荒漠草原土壤有机质碳稳定同位素特征研究

应用碳稳定同位素分析方法对内蒙古短花针茅荒漠草原土壤有机质及其δ13 C值垂直分布特征、表土δ13C值与建群种-短花针茅δ13 C值的相互关系进行分析,并测定土壤部分理化性质。结果显示:表土有机质含量变化范围为4.17～20.45g/kg;随深度增加,土壤有机碳(SOC)含量呈指数降低,其变化范围为17.98～1.39g/kg,而δ13C值则随剖面深度增加而明显富集,到75cm深度时δ13C值又迅速降低,变化范围为-26.38‰～-13.72‰,变幅>3‰,说明该地区气候和植被状况可能发生过剧烈变化;表土和植物δ13C值分馏程度较其它地区偏大,二者呈极显著相关(r=0.555,P<0.01),进一步说明地上植被状况是影响土壤有机质δ13 C值垂直分布特征的决定性因素。     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO₂浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO₂浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO₂浓度水平(310μmol/mol和400μmol/mol),针对主要C₃作物水稻、小麦和大豆,研究"绿色革命"以来大气CO₂浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO₂浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

土壤酶活性对温度和CO2浓度升高的响应研究

作为土壤生态系统中的重要组成部分及生物元素循环的积极参与者,土壤酶在陆地生态系统地下生态过程中扮演着十分重要的角色。升高温度和(或)大气CO2浓度可能直接或者间接影响其活性。但目前对温度和(或)大气CO2浓度升高对土壤酶的影响机理、过程及土壤酶对其的响应机制研究相对薄弱。本文初步总结了国内外关于温度和(或)大气CO2浓度升高对土壤酶活性影响研究的现状,并指出了目前研究中存在的不足。     

超临界CO2流体技术精制栀子黄色素的研究

以市售栀子黄色素为原料,比较系统地探讨了超临界状态下萃取压力、温度、时间、ＣＯ₂流量、夹带剂对栀子黄色素ＯＤ值比率的影响。结果表明：高温、高压、添加夹带剂的条件下有利于降低栀子黄色素的ＯＤ值比率,达到精制的目的。     

黄土区土壤CO2释放及其影响因素研究

研究表明黄土区土壤CO2释放具有一定特殊性。从当日清晨至次日晨土壤CO2释放量呈由高至低再变高的规律,其变化趋势大体与温度变化一致,但时间上有一定滞后性。土壤CO2释放量有明显季节变化,夏季日释放量最高,秋季次之,冬季最低。不同覆被土壤CO2释放量存在差异,裸地释放量较高。CO2释放量对土质变化敏感,致密土壤则释放量小。     

滨海防护林土壤CO2排放和土壤因子对计划火烧的响应

为研究林火对滨海沙地森林生态系统碳循环的干扰作用,以尾巨桉防护林(Eucalyptus urophylla×Eucalyptus grandis)和木麻黄防护林(Casuarina equisetifolia)为研究对象,利用LI-8100土壤CO₂通量全自动测量系统测定不同防护林火烧迹地和对照样地的土壤CO₂通量,同时测定样地内土壤温湿度和土壤pH、全量碳氮和矿质氮含量,并分析不同林地土壤CO₂通量与水热因子关系以及土壤理化特性的变化。结果表明：2种防护林火烧迹地土壤CO₂通量均显著低于对照样地,尾巨桉林火烧迹地和对照样地土壤CO₂通量月平均值分别为2.47,3.32μmol/(m²·s),木麻黄林分别为2.48,3.28μmol/(m²·s)。林火干扰后2种防护林土壤温度和湿度均高于对照样地,在指数函数模型中尾巨桉林和木麻黄林10 cm处土壤温度解释土壤总呼吸的10.4%～21.4%,在二项式函数模型中尾巨桉林和木麻黄林10 cm...     

高CO2浓度下羊草对土壤干旱胁迫的响应

在高CO2浓度下羊草对土壤干旱胁迫响应的人工模拟试验分析表明，CO2浓度升高对羊草具有“施肥”效应，羊草生物量增加20％以上，光合速率提高50％左右，气孔阻力增大，蒸腾速率下降，水分利用效率提高，土壤干旱胁迫对羊草的影响为负效应，与此相反，高CO2浓度下发生土壤干旱胁迫一定程度抑制了CO2的施肥效应。     

