Carbon assimilation characteristics of plants in oasis-desert ecotone and their response to CO2 enrichment

Six species of more than 20-year-old desert woody plants in the oasis-desert ecotone were selected for study. The results showed that: (1) in different growing seasons δ¹³C values of assimilating organ varied between -14%. and -16%. for Haloxylon ammodendron (HA),-14%. - -15%. for Calligonum mongolicum (CM) and -25%. - -28%. for Caragana korshinskii (CK), Nitraria sphaerocarpa (NS) and Hedysarum scoparium (HS). (2) The net photosynthetic rate (Pn) of HA and CM was significantly higher than those of the other species. With the decrease in Pn for the six species, their intercellular CO₂ concentration increased, but stomatal limitation value decreased under the intensive light. At the same time, the photochemical efficiency of PS II dropped to different degrees. (3) The CO₂ enrichment experiment demonstrated that, Pn of HA and CM increased to different extent under 450 μmol/mol, but their Pn reduced or approximated to the current condition under 650 μmol/mol. Under 450 μmol/mol the efficiency for solar energy utilization of CK and HS significantly reduced and under 650 μmol/mol their respiration rate exceeded photosynthesis rate. It can be concluded that HA and CM have some function of pathway for C₄ but the other three species have the function for C₃. The decline in their Pn is mainly caused by non-stomatal factors. HA, CM, CK and HS exhibited photoinhibition, which disappeared in a short time. This is a kind of positive readjustment to adapting to the desert environment. HA and CM can adapt to the high CO₂ environment, but CK and HS cannot. With the rise in atmospheric CO₂ concentration and climate warming, the latter two species in the oasis-desert ecotone may be gradually degraded or even disappear.

     

Carbon assimilation characteristics of plants in oasis-desert ecotone and their response to CO<Subscript>2</Subscript> enrichment

Six species of more than 20-year-old desert woody plants in the oasis-desert ecotone were selected for study. The results showed that: (1) in different growing seasons δ¹³C values of assimilating organ varied between -14%. and -16%. for Haloxylon ammodendron (HA),-14%. - -15%. for Calligonum mongolicum (CM) and -25%. - -28%. for Caragana korshinskii (CK), Nitraria sphaerocarpa (NS) and Hedysarum scoparium (HS). (2) The net photosynthetic rate (Pn) of HA and CM was significantly higher than those of the other species. With the decrease in Pn for the six species, their intercellular CO₂ concentration increased, but stomatal limitation value decreased under the intensive light. At the same time, the photochemical efficiency of PS II dropped to different degrees. (3) The CO₂ enrichment experiment demonstrated that, Pn of HA and CM increased to different extent under 450 μmol/mol, but their Pn reduced or approximated to the current condition under 650 μmol/mol. Under 450 μmol/mol the efficiency for solar energy utilization of CK and HS significantly reduced and under 650 μmol/mol their respiration rate exceeded photosynthesis rate. It can be concluded that HA and CM have some function of pathway for C₄ but the other three species have the function for C₃. The decline in their Pn is mainly caused by non-stomatal factors. HA, CM, CK and HS exhibited photoinhibition, which disappeared in a short time. This is a kind of positive readjustment to adapting to the desert environment. HA and CM can adapt to the high CO₂ environment, but CK and HS cannot. With the rise in atmospheric CO₂ concentration and climate warming, the latter two species in the oasis-desert ecotone may be gradually degraded or even disappear.     

Seasonal variations in energy exchange and evapotranspiration of an oasis-desert ecotone in an arid region

Knowledge of exchanges of energy and water over terrestrial surfaces is the first step towards understand the ecohydrological mechanisms, particularly in water-limited ecosystems in dryland environments. However, patterns of energy exchange and evapotranspiration (ET) are not well understood in the oasis-desert ecotone, which plays an important role in protecting oases against the threat of desertification in arid regions of northwestern China. Here, the continuous measurements of surface energy fluxes were made using eddy covariance in conjunction with auxiliary measurements for 2 years (2014–2015) in an oasis-desert ecotone mainly covered by phreatophyte shrubs Haloxylon ammodendron, Nitraria tangutorum/sphaerocarpa, and Calligonum mongolicum in arid northwestern China. Based on the collated data for 2 years, statistical analysis on a 30-min time scale indicated that approximately 50% of daytime net radiation (R_n) in the ecotone was dissipated as H on average, and one-third of R_n was consumed by soil heat flux (G). Only 9% of R_n was consumed for latent heat flux (λE), which peaked in summer (21% in 2014 and 16% in 2015), corresponding to the highest rainfall season. Daily mean ET was approximately 1 mm days⁻¹ during the growing season of the shrub species. Accumulated annual ET was 195 and 181 mm in 2014 and 2015, respectively, exceeding the corresponding precipitation (P) by approximately 87 and 77 mm, indicating that groundwater may be another important source of water for ET in the ecotone aside from rainfall. Results within provide valuable insights into the mechanisms responsible for sustaining energy and water balance in the ecotone, a potentially groundwater-dependent ecosystem. These results also offer a foremost ecohydrological implication for water and land resources management and ecotone conservation, such as avoiding heavy groundwater pumping for extensive agricultural irrigation use to sustain groundwater availability for these shrub species in the ecotone.     

