药用植物连作障碍研究评述和发展透视

连作障碍作为现代农业生产中较普遍的问题,在药用植物栽培生产中表现尤为严重,据统计约70%以块根类入药的药用植物在种植过程中都存在严重的连作障碍问题。连作障碍已经成为制约药用植物品质和发展的关键性因素。本研究从药用植物连作障碍问题研究现状出发,分析了当前药用植物连作障碍形成的三大共性问题,即根系分泌物诱导根际土壤酸化、根际微生物群落结构失衡和植株病毒病严重,具体体现在:根系分泌物诱导根际土壤微生物差异性演化、土传病原菌的化感互作、根际微生物区系的失衡加大土壤酸化、根际病原菌增多和有益菌减少导致的土存真菌病害加重、病毒病伴生和发展。并分析了土壤灭菌法、功能微生物调控、作物多样性栽培和生物质炭改良的根际调控策略在减缓药用植物连作障碍中的潜在作用。作者呼吁从事连作障碍研究的工作者应重视从根际生态学角度出发,以土壤食物网为切入点,应用现代系统生物学和化学生态学技术与方法,全面系统探究根系分泌物介导下植物-土壤-微生物的相互作用过程与机制,并着重关注土壤线虫和土壤病毒在连作障碍发生发展中的生态位关系,以深入阐明连作介导土壤酸化的生态学机制和病原菌响应根系分泌物的协同进化机理,在此基础上,采用多种根际调控相结合的策略减缓连作障碍问题,全面考虑经济、社会和生态效益,做到"生态预防为主、综合治理为要"。     

低产水稻土改良与管理研究策略

我国耕地后备资源极端缺乏,改良低产田是提高粮食产量的重要途径。低产水稻土作为低产田的重要组成部分,相关肥力特征及其改良技术研究比较零散,缺乏系统科学的调控管理策略。本文从低产水稻土类型、新的改良研究方法角度,探索可能的技术突破。基于农业部统计数据,因环境条件不良或土壤自身存在障碍因素,全国约有7.67×106hm2低产水稻土。按其主导成因,低产水稻土可分为冷潜型、粘结型、沉板型、毒质型四类。土壤质量评价是低产水稻土研究的重要方面,其评价方法主要包括土壤质量动力学法、土壤质量综合评分法、多变量指标克立格法、土壤相对质量评价法,现已发展了基于GIS的区域尺度水稻土质量评价方法,以及基于土壤生物学性状的质量评价方法。低产水稻土改良研究更多关注新技术和新方法,稳定性同位素探针技术、傅里叶变换红外光谱法(FTIR)和固相交叉极化魔角自旋13C核磁共振(CPMS13C-NMR)波谱技术的应用,将土壤有机碳的微团聚体分布、腐殖质的转化及其与土壤矿物结合机制深入到微观水平;同时高通量测序、土壤宏基因组学、宏转录组学等方法将相关研究推向分子水平。低产水稻土改良与管理的技术主要涉及到冷潜型、粘结型、沉板型、毒质型四大类低产水稻土的改良技术,基于产量反应和农学效率的推荐施肥方法是水稻土养分管理方法的重要发展方向。1)在低产水稻土质量评价方面,未来要结合不同低产类型的障碍因素开展个性化的土壤质量评价,如白土的质地和耕层厚度,加强引入土壤生物学指标进行土壤质量评价研究。2)在低产水稻土改良方面,要研究稻田障碍层次的形成机理与调控途径;研究其他低产类型如新垦水稻土、盐渍化水稻土、石灰化水稻土和污染水稻土的改良技术;研究长期改良措施对不同粒级团聚体腐殖质结构、酶类、微生物多样性和功能基因的影响。3)在低产水稻土管理方面,着重研究秸秆还田技术、推荐施肥技术、抗逆品种技术、群体控制技术。     

花生连作土壤障碍机制研究进展

花生是我国主要经济作物和油料作物,连作障碍问题严重影响花生的产量与品质,制约着我国花生产业可持续发展。已有研究认为自毒物质积累、病菌增加、土壤微生物群落失衡及土壤理化性质恶化是花生连作障碍的主要因子,但大多停留在单因子水平上,有的认识缺乏直接的证据。本文简要综述了花生连作障碍的危害、机制及调控措施,结合作者近几年来相关研究,主要从花生根系分泌物效应、化感物质存留特征、土壤生物群落演变等方面介绍了花生连作障碍机制研究进展,最后对花生连作障碍的进一步研究及防控技术发展方向提出展望。     

我国土壤资源浅析

扼要论述了我国土壤资源数量、主要土类及其分布，并侧重分析了耕作土壤资源的特点及其肥力水平。经统计相关资源，说明我国耕地约有１／３缺乏有机质，约１／２缺磷，在局部农业区钾有透支。另针对我国耕地面积逐年下滑的态势，指出我国土壤资源前景不容乐观。文中还分析了土壤中影响产量的因子，其中以侵蚀，土层浅薄，渍涝，盐化及潜充化问题最为突出。受各种障碍因子交相作用的低产田约占耕地面积１／３。此外还讨论了我国土壤的     

