茶树不同叶位碳氮氢氧稳定同位素分布及变化特征

为探究茶树不同叶位的传统稳定同位素分布及其随时间的变化特征,本研究以龙井43#品种茶树为研究对象,采用元素分析-同位素比值质谱仪(EA-IRMS)对不同叶位叶片的碳同位素(δ¹³C)、氮同位素(δ¹⁵N)、氢同位素(δ²H)和氧同位素(δ¹⁸O)进行分析。结果表明,随叶位自上向下递增,叶片中δ¹³C、 δ¹⁵N和δ²H显著贫化,而δ¹⁸O呈现相对较弱的贫化,且第2~第5叶位叶片的同位素比值最高(21.0‰~25.0‰),相邻叶位的同位素分馏系数差异不大。此外,随着采样时间的变化和环境气候影响,前三叶位叶片的δ¹³C和δ¹⁵N总体呈现富集特征,而δ²H和δ¹⁸O出现先贫化后富集的变化特征。本研究结果为探究茶树不同叶位茶叶传统稳定同位素的分布提供了数据支撑,也为研究茶叶分馏机制和数据库构建奠定了基础。     

Soil carbon and nitrogen dynamics using stable isotopes in 19- and 10-year-old tropical agroforestry systems

Conversion of forests to agricultural land in the American tropics, through traditional agricultural practices such as shifting cultivation, has not been able to maintain stocks of soil organic carbon (SOC), and increasing population pressure has led to shortened fallow periods, causing further losses of soil fertility. However, land management practices such as agroforestry can provide a sustainable alternative to single cropping because of its ability to maintain or increase the SOC pool. This study quantified SOC and nitrogen (N) pools, gross SOC turnover, residue stabilization efficiency (RSE_AC) in the alley crop, soil δ¹³C partitioning, C₃-C abundance and δ¹⁵N dynamics in 19- and 10-year Gliricidia sepium and Erythrina poeppigiana alley cropping system. Each system was studied at two fertilizer levels (tree prunings only [−N or −A], and tree prunings plus chicken manure [+N], or Arachis pintoi as a groundcover [+A]), and was compared to a sole crop system. The SOC and N pools were significantly higher (p < 0.05) in the 19-year-old alley crop compared to the sole crop, but not significantly different (p < 0.05) in the 10-year-old system. Soil C and N (%) showed a similar trend as that of the SOC and N pools in both 19- and 10-year-old systems. Gross SOC turnover, to a 20 cm depth, ranged from 12 to 21 years in the 19-year-old alley crop compared to 50 years in the sole crop, and from 20 to 32 years in the 10-year-old alley crop compared to 106 years in the sole crop. The RSE_AC ranged from 10% to 58% in the 19-year-old system, and from 3% to 43% in the 10-year-old system. The δ¹³C signature of the soil shifted significantly (p < 0.05) towards that of C₃ vegetation in the alley crop due to the greater input of organic residues from tree prunings compared to the sole crop. The proportion of input from tree prunings only in the 19-year-old alley crop ranged from 14% to 20%, and from 9% to 11% in the 10-year-old system to a soil depth of 20 cm. The δ¹⁵N signature of the soil showed two patterns: that of the 19-year-old system being enriched in δ¹⁵N, and that of the 10-year-old system being depleted in δ¹⁵N compared to the sole crop. The addition of manure in the 19-year-old system has enriched the soil δ¹⁵N and in the 10-year-old system the soil was depleted due to the N₂-fixing groundcover A. pintoi.     

