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101.
Temperature and substrate controls on intra-annual variation in ecosystem respiration in two subarctic vegetation types 总被引:3,自引:0,他引:3
Arctic ecosystems are important in the context of climate change because they are expected to undergo the most rapid temperature increases, and could provide a globally significant release of CO2 to the atmosphere from their extensive bulk soil organic carbon reserves. Understanding the relative contributions of bulk soil organic matter and plant‐associated carbon pools to ecosystem respiration is critical to predicting the response of arctic ecosystem net carbon balance to climate change. In this study, we determined the variation in ecosystem respiration rates from birch forest understory and heath tundra vegetation types in northern Sweden through a full annual cycle. We used a plant biomass removal treatment to differentiate bulk soil organic matter respiration from total ecosystem respiration in each vegetation type. Plant‐associated and bulk soil organic matter carbon pools each contributed significantly to ecosystem respiration during most phases of winter and summer in the two vegetation types. Ecosystem respiration rates through the year did not differ significantly between vegetation types despite substantial differences in biomass pools, soil depth and temperature regime. Most (76–92%) of the intra‐annual variation in ecosystem respiration rates from these two common mesic subarctic ecosystems was explained using a first‐order exponential equation relating respiration to substrate chemical quality and soil temperature. Removal of plants and their current year's litter significantly reduced the sensitivity of ecosystem respiration to intra‐annual variations in soil temperature for both vegetation types, indicating that respiration derived from recent plant carbon fixation was more temperature sensitive than respiration from bulk soil organic matter carbon stores. Accurate assessment of the potential for positive feedbacks from high‐latitude ecosystems to CO2‐induced climate change will require the development of ecosystem‐level physiological models of net carbon exchange that differentiate the responses of major C pools, that account for effects of vegetation type, and that integrate over summer and winter seasons. 相似文献
102.
Pete Smith Olof Andrén† Thord Karlsson† Paula Perälä‡ Kristiina Regina‡ Mark Rounsevell§ Bas Van Wesemael§ 《Global Change Biology》2005,11(12):2153-2163
Yearly, per‐area carbon sequestration rates are used to estimate mitigation potentials by comparing types and areas of land management in 1990 and 2000 and projected to 2010, for the European Union (EU)‐15 and for four country‐level case studies for which data are available: UK, Sweden, Belgium and Finland. Because cropland area is decreasing in these countries (except for Belgium), and in most European countries there are no incentives in place to encourage soil carbon sequestration, carbon sequestration between 1990 and 2000 was small or negative in the EU‐15 and all case study countries. Belgium has a slightly higher estimate for carbon sequestration than the other countries examined. This is at odds with previous reports of decreasing soil organic carbon stocks in Flanders. For all countries except Belgium, carbon sequestration is predicted to be negligible or negative by 2010, based on extrapolated trends, and is small even in Belgium. The only trend in agriculture that may be enhancing carbon stocks on croplands at present is organic farming, and the magnitude of this effect is highly uncertain. Previous studies have focused on the potential for carbon sequestration and have shown quite significant potential. This study, which examines the sequestration likely to occur by 2010, suggests that the potential will not be realized. Without incentives for carbon sequestration in the future, cropland carbon sequestration under Article 3.4 of the Kyoto Protocol will not be an option in EU‐15. 相似文献
103.
Accelerated belowground C cycling in a managed agriforest ecosystem exposed to elevated carbon dioxide concentrations 总被引:2,自引:0,他引:2
We investigated the effects of three elevated atmospheric CO2 levels on a Populus deltoides plantation at Biosphere 2 Laboratory in Oracle Arizona. Stable isotopes of carbon have been used as tracers to separate the carbon present before the CO2 treatments started (old C), from that fixed after CO2 treatments began (new C). Tree growth at elevated [CO2] increased inputs to soil organic matter (SOM) by increasing the production of fine roots and accelerating the rate of root C turnover. However, soil carbon content decreased as [CO2] in the atmosphere increased and inputs of new C were not found in SOM. Consequently, the rates of soil respiration increased by 141% and 176% in the 800 and 1200 μL L?1 plantations, respectively, when compared with ambient [CO2] after 4 years of exposure. However, the increase in decomposition of old SOM (i.e. already present when CO2 treatments began) accounted for 72% and 69% of the increase in soil respiration seen under elevated [CO2]. This resulted in a net loss of soil C at a rate that was between 10 and 20 times faster at elevated [CO2] than at ambient conditions. The inability to retain new and old C in the soil may stem from the lack of stabilization of SOM, allowing for its rapid decomposition by soil heterotrophs. 相似文献
104.
