuries to millennia.

Interactions Among Fuel Management, Species Composition, Bark Beetles, and Climate Change and the Potential Effects on Forests of the Lake Tahoe Basin

Climate-driven increases in wildfires, drought conditions, and insect outbreaks are critical threats to forest carbon stores. In particular, bark beetles are important disturbance agents although their long-term interactions with future climate change are poorly understood. Droughts and the associated moisture deficit contribute to the onset of bark beetle outbreaks although outbreak extent and severity is dependent upon the density of host trees, wildfire, and forest management. Our objective was to estimate the effects of climate change and bark beetle outbreaks on ecosystem carbon dynamics over the next century in a western US forest. Specifically, we hypothesized that (a) bark beetle outbreaks under climate change would reduce net ecosystem carbon balance (NECB) and increase uncertainty and (b) these effects could be ameliorated by fuels management. We also examined the specific tree species dynamics—competition and release—that determined NECB response to bark beetle outbreaks. Our study area was the Lake Tahoe Basin (LTB), CA and NV, USA, an area of diverse forest types encompassing steep elevation and climatic gradients and representative of mixed-conifer forests throughout the western United States. We simulated climate change, bark beetles, wildfire, and fuels management using a landscape-scale stochastic model of disturbance and succession. We simulated the period 2010–2100 using downscaled climate projections. Recurring droughts generated conditions conducive to large-scale outbreaks; the resulting large and sustained outbreaks significantly increased the probability of LTB forests becoming C sources over decadal time scales, with slower-than-anticipated landscape-scale recovery. Tree species composition was substantially altered with a reduction in functional redundancy and productivity. Results indicate heightened uncertainty due to the synergistic influences of climate change and interacting disturbances. Our results further indicate that current fuel management practices will not be effective at reducing landscape-scale outbreak mortality. Our results provide critical insights into the interaction of drivers (bark beetles, wildfire, fuel management) that increase the risk of C loss and shifting community composition if bark beetle outbreaks become more frequent.

Carbon and Water Budgets in Multiple Wheat-Based Cropping Systems in the Inland Pacific Northwest US: Comparison of CropSyst Simulations with Eddy Covariance Measurements

Accurate carbon and water flux simulations for croplands are greatly dependent on high quality representation of management practices and meteorological conditions, which are key drivers of the surface-atmosphere exchange processes. Fourteen site-years of carbon and water fluxes were simulated using the CropSyst model over four agricultural sites in the inland Pacific Northwest US from October 1, 2011 to September 30, 2015. Model performance for field-scale net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) was evaluated by comparing simulations with long-term eddy covariance measurements. The model captured the temporal variations of NEE and ET reasonably well with an overall r of 0.78 and 0.80, and a low RMSE of 1.82 g C m-2 d-1 and 0.84 mm d-1 for NEE and ET, respectively. The model slightly underestimated NEE and ET by 0.51 g C m-2 d-1 and 0.09 mm d-1, respectively. ET simulations showed better agreement with eddy covariance measurements than NEE. The model performed much better for the sites with detailed initial conditions (e.g. SOC content) and management practice information (e.g. tillage type). The CropSyst results showed that the winter wheat fields could be annual net carbon sinks or close to neutral with the net ecosystem carbon balance (NECB) ranging from 92 to -17 g C m-2, while the spring crop fields were net carbon sources or neutral with an annual NECB of -327 to -3 g C m-2. Simulations for the paired tillage sites showed that the no-till site resulted in lower CO2 emissions for the crop rotations of winter wheat-spring garbanzo, but had higher carbon loss into the atmosphere for spring canola compared to the conventional tillage site. Water budgets did not differ significantly between the two tillage systems. Winter wheat in the high-rainfall area had higher crop yields and water use efficiency but emitted larger amounts of CO2 into the atmosphere than in the low-rainfall area. Based on model evaluations in this study, CropSyst appears promising as a tool to simulate field-scale carbon and water budgets and assess the effects of different management practices and local meteorological conditions for the wheat-based cropping systems in this region.

