Urban Form,Air Pollution,and CO2 Emissions in Large U.S. Metropolitan Areas

In this article we explore the relationships between urban form and air pollution among 86 U.S. metropolitan areas. Urban form was quantified using preexisting sprawl indexes and spatial metrics applied to remotely sensed land cover data. Air pollution data included the nonpoint source emission of the ozone (O₃) precursors nitrogen oxides (NOx) and volatile organic compounds (VOCs), the concentration of O₃, the concentration and nonpoint source emission of fine particulate matter (PM2.5), and the emission of carbon dioxide (CO₂) from on-road sources. Metropolitan areas that exhibited higher levels of urban sprawl, or sprawl-like urban morphologies, generally exhibited higher concentrations and emissions of air pollution and CO₂ when controlling for population, land area, and climate.     

Very high CO2 exchange fluxes at the peak of the rainy season in a West African grazed semi-arid savanna ecosystem

Africa is a sink of carbon, but there are large gaps in our knowledge regarding the CO₂ exchange fluxes for many African ecosystems. Here, we analyse multi-annual eddy covariance data of CO₂ exchange fluxes for a grazed Sahelian semi-arid savanna ecosystem in Senegal, West Africa. The aim of the study is to investigate the high CO₂ exchange fluxes measured at the peak of the rainy season at the Dahra field site: gross primary productivity and ecosystem respiration peaked at values up to ?48 μmol CO₂ m^?2 s^?1 and 20 μmol CO₂ m^?2 s^?1, respectively. Possible explanations for such high fluxes include a combination of moderately dense herbaceous C4 ground vegetation, high soil nutrient availability and a grazing pressure increasing the fluxes. Even though the peak net CO₂ uptake was high, the annual budget of ?229 ± 7 ± 49 g C m^?2 y^?1 (±random errors ± systematic errors) is comparable to that of other semi-arid savanna sites due the short length of the rainy season. An inter-comparison between the open-path and a closed-path infrared sensor indicated no systematic errors related to the instrumentation. An uncertainty analysis of long-term NEE budgets indicated that corrections for air density fluctuations were the largest error source (11.3% out of 24.3% uncertainty). Soil organic carbon data indicated a substantial increase in the soil organic carbon pool for the uppermost .20 m. These findings have large implications for the perception of the carbon sink/source of Sahelian ecosystems and its response to climate change.     

Photosynthetic responses of Larrea tridentata to a step-increase in atmospheric CO2at the Nevada Desert FACE Facility

Of all terrestrial ecosystems, the productivity of deserts has been suggested to be the most responsive to increasing atmospheric CO₂. The extent to which this prediction holds will depend in part on plant responses to elevated CO₂under the highly variable conditions characteristic of arid regions. The photosynthetic responses ofLarrea tridentata , an evergreen shrub, to a step-increase in atmospheric CO₂(to 550 μmolmol⁻¹) were examined in the field using Free-Air CO₂Enrichment (FACE) under seasonally varying moisture conditions. Elevated CO₂substantially increased net assimilation rate (A_net) in Larrea during both moist and dry periods of the potential growing season, while stomatal conductance (g_s) did not differ between elevated and ambient CO₂treatments. Seasonal and diurnal gas exchange dynamics in elevated CO₂mirrored patterns in ambient CO₂, indicating that elevated CO₂did not extend photosynthetic activity longer into the dry season or during more stressful times of the day. Net assimilation vs. internal CO₂(A/C_i) responses showed no evidence of photosynthetic down-regulation during the dry season. In contrast, after significant autumn rains, A_max(the CO₂saturated rate of photosynthesis) and CE (carboxylation efficiency) were lower in Larrea under elevated CO₂. In situ chlorophyll fluorescence estimation ofLarrea Photosystem II efficiency (F_v/F_m) responded more to water limitation than to elevated CO₂. These findings suggest that predictions regarding desert plant responses to elevated CO₂should account for seasonal patterns of photosynthetic regulatory responses, which may vary across species and plant functional types.     