Long-term cultivation impacts on selected soil properties in the northern Great Plains

Long-term cultivation impacts soil properties. During the early 1920s a study comparing non-cultivated and cultivated soils was done in eastern SD (Beadle, McCook, Minnehaha, and Union Counties), USA. The objectives of the current study were to: (1) determine the long-term (>80 years) impact of cultivation on selected soil properties; and (2) establish baseline soil data that can be used for future comparisons. Sample sites were located in well-drained summit and upper backslope positions. These topographic positions are strongly influenced by erosion processes from tillage, wind, and water. Previous studies at other locations in the region suggest that one might expect a loss of 10–20 cm of soil in >80 years of cultivation at these topographic positions. In the early 1920s the soils were tested for carbon (C) (total, organic, inorganic), total nitrogen (N), total sulfur (S), total calcium (Ca), total phosphorus (P), total potassium (K), and total magnesium (Mg). The 1920s study sites were resampled at 0–15, 15–50, and 50–100 cm depths and analyzed for C (total, organic, inorganic), N (total, nitrate-N), extractable P, extractable K, delta N (¹⁵N/¹⁴N or δ¹⁵N) for total N, delta C (¹³C/¹²C or δ¹³C) for total C, and pH. Long-term cultivation (>80 years) in the northern Great Plains of the United States has caused many significant reductions in surface soil (0–15 cm) extractable P, extractable K, surface pH, total C, organic C, total N, and δ¹⁵N for total N. In addition, the organic C to total N ratio for the 15–50 cm depth of cultivated soils was significantly lower when compared to non-cultivated soils. Cultivation caused significant increases in nitrate-N, delta C, inorganic C, and in the total C to total N and inorganic C to total N ratios (15–100 cm depths). Soil properties varied significantly with increasing soil depth. Soil pH, δ¹³C for total C, inorganic C, total C to total N ratio, and inorganic C to total N ratio increased significantly as soil depth increased. Nitrate-N, extractable P, extractable K, δ¹⁵N for total N, organic C, and total N decreased significantly as soil depth increased. Soil carbon changes at the sample sites are a combined result of differences in the reference surface elevation, carbon mineralization, and redistribution of carbon due to erosion. Changes in soil nutrient levels reflect crop removal, leaching, erosion, and pedogenic processes.     

Indirect effects of earthworms on microbial assimilation of labile carbon

Interactions between earthworms and microorganisms can be important in regulating the rate of soil carbon turnover and maintaining soil fertility in agroecosystems. Despite the significance of earthworms in nutrient cycling in agroecosystems, the indirect influence of earthworms on C assimilation by microorganisms has not been adequately quantified. We assessed microbial assimilation of ¹³C-labeled acetate in earthworm (Lumbricus terrestris) middens and surrounding soil collected from maize agroecosystems. Incorporation of ¹³C into microbial lipids was used as an indicator of microbial growth rates. Earthworm middens had significantly lower concentrations of microbial phospholipid phosphates and lower natural abundance δ¹³C than the surrounding soil. After incubation with ¹³C-labeled acetate, microbial communities in earthworm middens had greater ¹³C/¹²C ratios of microbial lipids than microbial communities from surrounding soil. The ¹³C enrichment per unit of microbial phospholipid was much greater in middens than in surrounding soil indicating that: (i) microbial lipid synthesis was significantly higher in the earthworm middens; (ii) microbial assimilation efficiency for ¹³C-labeled acetate was greater in midden soil; or (iii) assimilation of ¹³C-labeled acetate relative to other C sources was proportionately greater in middens than in the surrounding soil. Our results suggest that there were functional differences between microbial communities in earthworm middens and surrounding soil, probably due to a combination of physical, chemical, and biological changes in the midden microenvironment. The resulting differences in microbial communities or activity increased microbial growth rates and assimilation of readily available C substrates in middens relative to surrounding soil.     

Consistent patterns of N distribution through soil profiles in diverse alpine and tundra ecosystems

