Anuran responses to spatial patterns of agricultural landscapes in Argentina

Context

Amphibians are declining worldwide and land use change to agriculture is recognized as a leading cause. Argentina is undergoing an agriculturalization process with rapid changes in landscape structure.

Objectives

We evaluated anuran response to landscape composition and configuration in two landscapes of east-central Argentina with different degrees of agriculturalization. We identified sensitive species and evaluated landscape influence on communities and individual species at two spatial scales.

Methods

We compared anuran richness, frequency of occurrence, and activity between landscapes using call surveys data from 120 sampling points from 2007 to 2009. We evaluated anuran responses to landscape structure variables estimated within 250 and 500-m radius buffers using canonical correspondence analysis and multimodel inference from a set of candidate models.

Results

Anuran richness was lower in the landscape with greater level of agriculturalization with reduced amount of forest cover and stream length. This pattern was driven by the lower occurrence and calling activity of seven out of the sixteen recorded species. Four species responded positively to the amount of forest cover and stream habitat. Three species responded positively to forest cohesion and negatively to rural housing. Two responded negatively to crop area and diversity of cover classes.

Conclusions

Anurans within agricultural landscapes of east-central Argentina are responding to landscape structure. Responses varied depending on species and study scale. Life-history traits contribute to responses differences. Our study offers a better understanding of landscape effects on anurans and can be used for land management in other areas experiencing a similar agriculturalization process.

     

Prevalence of Toxoplasma gondii in dogs from Colombia, South America and genetic characterization of T. gondii isolates

The prevalence of Toxoplasma gondii in 309 unwanted dogs from Bogotá, Colombia, South America was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT) and found in 52 (16.8%) of 309 dogs with titers of 1:20 in 20, 1:40 in six, 1:80 in 17, 1:160 in three, 1:320 in three, 1:1280 or higher in three. Some organs obtained after necropsy of dogs (hearts, tongues and brains, either separately or pooled) were used in bioassays carried out in mice (37 samples, of which 20 were assayed with separate organs and 17 were assayed with pooled organs), cats (pooled organs from six) and pooled organs of two dogs both in mice and cat. Mice receiving dog tissues were examined for T. gondii infection. Feces of cats that received dog tissues were examined for oocyst shedding. In total, T. gondii was isolated from tissues of 20 dogs (16 by bioassays in mice, 3 by bioassay in cats and 1 by bioassay in mice and cat). All infected mice from 7 of 17 isolates bioassayed in this host died of toxoplasmosis during primary infection. Only 10 of the 20 dogs whose tissues were bioassayed separately induced infections in mice. Interestingly, dog organs varied in their capacity to induce T. gondii infection in mice, hearts and tongues producing more positive results than the brain. The 20 T. gondii isolates obtained from seropositive dogs were PCR-RFLP genotyped using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, a new SAG2 and an apicoplast marker Apico. Ten genotypes were revealed. These genotypes are different from the three predominant Types I, II and III lineages that are widely spread in North America and Europe. A new allele denoted u-3 at PK1 locus was identified in three isolates. This result supports previous findings that T. gondii population is highly diverse in Colombia.     

氮磷钾氯平衡施肥对菜心产量及品质的影响

在大棚无土栽培条件下,采用"416-B"最优混合设计研究N、P2O5、K2O、Cl配比对菜心产量和硝酸盐积累的效应及其最佳配比进行研究.结果表明:N、P2O5、K2O、Cl合理配施能提高菜心产量,降低菜心硝酸盐含量.其中N、P2O5、K2O与产量呈正效应,Cl与产量呈负效应,N与菜心硝酸盐含量呈正效应,P2O5、K2O、Cl与菜心硝酸盐含量呈负效应.综合考虑,确定高产优质菜心的最佳营养配方:N、P2O5、K2O、Cl的编码值(真实值,g/0.9 m2)分别为0.49(18.58),1.49(8.95),1.16(22.11),0.23(33.31),对应的产量707.12 g/0.9 m2,硝酸盐含量612.01 mg/kg,Vc含量170.42 mg/kg.     