Latitudinal distribution of soil CO2 efflux and temperature along the Dalton Highway,Alaska

In this paper, we investigate spatial variations in soil CO₂ efflux and carbon dynamics across five sites located between 65.5°N and 69.0°N in tundra and boreal forest biomes of Alaska. Growing and winter mean CO₂ effluxes for the period 2006–2010 were 261 ± 124 (Coefficients of Variation: 48%) and 71 ± 42 (CV: 59%) gCO₂/m², respectively. This indicates that winter CO₂ efflux contributed 24% of the annual CO₂ efflux over the period of measurement. In tundra and boreal biomes, tussock is an important source of carbon efflux to the atmosphere, and contributes 3.4 times more than other vegetation types. To ensure that representativeness of soil CO₂ efflux was determined, 36 sample points were used at each site during the growing season, so that the experimental mean fell within ±20% of the full sample mean at 80% and 90% confidence levels. We found that soil CO₂ efflux was directly proportional to the seasonal mean soil temperature, but inversely proportional to the seasonal mean soil moisture level, rather than to the elevation-corrected July air temperature. This suggests that the seasonal mean soil temperature is the dominant control on the latitudinal distribution of soil CO₂ efflux in the high-latitude ecosystems of Alaska.     

How well do sediment indicators record past climate? An evaluation using annually laminated sediments

The reliability of paleoclimatic inferences from lake-sediment records rests on the understanding of how various sediment indicators respond to environmental changes. Despite the recent proliferation of paleoclimatic records, only a limited number of studies have rigorously evaluated potential indicators by comparing lake-sediment records with instrumental weather data. We analyzed annually laminated sediments of the past 100 years from a lake in north-central Minnesota for a suite of variables commonly used for climatic reconstructions. Results were compared with time series of climatic or climate-derived variables, as well as with indices of climate modes thought to influence the regional climate of the midwestern United States. The oxygen-isotopic composition of calcite (δ¹⁸O_c) shows trends similar to those of effective moisture (as measured by precipitation [P] minus actual evapotranspiration [AET], P-AET, and the Palmer Drought Severity Index [PDSI]), with high δ¹⁸O_c values generally corresponding to low P-AET and low PDSI. δ¹⁸O_c also exhibits striking correspondence with the index of Pacific Decadal Oscillation (PDO) but it lags behind PDO by 3 years. Elevated δ¹⁸O_c values during the warm PDO phase probably reflect warm and dry climatic conditions in the midwestern US, especially during winter months. The carbon-isotopic composition of calcite (δ¹³C_c) shows some similarity with δ¹⁸O_c but also displays stratigraphic patterns resembling those of lake-productivity indicators, including biogenic silica, inverse of inorganic carbon, ratio of organic carbon to nitrogen, and to a lesser extent, organic carbon. δ¹³C_c is correlated with mean annual air temperature (MAAT) and the index of Atlantic Multidecadal Oscillation (AMO), probably because elevated MAAT stimulates the rate of algal carbon uptake, lengthens growing season, and/or enhances CO₂ degassing. Varves are typically thicker during periods of lower δ¹⁸O_c and higher P-AET (or PDSI) values, because wet climatic conditions probably increase nutrient availability and lake productivity. Gray-scale intensity does not co-vary with any of the above climatic variables or climate-mode indices. These results demonstrate the utility of lake-sediment analyses for reconstructing temperature, drought, and large-scale climatic modes at Steel Lake. However, application to down-core reconstructions may be compromised by a number of factors, including the site specificity and non-stationarity of such relationships.     

赣江上游河流水化学的影响因素及DIC来源

对赣江上游38 处水体采样点的水化学特征和溶解无机碳稳定同位素的分析, 发现其总溶解质浓度较低, 其中, 阳离子以Na⁺、Ca²⁺ 为主, 阴离子以Cl^- 和HCO₃ ^- 为主, Si 的浓度较高, 表征了典型硅酸盐地区河流的水化学组成特征。通过海盐校正分析得出, 研究区大气降水对河水溶解质的贡献率为11.5%, 扣除降水的贡献部分, 利用主成分分析的方法, 计算得出赣南流域受硅酸盐岩风化作用强烈, 同时由于受附近盐矿的影响, 蒸发盐岩的风化作用显著。另外, 根据δ¹³C 溶解无机碳DIC 的测量值约为-8.35‰~-13.74‰, 平均为-11.65‰, 利用质量平衡计算得出, 研究区DIC 的主要来源, 约68.5%来自于土壤CO₂, 31.5%来自于碳酸盐矿物的溶解, 进而得出流域岩石化学风化过程消耗的土壤CO₂ 为2.11×105 mol/yr·km², 来自碳酸盐本身的HCO₃ ^-含量为9.6×104 mol/yr·km²。由于地理位置和流域环境以及人为因素的差异, 各支流DIC 来源的比例亦有所差异。     

