Impact of human activities on soil respiration: A review

Soil respiration is one of the primary fluxes of carbon between soils and the atmosphere.It is produced by rhizosphere respiration and soil microbial respiration.Soil respiration is not only affected by environmental factors,but also changes with the hu-man-induced disturbances of ecosystems.Land-use,the measures of land management,the pollution of soil,and so on can affect soil respiration and change the soil efflux.According to some research,the authors summed up their impacts on soil respiration by human activities through land-use changes and land-management measures among agroecosystem,grassland ecosystem,and for-est ecosystem.The results showed that (1) when adding fertilization to farmland,the soil respiration will increase;(2) fenced land can decrease soil respiration,while soil respiration in the grazed land at a grassland ecosystem will decline with the increasing of grazing intensity;(3) with grassland fertilization;farmland cultivation;fire,fertilization,and cutting of forest,conflicting results were found in the changes of soil respiration.Perhaps plant species,site condition,and measurement season can lead to different results on soil respiration.     

The response of Caragana microphylla seedlings to water table changes in Horqin Sandy Land, China

This paper focuses on the growth response of Caragana microphylla seedlings to changes of artificially controlled water table in Horqin Sandy Land, China. Monitoring results of soil water content shows that soil moisture is closely correlated to groundwater depths. Soil volumetric water increased rapidly when close to water sources and finally stabilized in a saturated state. The soil moisture trend of CK(control) increased gradually at 0–50 cm of soil depth then decreased to 4% below 50 cm soil depth. C. microphylla can adapt to different soil environments by changes in ecological and physiological characteristics. By comparing the ecological characteristics of C. microphylla seedlings at various water tables, we found that a shallow water table of 40 cm depth inhibited seedling growth because of weak ecological characteristics. A groundwater depth of 120 cm was more advantageous for plant height and canopy growth of C. microphylla seedlings. During the first two years, the most suitable water depth for root biomass was 120 cm, and 180 cm for root length. The growth of vertical roots is positively correlated with groundwater depth, and root thickness is the determinate factor for root biomass while the fine root is the determinate factor for root length. A thick root would grow much more in a natural drought environment while access to ground water promotes the growth of fine roots.     

Influence of environmental, root, and stand parameters on soil surface CO2 efflux in a Populus euphratica of desert forest in extreme arid region

Spatial variation in soil surface CO2 efflux was measured in a stand of Populus euphratica in the Ejina Oasis of desert riparian forest in the extreme arid region in northwestern China from April 2007 through October 2007.Measurements were taken with a gas-exchange analyzer linked to a soil-respiration chamber.The mean soil CO2 efflux in the stand was 2.71 μmol/(m2·s) during the growing season and 1.38 μmol/(m2·s) in the nongrowing season.The seasonal maximum (end of May through early June) andminimum (October) CO2 efflux were 3.38 and 0.69 μmol/(m2·s),respectively.The diurnal fluctuation of CO2 efflux was relatively small (< 20 percent),with theminimum appearing around 05:00 and the maximum around 15:00.Linear regression analysis showed soil-surface CO2 efflux to be most highly correlated with soil temperature (R2=0.435) and soil moisture (R2=0.213).When all variables were considered simultaneously,only soil temperature (R2=0.378),soil moisture (R2=0.147),and root volume density (R2=0.021) explained a significant amount of variance in soil surface CO2 efflux.Stand volumes were not correlated with soil CO2 efflux on our sites.     

