Influence of inoculation with arbuscular mycorrhizal fungi on stable isotopes of nitrogen in Phaseolus vulgaris

The interactions between Phaseolus vulgaris, Rhizobium spp. strains nodulating P. vulgaris, and arbuscular mycorrhizal (AM) fungi were assessed under greenhouse conditions in a nonsterilized Typic Haplustalf soil from Cauca, Colombia. Our results indicate a specific involvement of AM fungal species in nitrogen acquisition by the legume plants from symbiotic nitrogen fixation and from soil. A significant specific influence of inoculation with Glomus spp. on the ¹⁵N/¹⁴N ratio in plant shoots was dependent on the inoculated rhizobial strain, but AM fungal inoculation had no significant effect on shoot dry weight or nodule occupancy in the two different rhizobial strain treatments. The results imply that in low P soils the effects of an improved mycorrhizal symbiosis may include improved symbiotic N₂ fixation efficiency and/or improved soil N uptake. Received: 11 May 1996     

土壤水稳定同位素研究进展

本文从影响土壤水稳定同位素变化的因素、时空变化规律以及"土壤-植物-大气"界面水分转化和循环过程等方面综述了国内外土壤水同位素研究的主要成果,认为同位素方法在研究土壤水运移、降水入渗及土壤蒸发问题上优势比较明显,并且有助于从宏观和微观上阐明土壤水的特征及其运动规律;指出了当前土壤水分同位素研究存在的问题和今后研究的重点,并对同位素技术与方法在土壤水中应用前景进行了展望。     

基于稳定同位素的土壤水分运动特征

土壤水分受降雨和地下水的共同补给作用,是陆地水循环的重要环节。通过模拟试验,结合土壤水同位素特征,以黄土高原黄绵土为研究对象,研究降雨入渗和地下水补给方式下土壤水分的运移变化特点。结果表明:土壤体积含水量随时间的延长而增大,最终趋于稳定,土壤水分的运移有明显滞后效应;土壤水氢同位素受补给水源、交换混合以及蒸发的影响,随时间的延长,补给水源的影响逐渐减弱,水分的交换混合和蒸发作用逐渐显现,土壤水最终达到动态平衡状态;两种补给条件下,土壤水运移方式均为活塞式推进,降雨入渗方式土壤水δD随土层深度的增加先减小后增大最终趋于稳定,表层0~5cm土壤水由于蒸发富集重同位素,5~20cm土壤水滞留时间最长,保水能力最强,地下水补给方式下土壤水δD随土层深度的增加而减小,上层土壤水δD由于蒸发富集重同位素,下层受地下水补给影响贫化;两种补给方式下土壤水δD与δ18O有良好线性关系,降雨入渗方式土壤水蒸发分馏作用大于地下水补给方式,地下水补给具有较好的保水效果。     

Oenological influences on the D/H ratios of wine ethanol

Within the European Union the determination of chaptalization of wine involves the comparison of the D/H ratios of ethanol with the ratios of authentic wine samples that are similar to the suspect wine in terms of geographical origin, grape variety, and vintage. In the frame of a databank project comparison, wines are produced under official control on a small scale. To clarify the influence of the different production conditions between commercial wines and these databank wines, wines that were produced under varying conditions were investigated by the (2)H NMR method. None of the parameters under investigation, such as yeast strain, fermentation temperature, or wine fining, showed a significant influence on the (D/H)(I) ratio of wine ethanol, which is the most indicative parameter for the determination of the addition of extraneous sugar to wine. For the (D/H)(II) ratio, different values were found for different yeast strains used for fermentation and a slight decrease was observed with increasing fermentation temperature. At increasing points of fermentation yield an increase of the D/H ratios was found in the present alcohol. The total increase of the (D/H)(I) ratio throughout the fermentation was approximately 1 ppm, so that with a fermentation yield of more than 50% no statistical difference could be observed.     

Feeding guilds in Collembola based on nitrogen stable isotope ratios

In soil a high number of species co-exist without extensive niche differentiation, which was assigned as ‘the enigma of soil animal species diversity’. In particular, the detritivores are regarded as food generalists. We have investigated nitrogen stable isotope ratios (¹⁵N/¹⁴N) of a major decomposer group, the Collembola, to evaluate trophic relationship and determine feeding guilds. Additionally, the δ¹⁵N values of potential food sources such as mosses, lichens and other plant derived material (bark, nuts, leaves) were analysed. The natural variation in nitrogen isotopes was assessed in 20 Collembola taxa from three deciduous forest stands. The δ¹⁵N signature formed a continuum from phycophages/herbivores to primary and secondary decomposers, reflecting a gradual shift from more detrital to more microbial diets. The δ¹⁵N gradient spanned over 9 δ units, which implies a wide range in food sources used. Assuming a shift in ¹⁵N of about 3 ‰ per trophic level, the results indicate a range of three trophic levels. These variations in ¹⁵N/¹⁴N ratios suggest that trophic niches of Collembola species differ and this likely contributes to Collembola species diversity.     

