干旱胁迫下野生大豆水通道蛋白GsPIP2;7功能研究

水通道蛋白（AQPs）是植物中重要的水分转运蛋白，在植物对抗干旱胁迫中发挥着重要功能。为明确野生大豆水通道蛋白在植株抗旱反应中的分子功能，本研究对野生大豆（Glycine soja）中的水通道蛋白的蛋白结构及其在干旱胁迫下的表达模式进行分析，并对筛选的AQPs基因功能进行验证。研究鉴定了野生大豆中69个AQPs蛋白，其中10个在干旱胁迫的高耐野生大豆材料中表达差异达到显著水平。筛选到GsPIP2;7在干旱胁迫后与对照相比显著上调，克隆GsPIP2;7到过表达载体中并侵染转化拟南芥（Arabidopsis thaliana），通过转基因后代筛选获得了稳定表达的T3代转基因拟南芥。与野生型拟南芥相比，转基因植株在干旱胁迫下根系总长度、叶干重、根干重、根冠比和单株叶面积显著增加，过氧化物酶（POD）、过氧化氢酶（CAT）和超氧化物歧化酶（SOD）活性显著提升，丙二醛（MDA）含量显著降低，表现出较强的耐旱能力。本研究结果说明GsPIP2;7对拟南芥耐旱具有正向调控作用，为明确野生大豆耐旱机制奠定了理论基础。     

基于RNA-seq的谷子萌芽期抗旱相关基因挖掘与分析

为了明确响应干旱胁迫的关键基因,解析谷子抗旱机制,本研究以谷子抗旱品种山西2010和干旱敏感品种K359*M4-1为材料,应用RNA-seq技术对两个品种干旱胁迫前后萌发期种子进行转录组测定。结果表明,在山西2010和K359*M4-1中分别鉴定出2 300个和3 652个差异表达基因(DEG),包括编码类锌诱导的促进因子、类萌发素蛋白、蛋白磷酸化酶、转运蛋白、胚胎发育晚期丰富蛋白(LEA)、转录因子、过氧化物酶等基因。通过对鉴定到的DEG进行GO和KEGG代谢途径富集分析,发现山西2010和K359*M4-1中的DEG分别富集在52个和21个生物学过程。KEGG 富集分析发现,DEG主要富集在淀粉和蔗糖代谢, 植物激素信号转导,光合作用-天线蛋白,苯丙素生物合成,角质、亚氨酸和蜡生物合成,次生代谢物生物合成等途径。本研究结果为挖掘谷子抗旱关键基因、解析谷子抗旱机制奠定了基础。     

大白菜ABCB/PGP基因家族的鉴定与分析

ABCB/PGP蛋白为ABC转运蛋白的一个亚家族,能够参与植物中生长素的极性运输,在植物生长发育过程中具有重要作用。为深入认识大白菜ABCB/PGP基因家族,利用生物信息学方法对大白菜中ABCB/PGP基因家族成员进行了全基因组水平鉴定,并对其基因组信息、蛋白质生理生化特征、基因结构和系统进化等方面进行研究。结果表明,大白菜基因组中共鉴定到31个ABCB/PGP基因,这些基因在大白菜的10条染色体上分布不均,其中第3、4、6、7和9号染色体上分布有较多的家族成员。外显子-内含子基因结构分析表明,大部分ABCB/PGP基因都具有4～13个外显子。亚细胞定位预测分析发现,ABCB/PGP蛋白多数定位在细胞质膜上。进一步的系统进化分析表明,大白菜ABCB/PGP基因被聚类成6个分支,分别为CladeⅠ、CladeⅡ、CladeⅢ、CladeⅣ、CladeⅤ和CladeⅥ。上述研究结果为大白菜ABCB/PGP基因功能的研究奠定了一定的基础。     

毛竹ABCG基因鉴定及其表达模式研究

ATP结合盒转运蛋白G亚家族（ABCG）在植物体内的物质运输过程中发挥着重要作用。为探究毛竹（Phyllostachys edulis）中ABCGs的分子特征、表达模式及转录因子对PeABCG15的调控关系，本研究利用生物信息学方法鉴定毛竹ABCG基因家族成员，对其基因结构、编码蛋白的理化性质和系统进化等进行系统分析，通过实时荧光定量PCR(qRT-PCR)技术对毛竹ABCG基因表达模式进行研究，借助酵母单杂交验证转录因子与ABCG基因的调控关系。结果表明，在毛竹基因组中共鉴定到77个ABCG基因（PeABCG1～PeABCG77），其启动子中含有多种激素和非生物胁迫响应元件，其中脱落酸响应元件ABRE最多，出现在74个基因的启动子中。系统进化分析发现，PeABCGs分为白棕色复合体（WBC）和多效性耐药复合体（PDR）两个亚组，与水稻的亲缘关系较近。qRT-PCR结果显示，在脱落酸（ABA）处理后，7个与ABA运输相关的PeABCGs中有6个呈上调表达趋势，而未检测到PeABCG34表达；在低温处理条件下，7个PeABCGs均受到诱导表达；在干旱处理条件下，有2个PeABCGs的表达...     