Contributions of wildland fire to terrestrial ecosystem carbon dynamics in North America from 1990 to 2012

AbstractBurn area and the frequency of extreme fire events have been increasing during recent decades in North America, and this trend is expected to continue over the 21st century. While many aspects of the North American carbon budget have been intensively studied, the net contribution of fire disturbance to the overall net carbon flux at the continental scale remains uncertain. Based on national scale, spatially explicit and long‐term fire data, along with the improved model parameterization in a process‐based ecosystem model, we simulated the impact of fire disturbance on both direct carbon emissions and net terrestrial ecosystem carbon balance in North America. Fire‐caused direct carbon emissions were 106.55 ± 15.98 Tg C/yr during 1990–2012; however, the net ecosystem carbon balance associated with fire was −26.09 ± 5.22 Tg C/yr, indicating that most of the emitted carbon was resequestered by the terrestrial ecosystem. Direct carbon emissions showed an increase in Alaska and Canada during 1990–2012 as compared to prior periods due to more extreme fire events, resulting in a large carbon source from these two regions. Among biomes, the largest carbon source was found to be from the boreal forest, primarily due to large reductions in soil organic matter during, and with slower recovery after, fire events. The interactions between fire and environmental factors reduced the fire‐caused ecosystem carbon source. Fire disturbance only caused a weak carbon source as compared to the best estimate terrestrial carbon sink in North America owing to the long‐term legacy effects of historical burn area coupled with fast ecosystem recovery during 1990–2012.

Detecting small-scale spatial heterogeneity and temporal dynamics of soil organic carbon (SOC) stocks: a comparison between automatic chamber-derived C budgets and repeated soil inventories

Abstract. Carbon (C) sequestration in soils plays a key role in the global C cycle. It is therefore crucial to adequately monitor dynamics in soil organic carbon (ΔSOC) stocks when aiming to reveal underlying processes and potential drivers. However, small-scale spatial (10–30 m) and temporal changes in SOC stocks, particularly pronounced in arable lands, are hard to assess. The main reasons for this are limitations of the well-established methods. On the one hand, repeated soil inventories, often used in long-term field trials, reveal spatial patterns and trends in ΔSOC but require a longer observation period and a sufficient number of repetitions. On the other hand, eddy covariance measurements of C fluxes towards a complete C budget of the soil–plant–atmosphere system may help to obtain temporal ΔSOC patterns but lack small-scale spatial resolution. To overcome these limitations, this study presents a reliable method to detect both short-term temporal dynamics as well as small-scale spatial differences of ΔSOC using measurements of the net ecosystem carbon balance (NECB) as a proxy. To estimate the NECB, a combination of automatic chamber (AC) measurements of CO2 exchange and empirically modeled aboveground biomass development (NPPshoot) were used. To verify our method, results were compared with ΔSOC observed by soil resampling. Soil resampling and AC measurements were performed from 2010 to 2014 at a colluvial depression located in the hummocky ground moraine landscape of northeastern Germany. The measurement site is characterized by a variable groundwater level (GWL) and pronounced small-scale spatial heterogeneity regarding SOC and nitrogen (Nt) stocks. Tendencies and magnitude of ΔSOC values derived by AC measurements and repeated soil inventories corresponded well. The period of maximum plant growth was identified as being most important for the development of spatial differences in annual ΔSOC. Hence, we were able to confirm that AC-based C budgets are able to reveal small-scale spatial differences and short-term temporal dynamics of ΔSOC.

Mitigating Global Warming Potential and Greenhouse Gas Intensities by Applying Composted Manure in Cornfield: A 3-Year Field Study in an Andosol Soil

A 3-year study was conducted in cornfield to evaluate how composted cattle manure application affects net global warming potential (GWP; the sum of nitrous oxide (N2O) and methane (CH4) minus net ecosystem carbon balance (NECB)) and greenhouse gas intensity (GHGI; net GWP per unit of plant biomass yield). In the first experiment, conducted from 2010 to 2012, five fertilization strategies that included an unfertilized control plot, inorganic fertilizer-only plot, two plots with inorganic fertilizer plus composted cattle manure, and composted cattle manure-only plot were established. In the second experiment composted cattle manure was applied in autumn 2012 and the field was subdivided into three plots in spring 2013, with one plot receiving additional composted cattle manure, the second plot received additional inorganic fertilizer and the third plot did not receive any additional fertilization. Fluxes of N2O, CH4 and CO2 were measured using the static closed chamber method. NECB was calculated as carbon (C) inputs minus C output (where a negative value indicates net C loss). In experiment 1, manure application significantly increased NECB and reduced net GWP by more than 30% in each of the three years of the study. GHGI in the manure-amended plots was lower than in other plots, except in 2012 when the manure-only plot had higher GHGI than fertilizer-only plot. Application of inorganic fertilizer alone increased GWP by 5% and 20% in 2010 and 2011, but showed a 30% reduction in 2012 relative to the unfertilized control plot. However, due to higher net primary production (NPP), fertilizer-only plot had lower GHGI compared to the control. Application of inorganic fertilizer together with manure showed the greatest potential to reduce GWP and GHGI, while increasing NPP and NECB. In experiment 2, additional manure or inorganic fertilizer application in spring increased NPP by a similar amount, but additional manure application also increased NECB, and decreased GWP and GHGI. Manure application, as a partial substitute or supplemental fertilizer, shows potential to mitigate GWP and GHGI.