We studied the vertical patterns of δ¹⁵nitrogen in total N and exchangeable NH₄⁺-N through soil profiles in diverse alpine and tundra ecosystems. Soil samples were analyzed from 11 sites located in three mountain areas: NW Caucasus (Russia), the Khibiny Mountains (NW Russia) and Abisko region (N Sweden). Despite differences in the profile patterns of organic matter, nitrogen accumulation and nitrogen availability, we found consistent patterns of ¹⁵N distribution through all studied soil profiles. The δ¹⁵N values of total N were in general about zero or positive in the surface horizon and increased with soil depth. In contrast with total N, the δ¹⁵N values of exchangeable NH₄⁺-N were in general about zero or negative in the surface horizons and decreased with soil depth. NH₄⁺-N was significantly ¹⁵N-depleted compared with total N in all mineral horizons, while in the surface organic horizons differences between isotopic composition of total N and NH₄⁺-N were mostly not significant. We do not know the exact mechanism responsible for ¹⁵N depletion of NH₄⁺-N with soil depth and further research needs to evaluate the contributions of natural processes (higher nitrification activity and biological immobilization of “lighter” NH₄⁺-N near the soil surface) or artifacts of methodological procedure (contribution of the ¹⁵N-enriched microbial N and dissolved organic N near the soil surface). Nevertheless, our finding gives a new possibility to interpret variability in foliar δ¹⁵N values of plant species with different rooting depth in alpine and tundra ecosystems, because plants with deeper root systems can probably consume “lighter” rather than “heavier” NH₄⁺-N.     

Soil organic carbon and C abundance as related to tillage, crop residue, and nitrogen fertilization under continuous corn management in Minnesota

Long-term field experiments are among the best means to predict soil management impacts on soil carbon storage. Soil organic carbon (SOC) and natural abundance ¹³C (δ¹³C) were sensitive to tillage, stover harvest, and nitrogen (N) management during 13 years of continuous corn (Zea mays L.), grown on a Haplic Chernozem soil in Minnesota. Contents of SOC in the 0–15 cm layer in the annually-tilled [moldboard (MB) and chisel (CH)] plots decreased slightly with years of corn after a low input mixture of alfalfa (Medicago sativum L.) and oat (Avena sativa L.) for pasture; stover harvest had no effect. Storage of SOC in no-till (NT) plots with stover harvested remained nearly unchanged at 55 Mg ha⁻¹ with time, while that with stover returned increased about 14%. The measured δ¹³C increased steadily with years of corn cropping in all treatments; the NT with stover return had the highest increase. The N fertilization effects on SOC and δ¹³C were most evident when stover was returned to NT plots. In the 15–30 cm depth, SOC storage decreased and δ¹³C values increased with years of corn cropping under NT, especially when stover was harvested. There was no consistent temporal trend in SOC storage and δ¹³C values in the 15–30 cm depth when plots received annual MB or CH tillage. The amount of available corn residue that was retained in SOC storage was influenced by all three management factors. Corn-derived SOC in the 0–15 cm and the 15–30 cm layers of the NT system combined was largest with 200 kg N ha⁻¹ and no stover harvest. The MB and CH tillage systems did not influence soil storage of corn-derived SOC in either the 0–15 or 15–30 cm layers. The corn-derived SOC as a fraction of SOC after 13 years fell into three ranges: 0.05 for the NT with stover harvested, 0.15 for the NT with no stover harvest, and 0.09–0.10 for treatments with annual tillage; N rate had no effect on this fraction. Corn-derived SOC expressed as a fraction of C returned was positively biased when C returned in the roots was estimated from recovery of root biomass. The half-life for decomposition of the original or relic SOC was longer when stover was returned, shortened when stover was harvested and N applied, and sharply lengthened when stover was not harvested and N was partially mixed with the stover. Separating SOC storage into relic and current crop sources has significantly improved our understanding of the main and interacting effects of tillage, crop residue, and N fertilization for managing SOC accumulation in soil.     

东北三省和浙江木耳稳定同位素特征与产地溯源

为探究稳定同位素在黑木耳产地溯源中的可行性,本研究从东北(黑龙江、吉林、辽宁)、浙江产地采集74份代表性黑木耳样品,从新疆采集11份代表性黑木耳样品作为外部验证,采用元素分析-稳定同位素比率质谱仪测定δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值,结合化学计量学方法进行产地溯源判定。结果表明,东北黑木耳δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值分别为-24.5‰～-22.7‰、-0.9‰～3.1‰、-62.2‰～-34.6‰、15.9‰～19.4‰;浙江黑木耳δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值分别为-26.2‰～-24.5‰、-0.9‰～1.2‰、-24.9‰～-9.0‰、19.9‰～22.2‰,两产地黑木耳δ¹⁵N值差异不显著(P>0.05),δ¹³C、δ²H和...     