青藏高原生态系统固碳释氧价值动态测评

本文旨在定量评价青藏高原生态系统的固碳释氧价值及其动态变化,为改善区域生态环境提供参考。基于MODIS/NDVI数据,利用光能利用率模型测算净第一性生产(NPP)物质量,并通过光合作用方程式换算成固定CO₂和释放O₂的物质量,以此为基础,采用造林成本法和工业制氧法对青藏高原固碳释氧价值量进行估算。结果表明:2000年、2005年和2010年固定CO₂的价值分别为384.36×10⁹元、393.23×10⁹元和356.41×10⁹元,释放O₂的价值分别为408.31×10⁹元、415.02×10⁹元和378.61×10⁹元。2000-2005年固碳释氧价值增加了15.58×10⁹元,2005-2010年下降了73.23×10⁹元,而2000-2010年下降了57.65×10⁹元。固碳释氧价值在空间上呈现出从东南向西北递减的趋势,这与青藏高原的水热条件分布基本一致。在价值构成中,草原>森林>草甸>其它类型>灌丛>农田。2000-2010年青藏高原生态系统固碳释氧价值呈现减小趋势,表明近年来气候变化和人类活动导致青藏高原的生态环境出现了退化趋势。     

Relationships between Normalized Difference Vegetation Index (NDVI) and carbon fluxes of biologic soil crusts assessed by ground measurements

The aim of this research was to study the relationships between the biological soil crusts (BSC), spectral reflectance and photosynthetic activity. Twenty field campaigns, each lasting several days, were conducted during the 2002–2003 rainy season at sand dune and loess environments in the north-western Negev desert of Israel. Simultaneous measurements of CO₂ net exchange and spectral reflectance were carried out for several types of BSC. The Normalized Difference Vegetation Index (NDVI) was derived from the BSC reflectance and correlated with their CO₂ exchange data. The relationship between NDVI and CO₂ exchange is discussed in detail with respect to environmental factors, such as soil water content, air temperature, and light intensity. Fairly good correlations were found in the rainy season. The NDVI was useful in indicating the potential magnitude and capacity of the BSC assimilation activity. Furthermore, the index corresponded well with different rates of photosynthetic activity of the different types of microphytes. The results demonstrate that spectral reflectances of the BSC can be related to photosynthetic activities and posseses the potential to assess the amount of carbon sequestration by these microphytes on an areal scale using satellite images.     

Effect of exogenous application of salicylic acid on the drought stress responses of Gardenia jasminoides

The alleviative effects of exogenous salicylic acid(SA) on plants against drought stress were assessed in Gardenia jasminoides seedlings treated with different concentrations of SA.Drought stress was simulated to a moderate level by 15% polyethylene glycol(PEG) 6000 treatment.Seedlings exposed to 15% PEG for 14 days exhibited a decrease in aboveground and underground dry mass,seedling height,root length,relative water content,photosynthetic pigment content,net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs),and water use efficiency.In PEG-stressed plants,the levels of proline,malondialdehyde(MDA),hydrogen peroxide(H_2O_2),and electrolyte leakage rose significantly,whereas antioxidative activity,including superoxide,peroxidase,and catalase activities,declined in leaves.However,the presence of SA provided an effective method of mitigating PEG-caused physiological stresses on G.jasminoides seedlings,which depended on SA levels.PEG-treated plants exposed to SA at 0.5–1.0 mmol/L significantly eased PEG-induced growth inhibition.Application of SA,especially at concentrations of 0.5–1.0 mmol/L,considerably improved photosynthetic pigments,photosynthesis,antioxidative activity,relative water content,and proline accumulation,and decreased MDA content,H_2O_2 content,and electrolyte leakage.By contrast,the positive effects were not evident,or even more severe,in PEG+SA4 treatment.Based on these physiological and biochemical data,a suitable concentration of SA,potential growth regulators,could be applied to enhance the drought tolerance of G.jasminoides.     