The carbon balance of temperate grasslands part I: The impact of increased species diversity

Appropriate management of grasslands may aid the sequestration of carbon (C) in soil organic matter, thereby increasing soil quality and offsetting other CO2 emissions to the atmosphere. In ungrazed grassland trials, higher species diversity has been found to enhance soil C sequestration due to increases in plant production and C inputs to the soil via roots. Little is known about the impact of increased species diversity on the change in soil C stocks in intensively grazed pastoral systems common in temperate regions. Here, we report the CO2 and C balances of three blocks of an intensively managed dairy farm in temperate New Zealand. Two blocks underwent pasture renewal (PR): one block was renewed back to ryegrass-clover (NewRye), while the second was sown in a mix of higher species diversity including ryegrass, clover, timothy, prairie grass, lucerne, chicory and plantain (NewMix). A third block served as an undisturbed ryegrass-clover control (Control). We hypothesised that the block renewed to a more diverse pasture would have higher pasture production and C sink strength than either the unmodified pasture or the pasture renewed to ryegrass-clover. Net ecosystem production (NEP) was measured using eddy covariance, and other inputs and outputs of C (e.g. C in pasture removed by grazers and C deposited in dung) were calculated. NEP and the net ecosystem carbon balance (NECB) were determined for four years: one year before PR, and three years after. In the year before PR, we measured important differences in annual NEP (and thus NECB) which suggested unanticipated inherent site differences between blocks which affected C cycling: the NEP of the NewRye block was 116 to 160gCm−2y−1 higher than that of the other blocks. These differences between blocks were accounted for when considering differences in NECBs as a result of the treatments in years following renewal. During the three years following PR, dry matter production was similar for the NewMix and NewRye blocks (15,033 and 14,708kgDMha−1y−1 respectively) and greater than the Control block (13,116kgDMha−1y−1). For 11 out of the 12 block-years the soil-pasture systems lost C as indicated by negative NECBs. Taking into consideration the pre-treatment differences between blocks, the NewMix pasture had a higher NECB (by 254gCm−2 over 3 years) than the NewRye pasture, indicating smaller C losses at the NewMix block. In contrast, there was no difference in NECB between NewMix and Control blocks. When PR is undertaken to increase pasture performance, renewal to a more diverse sward may decrease C losses compared to renewal to a ryegrass-clover sward. In contrast, there was no evidence that PR to a higher diversity sward decreased C losses compared to an unmodified ryegrass-clover sward. Many C balance studies based on eddy covariance techniques have not accounted for pre-existing differences between treatment blocks and we have demonstrated that this may be critically important for drawing conclusions about the true effect of imposed treatments on C balances.

Annual balances and extended seasonal modelling of carbon fluxes from a temperate fen cropped to festulolium and tall fescue under two‐cut and three‐cut harvesting regimes

AbstractThis study reports the annual carbon balance of a drained riparian fen under two‐cut or three‐cut managements of festulolium and tall fescue. CO2 fluxes measured with closed chambers were partitioned into gross primary production (GPP) and ecosystem respiration (ER) for modelling according to environmental factors (light and temperature) and canopy reflectance (ratio vegetation index, RVI). Methodological assessments were made of (i) GPP models with or without temperature functions (Ft) to adjust GPP constraints imposed by low temperature (<10 °C) and (ii) ER models with RVI or GPP parameters as biomass proxies. The sensitivity of the models was also tested on partial datasets including only alternate measurement campaigns and on datasets only from the crop growing period. Use of Ft in GPP models effectively corrected GPP overestimation in cold periods, and this approach was used throughout. Annual fluxes obtained with ER models including RVI or GPP parameters were similar, and also annual GPP and ER fluxes obtained with full and partial datasets were similar. Annual CO2 fluxes and biomass yield were not significantly different in the crop/management combinations although the individual collars (n = 12) showed some variations in GPP (−1818 to −2409 g CO2‐C m−2), ER (1071 to 1738 g CO2‐C m−2), net ecosystem exchange (NEE, −669 to −949 g CO2‐C m−2) and biomass yield (556 to 1044 g CO2‐C m−2). Net ecosystem carbon balance (NECB), as the sum of NEE and biomass carbon export, was only slightly negative to positive in all crop/management combinations. NECBs, interpreted as emission factors, tended to favour the least biomass producing systems as the best management options in relation to climate saving carbon balances. Yet, considering the down‐stream advantages of biomass for fossil fuel replacement, yield‐scaled carbon fluxes are suggested to be given additional considerations for comparison of management options in terms of atmospheric impact.