Comparing and evaluating process-based ecosystem model predictions of carbon and water fluxes in major European forest biomes 总被引:7,自引:0,他引:7
Pablo Morales Martin T. Sykes I. Colin Prentice† Pete Smith‡ Benjamin Smith Harald Bugmann§ Bärbel Zierl§ Pierre Friedlingstein¶ Nicolas Viovy¶ Santi Sabaté Anabel Sánchez Eduard Pla Carlos A. Gracia Stephen Sitch†† Almut Arneth Jerome Ogee¶ 《Global Change Biology》2005,11(12):2211-2233
Process‐based models can be classified into: (a) terrestrial biogeochemical models (TBMs), which simulate fluxes of carbon, water and nitrogen coupled within terrestrial ecosystems, and (b) dynamic global vegetation models (DGVMs), which further couple these processes interactively with changes in slow ecosystem processes depending on resource competition, establishment, growth and mortality of different vegetation types. In this study, four models – RHESSys, GOTILWA+, LPJ‐GUESS and ORCHIDEE – representing both modelling approaches were compared and evaluated against benchmarks provided by eddy‐covariance measurements of carbon and water fluxes at 15 forest sites within the EUROFLUX project. Overall, model‐measurement agreement varied greatly among sites. Both modelling approaches have somewhat different strengths, but there was no model among those tested that universally performed well on the two variables evaluated. Small biases and errors suggest that ORCHIDEE and GOTILWA+ performed better in simulating carbon fluxes while LPJ‐GUESS and RHESSys did a better job in simulating water fluxes. In general, the models can be considered as useful tools for studies of climate change impacts on carbon and water cycling in forests. However, the various sources of variation among models simulations and between models simulations and observed data described in this study place some constraints on the results and to some extent reduce their reliability. For example, at most sites in the Mediterranean region all models generally performed poorly most likely because of problems in the representation of water stress effects on both carbon uptake by photosynthesis and carbon release by heterotrophic respiration (Rh). The use of flux data as a means of assessing key processes in models of this type is an important approach to improving model performance. Our results show that the models have value but that further model development is necessary with regard to the representation of the some of the key ecosystem processes. 相似文献
105.
Carbon fluxes from a tropical peat swamp forest floor 总被引:3,自引:0,他引:3
Jyrki Jauhiainen Hidenori Takahashi† Juha E. P. Heikkinen‡ Pertti J. Martikainen‡ Harri Vasander§ 《Global Change Biology》2005,11(10):1788-1797
A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO2) and methane (CH4) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO2 emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO2 m?2 and less than 1.36±0.57 g CH4 m?2. On the basis of the carbon emitted, CO2 is clearly a more important greenhouse gas than CH4. CO2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering. 相似文献
106.
Mona Vetter Christian Wirth Hannes Böttcher Galina Churkina Ernst-Detlef Schulze Thomas Wutzler Georg Weber† 《Global Change Biology》2005,11(5):810-827
Temperate forest ecosystems have recently been identified as an important net sink in the global carbon budget. The factors responsible for the strength of the sinks and their permanence, however, are less evident. In this paper, we quantify the present carbon sequestration in Thuringian managed coniferous forests. We quantify the effects of indirect human‐induced environmental changes (increasing temperature, increasing atmospheric CO2 concentration and nitrogen fertilization), during the last century using BIOME‐BGC, as well as the legacy effect of the current age‐class distribution (forest inventories and BIOME‐BGC). We focused on coniferous forests because these forests represent a large area of central European forests and detailed forest inventories were available. The model indicates that environmental changes induced an increase in biomass C accumulation for all age classes during the last 20 years (1982–2001). Young and old stands had the highest changes in the biomass C accumulation during this period. During the last century mature stands (older than 80 years) turned from being almost carbon neutral to carbon sinks. In high elevations nitrogen deposition explained most of the increase of net ecosystem production (NEP) of forests. CO2 fertilization was the main factor increasing NEP of forests in the middle and low elevations. According to the model, at present, total biomass C accumulation in coniferous forests of Thuringia was estimated at 1.51 t C ha?1 yr?1 with an averaged annual NEP of 1.42 t C ha?1 yr?1 and total net biome production of 1.03 t C ha?1 yr?1 (accounting for harvest). The annual averaged biomass carbon balance (BCB: biomass accumulation rate‐harvest) was 1.12 t C ha?1 yr?1 (not including soil respiration), and was close to BCB from forest inventories (1.15 t C ha?1 yr?1). Indirect human impact resulted in 33% increase in modeled biomass carbon accumulation in coniferous forests in Thuringia during the last century. From the forest inventory data we estimated the legacy effect of the age‐class distribution to account for 17% of the inventory‐based sink. Isolating the environmental change effects showed that these effects can be large in a long‐term, managed conifer forest. 相似文献
107.
Climate change is predicted to be dramatic at high latitudes. Still, climate impact on high latitude lake ecosystems is poorly understood. We studied 15 subarctic lakes located in a climate gradient comprising an air temperature difference of about 6°C. We show that lake water productivity varied by one order of magnitude along the temperature gradient. This variation was mainly caused by variations in the length of the ice‐free period and, more importantly, in the supply of organic carbon and inorganic nutrients, which followed differences in terrestrial vegetation cover along the gradient. The results imply that warming will have rapid effects on the productivity of high latitude lakes, by prolongation of ice‐free periods. However, a more pronounced consequence will be a delayed stimulation of the productivity following upon changes of the lakes terrestrial surroundings and subsequent increasing input of elements that stimulate the production of lake biota. 相似文献
108.