Gas exchange responses of a desert herbaceous perennial to variable sunlight in contrasting microhabitats

Over the course of a day, aridland plants experience a range of incident photosynthetic photon flux (PPF) spanning three orders of magnitude. Rapid photosynthetic responses to changes in PPF have large effects on individual plant carbon gain and water use patterns, hence are important to plant distribution and success. We investigated the response over time of photosynthesis (A), stomatal conductance (g), and inter-cellular CO₂ concentration (C_i) to step changes in PPF in a long-lived aridland perennial that typically occurs in two contrasting microhabitats, shade under shrubs of other species and unshaded inter-shrub spaces. An initial rapid response in A and C_i for plants in both microhabitats occurred after abrupt changes in PPF. This was followed by slower changes in these parameters during the rest of the light or dark period. Stomatal conductance responded more gradually to step changes in PPF. The initial increase in A after a dark cycle was significantly greater for plants under shrubs than for plants in inter-shrub spaces, but other changes in A, g and C_i did not differ. We attribute the similar responses in plants from different microhabitats to natural variations in solar radiation and limited selection for differentiation due to population gene pools dominated by plants in the open. Our results support the hypothesis that variable light regimes select for photosynthetic gas exchange processes that closely track changes in incident PPF. Our data also support the hypothesis that gas exchange responses to variable light regimes in aridland plants minimize trade-offs between carbon gain and water loss.     

Quantitative evaluation of the counterbalance between photosynthetic stimulation and depression caused by low partial pressure of O2 and CO2 in alpine atmospheres

To evaluate the effects of low atmospheric pressure on leaf photosynthesis, we compared the photosynthesis of identical leaves of Fagus crenata at lowland (0 m a.s.l.) and at highland (2360 m a.s.l.). At the high altitude, the atmospheric pressure and partial pressure of CO₂ at intercellular air spaces in the leaf (C_i360) decreased to 77% and 78% of those at the low altitude, respectively. On the other hand, the efficiency of photosynthetic CO₂-utilization was apparently higher at the high altitude because of a mitigation of the O₂-inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) under low ambient partial pressure of O₂. This stimulation of photosynthesis partly compensated a photosynthetic depression due to the low C_i360, and the net assimilation rate (A_n360) at the high altitude retained 94% of the value at the low altitude. A theoretical model indicated that the stimulation of photosynthesis at high altitudes depend on internal conductance (g_i) and/or on Rubisco content. The model demonstrated that low atmospheric pressure at high altitudes caused severe restrictions of photosynthesis when leaves had a small g_i and/or a large amount of Rubisco, whichever are repeatedly reported in alpine plants.     

Production of polysaccharide slime by microbial mats in the hypersaline environment of a Western Australian solar saltfield

Of the many microorganisms present in the hypersline environment of the saltfield studied, the cyanobacteriumSynechococcus was found to be the major producer of polysaccharide slime. When dissolved in the brine, this slime caused elevated brine viscosities which impaired the quality of the salt crystallised from such brine.Synechococcus was present in benthic microbial mats throughout the 6 concentrating ponds of the saltfield, but it dominated in the ponds where brine density was above 1.10 g cm^–3, corresponding to the saturation density of gypsum (CaSO₄·2H₂O). At such density,Synechococcus was always associated with copious amounts of slime. At lower density, the nature of the substratum over which the mat was growing affected the slime content and productivity of the mat, presumably relatively to its ability to supply nutrients to the mat. Under laboratory conditions, the addition of gypsum stimulated the growth ofSynechococcus in the presence of excess phosphate (>15 mg L^–1 PO₄-P). Slime production however was not stimulated by high salinity, addition of (CaSO₄·2H₂O), NaSO₄ or nitrate deficiency. Only as cultures entered a stationary phase of growth did slime production increase. It was concluded that a nutrient limitation was probably responsible for the activation of extracellular polysaccharide production, possibly as a means of disposing of excess photosynthetically fixed carbon.     

A large daylight geodesic dome for quantification of whole-ecosystem CO2 and water vapour fluxes in arid shrublands

We designed, constructed, calibrated and field-tested a lightweight (30 kg), 4.2 m diameter, 16.4 m³ polyethylene-covered dome static chamber ecosystem gas exchange cuvette that can quantify ecosystem CO₂ and water vapour fluxes as low as 0.1 μmol CO₂ m⁻² s⁻¹ and 0.1 mmol H₂O m⁻² s⁻¹ with little impact on environmental conditions. Fluxes measured in May 2001 in an intact Great Basin sagebrush ecosystem at midday were significantly higher than in an adjacent post-wildfire successional ecosystem, with observed ranges from –0.71 to 1.49 μmol CO₂ m⁻² s⁻¹ for CO₂ and from –0.09 to 0.53 mmol H₂O m⁻² s⁻¹ for water vapour.     