A carbon balance model for the great dismal swamp ecosystem

BackgroundCarbon storage potential has become an important consideration for land management and planning in the United States. The ability to assess ecosystem carbon balance can help land managers understand the benefits and tradeoffs between different management strategies. This paper demonstrates an application of the Land Use and Carbon Scenario Simulator (LUCAS) model developed for local-scale land management at the Great Dismal Swamp National Wildlife Refuge. We estimate the net ecosystem carbon balance by considering past ecosystem disturbances resulting from storm damage, fire, and land management actions including hydrologic inundation, vegetation clearing, and replanting.ResultsWe modeled the annual ecosystem carbon stock and flow rates for the 30-year historic time period of 1985–2015, using age-structured forest growth curves and known data for disturbance events and management activities. The 30-year total net ecosystem production was estimated to be a net sink of 0.97 Tg C. When a hurricane and six historic fire events were considered in the simulation, the Great Dismal Swamp became a net source of 0.89 Tg C. The cumulative above and below-ground carbon loss estimated from the South One and Lateral West fire events totaled 1.70 Tg C, while management activities removed an additional 0.01 Tg C. The carbon loss in below-ground biomass alone totaled 1.38 Tg C, with the balance (0.31 Tg C) coming from above-ground biomass and detritus.ConclusionsNatural disturbances substantially impact net ecosystem carbon balance in the Great Dismal Swamp. Through alternative management actions such as re-wetting, below-ground biomass loss may have been avoided, resulting in the added carbon storage capacity of 1.38 Tg. Based on two model assumptions used to simulate the peat system, (a burn scar totaling 70 cm in depth, and the soil carbon accumulation rate of 0.36 t C/ha−1/year−1 for Atlantic white cedar), the total soil carbon loss from the South One and Lateral West fires would take approximately 1740 years to re-amass. Due to the impractical time horizon this presents for land managers, this particular loss is considered permanent. Going forward, the baseline carbon stock and flow parameters presented here will be used as reference conditions to model future scenarios of land management and disturbance.

The carbon balance of temperate grasslands part II: The impact of pasture renewal via direct drilling

Pasture renewal (or pasture renovation) is a common management practice in grass-based production systems aimed at restoring pasture production and forage quality. It is important to understand the impact of pasture renewal on soil organic carbon stocks.Here we report the CO2 and C balance of three blocks of an intensively managed temperate grassland in New Zealand. Two blocks underwent pasture renewal using the spray and direct drill approach (no ploughing), while the third block served as an undisturbed Control. Net ecosystem production (NEP) was measured using eddy covariance, and additional in- and outputs of C (e.g. C in pasture removed by grazers and returned in dung) either measured or estimated.NEPs of the renewed blocks were between 149 and 212gCm−2 y−1 lower than the NEP of the Control block during the year of pasture renewal. While CO2 sink strength was obviously diminished as a result of pasture renewal, neither renewed block was a source for CO2, presumably due the relatively warm climate which enabled year-round growing conditions.Despite the non-negative NEPs during the year of pasture renewal, both renewed sites were found to lose soil C as indicated by the negative net ecosystem carbon balances (NECBs). NECBs of the renewed blocks were −156 and −222gCm−2y−1, compared to a near-neutral NECB of the Control block.Comparison of the findings from the current study on pasture renewal without ploughing to those from an earlier study on pasture renewal including ploughing led to the following conclusions: i) our data did not suggest lower rates of respiratory CO2 losses when spray-and-direct-drill approach was used instead of ploughing; ii) as both the direct CO2 losses due to microbial degradation and the decrease in CO2 uptake through photosynthesis contribute to the total impact of pasture renewal on NEP, the duration of fallow period was found to be important in determining the short-term CO2 losses due to pasture renewal, with shorter fallow period leading to lower net CO2 losses; iii) addition of C in the form of manure, effluent, or extra supplemental feed for cattle may help to reduce the negative impact of pasture renewal on soil C loss at the renewed site.