Influence of urea on the cherry leaf spot pathogen, Blumeriella jaapii, and on microorganisms in decomposing cherry leaves

Growth chamber and orchard experiments were carried out to clarify the response of the cherry leaf spot pathogen, Blumeriella jaapii, and microorganisms in the leaf litter to two levels of urea (2.5% or 5%) applied post leaf fall to sour cherry leaves. In general, urea application reduced the development of B. jaapii measured as biomass by quantitative PTA-ELISA in the leaf litter and spore counting in the spring and increased the overall microbial biomass (measured with biomarker phospholipid fatty acids (PLFAs)) and fungal activity (assessed as β-N-acetylglucosaminidase activity). The biomass increase of all groups of microorganisms in the litter generally began immediately after application of urea and, with the notable excepts of B. jaapii and Gram-negative bacteria containing the biomarker PLFA cyclo17:0, continued after the ammonia and pH levels had stabilized to levels similar to the control leaves approximately 10 days later. Application of 2.5% urea increased the biomass of most groups of saprotrophic microorganisms and accelerated litter decomposition to a higher extent than application of 5% urea and during the first week after treatment applications the 5% urea level inhibited the total microbial biomass. This may be ascribed to ammonia toxicity as 5% urea resulted in a markedly higher ammonia elevation than 2.5% urea, the first week after application. From then onwards in both the 2.5% and 5% treatments the fungal and Gram-positive communities benefited from a lowered C:N ratio, increasing their activities approximately 2 times compared to a water-treated control. Inhibition of B. jaapii coincided with the period of urea breakdown in which elevated levels of ammonia and leaf pH were measured in the treated leaves. This period lasted for approximately 10 days after which the biomass of B. jaapii in the treated leaves continued to decrease at a slow but faster rate than in the untreated leaves. Our results indicate that the urea application caused an elevation in leaf pH and ammonia levels, which together with an acceleration in litter decomposition, adversely affected the saprotrophic growth of B. jaapii, leading to reduced production of ascospores and winter-conidia the following spring.     

Trophic shift of stable isotopes and fatty acids in Collembola on bacterial diets

Fatty acid (FA) analysis is a promising tool to study trophic relationships in soil food webs. We determined FA biomarkers to trace bacterial food sources (Bacillus megaterium, Pseudomonas putida, Enterobacter aerogenes) of Collembola (Heteromurus nitidus, Protaphorura fimata, Folsomia candida). In addition, δ¹⁵N, δ¹³C, C/N ratio, body weight and NLFA/PLFA ratio (neutral lipid/phospholipid fatty acids) of Collembola were assessed. These measures indicated that P. putida ranked first, B. megaterium second and E. aerogenes third in food quality. FAs specific for bacteria were found in the NLFAs of the Collembola reflecting the respective bacterial diet. Biomarker FAs for gram-positive bacteria were methyl branched i14:0, i15:0, a15:0 and i17:0. Consumption of gram-negative bacteria was reflected by the cyclic form cy17:0 (E. aerogenes, P. putida) and by 16:1ω5 (P. putida).     

Enriched stable isotopes for determining the isotopically exchangeable element content in soils

The proportion of metals in soils in equilibrium with soil solution can be determined using isotopic dilution. For this purpose, an isotope dilution mass spectrometric (IDMS) technique has been applied for the elements Cd, Cr, Cu, Mo, Ni, Pb, Tl and Zn. Conventionally, sorbed amounts of heavy metals in soils are analysed by ethylenediamine tetra-acetic acid (EDTA) extraction. The IDMS technique and EDTA extraction were both applied to 115 soil samples and compared. For Cd, Cu, Ni, Pb and Zn, the results of the IDMS technique correlated well with the results of EDTA extractions ( r _s(Cd) = 0.965, r _s(Cu) = 0.916, r _s(Ni) = 0.878, r _s(Pb) = 0.922, r _s(Zn) = 0.962; all at P < 0.001). For Cd and Zn, no significant differences between the results of both methods could be observed, which suggests that EDTA and IDMS determined the same pool. EDTA extracted more Cu, Ni and Pb than was determined by IDMS (7, 26 and 13%, respectively). The correlation between EDTA extraction and IDMS for Cr was significant but weak ( r _s(Cr) = 0.361). For Tl and Mo, EDTA extraction and IDMS did not correlate, and IDMS yielded larger concentrations than EDTA. This can be explained by the fact that Tl and Mo do not form stable EDTA complexes, which are essential for the EDTA technique. Recovery experiments demonstrated that added Cd, Cu, Mo, Ni, Pb, Tl and Zn could be recovered successfully by IDMS analysis (mean recovery = 103 ± 9%). Adsorption isotherms for soil samples were determined for Tl, thereby demonstrating that IDMS gave a better estimation of the native content of sorbed Tl in soils than EDTA extraction.     

