北京山区辽东栎林的径级结构、种群起源及生态学意义

 北京山区的辽东栎(Quercus wutaishanica)林径级结构的调查分析结果表明,辽东栎林是稳定性的群落类型,其更新主要通过萌生来完成。能够与辽东栎长期共存的伴生种有色木(Acer mono)、大果榆(Ulmus macrocarpa)、大叶白蜡(Fraxinus rhynchophylla)等。萌生在辽东栎种群中十分普遍,除辽东栎伐桩、枯木和大树根际有较多的萌生茎干外,多年生实生苗也有萌生现象发生。辽东栎林的更新在辽东栎总体种群的幼树阶段(径级2)存在着明显的瓶颈现象,但萌生特性使辽东栎林在更新时或受到干扰后形成较大的萌生种群,使辽东栎的大幼树能够得到迅速的补充,顺利地通过瓶颈进行更新,保持群落的相对稳定。一定数量的辽东栎实生种群的存在对于维持辽东栎的遗传多样性、种群整体活力和群落的稳定,提高辽东栎种群对环境变化的反应能力等方面有着十分重要的生态学意义。     

Ascorbalamic acid: An ascorbigen-like plant constituent yielding in hot acid 3-(2-furoyl)alanine

Ascorbalamic acid (C₉H₁₃NO₈) was isolated from Brassica olerocea L. MS study of various methylated derivatives suggested a structure (Ia) derivable by CC coupling of C-3 of alanine with C-2 of ascorbic acid, followed by lactone → lactam rearrangement. Other derivatives provided supporting evidence, as did study of the reaction of L-3-chloroalanine with L-ascorbic acid in vitro. On treatment with hot 6 M HCl, ascorbalamic acid yielded L-aspartic acid and 3-(2-furoyl)alanine. For identification of the latter, DL-3-(2-furoyl)alanine and its N-2,4-dinitrophenyl and N-acetyl methyl ester derivatives were synthesized. Unlike ascorbigens, ascorbalamic acid is probably present in the living plant. It seemed to be present in all crucifers examined, but to have a capricious distribution in other orders. During permethylation, rearrangements of ester groups were observed, both with ascorbalamic acid and with pyrrolidonecarboxylic acid as a model.     

Rhizoctonia solani and orchid seed

Summary

One hundred and sixty-two agarics are recorded for Hirta and two from Dùn, two islands situated off the West coast of Scotland in the St. Kilda complex. The agarics are described in relation to the ecological noda proposed by McVean for the higher plant communities of the islands. Omphalina ericetorum and Nolanea staurospora were by far the commonest species: eighttaxa which are not in the New British Check List are recorded from Hirta. An appendix dealing with the taxonomy and nomenclature of the more critical species in the list is given.     

The effect of acetylsalicylic acid and oxalic acid on Myzus persicae and Aphidius colemani

Plants can respond to damage by pests with both induced direct defences and indirect defences by the attraction of their natural enemies. Foliar application of several plant-derived chemicals, such as salicylic acid and oxalic acid, can induce these defence mechanisms. The effect of acetylsalicylic acid and oxalic acid on the aphid Myzus persicae Sulzer (Homoptera: Aphididae) and its parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) was investigated. Experiments were carried out with direct application of acetylsalicylic and oxalic acids on these insects, as well as choice and no-choice tests using foliar application of both chemicals on Brussels sprouts plants, Brassica oleracea var. gemmifera L. (Brassicaceae). Parasitoids were given a choice between treated and untreated plants for oviposition, and the effects of the chemicals on aphid and parasitoid development were determined. Although direct application of both chemicals increased aphid mortality, their foliar application did not induce resistance against aphids. The foliar application of such compounds, even in low concentration as shown in the choice tests, has the potential to induce indirect plant defences against aphids by encouraging aphid parasitisation. Although the direct application of both chemicals reduced parasitoid emergence from their hosts, the foliar application of acetylsalicylic acid and low concentrations of oxalic acid did not have a negative effect on parasitoid emergence ability. However, 10 m m oxalic acid reduced the number of emerged parasitoids in no-choice experiments. This study shows that foliar application of acetylsalicylic and oxalic acids has the potential to encourage aphid parasitisation, but care is needed as high concentrations of oxalic acid can have a negative effect on these beneficial organisms.     

