增温施氮对高寒草甸生产力及生物量分配的影响

在青藏高原高寒草甸区设置模拟增温和氮添加处理,研究长期增温与外源氮输入对高寒草甸群落生产及其分配的影响.结果表明:开顶箱增温装置造成小环境暖干化,即显著提高地表空气温度1.6℃,提高表层土壤温度1.4℃,降低土壤含水量4.7%.2012、2013和2014年不施氮处理下增温分别降低地上生物量61.5%、108.8%和77.1%,在高氮(40和80kg N·hm^-2·a^-1)处理下增温对群落地上生物量无显著影响,这说明增温的影响依赖于氮添加水平,且施氮补偿了增温导致的土壤氮损失.增温导致根冠比增加,2012、2013和2014年不施氮处理下增温分别增加根冠比98.6%、60.7%和97.8%.在不增温处理下,植物群落地上、地下生物量的变化率均表现出低氮(10、20 kg N·hm^-2·a^-1)促进、高氮抑制的趋势,达到饱和阈值时的氮添加剂量分别为56.0和55.5 kg N·hm^-2·a^-1;而在增温处理下,地上、地下生物量随施氮量增加呈线性增加趋势.这说明增温改变了高寒草甸生物量分配对外源氮输入的响应模式,增温导致的土壤无机氮含量变化是生物量分配模式改变的主要原因.由氮添加试验估算的高寒草甸氮饱和阈值表明,高寒草甸对氮输入的敏感性高于其他类型草地.     

Activatable fluorescent probes in fluorescence-guided surgery: Practical considerations

Fluorescence-guided imaging during surgery is a promising technique that is increasingly used to aid surgeons in identifying sites of tumor and surgical margins. Of the two types of fluorescent probes, always-on and activatable, activatable probes are preferred because they produce higher target-to-background ratios, thus improving sensitivity compared with always-on probes that must contend with considerable background signal. There are two types of activatable probes: 1) enzyme-reactive probes that are normally quenched but can be activated after cleavage by cancer-specific enzymes (activity-based probes) and 2) molecular-binding probes which use cancer targeting moieties such as monoclonal antibodies to target receptors found in abundance on cancers and are activated after internalization and lysosomal processing (binding-based probes). For fluorescence-guided intraoperative surgery, enzyme-reactive probes are superior because they can react quickly, require smaller dosages especially for topical applications, have limited side effects, and have favorable pharmacokinetics. Enzyme-reactive probes are easier to use, fit better into existing work flows in the operating room and have minimal toxicity. Although difficult to prove, it is assumed that the guidance provided to surgeons by these probes results in more effective surgeries with better outcomes for patients. In this review, we compare these two types of activatable fluorescent probes for their ease of use and efficacy.     

短期增温对中亚热带杉木人工幼林土壤氮磷耦合作用的影响

全球变暖引起陆地生态系统和整个生物圈一系列生态问题,未来全球平均气温的持续增加将使这些问题进一步加剧。目前增温、氮沉降和森林更新方式对中亚热带土壤氮磷等养分的影响已有部分研究,但增温对亚热带森林的氮磷耦合作用的影响仍然未知。以中亚热带杉木(Cunninghamia lanceolate)幼苗为研究对象,设置埋设电缆以加热土壤增温实验(增温幅度(5±0.5)℃),研究短期增温对土壤含水量、微生物生物量氮(MBN)、微生物生物量磷(MBP)、土壤氮磷养分,以及氮(N)、磷(P)耦合作用的影响。结果表明:短期增温对全氮、全磷无显著影响;增温第1年显著提高了有效氮、铵态氮(NH_4~+)和有效磷的含量,显著降低了MBN含量。增温第2年,土壤中有效磷、NH_4~+和MBP含量显著下降;短期增温虽然对土壤全N/P,有效N/P的影响不显著,但是增温使铵态氮/硝态亚硝态氮(NH_4~+/(NO_3~-+NO_2~-))显著降低;此外,增温显著降低了MBN/MBP,缓解了微生物对磷的限制。相关性分析表明,耦合作用不仅受N和P之间相互作用的影响,也受土壤温度、水分含量等其他因素的影响。研究表明,短期增温并未对中亚热带杉木人工幼林土壤氮磷耦合作用产生显著影响,但增温后降低了有效氮、有效磷的含量。因此,在未来全球变暖背景下,研究结果为中亚热带森林生态系统的的健康发展和科学管理提供重要的理论依据。     

