Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands,in northern China

Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

土壤侵蚀过程中的养分富集率研究综述

伴随土壤流失过程的养分流失普遍存在着富集现象并可用富集率来表示。富集率是进行非点源污染评价与预报的重要参数。国内外氮、磷富集率大小和计算方法的研究成果表明：氮富集率变化于0.99～8.17之间,主要集中在1.11～2.99之间,磷富集率变化于0.84～16.12之间,主要集中在1.26～7.17之间;氮磷富集率的估算方法可以分为6种,可分别用土壤侵蚀量、含沙量、土壤质地、土壤比表面积、泥沙输移比和某种组合来计算。文中系统比较和分析了这些方法,对养分富集率的选用和研究有参考意义。     

植物根腐线虫鉴定及抗性机制研究进展

根腐线虫是植物三大病原线虫之一,广泛分布于世界各地,为害多种粮食及经济作物,给农业生产带来巨大损失.根腐线虫的识别与鉴定是防治工作的重要环节,研究植物线虫抗性机制有利于培育抗性品种.为此,回顾了近年来根腐线虫鉴定及植物对根腐线虫抗性方面的研究工作,强调了线虫准确鉴定的重要意义,分析讨论了植物抗线虫的机制.     

高温胁迫对海州常山形态和生理特性的影响

为研究海州常山(Clerodendrum trichotomum)的耐高温胁迫能力,以海州常山2年生根蘖苗为试材,研究了不同胁迫温度和时间对海州常山叶片形态和生理指标的影响.结果表明:35℃对海州常山的影响不大,植株生长正常;40℃时,随着胁迫时间的延长,植株形态和生理指标变化较大,叶片明显变黄,出现焦边和枯斑,说明植株受到了一定的高温伤害;45℃下,植株形态和各项生理指标急剧变化,叶片迅速失绿而不断黄化,枯斑不断增多,后期部分叶片枯死、脱落,植株受到了严重的高温伤害.随着胁迫温度的增加,脯氨酸、可溶性糖的质量分数不断增加,胁迫初期可溶性蛋白的质量分数和SOD活性呈上升趋势,表明海州常山在高温胁迫过程中主要通过增加渗透调节物质含量和提高细胞保护酶活性来抵御高温不良环境;随着胁迫温度的增加和时间的延长,叶绿素质量分数持续下降,相对电导率、MDA质量摩尔浓度呈持续增加趋势,这些现象是海州常山受到高温伤害的生理表现.     

不同退化程度下川滇高山栎群落土壤种子库特征研究

物种组成和种子密度是一个种子库的基本特征。对不同退化程度下川滇高山栎森林群落土壤种子库的物种组成、密度、多样性进行了比较及分析,并探讨了地上植被与土壤种子库间的相似性关系。结果显示:(1)轻度退化下土壤种子库储量密度为(412±64)粒/m2,显著高于中度退化、重度退化、极度退化土壤种子库储量;(2)Shan non-wiener指数、Margalef丰富度指数为:轻度退化、中度退化、重度退化、极度退化:(3)轻度退化和中度退化下土壤种子库物种相似性较高,重度退化和极度退化下相似性较低,表现为随着生境条件的转好,其相似性指数增高。     

张履祥与太湖地区农业知识的传播

张履祥农业知识传播与交流的典型耕读士人,他农业知识的来源以及自己农业知识的外传,进一步说明以他为代表的太湖地区底层士人对农业知识传播的贡献。张履祥和其生活范围内人士通过书信等方式的交流,通过这个过程把农业知识介绍给他人。这里介绍了张履祥获得农业知识的方式,包括书籍、实践、老农、家传等途径不断积累自己的农业知识。其次说明了张履祥通过血缘、地缘、结社交游、门人训导的方式将自己总结的农业知识传播出去。这个过程正是一种典型的农业知识传播方式,身为士人的张履祥是农业知识传播的纽带。     