Simulated effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region of the Northern Hemisphere

Soil freeze-thaw process is closely related to surface energy budget,hydrological activity,and terrestrial ecosystems.In this study,two numerical experiments(including and excluding soil freeze-thaw process)were designed to examine the effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region in the Northern Hemisphere based on the state-of-the-art Community Earth System Model version 1.0.5.Results show that in response to soil freeze-thaw process,the area averaged soil temperature in the shallow layer(0.0175?0.0451 m)decreases by 0.35℃in the TP(Tibetan Plateau),0.69℃in CES(Central and Eastern Siberia),and 0.6℃in NA(North America)during summer,and increases by 1.93℃in the TP,2.28℃in CES and 1.61℃in NA during winter,respectively.Meanwhile,in response to soil freeze-thaw process,the area averaged soil liquid water content increases in summer and decrease in winter.For surface heat flux components,the ground heat flux is most significantly affected by the freeze-thaw process in both summer and winter,followed by sensible heat flux and latent heat flux in summer.In the TP area,the ground heat flux increases by 2.82 W/m2(28.5%)in summer and decreases by 3.63 W/m2(40%)in winter.Meanwhile,in CES,the ground heat flux increases by 1.89 W/m2(11.3%)in summer and decreases by 1.41 W/m2(18.6%)in winter.The heat fluxes in the Tibetan Plateau are more susceptible to the freeze-thaw process compared with the high-latitude frozen soil regions.Soil freeze-thaw process can induce significant warming in the Tibetan Plateau in winter.Also,this process induces significant cooling in high-latitude regions in summer.The frozen ground can prevent soil liquid water from infiltrating to deep soil layers at the beginning of thawing;however,as the frozen ground thaws continuously,the infiltration of the liquid water increases and the deep soil can store water like a sponge,accompanied by decreasing surface runoff.The influence of the soil freeze-thaw process on surface hydrologic and thermal fluxes varies seasonally and spatially.     

Influence of short-term experimental warming on heat-water processes of the active layer in a swamp meadow ecosystem of the Qinghai-Tibet Plateau

Climate change is now evident in the Qinghai-Tibet Plateau(QTP), with impacts on the alpine ecosystem, particularly on water and heat balance between the active layer and the atmosphere. Thus, we document the basic characteristics of changes in the water and heat dynamics in response to experimental warming in a typical alpine swamp meadow ecosystem. Data sets under open top chambers(OTC) and the control manipulations were collected over a complete year. The results show that annual(2008) air temperatures of OTC-1 and OTC-2 were 6.7 °C and 3.5 °C warmer than the control. Rising temperature promotes plant growth and development. The freeze-thaw and isothermal days of OTCs appeared more frequently than the control, owing to comparably higher water and better vegetation conditions. OTCs soil moisture decreased with the decrease of soil depth; however, there was an obviously middle dry aquifer of the control, which is familiar in QTP. Moreover, experimental warming led to an increase in topsoil water content due to poorly drained swamp meadow ecosystem with higher organic matter content and thicker root horizons. The results of this study will have some contributions to alpine cold ecosystem water-heat process and water cycle under climate change.     

不同辐射对土壤湿度长程相关性的影响——以黑河流域阿柔超级站为例（英文）

Analyses of the soil moisture evolution trend and the influence of different types of radiation on soil moisture are of great significance to the simulation and prediction of soil moisture.In this paper,soil moisture(2–60 cm) and various radiation data from 2014–2015 at the A’rou superstation were selected.The radiation data include the net radiation(NR),shortwave and longwave radiation(SR and LR).Using adaptive fractal analysis(AFA),the long-range correlation(LRC) of soil moisture and long-range cross correlation(LRCC) between moisture and three types of radiation were analyzed at different timescales and soil depths.The results show that:(1) Persistence of soil moisture and consistency between soil moisture and radiation mutate at 18-d and 6-d timescales,respectively.The timescale variation of soil moisture persistence is mainly related to the influence process of radiation on soil moisture;(2) Both the soil moisture persistence and soil moisture-radiation consistency vary substantially with soil depth.The soil depth variation of soil moisture persistence is related to the influence intensity of radiation;(3) From 2–6 day timescales,LR displays the strongest influence on soil moisture at depths of 2–10 cm through negative feedback of radiation on the soil temperature.The influence intensity decreases with depth from 2–15 cm.Therefore,the soil moisture persistence is weak and increases with depth from 2–15 cm;and(4) At more than 6 day timescales,SR and NR display a stronger influence on the soil moisture persistence at depths of 2–40 cm through positive feedback of radiation on the soil temperature,especially at depths of 2–10 cm.This influence also weakens with depth.The soil moisture persistence at depths of 2–10 cm is the weakest and increases with depth from 2–40 cm.The research results are instructive for determining timescales and soil depths related to soil water in hydrological models.     