小兴安岭天然森林沼泽湿地生态系统碳源/汇

PDF HTML阅读 XML下载 导出引用 引用提醒 小兴安岭天然森林沼泽湿地生态系统碳源/汇 DOI: 10.5846/stxb201601250174 作者: 作者单位: 东北林业大学生态研究中心,东北林业大学生态研究中心,东北林业大学生态研究中心,东北林业大学生态研究中心,东北林业大学生态研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31370461） Carbon source or sink of natural forested wetland ecosystem in Xiaoxing'anling region of China Author: Affiliation: Center for Ecological Research，Northeast Forestry University,Center for Ecological Research，Northeast Forestry University,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用静态箱-气相色谱法与相对生长方程法，同步测定小兴安岭7种天然沼泽湿地（草丛沼泽-C、灌丛沼泽-G、毛赤杨沼泽-M、白桦沼泽-B、落叶松苔草沼泽-L-T、落叶松藓类沼泽-L-X、落叶松泥炭藓沼泽-L-N）的土壤呼吸（CO2、CH4）净碳排放量、植被年净固碳量，并依据生态系统净碳收支平衡，揭示温带天然沼泽湿地的碳源/汇作用规律。结果表明：①7种天然沼泽CH4年通量（0.006-7.756 mg m-2 h-1）呈M（高于其他类型1.0-1291.7倍，P < 0.05）> C、G、B（高于针叶林沼泽17.7-649.0倍，P >0.05）> 针叶林沼泽变化趋势，其季节动态存在3种类型（C、G单峰型、M、B多峰型及针叶林沼泽排放与吸收交替型）；②其CO2年通量（157.40-231.06 mg m-2 h-1）呈G（高于森林沼泽28.7%-46.8%，P < 0.05）> C（高于森林沼泽7.4%-22.5%，P > 0.05）> 森林沼泽的变化趋势，其季节动态存在2种类型（C、G、L-X和L-N双峰型和M、B、L-T单峰型）；③C、G、M、B、L-N CH4排放仅受0-40 cm不同土壤层温度所控制；7种天然沼泽土壤CO2排放均受气温及0-40 cm不同土壤层温度所控制，但B、L-X、L-N受温度与水位综合控制；④其植被年净固碳量（（2.05±0.09）-（6.75±0.27）tC hm-2 a-1）呈C（高于其他类型65.4%-229.3%，P < 0.05）> G、B、L-T、L-X、L-N（高于M 80.0%-99.0%，P < 0.05）> M变化趋势；⑤7种天然沼泽的碳源/汇（-2.32-2.09 tC hm-2 a-1）作用不同，C、B和L-N为碳吸收汇（C强汇、B和L-N弱汇），M、G、L-T和L-X则为碳排放源（M、G强源、L-T和L-X弱源）。因此，温带小兴安岭草丛沼泽为碳强汇、灌丛沼泽为碳强源、森林沼泽基本维持碳平衡（除M外）。 Abstract:Carbon (CO2 and CH4) emission fluxes, annual net carbon sequestration of vegetation, were studied from seven kinds of natural wetlands (Carex schmidtii marsh-C, Betula ovalifolia-C. schmidtii shrub swamp-G, Alnus sibirica-C. schmidtii swamp-M, B. platyphylla-C. schmidtii swamp-B, Larix gmelinii-C. schmidtii swamp-L-T, L. gmelinii-moss swamp-L-X, and L. gmelinii-Sphagnum spp. swamp-L-N) in Xiaoxing'anling region of China using the static chamber gas chromatography method and the relative growth equation method to evaluate the carbon source or sink of natural forested wetlands based on net ecosystem carbon balance. The results showed that: 1) seasonal dynamics of CH4 emission fluxes from seven kinds of natural wetlands could be divided into three types (single-peak, multi-peak, and emission and absorption alternating type) and CH4 emission flux (0.006-7.756 mg m-2 h-1) exhibited a different trend in M (which was 1.0-1291.7 times greater than the others, P < 0.05) > C, G, B (17.7-649.0 times greater than L-T, L-X, and L-N; P > 0.05) > L-T, L-X, and L-N; 2)seasonal dynamics of CO2 emission fluxes from the seven kinds of natural wetlands could be divided into two types (single-peak and double peak), and CO2 emission flux (157.40-231.06 mg m-2 h-1) exhibited an different trend in G (which was greater 28.7%-46.8% than forested wetlands, P < 0.05) > C(7.4%-22.5% than forested wetlands, P > 0.05) > five kinds of forested wetlands; 3)CH4 emission fluxes from C, G, M, B, and L-N were controlled by soil temperature, but that of L-T and L-X had no significant correlation with soil temperature at 0-40 cm. CO2 emission fluxes from C, G, M, and L-T were controlled by air temperature and soil temperature, and that of B, L-X, and L-N were controlled by air temperature, soil temperature, and the water table level; 4) the annual net carbon sequestration of vegetation ((2.05±0.09)-(6.75±0.27) tC hm-2 a-1) had a different trend in C (greater than the others by 65.4%-229.3%,P < 0.05)> G, B, L-T, L-X, and L-N (greater than M by 80.0%-99.0%, P < 0.05) > M; and 5) the sources and sinks of carbon were significantly different among the seven kinds of natural wetland types (-2.32-2.09 tC hm-2 a-1). For example, C, B, and L-N exhibited varying degrees of carbon sinks, yet M, G, L-T, and L-X exhibited varying degrees of carbon sources. Therefore, marsh wetlands were greater carbon sinks and shrub wetlands were greater carbon sources, yet forested wetlands maintained overall carbon balance (except M) in the Xiaoxing'anling region of China. 参考文献 相似文献 引证文献