土壤水分状况对CH4氧化,N2O和CO2排放的影响

实验室培育试验表明，土壤氧化ＣＨ４，排放Ｎ２Ｏ和ＣＯ２的最佳水分含不量。水稻土氧化ＣＨ４的最佳水分含同于半干旱草地土壤，均接近于土壤环境常年水分含量。水稻土Ｎ２Ｏ排放量随着水分含量的下降而增加，半干旱草地土壤则随着水分含量的下降而减少，表明背离土壤环境上水分含量越远，Ｎ２Ｏ的排放量越大。因而，ＣＨ４氧化和Ｎ２Ｏ排放对土壤水分含量的反应呈极显著的负相关性。ＣＯ２排放的最佳水分含量接近或高于ＣＨ４氧化     

间伐对杉木林土壤CO2通量的影响

Forest management is expected to influence soil CO₂ efflux (FCO₂) as a result of changes in microenvironmental conditions, soil microclimate, and root dynamics. Soil FCO₂ rate was measured during the growing season of 2006 in both thinning and non-thinning locations within stands ranging from 0 to 8 years after the most recent thinning in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations in Huitong Ecosystem Research Station, Hunan, China. Soil temperature and moisture were also measured to examine relationships between FCO₂ and soil properties. Forest thinning resulted in huge changes in FCO₂ that varied with time since cutting. Immediately following harvest (year 0) FCO₂ in thinning area increased by about 30%, declined to 20%-27% below pre-cutting levels during years 4-6, and recovered to pre-cutting levels at 8 years post-cutting. A similar temporal pattern, but with smaller changes, was found in non-thinning locations. The initial increase in FCO₂ could be attributed to a combination of root decay, soil disturbance, and increased soil temperature in gaps, while the subsequent decrease and recovery to the death and gradual regrowth of active roots. Strong effects of soil temperature and soil water content on FCO₂ were found. Forest thinning mainly influenced FCO₂ through changes in tree root respiration, and the net result was a decrease in integrated FCO₂ flux through the entire felling cycle.     

不同培肥措施下土壤CO2释放及其动力学研究

实验室恒温密闭培养法研究了 4种培肥措施连续培肥 23年后农田土壤的CO2释放状况及其动力学特征。结果表明 ,含水量 12%至 24%范围内 ,土壤CO2释放过程完全可以用一级反应动力学方程 y =A0(1-e-kt)进行定量描述 (r2=0.9812～0.995 9,P 0.01) ;土壤CO2释放量和潜在可释放C量A0 随含水量增加呈线性增加 (r2=0.9728～0.9987,P0.01) ,速率常数k则随含水量增加呈线性降低 (r2=0.9356～0.9939,P0.01)。不同培肥措施明显影响土壤CO2释放状况及其动力学特征参数 ;NP化肥和厩肥 +NP化肥 2种培肥措施较不施肥对照明显增加了土壤CO2释放量、潜在可释放C量A0和速率常数k ;秸秆 +NP化肥培肥措施较不施肥对照显著增加了土壤CO2释放量、潜在可释放C量A0,但却显著降低了释放速率常数k ;有机无机肥料配合措施 (秸秆 +NP、厩肥 +NP)与单施NP化肥措施比较 ,明显降低了释放速率常数k。     

鄂尔多斯高原脉冲降雨对油蒿灌丛群落土壤碳排放的影响

Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such water-limited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO₂ efflux, an artificial precipitation event (3 mm) was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8-4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO₂ production was between 2 047.0 and 7 383.0 mg m^-2. In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO₂ loss in desert ecosystems.     

Relationship between soil CO2 concentrations and forest-floor CO2 effluxes

To better understand the biotic and abiotic factors that control soil CO₂ efflux, we compared seasonal and diurnal variations in simultaneously measured forest-floor CO₂ effluxes and soil CO₂ concentration profiles in a 54-year-old Douglas fir forest on the east coast of Vancouver Island. We used small solid-state infrared CO₂ sensors for long-term continuous real-time measurement of CO₂ concentrations at different depths, and measured half-hourly soil CO₂ effluxes with an automated non-steady-state chamber. We describe a simple steady-state method to measure CO₂ diffusivity in undisturbed soil cores. The method accounts for the CO₂ production in the soil and uses an analytical solution to the diffusion equation. The diffusivity was related to air-filled porosity by a power law function, which was independent of soil depth. CO₂ concentration at all depths increased with increase in soil temperature, likely due to a rise in CO₂ production, and with increase in soil water content due to decreased diffusivity or increased CO₂ production or both. It also increased with soil depth reaching almost 10 mmol mol⁻¹ at the 50-cm depth. Annually, soil CO₂ efflux was best described by an exponential function of soil temperature at the 5-cm depth, with the reference efflux at 10 °C (F₁₀) of 2.6 μmol m⁻² s⁻¹ and the Q₁₀ of 3.7. No evidence of displacement of CO₂-rich soil air with rain was observed.Effluxes calculated from soil CO₂ concentration gradients near the surface closely agreed with the measured effluxes. Calculations indicated that more than 75% of the soil CO₂ efflux originated in the top 20 cm soil. Calculated CO₂ production varied with soil temperature, soil water content and season, and when scaled to 10 °C also showed some diurnal variation. Soil CO₂ efflux and concentrations as well as soil temperature at the 5-cm depth varied in phase. Changes in CO₂ storage in the 0–50 cm soil layer were an order of magnitude smaller than measured effluxes. Soil CO₂ efflux was proportional to CO₂ concentration at the 50-cm depth with the slope determined by soil water content, which was consistent with a simple steady-state analytical model of diffusive transport of CO₂ in the soil. The latter proved successful in calculating effluxes during 2004.     