草盛期不同类型高寒草甸CO2释放速率的比较研究

Potentilla fruticosa scrub, Kobresia humilis meadow and Kobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO2 emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO2 emission rates from various treatments were 672.09±152.37 mgm^-2h^-1 for FC (grass treatment); 425.41±191.99 mgm^-2h^-1 for FJ (grass exclusion treatment); 280.36±174.83 mgm^-2h^-1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm^-2h^-1 for GG (scrub+grass treatment); 528.48±205.67 mgm^-2h^-1 for GC (grass treatment); 268.97±99.72 mgm^-2h^-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm^-2h^-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore, Kobresia humilis meadow, Potentilla fruticosa scrub meadow and Kobresia tibetica meadow differed greatly in average CO2 emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, in Kobresia hurnilis meadow,heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, in Potentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration from Kobresia humilis meadow approximated 145 mgCO2m^-2h^-1,contributed 34% to soil respiration. During the experiment period, Kobresia humilis meadow and Potentilla fruticosa scrub meadow had a net carbon fixation of 111.11 gm^-2 and 243.89 gm^-2 respectively. Results also showed that soil temperature was the main factor which influenced CO2 emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and CO2 emission from GG, GC, FC and FJ treatments. In addition, soil moisture maybe the inhibitory factor of CO2 emission from Kobresia tibetica meadow, and more detailed analyses should be done in further research     

Study on the impact of vegetation degeneration to hydrology characteristic of the Alpine soil

Alpine soil infiltration process is an important part of the hydrological characteristics of alpine soil in permafrost. This research is carried out in the source region of the Yellow River where the permafrost is severely degraded, using various methods for choosing typical sample areas, and to experiment, study and simulate the soil water curve, soil saturated hydraulic conductivity, soil infiltration and soil moisture under different characteristics of degraded vegetation. The results indicate that the empirical equation θ=AS^−B, proposed by Gradner and Visser, is very reliable in simulating the soil moisture curve; soil saturated hydraulic conductivity and soil infiltration are significantly different under different vegetation coverage: in the soil surface within 0–10 cm, the saturated hydraulic conductivity and infiltration intensity of Black Beach are the strongest; respectively, in soil layers below 30 cm, vegetation has almost no impacts on the saturated hydraulic conductivity, infiltration intensity and soil moisture content. Significant reduction of soil moisture occurs in soil surfaces with degraded vegetation. The more serious the degradation, the more water loss, and it can be up to 38.6% in the worst situation. Soil moisture of developed vegetation root systems in depths within 10–20 cm has the greatest impact on the soil environment, and the loss of moisture induces difficulty in the restoration of degraded meadows. Through a comparative study, the Kostiakov infiltration equation f(t) = at^−b is more applicable for studies on the process of soil moisture infiltration of the alpine meadow in the source region of the Yellow River.     

Water sources of plants and groundwater in typical ecosystems in the lower reaches of the Heihe River Basin

Stable oxygen and hydrogen isotopic compositions （δ18O and δD） of soil water and shallow groundwater of a riparian forest, an artificial shrub forest, and Gobi of the lower reaches of the Heihe River Basin are used to study the recharge water sources of those ecosystems. IsoSource software is used to determine the δ180 values for root water of Populous euphratica and Tamarix ramosissima in the riparian forest ecosystem, Haloxylon ammodendron in the artificial shrub forest, and Reaumuria soongorica in the Gobi, as well as for local soil water and groundwater, and precipitation in the upper reaches of the Heihe River Basin. Our results showed that soil water and shallow groundwater of the riparian forest and the artificial shrub forest were recharged by river water which originated from precipitation in the upper reaches, and strong evaporation occurred in the artificial shrub forest. Soil water of the Gobi was not affected by Heihe River water due to this area being far away from the river channel. The main water sources of Populous euphratica were from 40-60-cm soil water and groundwater, and of Tamarix ramosissima were from 40-80-cm soil water in the riparian forest ecosystem. In the artificial forest, Haloxylon ammodendron used 200-cm saturated-layer soil water and shallow groundwater. The Reaumuria soongorica mainly used soil water from the 175-200-cm depth in the Gobi. Therefore, soil water and groundwater are the main water sources which maintain survival and growth of the plants in the extremely arid regions of the lower reaches of the Heihe River Basin.     