Colonization of a Deglaciated Moraine: Contrasting Patterns of Carbon Uptake and Release from C3 and CAM Plants.

IntroductionCurrent glacier retreat makes vast mountain ranges available for vegetation establishment and growth. As a result, carbon (C) is accumulated in the soil, in a negative feedback to climate change. Little is known about the effective C budget of these new ecosystems and how the presence of different vegetation communities influences CO2 fluxes.MethodsOn the Matsch glacier forefield (Alps, Italy) we measured over two growing seasons the Net Ecosystem Exchange (NEE) of a typical grassland, dominated by the C3 Festuca halleri All., and a community dominated by the CAM rosettes Sempervivum montanum L. Using transparent and opaque chambers, with air temperature as the driver, we partitioned NEE to calculate Ecosystem Respiration (Reco) and Gross Ecosystem Exchange (GEE). In addition, soil and vegetation samples were collected from the same sites to estimate the Net Ecosystem Carbon Balance (NECB).ResultsThe two communities showed contrasting GEE but similar Reco patterns, and as a result they were significantly different in NEE during the period measured. The grassland acted as a C sink, with a total cumulated value of -46.4±35.5 g C m-2 NEE, while the plots dominated by the CAM rosettes acted as a source, with 31.9±22.4 g C m-2. In spite of the different NEE, soil analysis did not reveal significant differences in carbon accumulation of the two plant communities (1770±130 for F. halleri and 2080±230 g C m-2 for S. montanum), suggesting that processes often neglected, like lateral flows and winter respiration, can have a similar relevance as NEE in the determination of the Net Ecosystem Carbon Balance.

Effects of irrigation and addition of nitrogen fertiliser on net ecosystem carbon balance for a grassland.

The ability to quantify the impacts of changing management practices on the components of net ecosystem carbon balance (NB) is required to forecast future changes in soil carbon stocks and potential feedbacks on atmospheric CO2 concentrations. In this study we investigated seasonal changes on the components of net ecosystem carbon balance resulting from the application of irrigation and nitrogen fertiliser to a temperate grassland in New Zealand where we simulated grazing events. We made seasonal measurements of the components of NB using chamber measurements in field plots with and without irrigation and addition of nitrogen fertiliser. We developed models to determine the physiological responses of gross canopy photosynthesis (A), leaf respiration (RL) and soil respiration (RS) to soil and air temperature, soil water content and irradiance and we estimated annual NB for the first year after treatments were applied. Overall, irrigation and nitrogen addition had a synergistic effect to increase annual estimates of above-ground components of carbon balance (A, RL and carbon exported through simulated grazing, Fexport), but there was no effect from adding nitrogen alone. Annual RS remained unchanged between treatments. The treatments resulted in increases in above-ground biomass production, but, with the high intensity of simulated grazing, these were not sufficient to offset ecosystem carbon losses, so all treatments remained a net source of carbon. There were no significant differences between treatments and annual NB ranged from -540gCm-2y-1 for the treatment with no irrigation and no nitrogen addition and -284gCm-2y-1 for the treatment with irrigation and nitrogen addition. Our findings from the first year of the treatments quantify the net benefits of addition of irrigation and nitrogen on increasing above-ground production for animal feed but show that this did not lead to a net increase carbon input to the soil.