外加碳酸盐增加石灰性土壤密闭培养过程中CO2的释放量

The closed-jar incubation method is widely used to estimate the mineralization of soil organic C. There are two C pools (i.e., organic and inorganic C) in calcareous soil. To evaluate the effect of additional carbonates on CO2 emission from calcareous soil during closed-jar incubation, three incubation experiments were conducted by adding different types (CaCO3 and MgCO3 ) and amounts of carbonate to the soil. The addition of carbonates significantly increased CO2 emission from the soil; the increase ranged from 12.0% in the CaCO3 amended soil to 460% in the MgCO3 amended soil during a 100-d incubation. Cumulative CO2 production at the end of the incubation was three times greater in the MgCO3 amended soil compared to the CaCO3 amended one. The CO2 emission increased with the amount of CaCO3 added to the soil. In contrast, CO2 emission decreased as the amount of MgCO3 added to the soil increased. Our results confirmed that the closed-jar incubation method could lead to an overestimate of organic C mineralization in calcareous soils. Because of its effect on soil pH and the dissolution of carbonates, HgCl2 should not be used to sterilize calcareous soil if the experiment includes the measurement of soil CO2 production.     

Active microbial RNA turnover in a grassland soil estimated using a CO2 spike

Rhizosphere microbes are critical to the initial transfer and transformation of root carbon inputs to the soil but our understanding of the activity of these organisms remains constrained by their limited culturability. In this study we combined isotopic ¹³C tracer and molecular approaches to measure the incorporation of recently assimilated plant C into soil microbial RNA and DNA pools as a means to determine the turnover of the ‘active’ rhizosphere community. This required the development of a method for the extraction, purification and preparation of small-sample soil DNA and RNA (<5 μg C) for isotope analysis. Soil, plant and respired CO₂ samples were collected from a ¹³CO₂ pulse-chase experiment at intervals for 20 days post-labelling. The peak of ¹³C release in soil/root respired CO₂ came between 5 and 48 h after ¹³CO₂ pulse-labelling and was followed by a secondary peak of soil heterotroph ¹³C respiration after 136 h. Results showed that both soil DNA and RNA rapidly incorporated recent photosynthate with greatest ¹³C found in the ‘active’ microbial RNA fraction reflecting higher rates of microbial RNA turnover. The dilution rate of the pulse derived ¹³C in RNA-C was used to estimate a microbial RNA turnover of approximately 20% day⁻¹ with a 15-20 day residence time for photosynthate derived ¹³C in the RNA pool. The findings of this work confirm the rapid transfer of photosynthate C inputs through soil microorganisms to the atmosphere as CO₂ and the potential of the biomolecular-isotope tracer approach in soil C research.     

A new technique to measure soil CO2 efflux at constant CO2 concentration

A new principle for measuring soil CO₂ efflux at constant ambient concentration is introduced. The measuring principle relies on the continuous absorption of CO₂ within the system to achieve a constant CO₂ concentration inside the soil chamber at ambient level, thus balancing the amount of CO₂ entering the soil chamber by diffusion from the soil. We report results that show reliable soil CO₂ efflux measurements with the new system. The novel measuring principle does not disturb the natural gradient of CO₂ within the soil, while allowing for continuous capture of the CO₂ released from the soil. It therefore holds great potential for application in simultaneous measurements of soil CO₂ efflux and its δ¹³C, since both variables show sensitivity to a distortion of the soil CO₂ profile commonly found in conventional chamber techniques.     

