下层土壤容重对玉米根际土壤微生物数量及微生物量碳、氮的影响

采用微区池栽模拟试验,研究下层(20～40cm 、40～60cm)土壤容重改变后,玉米根际微生物数量、微生物量C(MBC)和微生物量N(MBN)的动态变化规律.结果表明,玉米根际微生物(细菌、放线菌、真菌)数量、MBC和MBN随土层加深和下层土壤容重增加而降低,且相同层次不同容重的处理间差异达显著水平;不同层次土壤根际微生物数量、MBC和MBN既受本土层容重大小影响,也随相邻土层容重增大其降幅增加,且20～40cm土层容重对土壤微生物数量、MBC和MBN的影响远大于40～60cm土层容重.玉米生育期间,三者受下层土壤容重变化和玉米生长发育的双重影响,且玉米的生长发育过程放大了容重对根际微生物数量、MBC和MBN的影响效果.     

模拟不同雨量下沟垄集雨种植对春玉米生产力的影响

为了探明沟垄集雨种植适宜的降雨量范围,使沟垄集雨系统更加有效,通过大田模拟降雨试验,研究了不同雨量下沟垄集雨种植对农田水温状况及春玉米个体发育、生物量积累、水分利用效率(WUE)和产量的影响.结果表明,在230～440mm雨量下,与平作处理相比,沟垄集雨种植处理后,沟内土壤10cm处温度增加了0.7～1℃,沟内120cm土壤平均储水量增加了5%～12%,玉米的出苗期提前1～2d,生育期普遍提前,株高、功能叶面积和生物量显著增加 (P＜0.05) .玉米籽粒产量及WUE在230mm雨量下分别增加了82.8%和77.4%,340mm雨量下分别增加了43.4%和43.1%,440mm雨量下分别增加了11.2%和9.5%.沟垄集雨种植春玉米适宜的雨量上限可能在全生育期降雨量440mm以下.     

玉米秸秆还田对土壤线虫数量动态与群落结构的影响

通过大田玉米秸秆还田试验研究了其对农田土壤线虫数量动态、属的种类及群落结构等的影响。结果表明:2013—2014连续两年试验期间,蠡玉35玉米秸秆还田(CR)与不还田对照处理(CK)共鉴定到土壤线虫36个属(CR 36个属,CK 30个属);其中,植食性线虫12个属(CR 12属,CK 10属),食细菌线虫15个属(CR 15属,CK 14属),食真菌线虫5个属(CR 5属,CK4属),捕/杂食线虫4个属(CR 4属,CK 2属)。秸秆还田处理与不还田处理相比,植食线虫和食真菌线虫的相对丰度降低,而食细菌线虫和杂/捕食线虫的相对丰度提高,且食细菌线虫的相对丰度显著提高达42.95%。此外,秸秆还田处理土壤线虫总数高于不还田对照处理,但差异不显著;而秸秆还田处理可显著增加食细菌线虫数量,增幅高达16.3%—125.6%。与不还田处理对照相比,秸秆还田处理可显著提高土壤线虫群落多样性指数(H')、属类丰富度(S)和线虫通路指数(NCR),但对群落均匀度(J)、瓦斯乐斯卡指数(WI)和总成熟指数(∑MI)的影响不显著。可见,玉米秸秆还田具有重要的生态学意义,可在一定程度上增加土壤线虫数量和种类多样性,进而使土壤生态系统向稳定健康的方向发展。     

