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.     

Effect of CO2 enrichment on carbon and nitrogen interaction in wheat and soybean

Effect of CO₂ enrichment on the carbon-nitrogen balance in whole plant and the acclimation of photosynthesis was studied in wheat (spring wheat) and soybean (A62-1 [nodulated] and A62-2 [non-nodulated]) with a combination of two nitrogen application rates (0 g N land area m^-2 and 30 g N land area m^-2) and two temperature treatments (30/20°C (day/night) and 26/16°C). Results were as follows.

1. Carbon (dry matter)-nitrogen balance of whole plant throughout growth was remarkably different between wheat and soybean, as follows: 1) in wheat, the relationship between the amount of dry matter (DMt) and amount of nitrogen absorbed (Nt) in whole plant was expressed by an exponential regression, in which the regression coefficient was affected by only the nitrogen application rate, and not by CO₂ and temperature treatments, and 2) in soybean the DMt-Nt relationship was basically expressed by a linear regression, in which the regression coefficient was only slightly affected by the nitrogen treatment (at 0N, DMt-Nt balance finally converged to a linear regression). Thus, carbon-nitrogen interaction in wheat was strongly affected by the underground environment (nitrogen nutrition), but not by the above ground environment (CO₂ enrichment and temperature), while that in soybean was less affected by both under and above ground environments.

2. The photosynthetic response curve to CO₂ concentration in wheat and soybean was less affected by the CO₂ enrichment treatment, while that in wheat and soybean (A62-2) was affected by the nitrogen treatment, indicating that nitrogen nutrition is a more important factor for the regulation of photosynthesis regardless of the CO₂ enrichment.

3. Carbon isotope discrimination (..:1) in soybean was similar to that in wheat under ambient CO₂, while lower than that in wheat under CO₂ enrichment, suggesting that the carbon metabolism is considerably different between wheat and soybean under the CO₂ enrichment conditions.     

氯化胆碱和维生素K3饲料添加剂中二噁英类化合物浓度及其单体分布特征

本试验旨在调查2种常用饲料添加剂氯化胆碱和维生素K3中二噁英类化合物浓度及其单体分布特征。共检测17个氯化胆碱和29个维生素K3样品,二噁英化合物分别采用加速溶剂萃取仪和自动纯化系统进行提取和净化,并采用同位素稀释-高分辨气相色谱/高分辨双聚焦磁式质谱联用技术(HRGC/HRMS)进行准确定量分析检测。结果表明:氯化胆碱与维生素K3中二噁英类化合物浓度分别为4.370和13.871 pg/g,它们的毒性当量平均浓度分别是0.184和0.379 pg WHO-TEQ/g,其中有1个氯化胆碱样品和5个维生素K3样品中毒性当量浓度超过欧盟限量标准值(0.75 pg WHO-TEQ/g)。2种饲料添加剂均以八氯二苯并呋喃(OCDF)为最主要的污染同系物,毒性当量的主要贡献均以2,3,4,7,8-五氯二苯并呋喃(2,3,4,7,8-PeCDF)和1,2,3,4,7,8-六氯二苯并呋喃(1,2,3,4,7,8-HxCDF)为主,分别为42%和55%。污染同系物分布特征以氯化二苯并呋喃(PCDFs)为主要优势污染物。PCDFs在氯化胆碱和维生素K3中的贡献率分别占总浓度的88%和97%。     

不同解离方法对莱克多巴胺猪尿阳性样品的提取效果研究

采用同位素内标法和高效液相-串联质谱法对猪尿莱克多巴胺阳性样品进行三种不同解离处理方法比较试验。结果表明,三种方法差异明显,β-葡萄糖醛苷酶/芳基硫酸酯酶在37℃酶解16 h效果最好,在60℃酶解2 h效果次之,0.1%高氯酸酸解提取效果最差。     

玉米新品种浚单0898丰产稳产性分析

[目的]为浚单0898的推广应用提供科学依据。[方法]以区域试验和生产试验资料为基础,分析了玉米(Zea mays L.)新品种浚单0898的丰产性和稳产性。[结果]浚单0898在2年24点次的试验中,全部比对照品种浚单18显著增产,增产幅度达11.3%,丰产性突出,且变异系数小,对环境有较强的适应性。[结论]浚单0898是一个适应较广、丰产性突出、稳定性好的玉米新品种,推广前景十分广阔。     

Earthworms as seedling predators: Importance of seeds and seedlings for earthworm nutrition

