Localization and symbiotic function of a region on the Rhizobium leguminosarum Sym plasmid pRL1JI responsible for a secreted, flavonoid-inducible 50-kilodalton protein.

A previously described (R. A. de Maagd, C. A. Wijffelman, E. Pees, and B. J. J. Lugtenberg, J. Bacteriol. 170:4424-4427, 1988) Sym plasmid-dependent, naringenin-inducible 50-kilodalton protein of Rhizobium leguminosarum biovar viciae is further characterized in this paper. The protein was overproduced by constructing a strain containing multiple copies of the R. meliloti nodD gene, which facilitated its purification. An antiserum was used to screen Tn5 insertion mutants located in the pRL1JI region found to be responsible for the production of the 50-kilodalton protein. These inserts define a new nod locus left of the nod genes identified previously. Mutations in this region affect the nodulation ability in a way which is dependent on the bacterial background as well as on the host plant. The mutants nodulate normally in a strain RBL1532 (R. leguminosarum biovar viciae strain 248, cured of its Sym plasmid) background on all three tested host plant species. In contrast, in a strain RBL5045 (R. leguminosarum biovar trifolii strain RCR5, cured of its Sym plasmid) background, nodulation on Vicia sativa is severely impaired, whereas nodulation on Vicia hirsuta and Trifolium subterraneum is apparently unaltered.     

不同种植模式对作物根系生长、产量及根际土壤微生物数量的影响

采用多年大田试验研究了小麦-大豆(A1)、小麦-甘薯(A2)、玉米(A3)、小麦/玉米/大豆(A4)和小麦/玉米/甘薯(A5)5种种植模式的根际环境变化特征和根系生长特性.结果表明:与A1、A2、A3和A5相比,A4提高了小麦、玉米、大豆在开花期和成熟期的生物量、根系活力和根干质量,提高了各作物根际土壤细菌、真菌和放线菌数量.各种植模式之间,植株生物量和根际微生物数量的变化规律为套作＞单作、大豆茬口＞甘薯茬口、边行＞中行.小麦/玉米/大豆(A4)套作模式通过改善3种作物的根际环境,促进了作物地下部根系生长和地上部生物量的增加,从而实现作物增产.     

Effect of crop rotation and soil cover on alteration of the soil microflora generated by the culture of transgenic plants producing opines

The culture of transgenic Lotus corniculatus plants producing opines, which are bacterial growth substrates, leads to the selection of rhizospheric bacteria able to utilize these substrates. We have investigated the fate of the opine-utilizing community over time under different experimental conditions following elimination of selective pressure exerted by the transgenic plants. These plants were removed from the soil, which was either left unplanted or replanted with wild-type L. corniculatus or wheat plants. The density of opine-utilizing bacteria in the fallow soils remained essentially unchanged throughout the experiment, regardless of the soil of origin (soil planted with wild-type or transgenic plants). When wild-type Lotus plants were used to replace their transgenic counterparts, only the bacterial populations able to utilize the opines were affected. Long-term changes affecting the opine-utilizing bacterial community on Lotus roots was dependent upon the opine studied. The concentration of nopaline utilizers decreased, upon replacement of the transgenic plants, to a level similar to that of normal plants, while the concentration of mannopine utilizers decreased to levels intermediate between transgenic and normal plants. These data indicate that: (i) the opine-utilizing bacterial populations can be controlled in the rhizosphere via plant-exudate engineering; (ii) the interaction between the engineered plants and their root-associated micro-organisms is transgene specific; and (iii) alterations induced by the cultivation of transgenic plants may sometimes be persistent. Furthermore, opine-utilizing bacterial populations can be controlled by crop rotation. Therefore, favouring the growth of a rhizobacterium of agronomic interest via an opine-based strategy appears feasible.     

Indigenous organophosphate-degrading (opd) plasmid pCMS1 of Brevundimonasdiminuta is self-transmissible and plays a key role in horizontal mobility of the opd gene

A fosmid library of the 66kb indigenous organophosphate-degrading (opd) plasmid pCMS1 of Brevundimonas diminuta was tagged with mini-transposon EZTn5 , to determine its sequence using transposon-specific primers. The sequence revealed the presence of a number of tra genes suggesting their role in conjugal transfer of pCMS1. Consistent with the presence of the tra genes, the B. diminuta plasmid, pCMS1::tet, generated by replacing the opd gene with opd::tet, served as a donor for transferring pCMS1::tet into recipient strain Pseudomonas putida. The self-transmissibility of the opd-containing plasmid pCMS1 and the existence of identical opd genes on otherwise dissimilar plasmids suggests a probable role of indigenous opd plasmids like pCMS1 in transferring the opd gene among soil bacteria.     