Distribution of dissolved organic carbon and dissolved fulvic acid in mesotrophic Lake Biwa, Japan 总被引:1,自引:0,他引:1
The dissolved organic carbon (DOC) concentrations in mesotrophic Lake Biwa were determined by a total organic carbon (TOC)
analyzer, and DOC molecular size distributions were determined by size exclusion chromatography (SEC) using a fluorescence
detector at excitation/emission (Ex/Em) levels of 300/425 nm with the eluent at pH 9.7. The fluorescence wavelengths for detection
were chosen from the result of excitation–emission matrix spectrometry (EEM) analysis for dissolved fulvic acid (DFA) extracted
from Ado River (peak A, Ex/Em = 260–270/430–440 nm; peak B, Ex/Em = 300–310/420–430 nm). Ado River DFA was eluted with a retention
time (RT) of 7.4–8.9 min and the apparent molecular weight was estimated at 22–87 kDa based on the elution curve for the spherical
protein molecular weight standard. A DFA peak eluted at the same retention time as Ado River DFA also appeared in all the
samples of Lake Biwa water. From the linear relationship between the peak areas with an RT of 7.4–8.9 min by SEC analysis
and DOC values of DFA by TOC analysis of a series of DFA samples (r2 = 0.9995), the concentrations of DFA in the lake water were roughly calculated. DFA was distributed within the range 0.25–0.43 mg C l−1 and accounted for 15%–41% of DOC, with the highest ratios observed at a depth of 70 m in August and the lowest at 2.5 m in
May. 相似文献
109.
Using Satellite Remote Sensing to Estimate the Colored Dissolved Organic Matter Absorption Coefficient in Lakes 总被引:4,自引:0,他引:4
Tiit Kutser Donald C. Pierson Lars Tranvik Anu Reinart Sebastian Sobek Kari Kallio 《Ecosystems》2005,8(6):709-720
Given the importance of colored dissolved organic matter (CDOM) for the structure and function of lake ecosystems, a method
that could estimate the amount of CDOM in lake waters over large geographic areas would be highly desirable. Satellite remote
sensing has the potential to resolve this problem. We carried out model simulations to evaluate the suitability of different
satellite sensors (Landsat, IKONOS, and the Advanced land Imager [ALI]) to map the amount of CDOM in concentration ranges
that occur in boreal lakes of the Nordic countries. The results showed that the 8-bit radiometric resolution of Landsat 7
is not adequate when absorption by CDOM at 420 nm is higher than 3 m−1. On the other hand, the 16-bit radiometric resolution of ALI, a prototype of the next generation of Landsat, is suitable
for mapping CDOM in a wider range of concentrations. An ALI image of southern Finland was acquired on 14, July 2002 and in
situ measurements were carried out in 15 lakes (18 stations). The results showed that there is a high correlation (R2 = 0.84) between the 565 nm/660 nm ALI band ratio and the CDOM absorption coefficient in lakes. Analysis of 245 lakes in the
acquired satellite image showed a normal distribution of CDOM concentration among the lakes. However, the size distribution
of lakes was highly skewed toward small lakes, resulting in the CDOM concentration per unit lake area being skewed toward
high values. We showed that remote sensing enables synoptic monitoring of the CDOM concentration in a large number of lakes
and thus enables scaling up to the level of large ecosystems and biomes. 相似文献
110.
Ecosystem tracer-level additions would benefit from a stable isotope-labeled source of complex organic molecules. We tested
a method to label tree C with 13C and create a stable isotope tracer for stream dissolved organic carbon (DOC) using tulip poplar (Liriodendron tulipifera L.) seedlings. In 2000, seedlings were grown with 0.82 moles of 13CO2 to assess the distribution and level of 13C enrichment in the tree tissues. In 2001, seedlings were grown with 25 times more 13CO2 to generate tissues with a 13C signal strong enough for a 13C-DOC stream tracer addition. 13C enrichment in the trees varied in each year and by tissue age and type. Tissues formed during labeling (new) were more enriched
in 13C than tissues established prior to the 13CO2 injection (old). Stems were most enriched in 13C in both new and old tissues. A higher percentage of 13CO2 was incorporated into seedlings in 2000 (59% ±1) than 2001 (43% ±0). Percent 13C incorporation among tree tissue types paralleled biomass distributions. Although tree C and 13C were equally soluble in both years, a greater percentage of tree C went into solution in 2001 (30%) than 2000 (20%). The
water-soluble tree C accounted for approximately 12% of the injected 13CO2 and had both humic and polysaccharide components. Results from a whole-stream 13C-DOC tracer addition demonstrated that tree C could be sufficiently labeled with 13CO2 to create a stream DOC isotope tracer with some polymeric constituents. 相似文献