模拟氮沉降对华西雨屏区天然常绿阔叶林凋落叶分解过程微生物生物量的影响

为进一步深化氮沉降对凋落物分解影响的研究,2016年3月—2017年3月,在华西雨屏区天然常绿阔叶林内,用凋落叶分解袋法研究了模拟氮沉降对凋落叶分解过程中微生物生物量碳(MBC)、微生物生物量氮(MBN)和微生物生物量磷(MBP)的影响。实验设置了对照(0 g N m~(-2)a~(-1))、低氮(5 g N m~(-2)a~(-1))、中氮(15 g Nm~(-2)a~(-1))和高氮沉降(30 g N m~(-2)a~(-1)) 4个处理。结果表明:低氮和中氮处理显著增加了凋落叶分解过程中的MBC和MBN,以低氮处理增加幅度最高;低氮和中氮处理对凋落叶分解过程中的MBP影响不显著;高氮处理显著降低了分解过程中的MBC、MBN和MBP。随模拟氮沉降量的递增,凋落叶分解过程中微生物生物量碳氮比逐渐减少,微生物生物量碳磷比呈现先增加后下降的趋势。研究结果说明,氮沉降影响了华西雨屏区天然常绿阔叶林凋落物分解过程中微生物生物量,进而改变了凋落物的分解过程。     

植被恢复过程中芒萁覆盖对侵蚀红壤氮组分的影响

氮素是限制陆地生态系统生产力的重要因子。采用时空代换法,以红壤侵蚀区未治理、恢复12年和30年的马尾松林为研究对象,对比分析了林下芒萁覆盖地与裸地表层土壤之间氮同位素、不同形态氮组分含量以及不同组分氮含量所占比例之间的差异。结果表明:在所有马尾松林中,芒萁覆盖增加了表层土壤的全氮含量,δ~(15)N值则比林下裸地显著降低了33. 8%—83.1%(P0.05)。随着恢复年限增加,林下芒萁覆盖地表层土壤δ~(15)N值显著下降,而林下裸露地δ~(15)N值没有显著变化(P0.05)。不同恢复年限马尾松林的芒萁覆盖地表层土壤微生物生物量氮、可溶性有机氮和铵态氮含量显著高于林下裸地(P 0.05),而硝态氮含量则显著低于林下裸地(P0.05)。随恢复年限增加,表层土壤微生物生物量氮、可溶性有机氮、铵态氮含量均呈增加趋势,而硝态氮含量则呈下降趋势,不同形态氮占全氮比例表现为:微生物生物量氮铵态氮可溶性有机氮硝态氮。相关分析表明土壤δ~(15)N值与硝态氮极显著正相关,与其他氮组分极显著负相关(P0.01)。由此可见,与林下裸地相比,芒萁覆盖在植被恢复过程中有助于提高表层土壤中全氮、微生物生物量氮、可溶性有机氮和铵态氮含量,降低硝态氮的淋溶损失风险,促进土壤氮保持和积累,从而有利于退化红壤生态系统的恢复。     

矮化苹果氮肥施用技术

以8年生烟富3/M26/平邑甜茶为试材,采用¹⁵N同位素示踪技术,研究不同施氮方式(Ⅰ:春季1次性施氮,Ⅱ:分2次施氮,Ⅲ:集约技术施氮,即氮肥减量和分次施氮)对烟富3/M26/平邑甜茶¹⁵N-尿素吸收、利用、损失和果实品质的影响.结果表明:处理Ⅲ植株叶片的叶面积、叶绿素含量(SPAD)、光合速率(P_n)、叶片全氮含量和生物量(果实除外)显著高于处理Ⅰ和处理Ⅱ,植株根冠比也显著增加.处理Ⅲ显著提高了叶片的保护酶活性(超氧化物歧化酶、过氧化物酶和过氧化氢酶),降低了叶片丙二醛(MDA)含量.3个处理各器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率(Ndff)表现一致,果实的Ndff值最大,其次是一年生枝、叶片和根,且各器官的Ndff值均以处理Ⅲ最大.在果实成熟期,处理Ⅲ的单株总氮含量为93.0 mg·kg^-1,显著高于处理Ⅰ(70.2 mg·kg^-1)和处理Ⅱ(81.9 mg·kg^-1);处理Ⅲ的¹⁵N肥料利用率为33.6%,显著高于处理Ⅰ(20.4%)和处理Ⅱ(26.0%);而¹⁵N损失率为46.9%,显著低于处理Ⅰ(56.5%)和处理Ⅱ(52.9%).不同施氮方式下植株的平均单果质量、可溶性固形物、硬度、可溶性糖、可滴定酸、糖酸比均存在显著差异,且均以处理Ⅲ最高,其次是处理Ⅱ,处理Ⅰ最低.     