晋西北地区土地退化特征及危害研究

土地退化是当前世界重要的环境问题,它严重地制约着社会经济的可持续发展。根据野外调查和前人的研究成果,探讨了晋西北地区土地退化的表现特点,成因和危害,并提出了土地退化的防治对策。     

森林植被垂直截留作用与水土保持

本文分析了林冠层、灌木草本层、枯枝落叶层的截留量及其削减的降雨能量,并以六盘山林区各森林流域为例。评论了垂直截留作用对林地土壤和森林流域水量收入的影响,阐明了森林植被垂直结构中各层次在保持水土中的地位。     

窝铺山区生态农业的建设研究

文章探讨了发展山区农业经济的问题,如何利用自然资源,利用现代科学技术建设生态农业系统工程,发展农业生产、振兴山区经济.按照“多层利用型”、“综合利用型”及“循环利用型”三种生态农业单元进行建设与研究.运用生态经济学原理与系统工程方法,以小流域综合治理、保持水土为基础,以发展林果业、城郊型畜牧业为重点,充分利用光、热、水、土等自然资源和现代科学技术,走种、养、加的路子,实现物质能量的多层次循环利用与转换,提高了农民的科学文化素质,获得了良好的经济效益、生态效益和社会效益.     

杜仲优树苗木水分生理状况的研究

本文利用Ｐ─Ｖ技术,对从湘、黔、川、陕四省选出的１８个杜仲无性系优树进行了水分生理状况测定,结果表明：在充分吸胀时和膨压为零时具有较低渗透势的耐旱品系依次为湘１１号、黔９号、黔１号、略４１号、略２７号、略３３号、黔８号、略１６号、湘１８号、略４９号、略７号、略１４号、灌３号、湘３号、灌２号、黔１１号、略１号、灌１号;依据膨压（ＰＶＡＴ）、细胞弹性模量（ε）和细胞体积比（ＲＣＶ）的相互关系,将１８个杜仲优树分成两大类型：具有较大ＰＶＡＴ、ε值和较小ＲＣＶ值的为一类,具有较小ＰＶＡＴ、ε值和较大ＲＣＶ值的为另一类,显示了它们在抗旱机制中的差异性。     

赤霉素(GA3)及吲哚丁酸(IBA)处理宿根甘蔗促进发株及幼苗生长的研究

<正> 目前国内一些蔗区反映宿根甘蔗发株不齐、不全,缺株断垄多,有效茎数少,产量比新植庶低。生产上促进宿根甘蔗的发株,各地采用了不少措施,均有一定的效果,但仍有一定的局限性,需寻找更简单易行而有效的方法。从报道资料看,乙烯利和吲哚丁酸对促进分株和分蘖有良好的效果。本试验用赤霉素及吲哚丁酸处理宿根蔗头,研究     

小四轮拖拉机播前压地对土壤物理特性及作物生长的影响

采用小四轮拖拉机在冬小麦种床上压地１遍,小麦播种后测定土壤的体积密度,含水率及温度,并与种床未经碾压的处理进行比较,结果表明：压实对２０ｃｍ内耕层土壤的物理特性有一定的影响。尽管这种影响可以通过耦作来消除,但播前压实却会对作物的出苗或生长带来危害。     

水涨龙眼果实内源激素含量变化对生理落果的影响

应用酶联免疫法（ＥＬＩＳＡ）测定了水涨龙眼生理落果期间正常幼果和脱落幼果中内源激素ＡＢＡ、ＩＡＡ、ＧＡｓ及ｉＰＡｓ含量的变化。结果表明,整个生理落果期,幼果中内源激素平均含量ＡＢＡ〉ＩＡＡ〉ＧＡｓ〉ｉＰＡｓ。生理落果期,特别是落果最高峰期,正常幼果中ＡＢＡ含量低,而ＩＡＡ、ＧＡｓ和ｉＰＡｓ含量高,脱落幼果则相反。幼果中ＡＢＡ含量高,ＩＡＡ、ＧＡｓ及ｉＰＡｓ含量低会导致生理果,幼果中生长抑制剂（ＡＢ