Cultivar‐specific plant odour preferences of a generalist aphid parasitoid Aphidius colemani and a possible mechanism for maternal priming of resistance to toxic plant chemistry

Aphidius colemani Viereck, emerging from Myzus persicae (Sulzer) mummies on the Brussels sprout cultivar ‘Bedford Winter Harvest’ (BWH), responds positively in the olfactometer to the odour of that cultivar in comparison with air. Responses to the odours of other sprout cultivars, cabbage and broad bean could be explained by the humidity from plant leaves. In a choice between BWH and other sprout cultivars, the BWH odour is preferred, or that of cv. ‘Red Delicious’ (RD) if the parasitoids are reared on RD. This confirms previous work showing that the secondary chemistry of a cultivar is learnt from the mummy cuticle during emergence. Adults emerging from pupae excised from the mummy show a similar but less pronounced preference. Parasitoids developing in aphids on an artificial diet do not discriminate between the odours of BWH and RD, unless allowed contact with a mummy from the same cultivar that the mother develops on. This suggests a cultivar‐specific maternal cue. This cue is speculated to consist of a small amount of the secondary chemistry (probably glucosinolates in the present study) that are left in or on the egg at oviposition, which subsequently induces enzymes that detoxify plant‐derived toxins in the aphid host. Indeed, when parasitoids emerging from diet‐reared aphids are released on aphid‐infested sprout plants, fewer mummies are produced than by parasitoids emerging from mummies of plant‐reared aphids or from excised pupae. Only parasitoids that emerge from mummies of plant‐reared aphids prefer the cultivar of origin as shown by the number of mummified hosts.     

四环素残留对黄豆芽营养品质及根际微生物的影响北大核心

【目的】探究土壤中四环素残留对土培黄豆芽的生长发育、根际微生物及营养品质的影响,为正确评估抗生素残留对蔬菜种植业的影响及制定土壤-蔬菜系统中抗生素污染防控策略提供理论基础。【方法】模拟土壤中不同四环素残留水平(0、25、50mg/kg),采用高效液相色谱(high performance liquid chromatography,HPLC)方法测定黄豆芽中的四环素残留量、理化方法测定黄豆芽的营养品质、高通量技术测定根际微生物群落。【结果】黄豆芽中四环素累积量随土壤中四环素残留量的增加而增加,累积量分布表现为根>下胚轴>子叶;四环素残留显著抑制黄豆芽的根和下胚轴的发育及其生物量、维生素C含量和抗氧化性,但增加了纤维素含量。在这些指标中维生素C含量的变化最显著,在黄豆芽生长第5天,25mg/kg和50mg/kg四环素残留组中,黄豆芽中维生素C含量较对照组分别降低41.35%和49.80%;此外,四环素残留显著影响黄豆芽根际微生物群落结构,尤其是与氮循环相关的属。其中,明显增加了不动杆菌属(Acinetobacter)和栖热菌属(Thermus)的相对丰度,减少了假黄色单胞菌属(Pseudoxanthomonas)和氢嗜菌属(Hydrogenophaga)的相对丰度。【结论】土壤中的四环素残留显著影响黄豆芽的生长发育、根际微生物群落结构以及维生素C等重要营养品质指标。     

The Wageningen Rhizolab — a facility to study soil-root-shoot-atmosphere interactions in crops

Roots in the Wageningen Rhizolab are observed using two methods: (i) non-destructively, using horizontal, glass minirhizotrons at intervals of 14 days between observations; (ii) with destructive sampling using augers on three dates in the season. This paper reports changes with depth and time in root numbers per unit interface area of the minirhizotron tube (number of intersections) of four crop species (wheat, Brussels sprouts, leek and potato). The number of root intersections of Brussels sprouts, wheat and potato declined with depth at any time, whereas leek showed a different pattern because maximum root growth was observed at a depth of 10–20 cm. Root density generally decreased in the following order: Brussels sprouts, wheat, potato and leek. Plots of root length densities, L_rv(cm. cm^-3), obtained by auger sampling, versus the number of intersections showed considerable variation in slope with species, time in the season and year, implying that a single, universal equation to convert minirhizotron observations into volumetric root densities does not exist. Causes of variation in the slopes are discussed. It is concluded that limited auger sampling combined with minirhizotron observations yield adequate quantitative estimates of relevant root properties.     

Effect of silver nitrate and 2,4-D on anther culture of Brussels sprouts (Brassica oleracea var. gemmifera)

The response to anther culture, of six genotypes of Brussels sprouts was tested on six media which included two levels of 2,4-D and the presence or absence of silver nitrate. The presence of silver was usually beneficial, and with some genotypes had a very large effect. Increasing 2,4-D could be beneficial in the absence of silver nitrate, but was sometimes detrimental in the presence of silver. Replacing agar with highly purified agarose was not particularly beneficial. Genotype, medium and genotype × medium interactions were all significant factors, with genotype being the most important.