Molecular and carbon isotopic compositions of gas inclusions of deep carbonate rocks in the Tarim Basin

Gaseous components of gas inclusions in deep carbonate rocks (>5700 m) from the Tacan 1 well were analyzed by online mass spectrometry by means of either the stepwise heating technique or vacuum electromagnetism crushing. The carbon isotopic compositions of gases released by vacuum electromagnetism crushing were also measured. Although the molecular compositions of gas inclusions show differences between the two methods, the overall characteristics are that gas inclusions mainly contain CO2, whilst hydrocarbon gases, such as CH4, C2H6 and C3H8, are less abundant. The content of CO is higher in the stepwise heating experiment than that in the method of vacuum electromagnetism crushing, and there are only minor amounts of N2, H2 and O2 in gas inclusions. Methane δ13C values of gas inclusions in Lower Ordovician and Upper Cambrian rocks (from 5713.7 to 6422 m; -52‰-63‰) are similar to those of bacterial methane, but their chemical compositions do not exhibit the dry character in comparison with biogenic gases. These characteristics of deep gas inclusions may be related to the migration fractionation. Some deep natural gases with light carbon isotopic characteristics in the Tazhong Uplift may have a similar origin. The δ13C1 values of gas inclusions in Lower Cambrian rocks (7117-7124 m) are heavier (-39‰), consistent with highly mature natural gases. Carbon isotopic compositions of CO2 in the gas inclusions of deep carbonate rocks are similar (from -4‰ to -13‰) to those of deep natural gases, indicating predominantly an inorganic origin.     

Comparative study on CO2 sources in soil developed on carbonate rock and non-carbonate rock in Central Guizhou

In this paper, by using concentration and carbon stable isotope the CO2 sources of soil profiles developed on limestone, dolostone and claystone basements in Central Guizhou, China are comparatively studied. The results show that CO2 concentration of soil profiles developed on different basements is different, having the following sequence: limestone>dolostone>claystone. Below the soil depth of 20 cm from the surface the ? 13C value of CO2 in soil profile developed on limestone ranges from -12.811‰ - -13.492‰(PDB), that in soil profile developed on dolostone varys from -13.212‰ - -14.271‰(PDB) and that in soil profile developed on claystone is about -20.234‰ - -21.485‰(PDB). Taking the carbon isotope of soil organic matter and carbonate rock as two isotopic endmembers, the proportion of soil CO2 generated by dissolution of carbonate rock is calculated, about 21%-25% for soil profile developed on limestone basement, 19%-21% for soil profile developed on dolostone basement. There is almost no influx of CO2 generated by the dissolution of carbonate rock in soil profile developed on claystone basement.     

Fluid mixing as the mechanism of formation of the Dajing Cu-Sn-Ag-Pb-Zn ore deposit,Inner Mongolia ——Fluid inclusion and stable isotope evidence

Since the 1990s, interest in the magmatic fluids and their relation to mineralization has been re-aroused[1—6]. Studies on stable isotopes of low-sulfidation deposits commonly show the predominance of meteoric water[7]. Paradoxically, the evidence for me…     

Simulation of oasis breeze circulation in the arid region of the Northwestern China

In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V = 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary,the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis.Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00.     

Simulation of oasis breeze circulation in the arid region of the Northwestern China

In this paper, the process of oasis-desert circulation (ODC) is simulated by MM5V3.5 model through designing an ideal oasis-desert scheme and assuming that initial atmosphere is at rest (V= 0). The findings showed that the key of forming special oasis boundary structure is the difference of energy and water between oasis and desert. The evaporation of oasis surface consumes heat energy, and the low temperature of oasis causes an oasis breeze circulation (OBC), which drives an ODC with a downdraft over the oasis and an updraft over the desert. Later, the cold, dry and stable boundary over oasis is gradually formed, on the contrary, the atmospheric boundary over desert on the edge of oasis is hot, humid and unstable and its height is about 600 hPa. The updraft over the desert forms a wet ring that acts as a vertical wall weakening the low-level moisture exchange between the oasis and desert. The downdraft of OBC increases the atmospheric stability that reduces the oasis evaporation. The low-level outflow from the oasis (into the desert) prevents the dry, hot air flowing from the desert into the oasis. Thus an oasis self-preservation mechanism may be formed due to OBC. The horizontal area influenced by oasis is twice as oasis area and the vertical range is four times as oasis. The ODC is strong in the daytime and reaches the strongest at 17:00, and the influenced area is the largest at 20:00.     