Modeling excess sulfur deposition on wetland soils using stable sulfur isotopes

Freshwater wetlands exposed to excess S deposition can potentially store significant amounts of reduced S in soils by dissimilatory sulfate reduction. If this storage is permanent, the harmful environmental effects of S deposition and the accompanying acidity are reduced, particularly on surface waters into which wetlands drain. Total non-sulfate S in freshwater peat is divided into three fractions: reduced inorganic S, ester sulfate and carbon-bonded sulfur (CBS). Each fraction is further divided based on its origin: assimilatory via plant and microbial uptake, and dissimilatory via microbial reduction. The CBS fraction dominates in peat, so the amount of dissimilatory CBS in the soil is a direct measure of the beneficial effect of storage of reduced S. Unfortunately, there is no way to directly measure dissimilatory CBS. A model is developed which, with three assumptions, provides a method to calculate dissimilatory CBS using S pool size and stable isotope measurements. Application of the model to a wetland in the New Jersey Pinelands, U.S.A., shows that large amounts of reduced dissimilatory S are stored in the soil. As a consequence, the impact of S deposition and acidity on the surface water environment is significantly reduced.     

Assessment of stable nitrogen isotopes in fingerprinting surface water inorganic nitrogen sources

In many coastal areas of Louisiana, surface water quality is deteriorating rapidly due to elevated nutrient input from agricultural, domestic and industrial sources. This study investigates the potential use of natural abundance variations in ¹⁵N/¹⁴N ratios for identification and tracing surface water inorganic N sources. Surface water samples were collected from streams and point sources in Louisiana and analyzed for NH₄ ⁺-N, NO₃ ^?-N and associated ¹⁵N/¹⁴N (δ¹⁵N ‰) concentrations. Ammonium-N from domestic sewage and industrial discharge point sources was found to have distinct δ¹⁵N ranges. Domestic sewage discharge into a slow flowing stream was traced for about 30 km downstream using ¹⁵N/¹⁴N ratios. At the sewage point source NH₄ ⁺-δ¹⁵N values averaged +43%o and increased linearly to +162‰ with distance from the discharge. In a larger stream with a greater flow velocity the NH₄ ⁺-δ¹⁵N surface water signature of an industrial discharge source was identifiable for approximately 1 km from the point source. Surface water NO₃ ^?-°¹⁵N values generally ranged from +1 to +99‰ and no significant association was observed between δ¹⁵N values with distance from the domestic sewage and industrial point sources. The discrete NH₄ ⁺-δ¹⁵N signatures of domestic sewage and industrial point sources compared to downstream surface water NH₄ ⁺-δ¹⁵N values suggest that N isotopic ratios have the potential to be used as tracers in surface waters contaminated with inorganic N.     

基于稳定同位素的石漠化地区桑树根系水来源研究

土壤水分亏缺是阻碍石漠化地区植被恢复重建的主要生态因子之一。然而,桑树(MorusalbaL.)用于石漠化治理已取得良好效果,但其水分利用策略尚不清楚。该文基于氢、氧稳定同位素技术研究石漠化地区桑树根系在生长期内对不同深度土壤水分的利用程度,反映桑树根系在不同季节的吸水能力变化,揭示桑树生长期内水分利用策略。结果发现:桑树生长前期(春季,4-6月)降水中氢氧稳定同位素丰度较为偏正,比生长后期(秋季,9-11月)降水富集氢氧稳定同位素。土壤水氢氧稳定同位素随春季、秋季降雨的季节变化呈现下降趋势,并且受降雨、蒸发等影响,表现出不同的剖面垂直变化规律。桑树水与土壤水氢、氧稳定同位素变化相似,说明桑树生长所需的水分主要靠土壤水分提供。通过直观相关法和多元线性混合模型法判断出桑树在不同季节对土壤水分的吸收利用策略不同,其中春季先主要吸收10～30 cm土层水,随着降雨增多开始主要吸收利用50～60 cm深层水;进入秋季降雨量较大时亦是主要吸收利用50～60 cm的深层水,而降雨减少时转变为主要吸收利用0～10 cm的土壤水。研究可为桑树在石漠化治理中的应用提供依据。     