Effects of soil moisture and temperature on CO2 and CH4 soil-atmosphere exchange of various land use/cover types in a semi-arid grassland in Inner Mongolia, China

The aim of this study was to investigate the combined effects of soil moisture and temperature as well as drying/re-wetting and freezing/thawing on soil-atmosphere exchange of CO₂ and CH₄ of the four dominant land use/cover types (typical steppe, TS; sand dune, SD; mountain meadow, MM; marshland, ML) in the Xilin River catchment, China. For this purpose, intact soil cores were incubated in the laboratory under varying soil moisture and temperature levels according to field conditions in the Xilin River catchment. CO₂ and CH₄ fluxes were determined approximately daily, while soil CH₄ gas profile measurements at four soil depths (5 cm, 10 cm, 20 cm and 30 cm) were measured at least twice per week. Land use/cover generally had a substantial influence on CO₂ and CH₄ fluxes, with the order of CH₄ uptake and CO₂ emission rates of the different land use/cover types being TS ≥ MM ≥ SD > ML and MM > TS ≥ SD > ML, respectively. Significant negative soil moisture and positive temperature effects on CH₄ uptake were found for most soils, except for ML soils. As for CO₂ flux, both significant positive soil moisture and temperature effects were observed for all the soils. The combination of soil moisture and temperature could explain a large part of the variation in CO₂ (up to 87%) and CH₄ (up to 68%) fluxes for most soils. Drying/re-wetting showed a pronounced stimulation of CO₂ emissions for all the soils —with maximum fluxes of 28.4 ± 2.6, 50.0 ± 5.7, 81.9 ± 2.7 and 10.6 ± 1.2 mg C m⁻² h⁻¹ for TS, SD, MM and ML soils, respectively—but had a negligible effect on CH₄ fluxes (TS: −3.6 ± 0.2; SD: 1.0 ± 0.9; MM: −4.1 ± 1.3; ML: −5.6 ± 0.8; all fluxes in μg C m⁻² h⁻¹). Enhanced CO₂ emission and CH₄ oxidation were observed for all soils during thawing periods. In addition, a very distinct vertical gradient of soil air CH₄ concentrations was observed for all land use/cover types, with gradually decreasing CH₄ concentrations down to 30 cm soil depth. The changes in soil air CH₄ concentration gradients were in accordance with the changes of CH₄ fluxes during the entire incubation experiment for all soils.     

Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting

Soil compaction and soil moisture are important factors influencing denitrification and N₂O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N₂O, N₂ and CO₂ from undisturbed soil cores fertilized with (150 kg N ha⁻¹) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρ_D=1.03 g cm⁻³), the interrow area (ρ_D=1.24 g cm⁻³), and the tractor compacted interrow area (ρ_D=1.64 g cm⁻³), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N₂O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N₂ production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N₂O-N emission in most cases. There was no soil moisture effect on CO₂ emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N₂O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O₂ consumption induced by soil drying and rewetting for the emissions of N₂O.     

Differences in soil CO2 flux between different land use types in mid-subtropical China

It is crucial to advance the understanding of the soil carbon dioxide (CO₂) flux and environmental factors for a better comprehension of carbon dynamics in subtropical ecosystems. Red soil, one of the typical agricultural soils in subtropical China, plays important roles in the global carbon budget due to their large potential to sequester C and replenish atmospheric C through soil CO₂ flux. We examined the relationship between soil CO₂ flux and environmental determinants in four different land use types of subtropical red soil-paddy (P), orchard (O), woodland (W) and upland (U) using static closed chamber method. Objectives were to evaluate the relationship of soil temperature, water-filled pore space (WFPS), and dissolved organic carbon (DOC) with the soil CO₂ flux. Soil CO₂ fluxes were measured on each site about every 14 days between 09:00 and 11:00 a.m. during 14-July 2004 to 25-April 2007 at the experimental station of Heshengqiao at Xianning, Hubei, China. Soil CO₂ fluxes revealed seasonal fluctuations, with the tendency that maximum values occurred in summer, minimum in winter and intermediate values in spring and autumn except for paddy soil when it was submerged. Further, significant differences in soil CO₂ fluxes were observed among the four soils, following the order of P > O > U  W. Average soil CO₂ fluxes were estimated as 901 ± 114, 727 ± 55, 554 ± 22 and 533 ± 27 (±S.D.) g CO₂ m⁻² year⁻¹ in paddy, orchard, upland and woodland soils, respectively. Variations in soil CO₂ flux were related to soil temperature, WFPS, and dissolved organic carbon with a combined R² of 0.49–0.75. Soil temperature was an important variable controlling 26–59% of soil CO₂ flux variability. The interaction of soil temperature and WFPS could explain 31–60% of soil CO₂ flux variations for all the land use types. We conclude that soil CO₂ flux from red soil is under environmental controls, soil temperature being the main variable, which interact with WFPS and DOC to control the supply of readily mineralizable substrates.     