Carbon isotope ratios of C_4 plants in loess areas of North China

Recent stable carbon isotope studies have shown that the occurrence of C4 plants on the Earth was much later than that of C3 plants and there was a global ex-pansion of C4 biomass around 5―8 million years ago[1]. Although far fewer species use the C4 pat…     

Carbon isotopes in the rivers from the Lesser Antilles: origin of the carbonic acid consumed by weathering reactions in the Lesser Antilles

In this paper, we use carbon isotopes in the dissolved load of rivers from the Lesser Antilles volcanic arc (Guadeloupe, Martinique and Dominica islands) to constrain the source of the carbon dioxide (CO₂) involved in the neutralization reactions during water–rock interactions. The δ¹³C data span a large range of variations, from –19‰ to –5 · 2‰ for DIC (dissolved inorganic carbon) concentrations ranging from 11 μM to 2000 μM. Coupled with major element concentrations, carbon isotopic ratios are interpreted as reflecting a mixture of magmatic CO₂ (enriched in heavy carbon (δ¹³C ≈ –3 · 5‰) and biogenic CO₂ produced in soils (enriched in light carbon (δ¹³C < –17‰)). Carbon isotopes show that, at the regional scale, 23 to 40% of CO₂ consumed by weathering reactions is of magmatic origin and is transferred to the river system through aquifers under various thermal regimes. These numbers remain first‐order estimates as the major uncertainty in using carbon isotopes as a source tracer is that carbon isotopes can be fractionated by a number of processes, including soil and river degassing. Chemical weathering is clearly, at least, partly controlled by the input of magmatic CO₂, either under hydrothermal (hot) or surficial (cold) weathering regimes. This study shows that the contribution of magmatic CO₂ to chemical weathering is an additional parameter that could explain the high weathering rates of volcanic rocks. The study also shows that a significant part of the carbon degassed from the Earth's interior is not released as CO₂ to the atmosphere, but as DIC to the ocean because it interacts with the groundwater system. This study calls for a better understanding of the contributions of deep carbon to the hydrosphere and its influence on the development of the Critical Zone. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigating landfill‐impacted groundwater seepage into headwater streams using stable carbon isotopes

The impact of landfill contaminated groundwater along a reach of a small stream adjacent to a municipal landfill was investigated using stable carbon isotopes as a tracer. Groundwater below the stream channel, groundwater seeping into the stream, groundwater from the stream banks and stream water were sampled and analysed for dissolved inorganic carbon (DIC) and the isotope ratio of DIC (δ¹³C_DIC). Representative samples of groundwater seeping into the stream were collected using a device (a ‘seepage well’) specifically designed for collecting samples of groundwater seeping into shallow streams with soft sediments. The DIC and δ¹³C_DIC of water samples ranged from 52 to 205 mg C/L and ?16·9 to +5·7‰ relative to VPDB standard, respectively. Groundwater from the stream bank adjacent to the landfill and some samples of groundwater below the stream channel and seepage into the stream showed evidence of δ¹³C enriched DIC (δ¹³C_DIC = ?2·3 to +5·7‰), which we attribute to landfill impact. Stream water and groundwater from the stream bank opposite the landfill did not show evidence of landfill carbon (δ¹³C_DIC = ?10·0 to ?16·9‰). A simple mixing model using DIC and δ¹³C_DIC showed that groundwater below the stream and groundwater seeping into the stream could be described as a mixture of groundwater with a landfill carbon signature and uncontaminated groundwater. This study suggests that the hyporheic zone at the stream–groundwater interface probably was impacted by landfill contaminated groundwater and may have significant ecological implications for this ecotone. Copyright © 2004 John Wiley & Sons, Ltd.     

