Diet and trophic niche overlap of native and nonnative fishes in the Gila River,USA: implications for native fish conservation

Pilger TJ, Gido KB, Propst DL. Diet and trophic niche overlap of native and nonnative fishes in the Gila River, USA: implications for native fish conservation. Ecology of Freshwater Fish 2010: 19: 300–321. © 2010 John Wiley & Sons A/S Abstract –  The upper Gila River basin is one of the few unimpounded drainage basins west of the Continental Divide, and as such is a stronghold for endemic fishes in the region. Nevertheless, multiple nonindigenous fishes potentially threaten the persistence of native fishes, and little is known of the trophic ecology of either native or nonnative fishes in this system. Gut contents and stable isotopes (¹³C and ¹⁵N) were used to identify trophic relationships, trophic niche overlap and evaluate potential interactions among native and nonnative fishes. Both native and nonnative fishes fed across multiple trophic levels. In general, adult native suckers had lower ¹⁵N signatures and consumed more algae and detritus than smaller native fish, including juvenile suckers. Adult nonnative smallmouth bass (Micropterus dolomieu), yellow bullhead (Ameiurus natalis) and two species of trout preyed on small‐bodied fishes and predaceous aquatic invertebrates leading to significantly higher trophic positions than small and large‐bodied native fishes. Thus, the presence of these nonnative fishes extended community food‐chain lengths by foraging at higher trophic levels. Although predation on juvenile native fishes might threaten persistence of native fishes, the high degree of omnivory suggests that impacts of nonnative predators may be lessened and dependent on environmental variability.     

烟叶稳定碳同位素组成受控因素分析

【目的】探讨烟叶稳定碳同位素组成的受控因素,为烟草种植评价指标体系的完善及生态适应性机理研究提供新的理论依据。【方法】选取我国西南、东南、长江中上游和黄淮4个主要一级烟草种植区生理成熟期烟叶进行稳定碳同位素组成(δ~(13)C)分析。【结果】供试烟叶样本δ~(13)C值分布在-27.76‰～-25.39‰,平均值为-26.46‰。烟叶δ~(13)C值与经度呈显著负相关关系,经度每增加1°,烟叶δ~(13)C值减小0.09‰;与纬度呈二次抛物线关系。不同叶位烟叶δ~(13)C值具有显著差异,表现为上部叶片中部叶片下部叶片。4个种植区烟叶δ~(13)C值为西南种植区≈黄淮种植区长江中上游东南种植区。利用碳同位素对不同香型烟叶聚类结果表明,不同产地的清香甜香型和醇甜香型烤烟能够被明确聚类,而对焦甜焦香型、清甜蜜甜香型、焦甜醇甜香型和蜜甜香型4种香型烤烟没有明显的聚类效果。【结论】烟叶稳定碳同位素组成与经度呈负相关关系,与纬度呈二次抛物线关系,不同叶位烟叶稳定碳同位素组成不同,利用δ~(13)C值可以对清香甜香型和醇甜香型烤烟进行有效聚类。     

水稻新品种镇稻10号的丰产稳产性及其利用

[目的]为水稻生产中合理利用镇稻10号提供依据。[方法]以2004~2005年度江苏省水稻新品种区域试验和生产试验结果为分析资料,采用高稳系数法,结合产量变异系数和适应度,对镇稻10号和对照武运粳7号进行比较。[结果]在2004~2005年区域试验、2005~2006年区域试验和生产试验中,镇稻10号的平均产量分别为9 008.258、655.008、319.15 kg/hm2,分别比对照增产3.27%、3.59%、5.37%;高稳系数分别为90.56%、86.33%和70.41%,均大于对照;产量变异系数分别为3.53%、8.33%、26.50%,均小于对照;适应度分别为57.14%、71.43%、75.00%,均大于对照。[结论]镇稻10号是一个高产稳产、丰产性好的晚粳稻新品种,具有较好的广适性,增产潜力大,适宜在沿江和苏南等中高产地种植。     

Field-applying an inexpensive, 13C-depleted,labile carbon source to study in situ fate and short-term effects on soils

Background

Labile carbon (C_labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C_labile additions use laboratory incubations. We need to field-apply C_labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and ¹³C-depleted source of C_labile—crude glycerol carbon (C_glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied C_glyc at three rates (0, 216, and 866 kg C ha⁻¹) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C_glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO₃⁻–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

C_glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C_glyc added). The δ¹³C values of the other measured C pools were too variable to accurately track the C_labile fate. NO₃⁻–N was decreased by 13%–57% with the 216 and 866 kg C ha⁻¹ rates, respectively, and was strongly related to greater microbial uptake of C_glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, C_labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO₃⁻–N.     