喀斯特石漠化地区不同退耕年限下桂牧1号杂交象草植物-土壤-微生物生态化学计量特征

耕地农作物种植与退耕地种草养畜是喀斯特主要的农业生产模式。以喀斯特地区农耕玉米地为对照,研究退耕还草1、5、7a(恢复初期、旺盛期、衰退期)3种年限下桂牧1号杂交象草地植物-土壤-微生物C、N、P生态化学计量特征及内在关联。结果表明:1)牧草地植物地上部分N、P含量均为5a牧草1a牧草7a牧草,C含量则刚好相反;3种退耕年限牧草地植物地上部分C∶N、C∶P、N∶P分别为26.50—33.91、631.70—2254.33、23.89—67.21,且均表现为7a牧草1a牧草5a牧草。2)土壤表层(0—10 cm)C、N、P含量均以玉米地最低,3种退耕年限牧草地中则均为5a牧草地最低;土壤C∶N、C∶P、N∶P在玉米及退耕牧草地之间均无显著差异(P0.05),平均值分别为9.20,27.88,3.38。3)玉米及牧草地土壤MB_C、MB_N、MB_P含量存在显著差异(P0.05);玉米地MB_C/SOC、MB_N/TN、MB_P/TP均高于牧草地,3种退耕年限牧草地中,则均为5a牧草地最高。4)MB_C、MB_P与土壤C、P含量分别呈显著线性正相关(P0.05);植物C、C∶N与土壤C、N含量均呈极显著线性负相关(P0.01)。分析表明,退耕还草地中植物与土壤系统C-N-P化学计量比表现出不一致的时间变化特征,且牧草地植物受P限制严重,尤以恢复旺盛期为甚。     

土壤水分变化对玉米苗期吸收积累镉的影响

采用土壤盆栽试验研究不同土壤水分含量对玉米苗期吸收积累 Cd的影响。试验结果表明 ,玉米生物量及其吸收 Cd量在玉米不同的生长时期差异较大。2 2 d收获时 ,玉米地上部和地下部生物量均随着田间持水量 (35 %～ 85 % )的增加而提高 ;而 16 d收获时 ,玉米生物量在田间持水量为 35 %和 85 %时比在其它水分时低许多。 16 d和 2 2 d收获时 ,玉米地上部 Cd含量在田间持水量 5 5 %时分别达到最大值 ,5 5 .4 1mg/ kg和 39.33mg/ kg;而在田间持水量 85 %时分别达最小值 ,2 7.97mg/ kg和 2 3.5 2 m g/kg。在玉米根系的影响下 ,土壤溶液 Cd含量基本上随着玉米的不断生长而降低。田间持水量为 6 5 %时的土壤溶液 Cd含量比田间持水量为 75 %和 85 %时大。玉米总吸 Cd量与水分蒸腾量之间呈极显著的线性正相关关系     

转Bt基因玉米叶片次生代谢物DIMBOA和酚酸类物质含量的变化

异羟肟酸和酚酸类物质是玉米植株中重要的次生代谢物,可以帮助抵御多种病原菌、害虫、线虫和其它植物的危害。采用HPL C法研究了Bt玉米34B2 4、G30、农大6 1(Nongda6 1)和14 2 6×14 82以及部分相应的非转基因玉米叶片DIMBOA和酚酸类物质含量的变化。试验结果表明,不同玉米品种之间DIMBOA含量的差异很大;各Bt玉米品种叶片的DIMBOA含量普遍低于相对应的非转基因近等基因系。从不同部位的叶片看,玉米幼嫩叶片中的DIMBOA含量普遍较高;不同品种叶片DIMBOA含量的差异主要表现在幼叶之间,而老叶间的差异普遍较小。无论是Bt玉米还是非转基因玉米,随着生长时间的增加,各品种玉米幼苗全株叶片的DIMBOA含量急剧减少;各品种倒1叶的DIMBOA含量也都随着生长期的增加而减少,倒3叶却没有这样的规律。Bt玉米叶片的DIMBOA含量在单一的干旱胁迫或缺氮胁迫下的变化规律与非转基因玉米相似,即单一的干旱胁迫或缺氮胁迫下玉米各部位叶片的DIMBOA含量均显著升高;然而,在干旱和缺氮双重胁迫下,Bt玉米14 2 6×14 82在生长的中后期各部位叶片的DIMBOA含量却低于正常生长条件,明显不同于非转基因玉米的变化规律。与相应的非转基因近等基因系相比,虽然Bt玉米中香草酸和丁香酸的含量没有显著减少,但阿魏酸的含量显著降低。这一结果表     