北苍术对持续干旱的生理和转录组响应分析

为了探究北苍术响应干旱胁迫的生理和分子机制，本试验采用穴盘育苗法，分析持续自然干旱3～18 d北苍术响应干旱胁迫的生理特征；利用高通量转录组测序技术，分析干旱胁迫下北苍术的分子响应特征。结果表明，持续干旱6 d起，北苍术植株相对含水量极显著低于对照，可溶性糖、脯氨酸和丙二醛含量、抗氧化酶活性均显著或极显著高于对照；复水15 d时，北苍术过氧化氢酶（CAT）活性和植株相对含水量恢复到与对照无显著差异，但其他指标均仍极显著高于对照。主成分分析结果表明，可溶性糖和总蛋白含量、超氧化物歧化酶（SOD）和CAT活性可较好地反应北苍术的抗旱能力，干旱胁迫下北苍术隶属函数综合评价D值为0.765～0.865。转录组分析共获得14 538个差异表达基因（DEGs）,GO功能注释最多的Unigene与细胞组分相关，KEGG分类中注释最多的Unigene是糖代谢；注释到萜类与聚酮类代谢途径的Unigene共71条，其中12条编码倍半萜和三萜类生物合成途径中的7个关键酶。综合分析可知，干旱胁迫影响北苍术相关功能基因表达，进而影响其生理特征。本试验为北苍术的抗旱机理和主要活性成分生物合成途径研究提供了参考。     

利用cDNA-AFLP技术分析东乡野生稻干旱胁迫的差异表达基因

为探索东乡野生稻抗旱性分子调控机制,以东乡野生稻、协青早B和渐渗系后代M749为材料,利用c DNA-AFLP技术,分析了东乡野生稻干旱胁迫相关的差异表达基因。结果表明,使用6对引物组合对材料进行选择性扩增,共分离得到27条差异表达的转录衍生片段(TDFs),对这些TDFs进行测序分析,发现其可能编码多种类型蛋白,包括转座子和逆转座子蛋白、D-甘露糖结合凝集素家族蛋白、驱动蛋白马达结构域蛋白、植物PDR ABC转运相关结构域蛋白、细胞壁联合受体激酶3前体蛋白、乳酸/苹果酸脱氢酶蛋白、氧化还原酶蛋白、萜烯合成酶蛋白、富甘氨酸蛋白以及血红素结合蛋白等,其中一些蛋白与植物应答干旱胁迫密切相关。利用荧光定量PCR技术检测5个差异表达TDFs,其结果与c DNAAFLP表达谱结果一致,说明研究结果稳定可靠,这为进一步探讨东乡野生稻抗旱性分子调控机制和相关基因的克隆提供了理论依据。     

基于高通量测序的青花菜早期发育小孢子转录组分析与基因功能注释

为探明青花菜小孢子胚胎发育的分子生物学机制,本研究利用Illumina Hi Seq TM 2000平台对在32.5℃环境下分别培养17 h和24 h以及25℃环境下分别培养0、1和6 d的小孢子进行转录组分析及基因功能注释。结果表明,共获得174 324条Unigenes,其中有144 194条注释到GO、COG、KEGG、NR、Swissprot和Pfam数据库。GO注释显示,小孢子差异表达基因在细胞部分、细胞和细胞器、结合和催化活性、代谢过程、细胞过程和单一生物过程功能亚类中所占比较最高;功能分类中一般功能预测(R)、复制、重组与修复(L)、转录(K)、信号转导机制(T)和翻译后修饰、蛋白质周转、分子伴侣(O)在COG同源分类所占比例最高;KEGG注释结果表明,热击后小孢子差异基因最显著富集通路为内质网蛋白加工代谢途径、植物病原互作及植物激素信号转导剪接体途径。本试验结果为进一步深入研究青花菜小孢子胚胎发生的生理生化和分子机制奠定了理论基础。     