FACE facility CO2 concentration control and CO2 use in 1990 and 1991

CO₂ treatment level control and CO₂ use are reported for free-air carbon dioxide enrichment (FACE) facility operations at the University of Arizona's Maricopa Agricultural Center in 1990 and 1991. These are required for evaluation of the validity of biological experiments conducted in four replicates of paired experimental and control plots in a large cotton field and the cost-effectiveness of the plant fumigation facility. Gas concentration was controlled to 550 γmol mol^-1 at the center of each experimental plot, just above the canopy. In both years, season-long (April–September) average CO₂ levels during treatment hours (05:00–19:00 h Mountain Standard Time) were 550 γmol mol⁻¹ measured at treatment plot centers when the facility was operating. Including downtime, the season average was 548 γmol mol⁻¹ in 1991. In 1990, the season averages for the four elevated CO₂ treatments varied from 522 to 544 γmol mol⁻¹, owing to extended periods of downtime after lightning damage. Ambient CO₂ concentration during treatment was 370 γmol mol⁻¹. Instantaneous measurements of CO₂ concentration were within 10% of the target concentration of 550 γmol mol⁻¹ more than 65% of the time when the facility was operating, and 1 min averages were within 10% of the target concentration for 90% of the time. The long-term average of CO₂ concentration measured over the 20 m diameter experimental area of one array at the height of the canopy was in the range 550–580 γmol mol⁻¹ during July 1991, with the higher values near the edges. In 1991, CO₂ demand averaged 1250 kg per array per 14 h treatment day, or 4 kg m⁻² of fumigated plant canopy. The FACE facility provided good temporal and spatial control of CO₂ concentration and was a cost-effective method for large-scale field evaluations of the biological effects of CO₂.     

Influence of warming and enchytraeid activities on soil CO2 and CH4 fluxes

To determine the sum of ‘direct’ and ‘indirect’ effects of climatic change on enchytraeid activity and C fluxes from an organic soil we assessed the influence of temperature (4, 10 and 15 °C incubations) on enchytraeid populations and soil CO₂ and CH₄ fluxes over 116 days. Moisture was maintained at 60% of soil dry weight during the experimental period and measurements of enchytraeid biomass and numbers, and CO₂ and CH₄ fluxes were made after 3, 16, 33, 44, 65, 86 and 116 days. Enchytraeid population numbers and biomass increased in all temperature treatments with the greatest increase produced at 15 °C (to over threefold initial values by day 86). Results also showed that enchytraeid activity increased CO₂ fluxes by 10.7±4.5, 3.4±4.0 and 26.8±2.6% in 4, 10 and 15 °C treatments, respectively, with the greatest CO₂ production observed at 15 °C for the entire 116 day incubation period (P<0.05). The soil respiratory quotient analyses at lower temperatures (i.e. 4-10 °C) gave a Q₁₀ of 1.7 and 1.9 with and without enchytraeids, respectively. At temperatures above 10 °C (i.e. 10-15 °C) Q₁₀ significantly increased (P<0.01) and was 25% greater in the presence of enchytraeids (Q₁₀=3.4) than without (Q₁₀=2.6). In contrast to CO₂ production, no significant relationships were observed between net CH₄ fluxes and temperature and only time showed a significant effect on CH₄ production (P<0.01).Total soil CO₂ production was positively linked with enchytraeid biomass and mean soil CO₂-C production was 77.01±6.05 CO₂-C μg mg enchytraeid tissue⁻¹ day⁻¹ irrespective of temperature treatment. This positive relationship was used to build a two step regression model to estimate the effects of temperature on enchytraeid biomass and soil CO₂ respiration in the field. Predictions of potential CO₂ production were made using enchytraeid biomass data obtained in the field from two upland grassland sites (Sourhope and Great Dun Fell at the Moor House Nature Reserve, both in the UK). The findings of this work suggest that a 5 °C increase in atmospheric temperature above mean ambient temperature could have the potential to produce a significant increase in enchytraeid biomass resulting in a near twofold increase in soil CO₂ release from both soil types. The interaction between temperature and soil biology will clearly be an important determinant of soil respiration responses to global warming.