Effect of rain enrichment on soil respiration of Nitraria sphaerocarpa community in a hyperarid area

In order to analyze the effect of rain enrichment on soil respiration rate of a Nitraria sphaerocarpa community, we measured soil respiration rate in bare and vegetated areas in a hyperarid area （Dunhuang） during the growing season. Results show that rain enrichment can increase bare and vegetated soil respiration rates. The more rainfall enrichment, the greater the increment and the longer duration time effect for soil respiration rate. 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase bare soil respiration rates by 90% and 106% （P〈0.01）, respectively. By contrast, areas with 100% （8 mm）, 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase shrub area respiration rates by 68%, 157% and 205% （P〈0.01）, respectively. The response time of bare and vegetated soil respiration to rainfall enrichment is asynchronous. Response variable of soil respiration in vegetated soil is higher （118%） than in bare soil. There was significant positive correlation between soil respiration rate and soil water content during the growing season （P〈0.01）. For every 1 mm increment of precipitation, soil respiration rate increased by 0.01 and 0.04 pmol/（m2.s）, respectively in vegetated and bare soils.     

Influencing factors and partitioning of respiration in a Leymus chinensis steppe in Xilin River Basin, Inner Mongolia, China

Based on the static opaque chamber method, the respiration rates of soil microbial respiration, soil respiration, and ecosystem respiration were measured through continuous in-situ experiments during rapid growth season in semiarid Leymus chinensis steppe in the Xilin River Basin of Inner Mongolia, China. Soil temperature and moisture were the main factor affecting respiration rates. Soil temperature can explain most CO2 efflux variations (R2=0.376–0.655) excluding data of low soil water conditions. Soil moisture can also effectively explain most of the variations of soil and ecosystem respiration (R2=0.314–0.583), but it can not explain much of the variation of microbial respiration (R2=0.063). Low soil water content (≤5%) inhibited CO2 efflux though the soil temperature was high. Rewetting the soil after a long drought resulted in substantial increases in CO2 flux at high temperature. Bivariable models based on soil temperature at 5 cm depth and soil moisture at 0–10 cm depth can explain about 70% of the variations of CO2 effluxes. The contribution of soil respiration to ecosystem respiration averaged 59.4%, ranging from 47.3% to 72.4%; the contribution of root respiration to soil respiration averaged 20.5%, ranging from 11.7% to 51.7%. The contribution of soil to ecosystem respiration was a little overestimated and root to soil respiration little underestimated because of the increased soil water content that occurred as a result of plant removal.     

内蒙古羊草草原呼吸的影响因素分析和区分

利用静态暗箱-气相色谱法在植物生长旺季测算了内蒙古锡林河流域羊草草原的土壤微生物呼吸、土壤呼吸和生态系统呼吸。地温和水分是植物生长旺季呼吸最重要的影响因素。地温在水分条件适宜的情况下可以解释CO₂通量的部分变化(R² = 0.376~0.655)。土壤水分含量也可以解释土壤呼吸和生态系统呼吸的部分变化(R² = 0.314~0.583),但基本不能解释土壤微生物呼吸的变化(R² = 0.063)。即使在较高温度下,较低的土壤水分含量(≤ 5%) 也会显著的抑制CO₂排放。长期干旱后降雨使CO₂通量在高温下迅速增大。基于5 cm地温和0~10 cm土壤水分含量的双变量模型可以解释CO₂通量约70%的变化。观测期间,土壤呼吸占生态系统呼吸的比例介于47.3%~72.4%之间,平均为59.4%;根呼吸占土壤呼吸的比例介于11.7%~51.7%之间,平均为20.5%。由于植物体去除引起的土壤水分含量上升可能使我们对土壤呼吸占生态系统呼吸比例的估计略微偏高,根呼吸占土壤呼吸的比例略微偏低。     