Comparison of carbon budget, evapotranspiration, and albedo effect between the biofuel crops switchgrass and corn

Interest in biofuels produced from perennial crops like switchgrass (Panicum virgatum L.) has increased over the past decades. It has been suggested that perennial biofuel crops have additional climate benefits compared to annual crops, such as carbon sequestration and albedo increase, but these effects have not been quantified in field studies. We compared carbon dioxide and water exchange results from eddy covariance measurements and surface albedo over a switchgrass and a corn field in Southwestern Ontario, Canada, for the year 2014. Results for the carbon budget showed more carbon uptake for switchgrass compared to corn (annual net ecosystem exchange NEE of −336±40 vs +64±41gCm−2). Switchgrass was a small sink of carbon with a net ecosystem carbon balance (NECB) of −66±59gCm−2 but corn was a source for a scenario where corn grain only is harvested (NECB 393±44gCm−2) and a 1.5 times larger source if both corn grain and stover are harvested (NECB 699±47gCm−2). Switchgrass had, however, a lower yield 568±93gm−2 than either corn scenario (751±40gm−2 for grain only and 1439±52gm−2 for grain plus stover). Results from the albedo measurements showed a negative radiative forcing on an annual basis for the switchgrass field compared to corn. Differences in albedo were especially pronounced during spring and fall when radiative forcing values of −10.2 and −5.5Wm−2 were observed, respectively. Qualitative analysis of the carbon budget, evapotranspiration, and albedo results from this study suggests that biofuel produced from switchgrass can have more climate benefits than biofuel produced from continuous corn cropping systems.

Integrating Winter Annual Cereal Rye or Triticale into a Corn Forage Biofuel Production System

ABSTRACTIntegrating cover crops into the corn (Zea mays L.) forage-production system could enhance growers’ profitability and improve ecosystem services. Field plots were established at two locations in Michigan during 2012--2014 to evaluate ethanol production, estimate carbon and energy balance, and the economics of corn forage plus cover crop, cropping systems. In the 2012--2013 crop cycle, which was characterized by a summer drought, the cereal rye (Secale cereale L.), and triticale (Triticale hexaploide Lart.), winter annual cover crops increased cropping system biomass yield by 44%, and total ethanol yield by 28% relative to the no-cover control. During the 2012--2013 cycle, cover crops provided sufficient biomass (6.5 and 8.1 Mg ha−1, respectively, for cereal rye and triticale) to result in a profitable harvest as a biofuel feedstock. However, following a harsh winter, such as that experienced in the 2013--2014 cycle, cover crop yield (1.6 and 1.2 Mg ha−1, respectively, for cereal rye and triticale) was compromised to the point that harvest was not economically justified. Incorporating cover crops into a corn forage cropping system increased total biomass and potential biofuel yield and generated a very favorable net ecosystem carbon and energy balance.

Net ecosystem methane and carbon dioxide exchange in relation to heat and carbon balance in lowland tropical rice

This paper reports on the annual net ecosystem exchanges of methane (CH4), carbon dioxide (CO2), sensible heat (H) and latent heat (LE) fluxes between tropical lowland rice and atmosphere as well as quantification of annual net ecosystem carbon (C) balance. This study included both wet and dry rice seasons and fallow periods as well. Cumulative annual net ecosystem CO2 exchange (NEE) was −7.47Mg C ha−1 and net ecosystem CH4 exchange (NEME) was +419.68kg CH4 ha−1, respectively, which were higher than the reported values in the same ecology. The range of NEE was much wider in dry season compared to wet season. However, NEME did not vary considerably between the seasons. As a whole, integrated NEE was 52% higher in dry season, whereas, integrated NEME was 24% higher in wet season. In lowland rice ecology LE outweighed H. The NEME showed positive correlation with H and LE in dry season, but the relationship of NEME with LE in wet season was negative. That might be due to changes in processes driving the methanogenesis versus methanotrophy in relatively dry soil and or less transportation of CH4 from soil to atmosphere through rice. Annual global warming potential (GWP)-based C balance was done by considering net ecosystem production (NEP), rhizodeposition, algal biomass, root plus stubble biomass, ratoon and compost addition as ecosystem C input, whereas, NEME and nitrous oxide (N2O) emission, C removal through harvest and dissolved organic C as ecosystem C outflux. Although (GWP)-based CO2C equivalent of CH4 and N2O emissions were sources of C loss from lowland rice ecosystem, but taking into account all the components of C balance within the system, this ecology reflected a good potential to store considerable amount of carbon (1.04Mg C ha−1) and hence, acted as net C sink. Future challenge is to quantify ecosystem carbon budgeting either by considering all sources of energy input and output and/or by using life cycle assessment method in lowland ecology and its up scaling.