黄土丘陵区阴坡和阳坡优势木本植物叶功能性状比较

通过比较阴坡和阳坡优势种（阴坡:山杨、油松、辽东栎和刺槐;阳坡:荆条、山桃、狼牙刺和黄刺玫）叶功能性状（比叶质量、膨压损失点对应的叶水势、叶碳同位素组成δ¹³C及叶N、P和K含量）的差异,探讨了植物对不同坡向的生存和适应机制。结果表明:（1）阳坡优势种较阴坡优势种具有高的叶δ¹³C,且在旱季具有较高的K含量,表明高水分利用效率和K素累积是阳坡植物适应其生境的重要手段。（2）阳坡优势种间叶性状差异小于阴坡优势种,阳坡植物叶性状表现出明显的趋同性。（3）8种优势植物中,刺槐的比叶质量最小,叶N和P含量最高,叶δ¹³C相对较高,反映了其高光合和高水分利用效率的特性,表明刺槐采取竞争性生存策略。相比之下,油松的比叶质量最大,其叶δ¹³C、N、P和K含量最低,表明油松采取防御性生存策略,其他6种植物介于中间。     

Soil quality indicators under continuous cropping systems in the Argentinean Pampas

Over the last two decades, soil cultivation practices in the southern Argentinean Pampas have been changing from a 7 year cash-crop production system alternated with 2–3 years under pasture, to a continuous cropping system. A better understanding of the impact of the period of time a field has been under continuous cropping on a broad spectrum of soil properties related to soil quality is needed to target for sustainable cropping systems. The objectives of this study were to: (i) assess the relationship between physical and chemical soil parameters related to soil quality and (ii) identify soil quality indicators sensitive to soil changes under continuous cropping systems in the Argentinean Pampas.

Correlation analysis of the 29 soil attributes representing soil physical and chemical properties (independent variables) and years of continuous cropping (dependent variable) resulted in a significant correlation (p < 0.05) in 78 of the 420 soil attribute pairs. We detected a clear relationship between hydraulic conductivity at tension h (K_h) and structural porosity (ρ_e); ρ_e being a simple tool for monitoring soil hydraulic conditions.

Soil tillage practice (till or no-till) affected most of the soil parameters measured in our study. It was not possible to find only one indicator related to the years under continuous cropping regardless of the cultivation practice. We observed a significant relationship between years under continuous cropping and K_h under no-till (NT) and wheat fallow (p < 0.001, R² = 0.70). Under these conditions, K₋₄₀ diminished as the number of years under continuous cropping increased.

The change in mean weight diameter (CMWD) was the only physical parameter related to the number of years under continuous cropping, explaining 36% of the variability in the number of years under continuous cropping (p < 0.001) The combination of three soil quality indicators (CMWD, partial R² = 0.38; slope of the soil water retention curve at its inflexion point (S), partial R² = 0.14 and cation exchange capacity (CEC), partial R² = 0.13) was able to explain, in part, the years under continuous cropping (R² = 0.65; p value > 0.001), a measure related to soil quality.     

A multi-step inflow method for estimating hydraulic conductivity at low pressure under the wetting process

The accurate determination of the wetting soil hydraulic properties for a wide range of water contents is essential for studying and predicting infiltration processes. We present a laboratory infiltration method for determining hydraulic conductivity function, K(θ), in the low-to-medium water content range. An initially air-dry soil core is subjected to infiltration from the bottom where the pressure head, ψ_bot, is controlled through a membrane. As soon as the wetting front arrives at the soil surface, the top 0.5-cm layer is sliced for measurement of the water content. The ψ_bot is stepwise increased as the hydraulic equilibrium is nearly attained at each step. The wetting water retention function, ψ(θ), is determined by curve-fitting the equilibrium inflow data and from the independently measured data obtained from vapor equilibrium. The parameter in the K(θ) is estimated inversely using the cumulative inflow and water content of the sliced layer. This method is verified through comparisons with K(θ) obtained by the Boltzmann transform method. Although requiring an additional operation, the slicing procedure is found to be valuable in enhancing the reliability of the optimized parameter. A sensitivity analysis shows that water vapor movement would be negligible under our experimental conditions.     