Production of Ga-68 with a General Electric PETtrace cyclotron by liquid target

PurposeIn recent years the use of ⁶⁸Ga (t_1/2 = 67.84 min, β⁺: 88.88%) for the labelling of different PET radiopharmaceuticals has significantly increased. This work aims to evaluate the feasibility of the production of ⁶⁸Ga via the ⁶⁸Zn(p,n)⁶⁸Ga reaction by proton irradiation of an enriched zinc solution, using a biomedical cyclotron, in order to satisfy its increasing demand.MethodsIrradiations of 1.7 M solution of ⁶⁸Zn(NO₃)₂ in 0.2 N HNO₃ were conducted with a GE PETtrace cyclotron using a slightly modified version of the liquid target used for the production of fluorine-18. The proton beam energy was degraded to 12 MeV, in order to minimize the production of ⁶⁷Ga through the ⁶⁸Zn(p,2n)⁶⁷Ga reaction. The product’s activity was measured using a calibrated activity meter and a High Purity Germanium gamma-ray detector.ResultsThe saturation yield of ⁶⁸Ga amounts to (330 ± 20) MBq/µA, corresponding to a produced activity of ⁶⁸Ga at the EOB of (4.3 ± 0.3) GBq in a typical production run at 46 µA for 32 min. The radionuclidic purity of the ⁶⁸Ga in the final product, after the separation, is within the limits of the European Pharmacopoeia (>99.9%) up to 3 h after the EOB. Radiochemical separation up to a yield not lower than 75% was obtained using an automated purification module. The enriched material recovery efficiency resulted higher than 80–90%.ConclusionsIn summary, this approach provides clinically relevant amounts of ⁶⁸Ga by cyclotron irradiation of a liquid target, as a competitive alternative to the current production through the ⁶⁸Ge/⁶⁸Ga generators.     

Capture of melon flies, Zeugodacus cucurbitae (Diptera: Tephritidae), in a food-baited Multilure trap: Influence of distance,diet, and sex

Many countries operate trapping programs to detect invasions of pestiferous fruit fly species (Diptera: Tephritidae). Surveillance relies heavily on traps baited with male lures, which, while highly attractive, have limited effectiveness, because (i) they are sex-specific and (ii) males of some species do not respond to the lures currently in use. For these reasons, detection programs also include food-baited traps that are neither sex- nor species-specific. Compared to male lure-baited traps, however, few studies have measured the attractiveness of food-based traps. The present study describes a mark-release-recapture study conducted in a fruit orchard in Hawaii that measured the attractiveness of a liquid protein hydrolysate-based (torula yeast/borax slurry) trap to adults of the melon fly Zeugodacus cucurbitae (Coquillett). Multiple release points were used at varying distances from a single, central trap to generate estimates of distance-dependent capture probabilities. The potential influences of sex and pre-release diet on capture probability were also examined. Flies were released at 14 d of age and were maintained on one of four dietary regimes that offered a protein hydrolysate-rich diet for varying intervals (i.e., 0, 3, 7, or 14?d, respectively). Recapture rates were similar between the sexes and over both sexes and all diets averaged 3.6%, 3.2%, and 0.6% for release distances of 10, 25, and 50?m, respectively. Pre-release diet had a significant effect on recapture probability for releases at 10 and 25?m: flies fed sugar only or protein hydrolysate-rich diet for only 3?d were captured more frequently than flies that had longer access to yeast extract prior to release.