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。     

SOIL CARBON DIOXIDE CONCENTRATIONS AND CLIMATE IN A HUMID SUBTROPICAL ENVIRONMENT

Soil carbon dioxide content, temperature, and moisture were measured biweekly for one year at Pigeon Mountain, GA. Levels of soil CO₂ ranged from 0.04% to 2.4% and were highest during the growing season, lowest during the winter. Soil temperature correlated positively with soil CO₂, accounting for 90% of CO₂ variation. Soil moisture variations decreased CO₂ concentration at times of high soil water content when CO₂ was flushed downward, and also at times of low soil moisture content when CO₂ production was inhibited. A predictive model of logistic form using 14-day means of daily actual evapotranspiration fit the data well (R²= 0.83). The model also tested well against soil CO₂ data acquired in the coastal plain at Rocky Point, NC. If actual evapotranspiration rates are known, the model permits estimation of soil CO₂ without preliminary field work, and can be used for studies of karst denudation, which require soil CO₂ data for seasonal and regional comparison of solution rates.     

Temporal and spatial variation in soil respiration of poplar plantations at different developmental stages in Xinjiang, China

Soil respiration is essential for the understanding of carbon sequestration of forest plantations. Soil respiration of poplar plantations at three developmental stages was investigated in 2007 and 2008. The results showed that mean soil respiration rate was 5.74, 5.10 and 4.71 μmol CO₂ m⁻² s⁻¹ for stands of 2-, 7- and 12-year-old, respectively, during the growing season. Soil temperature decreased with increasing plantation age and canopy cover. As plantation matured, fine root biomass also declined. Multiple regression analysis suggested that soil temperature in the upper layer could explain 73-77% of the variation in soil respiration and fine root biomass in the upper layer could explain further 5-8%. The seasonal dynamics of soil respiration was mainly controlled by soil temperature rhythm and fine root growth since soil water availability remained adequate due to monthly irrigation. Spatial variability of soil respiration varied considerably among three age classes, with the coefficient of variation of 28.8%, 22.4% and 19.6% for stands of 2-, 7- and 12-year-old, respectively. The results highlight the importance of the development stage in soil carbon budget over a rotation, since both temporal and spatial variation in soil respiration displayed significant differences at different developmental stages.     

Comparative study on Co<Subscript>2</Subscript> emissions from different types of alpine meadows during grass exuberance period

Potentilla fruticosa scrub,Kobresia humilis meadow andKobresia tibetica meadow are widely distributed on the Qinghai-Tibet Plateau. During the grass exuberance period from 3 July to 4 September, based on close chamber-GC method, a study on CO₂ emissions from different treatments was conducted in these meadows at Haibei research station, CAS. Results indicated that mean CO₂ emission rates from various treatments were 672.09±152.37 mgm^-2h^-1 for FC (grass treatment); 425.41± 191.99 mgm^-2h^-1 for FJ (grass exclusion treatment); 280.36±174.83 mgm^-2h^-1 for FL (grass and roots exclusion treatment); 838.95±237.02 mgm^-2h^-1 for GG (scrub+grass treatment); 528.48±205.67 mgm^-2h^-1 for GC (grass treatment); 268.97±99.72 mgm^-2h^-1 for GL (grass and roots exclusion treatment); and 659.20±94.83 mgm^-2h^-1 for LC (grass treatment), respectively (FC, FJ, FL, GG, GC, GL, LC were the Chinese abbreviation for various treatments). Furthermore,Kobresia humilis meadow,Potentilla fruticosa scrub meadow andKobresia tibetica meadow differed greatly in average CO₂ emission rate of soil-plant system, in the order of GG>FC>LC>GC. Moreover, inKobresia humilis meadow, heterotrophic and autotrophic respiration accounted for 42% and 58% of the total respiration of soil-plant system respectively, whereas, inPotentilla fruticosa scrub meadow, heterotrophic and autotrophic respiration accounted for 32% and 68% of total system respiration from GG; 49% and 51% from GC. In addition, root respiration fromKobresia humilis meadow approximated 145 mgCO₂m^-2h^-1, contributed 34% to soil respiration. During the experiment period,Kobresia humilis meadow andPotentilla fruticosa scrub meadow had a net carbon fixation of 111.11 gm^-2 and 243.89 gm^-2, respectively. Results also showed that soil temperature was the main factor which influenced CO₂ emission from alpine meadow ecosystem, significant correlations were found between soil temperature at 5 cm depth and emission from GG, GC, FC and FJ treatments. In addition, soil moisture may be the inhibitory factor of CO₂ emission fromKobresia tibetica meadow, and more detailed analyses should be done in further research.     