贵州草海湖泊系统碳循环简单模式

本文分析了贵州草海湖泊系统中的主要含碳物质－湖水DIC、表层沉积物有机质、水生植物的稳定碳同位素组成,其δ^13C值分别为：－3．70‰至－10．60‰,－20．90‰至－21．60％,－16．10‰至－17．40,通过质量平衡计算,建立了草海区域碳循环的简单模式,结果表明：对于草海这样一个水生植物茂盛的浅水富氧湖而言,光合一呼吸作用和有机质的降解对整个湖泊体系的稳定碳同位素组成具有决定性的作用。     

The carbon isotope composition of C_3 herbaceous plants in loess area of northern China

The application of stable carbon and oxygen isotopes in study of paleoenvironment has been becoming more and more extensive. It is well known that the d 18O curves of foraminifer crust in deep oceanic sediments and ice cores have made a great contribution…     

河库连续体中溶解性无机碳及其同位素的时空分异特征——以澜沧江云南段为例

河流及水库等水生态系统中的溶解性无机碳(DIC)是全球碳循环与大气、陆地和海洋之间碳相互作用的重要组成部分.以澜沧江云南段上游天然河段及下游梯级水库群形成的连续体为研究对象,分析了河库连续体表层水体中水化学特征、溶解性无机碳浓度及其碳同位素时空分布特征.研究结果表明:河库连续体水体中溶解无机碳(DIC)及其同位素(δ13 C DIC)组成特征总体表现为:DIC浓度丰水期较低,枯水期较高,平均值分别为2.59±0.44和3.30±0.37 mmol/L;δ13 C DIC值丰水期偏负、枯水期偏正,平均值分别为-8.52‰±0.38‰和-6.95‰±0.53‰,与自然河流的季节变化特征相似.水体DIC来源主要包括土壤及水体有机质分解生成的CO 2、碳酸盐风化和水气界面CO 2的交换过程.澜沧江河库连续体中DIC浓度及δ13 C DIC组成的时空异质性特征与流域岩性、土壤生物地球化学过程以及微生物活动强度等均有较大关系.当前,澜沧江梯级水库群建库时间短,梯级联合运行下调度复杂,水文条件多变,梯级水库对河流重要生源要素——碳累积影响方面的“水库效应”还不明显.     

Soluble iron sulfide species in natural waters: Reappraisal of their stoichiometry and stability constants

A wide range of stoichiometries has been previously proposed for soluble iron sulfide species and there is no general agreement on their importance in natural waters. The solubility of Fe(II) in 0.1 M NaClO₄ equilibrated at 20 - 0.1°C with various partial pressures of H₂S (0.1, 0.001, 0.0001, 0.00001 MPa) was measured in the pH range 3.1-7.9. Equilibrium was established within 1-6 h when amorphous FeS was the solid phase. The results could all be fitted using values for the solubility product constant (I = 0) of p*K_s = 3.00 - 0.12 and of the stability constant for a soluble Fe(HS) ₂ species (I = 0) of p#₂ = -6.45 - 0.12 where *K_s = aFe²⁺ · aHS-/aH⁺ and #₂ = aFe(HS) ₂/aFe²⁺ · (aHS^-)². Any soluble species of the form Fe_x (HS) _2x where x = &gif1; would fit the data equally well. Measurements at different partial pressures are inconsistent with labile species of the form Fe_xS_x. There was no evidence for a Fe(HS) ⁺ species. When a solution is saturated with respect to amorphous FeS, Fe(HS) ₂ will only be a significant proportion of Fe(II) when S(-II) is higher than 0.2mmoll^-1. The constants for Fe(HS) ₂ or Fe_x (HS) _2x (x S 2) are consistent with all freshwater data where constant values of measured ion activity products provide no evidence for soluble complex formation. For marine waters with high sulfide concentrations (S 6mmol l^-1), measured concentrations of Fe(II) are consistent with there being negligible soluble iron sulfide. The data are better fitted if the dissolved species are polymeric as predicted concentrations of the monomer Fe(HS) ₂ are significant. These findings suggest that rather than the dissolved species being Fe(HS) ₂, it is probably polymeric, that is Fe_x (HS) _2x (x S 2).     

Sorption of Eu~(3+) onto nano-size silica-water interfaces

A large amount of nuclear wastes has been pro-duced due to nuclear weapon development and nuclear electricity generation. One possible resolution for the disposal of the nuclear wastes is to seal them in an underground repository, which requires detailed knowledge on the mobility, chemical behavior and immobilization of radionuclides in underground water. In addition, toxic heavy metals are extensively present in ground and underground water, how to immobilize and remedy these toxic heavy meta…     

Effects of environmental stresses on the responses of mangrove plants to spent lubricating oil

The influence of different environmental stresses, including salinity (5-35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1-6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m(-2)) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2·-) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2·- release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P>0.05) except the stem of A. corniculatum (P=0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings.     