Anecic earthworms have been shown to collect, concentrate and bury seeds in their burrows. Moreover, recent studies suggest that earthworms function as granivores and seedling herbivores thereby directly impacting plant community assembly. However, this has not been proven unequivocally. Further, it remains unclear if earthworms benefit from seed ingestion, i.e., if they assimilate seed carbon. We set up a series of three laboratory experiments in order to test the following hypotheses: (1) anecic earthworms (Lumbricus terrestris L.) not only ingest seeds but also seedlings, (2) ingestion of seedlings is lower than that of seeds due to a ‘size refuge’ of seedlings (i.e., they are too big to be swallowed), and (3) seeds and seedlings contribute to earthworm nutrition. L. terrestris readily consumed legume seedlings in the radicle stage, whereas legume seeds and seedlings in the cotyledon stage, and grass seeds and seedlings in the radicle and cotyledon stage were ingested in similar but lower amounts. Importantly, ingestion of seedlings, in contrast to seeds, was lethal for all plant species. Moreover, earthworm weight change varied with the functional identity and vitality of seeds and natural ¹⁵N signatures in earthworm body tissue underlined the importance of seedlings for earthworm nutrition. The results indicate that the anecic earthworm L. terrestris indeed functions as a granivore and seedling herbivore. The selectivity in seedling ingestion points at the potential of direct earthworm effects on plant community assembly. Further, seeds and seedlings most likely contribute significantly to earthworm nutrition potentially explaining the collection and concentration of seeds by L. terrestris in its middens and burrows; however, the present results call for experiments under more natural conditions.     

汾河下游丰水和枯水期的河流硝酸盐污染来源特征

[目的]对汾河径流丰水期和枯水期的河流硝酸盐污染来源特征进行对比分析和研究,为汾河下游氮源污染治理提供理论支持。[方法]通过研究2018年汾河下游水体硝酸盐及其氮、氧同位素不同时期的变化,分析排入河流的硝酸盐来源雨期性变化特征,并引入IsoSoure模型,定量计算各污染源对汾河下游水体硝酸盐的贡献。[结果]在丰水期和枯水期,δ~(15)N值变化范围为3.45‰～11.19‰,δ~(18)O值变化范围为-0.72‰～3.17‰,硝酸盐污染源主要为农业化肥、土壤有机氮、生活污水与粪便;硝酸盐污染源主要与汾河下游周围土地利用类型相关,丰水期临汾段与M_5采样点硝酸盐污染源主要为粪便和污水,分别占比为58%,40%,72%和58%,M_6—M_9段农业化肥贡献率最高,占比分别45.4%,62%,56.6%,56.5%。枯水期所有采样点硝酸盐污染源贡献率最高的都为粪便和污水,占比为40%～73%。[结论]汾河径流硝酸盐污染来源主要为农业化肥、土壤有机氮、生活污水与粪便,并且污染来源与土地利用类型有很强相关性,不同水期硝酸盐污染来源大多为粪便和生活污水,差别主要体现在M_6—M_9取样点,丰水期主要污染物为农业化肥,而枯水期为粪便与生活污水。     

密集烘烤稳温时长对烟叶膜脂过氧化作用及烤后烟化学成分的影响

为了研究烟叶在烘烤过程中的膜脂过氧化作用,通过延长变黄末期与定色初期的稳温时长,分析烟叶生理指标的变化和烤后烟叶化学成分。结果表明,处理T₂和处理T₁的烟叶在烘烤过程中膜脂过氧化水平较低,抗氧化酶活性较高,且处理T₂的烤后烟叶多酚含量较高。在烟叶烘烤过程中,延长变黄末期与定色初期稳温时长有助于减少膜脂过氧化作用对烟叶的影响,提高烟叶品质。     

不同灌水条件下春小麦不同器官碳同位素分辨率与产量的相关性 国家自然科学基金项目(31060190)；宁夏回族自治区科技攻关项目；宁夏回族自治区国际合作项目；澳大利亚国际农业研究中心(ACIAR)项目(CIM/2005/111)；宁夏回族自治区自然科学基金项目（NZ12259）。

为确定碳同位素分辨率（Δ¹³C）用于春小麦高产节水品种选育的最佳测定时期和器官,以2个小麦地方品种、14个育成品种(系)和2个引进品种为试验材料进行不同灌水处理,分析了小麦旗叶、茎秆和籽粒Δ¹³C值的差异及其与产量的相关性。结果表明,同一品种不同部位Δ¹³C存在较大差异,籽粒Δ¹³C均低于开花期旗叶和基部秸秆、成熟期旗叶和基部秸秆的Δ¹³C。小麦材料相同部位的Δ¹³C在中度水分胁迫处理（T2）下低于其他灌水处理(T1 、T3和T4),在T2和轻度水分胁迫处理（T3）下,拔节期旗叶Δ¹³C与产量均呈显著负相关;在T3处理下,成熟期籽粒Δ¹³C与产量呈显著正相关。     

小麦碳同位素分辨率与叶片气孔相关指标的关系

为了探讨气孔相关指标替代碳同位素分辨率(△)作为评价指标的可行性,测定了56个小麦品种(系)的碳同位素分辨率(△),并分析了灌浆期不同阶段气孔相关指标与△值的相关性.结果表明,小麦旗叶和籽粒的△值均具有较好的遗传稳定性;灌浆中后期小麦旗叶的气孔导度和叶面温度都与△值有较强的相关性.因此,在育种中,可以通过测定灌浆中后期小麦旗叶的气孔导度和叶温代替△值对材料的蒸腾速率进行初步选择.