大棚土壤障碍因子综合改良技术研究初报

田间小区试验对土壤深翻+秸秆覆盖和土壤深翻+秸秆覆盖+土壤改良剂两种改良措施在大棚土壤改良效果进行研究,结果表明:两种改良技术均能明显改善和消除大棚土壤障碍因子,能使土壤>0.25mm水稳性团粒含量显著增加,表层土壤水溶性盐含量明显下降,土壤通透性改善,土壤疏松不板结,显著提高黄瓜、辣椒产量和品质,经济效益显著,以土壤深翻+秸秆覆盖+土壤改良剂处理改良效果最好,为大棚土壤障碍因子改良提供了新途径。     

我国华南地区不同利用条件下土壤演变对障碍因子的影响

华南地区不同土壤利用条件下土壤性质演变和障碍因子的识别,对该地区土壤发生过程和管理利用有重要参考价值。本文根据中国土壤系统分类的检索原则,在收集华南9省土种志典型剖面资料的基础上,确定了系统分类的土壤类型,并基于此,研究了不同利用条件下,土壤性质的演变,分析了土壤障碍因子及其影响程度。总的来看,发育在林地条件下的土壤,粉粒、pH、阳离子交换量(CEC)、盐基饱和度(BS)、速效磷、速效钾都明显低于旱耕地土壤,有机质、全氮则相反。林地土壤随着风化作用增强,从雏形土、淋溶土、富铁土到铁铝土,土壤黏粒含量逐渐增加,而土壤pH、CEC、有效CEC(ECEC)、有机质、全氮、速效磷、速效钾等逐渐降低。对旱耕地而言,各种土壤性质基本具有与林地土壤性质一致的变化趋势,但是增加或减少的程度有所不同。结合主成分中土壤性质的组合特征来分析土壤障碍,结果表明华南地区土壤在不同土壤利用和类型下都存在养分贫瘠化、酸化、黏化、磷和钾供应能力低下的主要障碍因子,但各障碍因子发生的次序不同,随着风化作用加强,土壤黏化成为最主要的障碍因子。因此,在土壤利用和管理过程中应因土制宜,根据土壤类型来确定适当的改良措施。     

基于CNKI数据库的土壤酸化文献计量分析

为探索近年来国内土壤酸化研究的热点与发展趋势,以CNKI数据库为基础,采用统计与聚类等分析方法,借助CiteSpace信息可视化软件及文献计量学知识,统计并绘制有关国内土壤酸化研究文献的机构、关键词、文献被引频次等信息图表,挖掘土壤酸化研究的整体发展趋势、高产机构、高频关键词等信息。研究发现我国土壤酸化研究的主题从森林土壤逐渐转移至农田土壤,酸沉降及土壤化学在土壤酸化研究中一直属于重点关注对象。研究机构主要集中在高校和科研院所,同时高频关键词显示国内土壤酸化研究主要集中在酸沉降、施肥管理、土壤结构、作物生长、酸化成因及改良、连作障碍及土壤污染等方面。该研究有助于全面了解国内土壤酸化研究现状及进展,为农田土壤酸化改良方面的研究及应用提供重要参考。     

基于甘肃省中低产田现状的改良措施及其应用效果

中低产田是指土壤存在一种或几种制约农业生产的障碍因素,农业单产相对低而不稳的耕地。研究和分析甘肃省中低产田的现状及其改良技术措施,有针对性地实施中低产田改良改造,对改善甘肃省的农业生产条件和生态环境,提高土地产出率和经济效益,具有重要而深远的意义。针对甘肃省中低产田面积大、分布广和相对集中的特征,在分析中低产田障碍因素成因和主要类型的基础上,梳理了近年甘肃省主要的中低产田改良集成技术措施及其应用效果,提出了中低产田改良和治理的对策建议。     

影响新能源商品化的因素分析

本文从系统的观点出发,分析了能源的供应、需求、技术、经济分析方法,政策法规以及社会习俗诸因素对新能源商品化进程的影响。分析表明:能源的供应与需求矛盾是新能源商品化发展的主要动力,而其它因素构成了影响新能源进入商品市场的障碍层。目前,在我国能源供需矛盾较突出的情况下,如果对障碍层中的诸要素采取适当的措施来减少新能源的发展阻力,就有可能使某些新能源进入实用阶段。     