镉同位素分馏在土壤-植物体系中的研究进展

镉污染土壤因其导致粮食作物超标以及通过食物链对居民健康构成威胁,引起了人们的高度关注。土壤镉的迁移转化、植物根部对镉的吸收、植物体内对镉的装载转运和贮存是土壤-植物体系镉生物地球化学循环的重要过程。近年来,稳定同位素分馏技术被广泛应用于土壤-植物系统中镉的迁移和储存,为研究镉在不同土壤库和植物部位中的迁移和转化提供了新的思路和视角。本文首先介绍了镉同位素组成分析的基本原理和方法;其次对土壤矿物溶解、共沉淀、吸附和有机质螯合配位等四个关键过程引起的镉同位素分馏方向和程度进行综述,并重点针对植物根部对镉的吸收、根部-地上部转运和籽粒储存等三个关键过程阐述植物体内镉同位素分馏机制;最后基于目前研究现状,展望了土壤-植物体系镉同位素分馏尚需解决的科学问题和未来的研究方向。有助于深入理解镉在土壤-植物体系中的生物地球化学过程与机制,以期为镉污染土壤的安全利用与治理修复、农产品减毒脱毒等应用技术的研发提供科学依据。     

塔里木河流域地表水和地下水的转化关系

[目的] 探究塔里木河流域地表水和地下水的转化关系,为该流域水资源形成机制研究和促进水资源合理开发利用提供科学依据。[方法] 以氧同位素（δ¹⁸O）作为示踪剂,采用稳定同位素技术和水化学原理分析了塔里木河流域地表水与地下水转化关系。2018年沿塔里木河上、中、下游采集了90组地表水样和地下水样,并测量相应的氘氧稳定同位素和水化学离子（Cl^-,SO₄^2-,HCO₃^-,Ca²⁺,Mg²⁺,Na⁺）,运用Gibbs图和Piper三线图探测了塔里木河流域地上和地下水化学特征及其转化关系。[结果] ①地下水和河水的δ¹⁸O值具有不同的变化情况：地下水δ¹⁸O值随着流向呈现明显的逐渐富集特点,而地表水则变化较小。通过总溶解固体（total dissolved solids,TDS）的沿程分析可知,对于上游地下水而言,由于河水下渗补给,加上侧向径流影响,δ¹⁸O呈现了大幅下降。随着河水补给的增加,其值不断富集。对于地表水而言,随着流向其δ¹⁸O值逐渐下降,此时地下水呈现富集,说明此时期地下水能够对地表水产生补给。②根据地下水和河水测试数据分别建立地下水线和河水线方程,且二者斜率均小于大气降水线斜率,说明地下水和河水同位素组成受到一定程度蒸发作用影响。③塔里木河上游地下水向地表水补给平均速率为1.76 m³/（d·m）,中游地下水向地表水补给平均速率为1.71 m³/（d·m）,下游地下水向地表水补给平均速率为1.65 m³/（d·m）。[结论] 地表水—地下水的频繁转化是塔里木河流域水资源循环的主要特征,地下水补给是河流水资源的主要补给来源。     

我国有机茶稳定同位素特征与δ15N标识相关性研究

为探明我国有机茶稳定同位素分布情况及δ¹⁵N标识的相关因素,本研究收集了全国不同地区申请有机茶认证企业的145个样品,采用元素分析-稳定同位素比率质谱仪测定稳定同位素比率(δ¹³C、δ¹⁵N、δ²H、δ¹⁸O),结合单因素方差分析和正态分布模型探究稳定同位素特征分布规律。结果表明,有机茶样品δ¹³C分布于-31.0‰ ~ -23.7‰之间,不同产地间差异不显著。δ²H和δ¹⁸O范围分别为-107.1‰ ~ -24.8‰和17.2‰ ~ 32.0‰,均存在显著地域差异。我国有机茶δ¹⁵N正态分布范围为-4.6‰ ~ 7.0‰,平均值为1.2‰。其中有机茶生产面积大的地区样品δ¹⁵N范围为1.6‰ ~ 5.8‰,显著高于生产面积小的地区(-2.5‰ ~ 0.4‰,P<0.01),表明δ¹⁵N指标作为有机茶标识特征与产区生产面积之间存在一定的相关性。本研究为基于稳定同位素技术的有机茶真伪鉴别提供了研究基础,为有机茶的认证与监管提供了一定的理论依据。     