基于iTRAQ技术的不同耐旱性甘薯苗期根系差异蛋白分析

为从蛋白水平揭示不同甘薯品种的苗期耐旱性差异,明确甘薯耐旱性生理机制,以耐旱性强的济薯21(JS)和耐旱性弱的济紫薯1(JH)为材料,采用PEG-6000模拟田间梯度干旱胁迫过程,采用i TRAQ技术开展甘薯苗期根系全蛋白组差异蛋白分析。结果表明,在4个比较组中,共筛选到567个差异表达蛋白,其中上调表达蛋白302个,覆盖率达20%以上的蛋白占鉴定总蛋白数的58.6%。GO分析发现,JS苗期根系差异蛋白主要集中在胁迫响应、非生物刺激响应等生物过程,而JH苗期根系差异蛋白主要集中在糖基复合物代谢和辅酶代谢等生物过程,干旱均主要影响2个品种的细胞质、细胞溶质等细胞组分,2个品种的差异蛋白分子功能均涉及催化活性、氧化还原酶活性等方面。KEGG分析发现,正常条件下,耐旱性强的较耐旱性弱的甘薯品种苗期根系中的过氧化物酶(POD)和肉桂醇脱氢酶(CAD)表达上调;在干旱条件下,次生代谢合成过程中的苯丙烷合成通路中上调表达的差异蛋白最多,耐旱性强的JS苗期根系中主要是胁迫响应相关蛋白,而耐旱性弱的JH苗期根系中主要是能量代谢相关蛋白。总之,干旱对甘薯苗期根系细胞质中次生物质合成和能量代谢影响较大,耐旱性强的甘薯苗期根系氧化还原酶类蛋白表达上调,不同耐旱性甘薯苗期根系在蛋白组学水平上响应干旱的生理调控途径存在明显差异。本研究为甘薯耐旱性品种生理鉴定和耐旱基因发掘提供了线索。     

盐碱胁迫下野生大豆CBL-CIPK通路表达分析

野生大豆(Glycine soja)是栽培大豆(Glycine max)的近缘野生种,含有栽培大豆中不存在的优异基因。为了明确类钙调磷酸酶B蛋白(CBL)与其互作蛋白激酶(CIPKS)组成的CBL-CIPK通路蛋白在野生大豆抗盐碱胁迫中的功能,本研究在盐碱胁迫下高耐及敏感野生大豆材料转录组分析的基础上,利用在线生物学工具对野生大豆CBL-CIPK通路蛋白结构、亚细胞定位、磷酸化位点及系统发育进行了分析。结果发现,10个野生大豆CBLs蛋白均含有3个EF手结构;7个CBLs蛋白定位于细胞核,另外3个分别定位于细胞质、叶绿体和内膜系统。38个CIPKs蛋白均含有ATP结合结构域、丝氨酸/苏氨酸蛋白激酶活性结构域和NAF结构域;20个CIPKs蛋白定位在细胞质中,9个定位在叶绿体中,6个定位在细胞核中,另有3个分别位于细胞器膜、线粒体和内膜系统。野生大豆与栽培大豆的CBL-CIPK通路基因高度同源,但野生大豆GsCIPK5_like基因与栽培大豆GmCIPK5亲缘关系较远,栽培大豆GmCIPK21基因与野生大豆GsCIPK21亲缘关系较远。在盐碱胁迫处理0和10 h后,GsCBL10基因在高耐材料中的表达量比敏感材料显著上调;在盐碱胁迫处理0 h后,GsCIPK10基因在高耐材料中的表达量也比敏感材料显著上调。本研究为阐明CBL-CIPK通路对野生大豆耐盐碱胁迫中的功能奠定了理论基础。     

番鸭攻击行为的转录组学研究

为从分子遗传学角度探讨番鸭(Cairna moschata)出现攻击行为的原因,本实验应用The Medial Recorder 2.0软件对选取的120只生长状况良好的番鸭进行为期1个月(每天24 h)的行为观察记录,并采用瞬时观察法和连续观察法筛选出表现攻击行为的番鸭(实验组)和未出现攻击行为且表现正常的番鸭(对照组)。对筛选出的对照和实验两组番鸭,本实验采用Illumina HiSeq 2000高通量转录组测序技术对实验和对照两组番鸭(每组3次重复)的下丘脑组织的差异表达基因进行筛选,利用基因本体(Gene Ontology,GO)和京都基因与基因组百科全书(Kyoto Encyclopedia of Genes and Genomes,KEGG)数据库对筛选的差异表基因进行功能注释,并进行差异表达基因聚类分析。结果显示,在出现攻击行为番鸭的下丘脑组织中,被注释到GO数据库中的差异表达基因有626个,其中上调基因137个,下调基因489个,参与调控番鸭攻击行为的差异表达基因有26个,其中上调基因4个,下调基因22个,KEGG数据库注释结果显示,这些差异基因显著富集的信号通路为:吞噬体、溶酶体、沙门氏菌感染、MAPK信号通路、孕激素介导的卵母细胞成熟、mTOR信号通路等6个通路。结果还显示在监管行动的细胞骨架和神经活性配体-受体相互作用通路上差异表达基因富集不显著,但富集程度很大,并在该通路上筛选到了番鸭攻击行为差异表达相关基因。通过GO和KEGG数据库的注释,本实验初步筛选出了33个与番鸭攻击行为相关联的候选基因及其调控机制,并发现ERBB信号通路可能是参与番鸭攻击行为调节的关键通路。该实验结果为从分子遗传学角度探讨番鸭攻击行为的发生机制奠定基础。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.