Carbon and nitrogen isotopic composition of different strains ofArtemia sp

Stable carbon and nitrogen isotope ratios have been determined on 41 strains ofArtemia sp. from different geographic regions around the world. The δ¹³C and δ¹⁵N values ranged between −13.7 to−25.0 per mil and −0.7 to 21.2 per mil respectively.Artemia δ¹³C values from coastal environments are consistent with a marine origin for the food sourceArtemia from inland salt lakes have a range of carbon isotope values suggesting C₃, C₄ and CAM based organic matter could form the base of theArtemia food chain. These data indicate thatArtemia having a wide range of carbon and nitrogen isotope values are available for tropho-dynamic research studies that quantify the effect of respired CO₂ on tissue and CaCO₃ shell¹³C/¹²C ratios. Such stable isotope variation also suggests that stable isotope fingerprinting remains a viable technique for identifying specificArtemia collection sites.     

Laboratory analysis of the effects of elevated atmospheric carbon dioxide on respiration in biological soil crusts

Metabolic activity of Biological Soil Crusts (BSCs) is principally dependent on moisture availability, but also on temperature and light conditions. Less understood is how BSCs respond to elevated atmospheric CO₂. This paper reports laboratory experimental results of elevated atmospheric CO₂ on carbon fluxes for cyanobacterial BSCs. The study uses newly designed dynamic gas exchange chambers in which the internal atmosphere was controlled. CO₂ flux was monitored during controlled experiments in two phases under simulated rainfall events (2 & 5 mm plus control with no wetting) each lasting 3 days with a dry period in between. Phase 1 subjected crusts to 392 ppm CO₂ (representing ambient level) in dry air; in phase 2, the CO₂ concentration was 801 ppm. Both phases exhibited significant efflux (respiration) of CO₂ immediately after wetting, followed by substantial influx (sequestration) of CO₂. Samples subject to 2 mm wetting sequestered an order of magnitude more C under elevated CO₂ than at ambient CO₂; for samples subject to 5 mm wetting, this increase was threefold. The findings highlight the role of BSCs in future carbon budgets by enabling greater sequestration into dryland soils even under enhanced atmospheric CO₂ concentrations, following both light and heavy rainfall events.     

生物肥部分替代化肥对甘蓝(Brassica oleracea)养分吸收、光合作用以及品质的影响

采用大田试验,研究了化肥减量20%~40%、配施生物肥对春茬甘蓝(Brassica oleracea)生长、养分吸收利用、光合作用以及品质的影响。结果表明:与当地施肥量(底肥:N 139.2kg·hm-2,P2O5255kg·hm-2,K2O 93.6kg·hm-2;追肥:N 208.8kg·hm-2)相比,化肥减量并配施生物肥使甘蓝生长前期、后期的茎粗变小;对甘蓝的叶片数、冠幅投影面积无显著影响;叶片的气孔导度、净光合速率均与对照无显著差异;促进了甘蓝叶球生长,叶球中硝酸盐和可溶性固形物含量降低,Vc含量增加;甘蓝叶球、叶片和根系氮含量降低,氮在叶球分配的比例提高,在叶片、根系分配的比例降低。化肥减量并配施生物肥提高了幼苗株高、增加了茎粗,气孔导度和净光合速率升高,降低了硝酸盐和可溶性固形物含量、叶球氮含量和根系的钾含量。     

Chemical weathering and CO2 consumption in the Xijiang River basin, South China

Monthly samples of riverine water were collected and analyzed for the concentrations of major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NO₃⁻), dissolved silicon, and total dissolved solids (TDS) at Wuzhou hydrological station located between the middle and lower reaches of the Xijiang River (XJR) from March 2005 to April 2006. More frequent sampling and analysis were carried out during the catastrophic flooding in June 2005. Stoichiometric analysis was applied for tracing sources of major ions and estimating CO₂ consumption from the chemical weathering of rocks. The results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the XJR. Some 81.20% of the riverine cations originated from the chemical weathering processes induced by carbonic acid, 11.32% by sulfuric acid, and the other 7.48% from the dissolution of gypsum and precipitates of sea salts within the drainage basin. The CO₂ flux consumed by the rock chemical weathering within the XJR basin is 2.37 × 10¹¹ mol y^− 1, of which 0.64 × 10¹¹ mol y^− 1 results from silicate rock chemical weathering, and 1.73 × 10¹¹ mol y^− 1 results from carbonate rock chemical weathering. The CO₂ consumption comprises 0.38 × 10¹¹ mol during the 9-d catastrophic flooding. The CO₂ consumption from rock chemical weathering in humid subtropical zones regulates atmospheric CO₂ level and constitutes a significant part of the global carbon budget. The carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention.     