对农业文化遗产“旅游化生存”的思考

分析了当下农业文化遗产旅游开发热所呈现的弊病,指出单纯依靠旅游开发将破坏农业文化遗产的多元价值体系,消解遗产传承主体的积极性,并将导致旅游资源的恶性竞争,影响农业文化遗产应有的产业功能。针对农业文化遗产旅游化生存所出现的问题,尝试提出了相应的解决办法,希望为农业文化遗产的开发找到新的有效思路,并为其构建了一副全景式的开发蓝图。     

白木香良种‘热科2号’的DNA条形码分子鉴定

奇楠沉香为极具收藏及药用价值的上品沉香,其鉴定目前以化学方法为主,但其种苗从苗期至采香之间则难以用传统分类和化学方法进行鉴定,DNA条形码的发展为这一产业难题的解决提供了新的思路。本研究在明确白木香良种‘热科2号’可产奇楠沉香的基础上,采用11对植物DNA条形码通用引物对‘热科2号’和普通白木香两个沉香品种进行分子鉴定探索,发现改良的CTAB法更适合白木香叶片样本的DNA提取,继而发现ITS、ITS2和源自叶绿体的8个DNA条形码在两个品种均无变异,而ITS1序列的第159个碱基在‘热科2号’中为T,在普通白木香中为A,多样本实验证明该变异位点可以作为‘热科2号’和普通白木香种苗鉴定的分子标记。本研究结果为白木香良种‘热科2号’及其幼苗的鉴定提供分子水平的技术支持,也为白木香良种的溯源提供新的思路。     

Determination of 49 organophosphorus pesticide residues and their metabolites in fish, egg, and milk by dual gas chromatography-dual pulse flame photometric detection with gel permeation chromatography cleanup

A new method for the quantitative determination of 49 kinds of organophosphorus pesticide residues and their metabolites in fish, egg, and milk by dual gas chromatography-dual pulse flame photometric detection was developed. Homogenized samples were extracted with acetone and methylene chloride (1 + 1, v/v), and then the extracts were cleaned up by gel permeation chromatography (GPC). The response of each organophosphorus pesticide showed a good linearity with its concentration; the linearity correlation was not less than 0.99. The detection limits (S/N = 3) of pesticides were in the range of 0.001-0.025 mg kg?1. The recovery experiments were performed by blank sample spiked at low, medium, and high fortification levels. The recoveries for fish, egg, and milk were 50.9-142.2, 53.3-137.2, and 50.3-139.4% with relative standard deviations (RSD, n = 6) of 2.3-24.9, 4.3-26.7, and 2.8-32.2%, respectively. The method was applied to detect organophosphorus pesticides in samples collected from the market, and satisfactory results were obtained. This quantitative method was highly sensitive and exact and could be applied to the accurate determination of organophosphorus contaminants in fish, egg, and milk.     

Capsaicin-mediated tNOX (ENOX2) up-regulation enhances cell proliferation and migration in vitro and in vivo

Cancer chemoprevention is employed to block or reverse the progression of malignancies. To date, several thousands of agents have been found to possess chemopreventative activity, one of which is capsaicin, a component of chili peppers that exhibits antigrowth activity against various cancer cell lines. However, the role of capsaicin in tumorigenesis remains controversial because both cancer prevention and promotion have been proposed. Here, we made the unexpected discovery that treatment with low concentrations of capsaicin up-regulates tNOX (tumor-associated NADH oxidase) expression in HCT116 human colon carcinoma cells in association with enhanced cell proliferation and migration, as evidenced by down-regulation of epithelial markers and up-regulation of mesenchymal markers. Importantly, tNOX-knockdown in HCT116 cells by RNA interference reversed capsaicin-induced cell proliferation and migration in vitro and decreased tumor growth in vivo. Collectively, these findings provide a basis for explaining the tumor-promoting effect of capsaicin and might imply that caution should be taken when using capsaicin as a chemopreventive agent.