The origin of carbonates in termite mounds of the Lubumbashi area, D.R. Congo

The origin of carbonate accumulations in termite mounds is a controversial issue. This study is an attempt to elucidate the processes of carbonate precipitation in Macrotermes mounds built on Ferralsols in Upper Katanga, D.R. Congo, whereby a differentiation between pedogenic and inherited carbonates is considered. Carbonate features were investigated for a 9 m deep termite-mound profile, and for an 18 m wide cross-section through a termite mound and the adjacent soil, using field and laboratory techniques. Field evidence for a pedogenic origin includes morphological type (soft powdery materials, nodules, and coatings on ped surfaces) and distribution patterns of the carbonates. Thin-section studies reveal that the carbonates occur predominantly as impregnative orthic nodules and less commonly as coatings, both clearly pedogenic; calcareous pellets are interpreted as locally reworked pedogenic carbonates. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectrometry (SEM-EDS) and stable isotope (δ¹³C) analyses show that all isolated carbonate features consist of high-Mg calcite (4.9-12.3 mol% MgCO₃) with δ¹³C signatures ranging from − 13.2‰ to − 11.5‰. Weddellite (CaC₂O₄. 2H₂O) is identified in a thin-section and by XRD analysis, and appears to be locally transformed into calcite. The stable isotope composition of carbon suggests that calcite precipitated in equilibrium with soil CO₂ generated during decomposition of soil organic matter, and locally most likely during oxidation of oxalate. This study proves that carbonates which accumulated in Macrotermes mounds are pedogenic precipitates, whose deposition is partly related to microbial decay of organic matter, subsequently redistributed to some extent by abiotic dissolution-reprecipitation and termite activity.     

氮肥种类和施用量对南洋杉苗期的影响

Nitrogenous fertilisers are under consideration for promoting the growth of nursery-reared hoop pine （Araucaria cunninghamii Alton ex A. Cunn） seedlings in the establishment phase of second rotation （2R） plantations. Using ^15N- labelled fertilisers, we investigated the effect of different forms （ammonium sulphate, ammonium nitrate, potassium nitrate and urea） and rates of application （0, 150 and 300 mg N kg^-1 dried soil） of fertilisers on the growth, ^15N recovery and carbon isotope composition （δ^13C） of hoop pine seedlings in a 12-month glasshouse trial in southeast Queensland, Australia. The ^15N-labelled fertilisers were applied to nursery-reared hoop pine seedlings, which were then grown in pots, containing ca. 1.2 kg dried soil, under well watered conditions for 12 months. Four seedlings from each treatment were harvested at 4-month intervals, divided into roots, stem and foliage, with a further subdivision for new and old foliage, and then analysed for ^15N, total N, δ^13C and total C. There was no significant response in the seedling growth to the form or rate of application of nitrogen （N） fertiliser within the 12-month period, indicating that the seedlings did not experience N deficiency when grown on second rotation hoop pine soils. While the combined ^15N recovery from soil and plant remained at around 70% throughout the experiment, the proportion of ^15N recovered from the plants increasing steadily over time. Nitrate containing fertilisers at 150 mg N kg^-1 soil gradually increased seedling foliage δ^13C over the 12-month period, indicating an increase in seedling water use efficiency.     

Development of on-line measurement system of bulk density based on on-line measured draught, depth and soil moisture content

On-line measurement of soil compaction is needed for site specific tillage management. The soil bulk density (ρ) indicating soil compaction was measured on-line by means of a developed compaction sensor system that comprised several sensors for on-line measurement of the draught (D) of a soil cutting tool (subsoiler), the soil cutting depth (d) and the soil moisture content (w). The subsoiler D was measured with a single shear beam load cell, whereas d was measured with a wheel gauge that consisted of a swinging arm metal wheel and a linear variable differential transducer (LVDT). The soil w was measured with a near infrared fibre-type spectrophotometer sensor. These on-line three measured parameters were used to calculate ρ, by utilising a hybrid numerical–statistical mathematical model developed in a previous study. Punctual kriging was performed using the variogram estimation and spatial prediction with error (VESPER) 1.6 software to develop the field maps of ρ, soil w, subsoiler d and D, based on 10 m × 10 m grid. To verify the on-line measured ρ map, this map was compared with the map measured by the conventional core sampling method.