基于产量的稻田肥力质量评价及障碍因子区划——以进贤县为例

土壤肥力质量评价及土壤肥力障碍因子分析,对于区域土壤利用和改良、指导农业生产结构布局具有重要意义。以江西省进贤县为研究区,通过水稻遥感解译测产,结合主成分分析进行土壤质量评价;采用综合指数法表征土壤肥力质量水平,分析该区域低肥力质量区域主要障碍因素,并进行障碍因子区划。结果表明,该地区土壤肥力质量评价的最小数据集(MDS)指标包括:有机质、阳离子交换量(CEC)、全钾(TK)、交换性钙(Ex.Ca)、容重、粉黏比;土壤质量综合指数与水稻产量相关系数达到0.73(p0.01),以当地水稻平均产量7.215 t hm~(-2)确定土壤质量综合指数阈值为0.65。分析得出,该地区影响土壤肥力的主要障碍包括有机质含量低和容重较大反映的低熟化度障碍、中量元素缺乏反映的酸化障碍、全钾含量低和高粉黏比反映的结构障碍等。根据障碍因素将研究区域划分为三大障碍区:东南部丘陵区主要障碍因子为酸化和土壤结构障碍;中西部低岗平原主要为土壤酸化障碍;北部滨湖区主要障碍为水稻土熟化程度低。通过对不同区域施行针对性改良措施有益于提高土壤肥力。     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

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     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.     

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl^–, NO₃ ^– and SO₄ ^2– were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a first-flush effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.     

The 5S rRNA gene diversity in the genus <Emphasis Type="Italic">Secale</Emphasis> and determination of its closest haplomes

We analyzed 127 rDNA sequences (5S DNA units) obtained from 23 seed accession samples from more or less 10 taxa in wild and cultivated rye, genus Secale L. The sequences fell into two known groups, here assigned to two unit classes, viz. long R1 and short R1 (designations to reflect on R haplome of rye). The different taxa could not be fully differentiated based on the 5S DNA units. We searched for 5S DNA sequences from known unit classes most closely similar to the long R1 and the short R1. One set with the long R1 unit class contained sequences of the long P1 unit class from Agropyron (P haplome) and from Kengyilia (StYP haplome), long J1 from Thinopyrum (J haplome), whereas the set with the short R1 included the long S1 from Pseudoroegneria (St haplome) and Kengyilia (StYP haplome), the short J1 from Thinopyrum (J haplome) and the short V1 from Dasypyrum (V haplome). Each of the two sets was analyzed separately by maximum likelihood (ML) phylogenetic analysis from which we were able to infer that the 5S DNA units of Secale differentiated in a non-clock fashion and followed the HKY substitution model in the gene tree with the long R1 unit class and the HKY + G in the gene tree with the short R1 unit class. A complementary Bayesian analysis yielded identical tree topologies to the ML ones for each of the two sequence sets. In the tree with the long R1 units the long P1 and long J1 unit classes were closest to the long R1 unit class, whereas in the tree with the short R1 units the long S1 and short J1 unit classes were closest to the short R1 unit class, indicating possibly a close relationship between the St, J and R haplomes.     

Leaf litter selection by detritivore and geophagous earthworms

Summary Litterbag experiments with 10 different kinds of leaf litter showed that detritivore (Lumbricus species) and geophagous (Aporrectodea species) earthworms prefer certain litter types over others, since different numbers of worms were found below the litter after 50–52 days of exposure in a pasture. The detritivores preferred Fraxinus, Tilia, and predecomposed Ulmus and Fagus litter to Fagus litter and paper, while geophages preferred Tilia litter to Alnus and Ulmus litter, so that the two groups of earthworms showed different preferences. The detritivores seemed to be more selective than the geophages. The palatability of the litter was examined in relation to the C: N ratio, the lignin concentration and the initial and final polyphenol concentration. The numbers of detritivores were significantly correlated with the C: N ratio and the final polyphenol concentration, so that selection of litter seems to be related to palatability. The numbers of geophages were not significantly correlated with any of the parameters for palatability. The disappearance of litter after 50–52 days appeared to be due to detritivore activity, since the numbers found below the litter were positively and significantly correlated with the litter disappearance. There was no significant correlation with geophage activity. This indicates that detritivores use litter as food, and therefore influence the composition of the litter layer.     

Nematode succession and microfauna-microorganism interactions during root residue decomposition

The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.     

Cycling of extracellular DNA in the soil environment

Upon entering the soil environment, extracellular DNA is subjected to dynamic biological, physical, and chemical factors that determine its fate. This review concerns the fate of both recombinant and non-recombinant sources of DNA. A schematic of DNA cycling coupled with genetic transformation is presented to understand its behavior in soil. Extracellular DNA may persist through cation bridging onto soil minerals and humic substances, be enzymatically degraded and restricted by DNases of microbial origin, and/or enter the microbial DNA cycle through natural transformation of competent bacteria. Lateral gene transfer may disseminate DNA through the microbial community. An understanding of DNA cycling is fundamental to elucidating the fate of extracellular DNA in the soil environment.