The influence of drought and heat stress on long-term carbon fluxes of bioenergy crops grown in the Midwestern USA.

Perennial grasses are promising feedstocks for bioenergy production in the Midwestern USA. Few experiments have addressed how drought influences their carbon fluxes and storage. This study provides a direct comparison of ecosystem-scale measurements of carbon fluxes associated with miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum), restored native prairie and maize (Zea mays)/soybean (Glycine max) ecosystems. The main objective of this study was to assess the influence of a naturally occurring drought during 2012 on key components of the carbon cycle and plant development relative to non-extreme years. The perennials reached full maturity 3-5 years after establishment. Miscanthus had the highest gross primary production (GPP) and lowest net ecosystem exchange (NEE) in 2012 followed by similar values for switchgrass and prairie, and the row crops had the lowest GPP and highest NEE. A post-drought effect was observed for miscanthus. Over the duration of the experiment, perennial ecosystems were carbon sinks, as indicated by negative net ecosystem carbon balance (NECB), while maize/soybean was a net carbon source. Our observations suggest that perennial ecosystems, and in particular miscanthus, can provide a high yield and a large potential for CO2 fixation even during drought, although drought may negatively influence carbon uptake in the following year, questioning the long-term consequence of its maintained productivity.

Regional carbon cycle responses to 25 years of variation in climate and disturbance in the US Pacific Northwest

Variation in climate, disturbance regime, and forest management strongly influence terrestrial carbon sources and sinks. Spatially distributed, process-based, carbon cycle simulation models provide a means to integrate information on these various influences to estimate carbon pools and flux over large domains. Here we apply the Biome-BGC model over the four-state Northwest US region for the interval from 1986 to 2010. Landsat data were used to characterize disturbances, and forest inventory data were used to parameterize the model. The overall disturbance rate on forest land across the region was 0.8 % year−1, with 49 % as harvests, 28 % as fire, and 23 % as pest/pathogen. Net ecosystem production (NEP) for the 2006–2010 interval on forestland was predominantly positive (a carbon sink) throughout the region, with maximum values in the Coast Range, intermediate values in the Cascade Mountains, and relatively low values in the Inland Rocky Mountain ecoregions. Localized negative NEPs were mostly associated with recent disturbances. There was large interannual variation in regional NEP, with notably low values across the region in 2003, which was also the warmest year in the interval. The recent (2006–2010) net ecosystem carbon balance (NECB) was positive for the region (14.4 TgC year−1). Despite a lower area-weighted mean NECB, public forestland contributed a larger proportion to the total NECB because of its larger area. Aggregated forest inventory data and inversion modeling are beginning to provide opportunities for evaluating model-simulated regional carbon stocks and fluxes.

Restoring forest structure and process stabilizes forest carbon in wildfire‐prone southwestern ponderosa pine forests

Changing climate and a legacy of fire-exclusion have increased the probability of high-severity wildfire, leading to an increased risk of forest carbon loss in ponderosa pine forests in the southwestern USA. Efforts to reduce high-severity fire risk through forest thinning and prescribed burning require both the removal and emission of carbon from these forests, and any potential carbon benefits from treatment may depend on the occurrence of wildfire. We sought to determine how forest treatments alter the effects of stochastic wildfire events on the forest carbon balance. We modeled three treatments (control, thin-only, and thin and burn) with and without the occurrence of wildfire. We evaluated how two different probabilities of wildfire occurrence, 1% and 2% per year, might alter the carbon balance of treatments. In the absence of wildfire, we found that thinning and burning treatments initially reduced total ecosystem carbon (TEC) and increased net ecosystem carbon balance (NECB). In the presence of wildfire, the thin and burn treatment TEC surpassed that of the control in year 40 at 2%/yr wildfire probability, and in year 51 at 1%/yr wildfire probability. NECB in the presence of wildfire showed a similar response to the no-wildfire scenarios: both thin-only and thin and burn treatments increased the C sink. Treatments increased TEC by reducing both mean wildfire severity and its variability. While the carbon balance of treatments may differ in more productive forest types, the carbon balance benefits from restoring forest structure and fire in southwestern ponderosa pine forests are clear.