碳氮稳定同位素检测能力的验证——2013年实验室间比对分析结果的汇总

稳定性同位素示踪技术,特别是碳、氮稳定性同位素已广泛地应用于农业化学、地球化学和环境化学。碳、氮同位素比值的质谱检测结果直接关系到示踪试验的可靠性。在目前缺乏富集碳、氮同位素的标准物质的条件下,通过实验室间的比对可以验证各实验室对碳、氮同位素比值检测能力、检测结果的准确性和可比性。我所在2013年组织和实施了一次由全国14个单位的检测实验室共17台仪器参加的农业、生态和环境样品中碳氮百分含量及其稳定性同位素比值的实验室间比对。我所制备了多种被检测的样品,有含碳氮的化学肥料、土壤和植物样品;在稳定性同位素富集度上,有自然丰度的和不同富集程度的同位素样品。除固体样品外,还有3种不同丰度的N2O和CO2气体样品。在进行检测结果的统计和评价时,采用Z比分衡量各实验室检测结果的可信度。本文汇总了2013年实验室间比对的结果。     

Influence of cultivar and processing on cherry (Prunus avium) allergenicity

Oral allergy syndrome is an immediate food allergic event that affects lips, mouth, and pharynx, is often triggered by fruits and vegetables, and may be associated with pollinosis. Here, we report on the allergenic pattern of different varieties of cherry (Prunus avium) and results obtained by applying several technological processes to the selected varieties. Whole cherries were submitted to chemical peeling, thermal treatment, and syruping processes, and the relative protein extracts were analyzed by in vitro (sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting analysis) and in vivo tests (skin prick test). Electrophoretic analyses demonstrated that there was no marked difference among cherry cultivars. Chemical peeling successfully removed Pru av 3, a lipid transfer protein (LTP) responsible for oral allergy syndrome in patients without pollinosis, leading to the industrial production of cherry hypoallergenic derivatives. Furthermore, the syruping process removed almost all allergenic proteins to whom patients with pollinosis are responsive. In vivo tests confirmed electrophoretic results.     

Prospects and problems of using the methods of geochemistry of stable carbon isotopes in soil studies

A review of world investigations into the geochemistry of stable isotopes—a new area for soil science—is presented. Studies of the behavior of stable isotopes in soils are being developed in two major directions: reconstruction of the environmental conditions and indication of the soil processes. Investigations into the reconstruction of the environmental conditions are based on the assumption that the isotopic composition of carbon in the soil humus is inherited from and reflects the isotopic composition of carbon in the corresponding vegetation (the source of soil humus). At the same time, studies into the indication of soil processes are based on the effects of fractionation of carbon isotopes in the course of transformation of carbon compounds. In this case, the isotopic composition of carbon in the soil humus should differ from that in the initial plant material. The analysis of available data suggests that the current state of research does not allow assessing the entire diversity of the effects of isotopic fractionation in soils. New data on the isotopic composition of carbon of soil organic matter and carbonates are being actively accumulated at present. However, it is obvious that the effect of isotopic fractionation should be taken into account in the paleoenvironmental and paleoclimatic reconstructions.     

Study of the influence of alcoholic fermentation and distillation on the oxygen-18/oxygen-16 isotope ratio of ethanol

A laboratory procedure for the analysis of the oxygen-18/oxygen-16 isotope ratios of ethanol derived from sugars and fruit juices by pyrolysis-isotope ratio mass spectrometry (IRMS) has been applied to the study of isotopic fractionation induced by the isotope effects of fermentation and distillation. For both processes, an experimental model has been established to describe and explain the observed fractionation phenomena. It is shown that reproducible results can be obtained when appropriate analytical conditions are used. Moreover, the ability of ethanol to act as a reliable indicator of the (18)O/(16)O ratio of sugars in orange juice (and therefore to be used as an internal reference for detecting water addition) is demonstrated both in theory and in practice.     

Comparison of oil recovered from tea tree leaf by ethanol extraction and steam distillation

Two methods for the determination of oil and oil major components from tea tree (Melaleuca alternifolia) leaf are quantitatively compared. A microwave assisted ethanol extraction and a 2-h hydrodistillation technique were used on both dry and fresh leaf from a low and a high oil concentration tree. There was no significant difference between dry and fresh leaf. The distillation technique recovered 88% and 82% of the extractable oil for the low and high concentration material, respectively. For both samples this distilled oil was composed of lower absolute amounts of sesquiterpenoids and marginally lower amounts of monoterpenoids. Extending the distillation to 6 h increased the sesquiterpenoid recovery but this resulted in a reduction in both the absolute and relative amounts of the oxygenated monoterpenoids, terpinen-4-ol and 1,8-cineole.     

混种密度比例对小麦品种竞争系数的影响

在生态学中,竞争是生物个体利用共享的有限资源发生的相互作用,并导致竞争个体适合度降低的现象,这种现象可以发生在物种之间,也可以发生在物种内部。