Effects of artificial and natural diets on success in tip recording and on galeal chemosensillum morphology of European Corn Borer larvae

Abstract. Larvae of Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae) were reared on artificial diet, fresh cut corn, or switched from diet to corn for 5 days prior to tip recording. Electrophysiological responses to a standard mixed chemical stimulus were obtained from the galeal uniporous chemosensilla of the early fifth-stadium larvae. Mouthparts of some larvae were briefly treated with protease, then recorded again. Larvae were then processed for scanning electron microscopy (SEM) of chemosensilla terminal pores. Spike:noise ratios were significantly higher for corn-reared, switched-to-corn, and protease- treated larvae, relative to diet-reared larvae. Morphology of the chemo- sensilla terminal pores, as assessed by SEM, reveals that apparent occlusion of the pore tip is significantly greater for diet-reared larvae relative to the other groups. The data suggest an association between quality of the electrophysiological recordings and physical blockage of the terminal sensillum pore. These data should serve as a caveat for those engaged in chemosensory studies of insect herbivores.     

Description of Males of Heterodera zeae

The male ofHeterodera zeae, the corn cyst nematode, is described and illustrated for the first time. Specimens were obtained from a culture originating from cysts collected in Kent County, Maryland, at the site of the first known infestation of H. zeae in the United States.     

THE STUDY OF THE INFLUENCE OF TEMPERATURE AND INITIAL GLUCOSE CONCENTRATION ON THE FERMENTATION PROCESS IN THE PRESENCE OF Saccharomyces cerevisiae YEAST STRAIN IMMOBILIZED ON STARCH GELS BY REVERSED-FLOW GAS CHROMATOGRAPHY

The technique of reversed-flow gas chromatography (RFGC) was employed for the determination of the alcoholic fermentation phases and of kinetic parameters for free and immobilized cell systems, at different initial glucose concentrations and temperature values. In addition to this, due to its considerable advantages over other techniques, RFGC was used for the characterization of a new biocatalyst, yeast cells immobilized on starch gel, and especially wheat starch gel. Immobilization of wine yeast Saccharomyces cerevisiae AXAZ-1 was accomplished on wheat and corn starch gels in order to prepare new biocatalysts with great interest for the fermentation industry. The RFGC led with great accuracy, resulting from a literature review, to the determination of reaction rate constants and activation energies at each phase of the fermentation processes. A maximum value of rate constants was observed at initial glucose concentration of 205 g/L, where a higher number of yeast cells was observed. The increase of glucose concentrations had a negative influence on the growth of AXAZ-1 cells and rate constants were decreased. The decrease of fermentation temperature caused a substantial reduction in the viability of immobilized cells as well as in rate constant values. Activation energies of corn starch gel presented lower values than those of wheat starch gel. However, the two supports showed higher catalytic efficiency than free cell systems, proving that starch gels may act as a promoter of the catalytic activity of the yeast cells involved in the fermentation process.     

DNA methylation and tissue culture-induced variation in plants

Summary Plant cells growing in an artificial culture environment make numerous genetic mistakes. These alterations are manifested as increased frequencies of single-gene mutations, chromosome breakages, transposable element activations, quantitative trait variations, and modifications of normal DNA methylation patterns. Evidence is presented that indicates a high frequency of DNA hypomethylation as the result of the tissue culture process. Fifteen percent of the methylation changes appear to have been homozygous in the original regenerated plants. A hypothesis is advanced that relates DNA methylation to the variety of genetic alterations found among maize tissue culture regenerants and their progenies. The epigenetic nature of DNA methylation raises questions concerning the stability of tissue culture-induced changes in self-pollinations and crosses. Presented in the Session-in-Depth Exploitation of Plant Cell Culture Variants at the 1992 World Congress on Cell and Tissue Culture, Washington, DC, June 20–25, 1992.