A new approach to develop the Raman carbonaceous material geothermometer for low‐grade metamorphism using peak width

The Raman spectra of carbonaceous material (CM) from 19 metasediment samples collected from six widely separated areas of Southwest Japan and metamorphosed at temperatures from 165 to 655°C show systematic changes with metamorphic temperature that can be classified into four types: low‐grade CM (c. 150–280°C), medium‐grade CM (c. 280–400°C), high‐grade CM (c. 400–650°C), and well‐crystallized graphite (> c. 650°C). The Raman spectra of low‐grade CM exhibit features typical of amorphous carbon, in which several disordered bands (D‐band) appear in the first‐order region. In the Raman spectra of medium‐grade CM, the graphite band (G‐band) can be recognized and several abrupt changes occur in the trends for several band parameters. The observed changes indicate that CM starts to transform from amorphous carbon to crystallized graphite at around 280°C, and this transformation continues until 400°C. The G‐band becomes the most prominent peak at high‐grade CM suggesting that the CM structure is close to that of well‐crystallized graphite. In the highest temperature sample of 655°C, the Raman spectra of CM show a strong G‐band with almost no recognizable D‐band, implying the CM grain is well‐crystallized graphite. In the Raman spectra of low‐ to medium‐grade CM, comparisons of several band parameters with the known metamorphic temperature show inverse correlations between metamorphic temperature and the full width at half maximum (FWHM) of the D1‐ and D2‐bands. These correlations are calibrated as new Raman CM geothermometers, applicable in the range of c. 150–400°C. Details of the methodology for peak decomposition of Raman spectra from the low to medium temperature range are also discussed with the aim of establishing a robust and user‐friendly geothermometer.     

Transpiration from three dominant shrub species in a desert‐oasis ecotone of arid regions of Northwestern China

Conservation management for the water dependent desert‐oasis ecotone in arid northwest China requires information on the water use of the dominant species. However, no studies have quantified their combined water use or linked species composition to ecotone transpiration. Here, the water use of three dominant shelterbelt shrubs (Haloxylon ammodendron, Nitraria tangutorum, and Calligonum mongolicum) within an ecotone was measured throughout the full leaf‐out period for three shrub species from 30 May to 16 October 2014, with sap flow gauges using the stem heat balance approach. Species‐specific transpiration was estimated by scaling up sap flow velocities measured in individual stems, to stand area level, using the frequency distribution of stem diameter and assuming a constant proportionality between sap flow velocity and basal cross‐sectional area for all stems. The mean peak sap flux densities (J_sn) for H. ammodendron, N. tangutorum, and C. mongolicum, were 40.12 g cm^?2 h^?1, 71.33 g cm^?2 h^?1, and 60.34 g cm^?2 h^?1, respectively, and the mean estimated daily area‐averaged transpiration rates (T_daily) for the same species were 0.56 mm day^?1, 0.34 mm day^?1, and 0.11 mm day^?1. The accumulative stand transpiration was approximately 140.8 mm throughout the measurement period, exceeding precipitation by as much as 42.1 mm. Furthermore, T_daily of these shrubs appeared to be much less sensitive to soil moisture as compared to atmospheric drivers, and the relationship between J_sn and atmospheric drivers was likely uninfluenced by soil moisture regimes in the whole profile (to 1‐m depth), especially for H. ammodendron and C. mongolicum. Results indicate that these shrubs may use deep soil water recharged by capillary rise, or may directly access shallow groundwater. This study provides quantitative data offering important implications for ecotone conservation and water and land resource management. Copyright © 2016 John Wiley & Sons, Ltd.     

A marine secondary producer respires and feeds more in a high CO2 ocean

Climate change mediates marine chemical and physical environments and therefore influences marine organisms. While increasing atmospheric CO(2) level and associated ocean acidification has been predicted to stimulate marine primary productivity and may affect community structure, the processes that impact food chain and biological CO(2) pump are less documented. We hypothesized that copepods, as the secondary marine producer, may respond to future changes in seawater carbonate chemistry associated with ocean acidification due to increasing atmospheric CO(2) concentration. Here, we show that the copepod, Centropages tenuiremis, was able to perceive the chemical changes in seawater induced under elevated CO(2) concentration (>1700 μatm, pH<7.60) with avoidance strategy. The copepod's respiration increased at the elevated CO(2) (1000 μatm), associated acidity (pH 7.83) and its feeding rates also increased correspondingly, except for the initial acclimating period, when it fed less. Our results imply that marine secondary producers increase their respiration and feeding rate in response to ocean acidification to balance the energy cost against increased acidity and CO(2) concentration.