Spatial and temporal variations in C3 and C4 plant abundance over the Chinese Loess Plateau since the last glacial maximum

Stable carbon isotopes of soil organic matter from 12 sites in the southern Chinese Loess Plateau are reviewed to examine spatial and temporal patterns of C₃ and C₄ plants in the arid to semiarid monsoonal region during three key periods - last glacial maximum, mid-Holocene, and modern. We have tentatively corrected the effects of atmospheric CO₂ concentrations and precipitation amounts on the δ¹³C endmembers for C₃ plants to reconstruct the relative proportion of C₄ plants because the δ¹³C values of C₃ plants are variable under different CO₂ and climate conditions. The results indicate that C₄ grasses increase from northwest to southeast spatially, which is consistent with present-day increasing precipitation and temperature patterns. This suggests that for a monsoon-dominant arid to semiarid region, such as the Loess Plateau, warm-season rainfall is a primary factor limiting C₄ plants growth, and thus C₄ grasses have been outcompeted by C₃ grasses/shrubs under cold-dry climate conditions. However, temporal fluctuations in atmospheric CO₂ concentration may also affect plant growth through altering water-use efficiency (WUE). Enhanced drought caused by decreased WUE due to low atmospheric CO₂ concentrations during glacial periods, combined with a cold-dry climate, leads to a decline in C₄ grasses, canceling out any advantages gained from lowered atmospheric CO₂ concentrations. To reconstruct accurately the abundance of C₃ and C₄ plants in an ecosystem and explore their controlling factors, process-based vegetation models integrating CO₂ and climatic parameters interactive with plant physiology are necessary.     

大气CO2浓度升高和施氮对棉田土壤理化性质及微生物区系的影响

针对耕地非农转化过程中产生的一系列社会问题,采用参与性农户调查方法,对西部欠发达地区西宁市郊区5个样本村190户农户进行了随机入户调查。根据城市开发进程、到市区距离和种植类型等条件,将调查样本村分为近郊城区化农村、近郊农村和远郊农村,就农户对耕地非农转换的基本认知及耕地非农转换的经济、社会和环境价值感知进行分析。结果表明:耕地征用后农户能理性感知和判别耕地非农转换价值,并普遍认为失去耕地后生活费用增加、生活保障降低、收入来源和就业机会少;感知主要受耕地数量、区位条件、耕地开发阶段等因素的影响;处于不同区位条件的农户对耕地非农转换的价值感知存在差异性,城区化农户已逐渐适应城市生活,近郊农户的非农转换经济和社会感知压力最大,远郊农民也感知经济和生活保障压力,但更希望能通过打工增加收入。     

科尔沁沙地玉米(Zea mays)田垄上和垄间土壤呼吸比较

采用动态密闭气室法测定分析了科尔沁沙地典型玉米(Zea mays)农田垄上和垄间土壤呼吸速率的差异及自养和异养呼吸特征,并估算了生态系统碳平衡。结果表明:(1)垄上和垄间土壤呼吸速率存在极显著差异(p0.001),且存在线性关系(p0.05);季节水平上垄上土壤呼吸可解释垄间土壤呼吸98.4%的变异。(2)季节水平上土壤总呼吸(RS)、异养呼吸(RH)和自养呼吸(RA)的温度敏感性指数Q10大小顺序为:RA(4.35)RS(3.10)RH(2.08)。(3)RS和RH之间存在显著差异,RA与RS和RH之间不存在显著差异;RA占RS比例的季节变化范围为28.1%~71.1%,生长季RH和RA占RS的比例均值分别为44.4%和55.6%。(4)科尔沁沙地典型农田生态系统在生长季为碳汇,可净固存大气CO2-C的量为659.1g·m-2。