The spherical semivariogram models, providing the best fit for all properties was used for kriging of different maps. Maps developed showed that no clear correlation could be detected between different parameters measured and subsoiler D. However, the D value was smaller at shallow penetration d, whereas large D coincided with large ρ values at few positions in the field. Maps of ρ measured with the core sampling and on-line methods were similar, with correlation coefficient (r) and the standard error values of 0.75 and 0.054 Mg m⁻³, respectively. On-line measured ρ exhibited larger errors at very dry zones. The normal distribution of the ρ error between the two different measurement methods showed that about 72% of the errors were less than 0.05 Mg m⁻³ in absolute values. However, the overall mean error of on-line measured ρ was of a small value of 2.3%, which ensures the method accuracy for on-line measurement of ρ. Measurement under very dry conditions should be minimised, because it can lead to a relatively large error, and hence, compacted zones at dry zones cannot be detected correctly.     

大豆鼓粒期叶片荧光参数与叶绿素含量的关系

叶绿素含量是研究大豆光合作用的重要生理指标,对大豆产量和品质具有重要影响,因此,进行叶绿素含量和光合功能的同步分析具有重要意义。本研究以鼓粒期大豆叶片为研究对象,对63个样本的叶绿素含量和荧光参数进行相关分析,建立回归模型,并用28个样本验证集进行验证及评价。结果表明,可变荧光与初始荧光比(F_v/F_o)、最大光化学效率(φ_PO)、初始时间点活性反应中心捕获的单个激子驱动除QA外的电子传递的效率(ψ_EO)、初始时间点用于电子传递的量子产额(φ_EO)、t=t_FM时单位面积内电子传递的量子产额(ET_O/CS_M)、性能指数(PI_ABS)、J点相对可变荧光(V_J)7个荧光参数与叶绿素含量相关性较好,相关系数分别为0.78、0.76、0.75、0.80、0.82、0.77、-0.75。回归模型方程为y=-0.138x₁+ 2.154x₂+0.002x₃+0.077x₄+0.076(R²=0.694)(x₁、x₂、x₃、x₄和y分别为F_v/F_o、φ_PO、ET_O/CS_M、 PI_ABS和叶绿素含量),验证模型决定系数(R²)=0.805 8,均方根误差(RMSE)=0.293 4,预测残差(RPD)=1.773 8,该模型具有较好的预测效果,可以丰富非生物逆境胁迫下无损监测大豆叶绿素估算方法。回归和通径分析发现,ET_O/CS_M对叶绿素含量直接作用最大,φ_PO次之,F_v/F_o对叶绿素含量起直接负作用,PI_ABS直接作用最小,直接通径系数分别为0.706、0.382、-0.303、0.078。本研究实现了大豆叶绿素含量与光合功能的同步分析,明确了荧光参数对叶绿素含量的影响效应,可为调节栽培措施,实现大豆高产提供理论基础。     

Chemical characteristics and potential source of fulvic acids leached from the plow layer of paddy soil

To understand better the chemical characteristics and source of dissolved organic matter (DOM) leached from the plow layer of rice paddies, a lysimeter study was conducted, which simulated submerged paddy topsoil during rice growth. The fulvic acid (FA) fraction in the percolation water from the lysimeter was collected by adsorption onto insoluble polyvinylpyrrolidone (PVP), and the temporal variations in its elemental composition, molecular size distribution, IR spectra, ¹³C CPMAS NMR spectra, and δ¹³C values were investigated. The proportion of the FA fraction to bulk DOM varied greatly, but the chemical characteristics of the FA fraction did not change appreciably during the experimental period. Thus, it is considered that the changes in the DOM composition in percolation water were mainly due to the differing contributions of the FA fraction. Further, to investigate the source of the FA fraction in the leachate, the chemical characteristics of the FA fraction in the leachate were compared with those extracted from the plow layer soil. A sequential extraction of the FA fraction was conducted using a sequence of water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5). It was found that the water- and 0.25 M Na₂SO₄-extractable fractions, which were most mobile, were not the only source of the FA fraction in the leachate. The small molecular size sub-fraction of the NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5)-extractable FAs, most of which are probably bound mainly to iron oxides, are considered to be another source of the FA fraction leached from the plow layer of paddy fields.     