黄土高原泾河小流域泥沙碳、氮同位素与生态环境示踪

以泾河(陕西彬县境内)4条支流表层沉积物为研究对象,对其有机质的稳定碳、氮同位素组成进行测定和研究.结果表明,4条河流表层沉积物有机质的碳同位素(δ13C)值变化范围为(-29.1‰)～(-20.4‰),平均值为-25.4‰.其δ13C值从上游到下游都有逐渐偏正的趋势,表明从上游到下游植被覆盖类型的变化影响了沿河表层沉积物有机质的δ13C值.4条河流表层沉积物有机质的氮同位素(δ15N)值和碳氮比(C/N)的变化范围分别为0～4.6‰和1.4～17.2,平均值分别为2.8‰和7.3.从上游到下游其δ15N值逐渐偏正,表明沿岸进入河中的泥沙比例越来越大,人类活动等对自然环境的影响增强.徐家河和拜家河下游采样点表层沉积物有机质的δ15N值有偏负趋势,可能与下游煤炭开采,煤等有机质进入河流表层沉积物有关.因此,对河流表层沉积物中有机质的碳、氮同位素组成特征和变化研究可以揭示流域土壤侵蚀状态和生态环境的变化.     

Relationships Between Carbon Isotope Discrimination and Yield of Spring Wheat Under Different Water and Nitrogen Levels

ABSTRACT

A greenhouse experiment was conducted to investigate the relationships between foliar carbon isotope discrimination (Δ) and above ground dry matter (ADM) at different stages during a plant's life cycle, and grain carbon isotope discrimination and grain yield (GY) at maturity of spring wheat (Triticum aestivum L.) under different nitrogen (N) and water levels. Results showed that ADM and GY both increased significantly with decreasing water stress, while the effects of nitrogen on ADM and GY varied with the water conditions. Foliar and grain carbon isotope discrimination decreased with increasing water stress and increasing nitrogen levels. For all water conditions, relationships between carbon isotope discrimination (foliar and grain) and yields (ADM and GY) were significantly positive (P < 0.001) at various growth stages. However, at the same water level, the correlations were complex, and under well-watered conditions, ADM and GY were strongly and negatively correlated with foliar and grain carbon isotope discrimination at all growth stages (P < 0.001). The correlations were inconsistent and not significant at moderate water level, but were positive under drought. Our results showed that water and nitrogen both significantly affected the relationships between yield and carbon isotope discrimination of spring wheat, that there are interactions between these two parameters, and that environmental conditions such as water and fertilizer must thus be considered in future research on the relationship between yield and carbon isotope discrimination of spring wheat.     

Effects of Nitrate and Potassium on Ammonium Toxicity in Cucumber Plants

ABSTRACT

Interactions between nitrate (NO₃ ^?), potassium (K⁺), and ammonium (NH₄ ⁺) were investigated using hydroponically grown cucumber (Cucumis sativus L.) plants. Ammonium as the sole nitrogen (N) source at 10 mM was toxic and led to overall growth suppression, chlorosis, and necrosis of leaves. After 20 days, 50% of the plants were dead. However, when NO₃ ^? was supplied at very low concentration together with high NH₄ ⁺ (only 1% of total 10 mM N) all seedlings survived and their growth was improved. High K⁺ concentration (5 mM) also alleviated NH₄ ⁺ toxicity and increased plant growth several fold compared to intermediate concentration of K⁺ (0.6 mM). Leaf total N and ¹⁵N derived from ¹⁵N-labelled NH₄ ⁺ increased in the presence of NO₃ ^?, but decreased at high K⁺ concentration. High K⁺ supply enhanced total carbon (C) and δ ¹³C and stimulated GS and PEPCase activities in leaves and roots. Nitrate supplementation had no effect on GS or PEPCase activities. It is concluded that K⁺ may alleviate NH₄ ⁺ toxicity, partly by inhibiting NH₄ ⁺ uptake, partly by stimulating C and N assimilation in the roots.