Carbon exchange rates in Polytrichum juniperinum moss of burned black spruce forest in interior Alaska

The Boreal black spruce forest is highly susceptible to wildfire, and postfire changes in soil temperature and substrates have the potential to shift large areas of such an ecosystem from a net sink to a net source of carbon. In this paper, we examine CO₂ exchange rates (e.g., NPP and Re) in juniper haircap moss (Polytrichum juniperinum) and microbial respiration in no-vegetation conditions using an automated chamber system in a five-year burned black spruce forest in interior Alaska during the fall season of 2009. Mean ± standard deviation microbial respiration and NEP (net ecosystem productivity) of juniper haircap moss were 0.27 ± 0.13 and 0.28 ± 0.38 gCO₂/m²/hr, respectively. CO₂ exchange rates and microbial respiration showed temporal variations following fluctuation in air temperature during the fall season, suggesting the temperature sensitivity of juniper haircap moss and soil microbes after fire. During the 45-day fall period, mean NEP of P. juniperinum moss was 0.49 ± 0.28 MgC/ha following the five-year-old forest fire. On the other hand, simulated microbial respiration normalized to a 10 °C temperature might be stimulated by as much as 0.40 ± 0.23 MgC/ha. These findings demonstrate that the fire-pioneer species juniper haircap moss is a net C sink in the burned black spruce forest of interior Alaska.     

干旱沙区典型人工植被群落下土壤剖面CO_2浓度变化特征及其驱动因子

对人工固沙植被区柠条(Caragana korshinskii)群落和油蒿(Caragana korshinskii)群落下不同深度的土壤气体采样,主要研究和讨论了不同类型人工植被区下土壤CO2浓度的变化特征及土壤温度和土壤水分对其的影响。结果表明:柠条和油蒿群落0~80cm处的土壤空气CO2浓度随着土壤深度的增加而增加,并且在0~40cm,油蒿群落下的土壤CO2浓度值大于柠条,而在40cm以下则相反。其平均值分别为1 229.3μmol·mol-1和1 242.7μmol·mol-1,大于同一深度流沙下土壤CO2浓度值978.9μmol·mol-1。土壤水分与二者的土壤CO2浓度变化趋势在年际尺度上具有一致性,浅层40cm内油蒿群落下的土壤CO2浓度和土壤水分含量的相关性明显大于柠条和流沙。而在40cm以下,则表现为柠条油蒿流沙。土壤温度对土壤CO2浓度的影响程度一般为流沙油蒿柠条,特别是流沙,在表层达到了极显著的水平,之后随着土壤深度的增加而降低。而土壤温度对油蒿和柠条样地土壤CO2浓度的影响较为复杂,呈现出先增加后减小的趋势。在年际尺度上,土壤水分含量是不同植被群落下土壤剖面CO2浓度的关键限制因子,而在日尺度上,土壤温度则为主要限制因子。据粗略估计,在0~80cm内,柠条和油蒿根系呼吸所占的比例约为30.7%和33.3%。     

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.     

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.