样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响

为研究样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响,分别选用3种保存温度(常温23℃/15 d、冷藏2℃/90 d、冷冻-18℃/360 d)、2种取样方式(虾仁取样、整虾取样),以新鲜沼虾样本为对照组,对比不同样本预处理方式对罗氏沼虾碳稳定同位素比值(δ¹³C)、氮稳定同位素比值(δ¹⁵N)、碳氮比(C/N)的影响。结果表明,不同保存温度和不同取样方式对罗氏沼虾δ¹³C、δ¹⁵N、C/N的影响明显。与对照组相比,常温保存条件下的δ¹⁵N偏移量最大(1.31‰~13.16‰,平均值为6.02‰),冷冻保存条件下的δ¹³C偏移量最大(2.34‰~2.84‰,平均值为2.57‰),室温保存条件下的C/N显著增加(P<0.05),冷藏和冷冻保存条件下的C/N显著减少(P<0.05)。不同取样方式对罗氏沼虾δ¹⁵N、δ¹³C的影响还取决于保存温度,在冷冻保存条件下,整虾取样的δ¹⁵N、δ¹³C显著高于虾仁取样,而在常温保存条件下,整虾取样的δ¹⁵N偏移量显著低于虾仁取样。因此,常温(23℃)和冷藏(2℃)条件不适合保存罗氏沼虾、冷冻(-18℃)保存罗氏沼虾的时间不宜超过60 d,建议新鲜沼虾采集后应立即干燥并开展碳和氮稳定同位素检测。本研究结果为水产品碳和氮稳定同位素比值检测的样本预处理方式提供了参考。     

花生油生产过程中稳定同位素变化规律及影响因素研究

花生油的稳定同位素特征研究是该技术应用于花生油掺假检测的基础,为探究花生油生产过程中碳、氢、氧的稳定同位素比值变化规律及其受产地、年份的影响,本试验收集了3个年份6个省份的花生样品,利用稳定同位素比值质谱仪(IRMS)测定油脂中3种元素的稳定同位素比值(δ¹³C、δ²H和δ¹⁸O)。结果表明,不同产地花生样品中,油脂的δ¹³C、δ²H和δ¹⁸O值均不相同。以δ¹³C为例,平均值由大到小依次为湖北>辽宁>广东>山东>河南>江苏,部分省份之间差异显著(P<0.05);因年份不同油脂稳定同位素特征也存在差异。另外,研究结果表明不同生产阶段的油脂中稳定同位素特征几乎一致,加工工艺的差异未改变油脂的稳定同位素分馏。可见,油脂中保留了花生的稳定同位素特征。本研究结果为花生油掺假检测技术研究提供了理论基础与应用可行性。     

Effect of temperature and rhizosphere processes on pedogenic carbonate recrystallization: Relevance for paleoenvironmental applications

In soils of arid and semiarid climates, dissolution of primary (lithogenic) carbonate and recrystallization with CO₂ from soil air leads to precipitation of pedogenic carbonates and formation of calcic horizons. Thus, their carbon isotope composition represents the conditions prevailing during their formation. However, the widespread use of the isotopic signature (δ¹³C, δ¹⁸O, Δ¹⁴C) of pedogenic carbonates for reconstruction of local paleovegetation, paleoprecipitation and other environmental conditions lacks knowledge of the time frame of pedogenic carbonate formation, which depends on climatic factors. We hypothesized that temperature-dependent biotic processes like plant growth and root and rhizomicrobial respiration have stronger influence on soil CaCO₃ recrystallization than abiotic temperature-dependent solubility of CO₂ and CaCO₃.To assess the effect of temperature on initial CaCO₃ recrystallization rates, loess with primary CaCO₃ was exposed to ¹⁴CO₂ from root and rhizomicrobial respiration of plants labeled in ¹⁴CO₂ atmosphere at 10, 20 or 30 °C. ¹⁴C recovered in recrystallized CaCO₃ was quantified to calculate amounts of secondary CaCO₃ and corresponding recrystallization rates, which were in the range of 10⁻⁶-10⁻⁴ day⁻¹, meaning that 10⁻⁴-10⁻²% of total loess CaCO₃ were recrystallized per day. Increasing rates with increasing temperature showed the major role of biological activities like enhanced water uptake by roots and respiration. The abiotic effect of lower solubility of CO₂ in water by increasing temperature was completely overcompensated by biotic processes. Based on initial recrystallization rates, periods necessary for complete recrystallization were estimated for different temperatures, presuming that CaCO₃ recrystallization in soil takes place mainly during the growing season. Taking into account the shortening effect of increasing temperature on the length of growing season, the contrast between low and high temperature was diminished, yielding recrystallization periods of 5740 years, 4330 years and 1060 years at 10, 20 and 30 °C, respectively. In summary, increasing CaCO₃ recrystallization rates with increasing temperature demonstrated the important role of vegetation for pedogenic CaCO₃ formation and the predominantly biotic effects of growing season temperature.Considering the long periods of pedogenic carbonate formation lasting to some millennia, we conclude that methodological resolution of paleoenvironmental studies based on isotope composition of pedogenic carbonates is limited not by instrumental precision but by the time frame of pedogenic carbonate formation and hence cannot be better than thousands of years.     

Assessment of microbial activity and bacterial community composition in the rhizosphere of a copper accumulator and a non-accumulator

Soil microorganisms may play an important role in the uptake of heavy metals from soils. However, assessments of bacterial activity and community composition in the rhizosphere of accumulators have been largely ignored. We studied potential effects of a copper (Cu)-accumulator, Elsholtzia splendens, and a non-Cu-accumulator plant, Trifolium repens, on soil microbial activity and community composition with increasing Cu addition. The results showed that concentrations of Cu in the shoots of E. splendens were 2.1, 2.2 and 2.4 times those of T. repens under the treatment of different Cu concentrations. Soil microbial biomass and phosphatase activity in the rhizosphere of E. splendens were higher than those of T.repens. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint analysis revealed that addition of Cu decreased the number of bands in bare soil and soil with T. repens. However, there was a significant increase in the number of bands in soil with E. splendens incorporated with either 200 or 500 mg kg⁻¹ Cu. The abundances of five phylogenetic groups related most closely to -, β-, γ-proteobacteria, Gram-positive bacteria and CFB group, respectively, were determined in the rhizosphere of plants. Some specific clone such as E13 (metal-contaminated soil clone K20-64) was found in the rhizosphere of E. splendens. Results indicated that E. splendens, as a Cu-accumulator, played an important role in governing soil microbial activity and bacterial community composition in the rhizosphere in response to Cu stress.     

明胶骨原料碳、氮稳定同位素的地域性差异研究

为探讨不同地域来源的明胶骨原料中碳、氮稳定同位素的分布特征及其相关性,本试验采用元素分析-稳定同位素比率质谱仪测定了广西、内蒙古和山东3个主产区的牛骨样品及当地牧草饲料样品中的¹³C和¹⁵N同位素组成,并结合线性回归讨论了牛骨样品中δ¹³C和δ¹⁵N值的相关性与牛食谱组成的关系。结果表明,广西地区骨样品中δ¹³C和δ¹⁵N值的相关性较好(R²=0.401 8),而内蒙古和山东地区骨样品中δ¹³C和δ¹⁵N值的相关性较差(R²<0.1),反映了3地牛食物的来源稳定性及主要成分存在明显差异,对各地牛食谱结构推测的结果与实际牧草饲料样品中δ¹³C和δ¹⁵N值的地区分布规律也较为一致。本研究初步揭示了明胶骨原料中碳、氮稳定同位素产生地域性差异的原因,不仅为动物生态学研究提供了有益信息,更为动物制品产地溯源研究提供了新思路。