甘草、麻黄根际土壤微生物的生态分布特性

对野生中麻黄(Ephedra intermedia)、膜果麻黄(Ephedra przewalskii)、乌拉尔甘草(Glycyrrhiza uralensis)和胀果甘草(Glycyrrhiza inflata)根际土壤微生物的种类、数量、分布规律及其与土壤肥力关系进行了研究,结果表明,麻黄和甘草根际土壤微生物均以细菌为主,其次是放线菌,真菌最少。甘草根际土壤微生物数量多于麻黄;乌拉尔甘草根际土壤微生物数量多于胀果甘草;中麻黄根际土壤微生物的数量多于膜果麻黄;通过测定土壤微生物数量可间接的判断土壤的肥力。麻黄根际分离的细菌可提高麻黄种子的发芽率。     

胞外多糖产生菌的筛选鉴定及其促生改土作用

【背景】一些微生物具有较强的产胞外多糖潜力,在改良盐碱土壤、促进作物生长方面潜力巨大。【目的】筛选耐盐碱且产胞外多糖的微生物,为开发具有盐碱土壤改良效果的菌剂提供菌种资源。【方法】从滨海盐碱植物根际土中筛选可在盐碱土壤中增殖、产胞外多糖、解有机磷和钾等能力的微生物菌株,并通过形态、生理生化、基于16S rRNA基因序列和gyrB基因的分子鉴定确定菌株类别,分析该菌株的生长、产胞外多糖特性受盐碱胁迫的影响,考察该菌对盐碱土壤不同粒径团聚体比例的影响,并结合盐碱土壤番茄种植试验考察对植物生长指标和土壤指标的影响。【结果】从727株滨海盐碱土壤菌株中筛选出一株产胞外多糖、具有较强盐碱土壤增殖能力且能解有机磷和钾的芽孢杆菌GBW HF-98,确定该菌为枯草芽孢杆菌沙漠亚种(Bacillus subtilis subsp. inaquosorum)。该菌可耐受pH值达10.0和NaCl浓度达110 g/L,在改善轻和中盐度土壤中不同粒径团聚体比例的效果较为显著。该菌的高剂量浓度T2组,在中度盐碱土壤的番茄种植试验中,与对照相比显著增加了壮苗指数、根干重、全株干重、茎粗和株高等指标,增幅分别为33.8%、59.3%、37.2%、12.3%和15.6% (P<0.05);显著降低pH、全盐含量和土壤容重,降幅分别为8.9%、27.9%和17.9%;显著提升土壤速效磷和速效钾指标,增幅分别为36.0%和17.4% (P<0.05)。【结论】GBW HF-98菌株具有较强的胞外多糖产生能力,在中度盐碱土壤中促进番茄生长和改良土壤的效果显著,可用于盐碱土壤改良菌剂的研制。     

根瘤菌对土壤铜、锌和镉形态分配的影响

以湖南郴州红壤和河北巩义褐土为供试土壤。制备Cu、Zn、Cd污染土壤。接种大豆根瘤菌(Rhi-zobium fredii)HN01,用连续提取法浸提土壤中不同形态的重金属．结果表明。褐土接种根瘤菌后固相结合态Zn总量降低10％。专性吸附态、氧化锰结合态和有机结合态Zn减少达9％～26％．红壤中结合态Zn的总量变化不显著,但专性吸附态和氧化锰结合态Zn含量显著减少。交换态Zn含量显著增加．褐土中接种根瘤菌抑制了Cu向土壤溶液的释放,固相结合态Cu总量增加18％,可交换态、专性吸附态、氧化锰结合态和有机结合态的Cu增加20％～54％．接种根瘤菌对土壤中Cd的溶解没有明显的抑制或促进作用,但改变了红壤中各形态Cd的含量高低顺序．Cd污染红壤中可交换态和有机结合态Cd含量分别增加22％和11％,专性吸附态和氧化锰结合态Cd分别减少14％和29％．根瘤菌对不同类型重金属及不同土壤中重金属形态影响的差异主要与土壤pH降低有关．     

The influence of crop management on the water balance of lupin and wheat crops on a layered soil in a Mediterranean climate

The influence of time of sowing and sowing density on evapotranspiration and drainage loss beneath wheat (Triticum aestivum cv. Spear) and lupin (Lupinus angustifolius cv. Gungurru) crops grown on a layered soil was investigated for three seasons in a Mediterranean climate in Western Australia. The aim of the study was to investigate whether managing crops to maximise their canopy growth would increase their water use and minimise groundwater recharge contributing to dryland salinity. A soil water balance approach was used to estimate evapotranspiration, with changes in soil water content measured with a neutron water meter. The study was carried out on a layered soil typical of agricultural soils in the region with variable depth to clay (0.22–0.38 m) and a marked contrast in hydraulic properties between the topsoil and subsoil. As a result of the low permeability subsoil, a perched water table occurred in the sandy topsoil in each of the three seasons under study during winter when rainfall was high and potential evaporation low. Perched water tables persisted for 2–3 months, with hydraulic gradients consistently downward causing drainage losses to occur. Although crop management had a large influence on shoot and root development, evapotranspiration from the different treatments was generally similar. Drainage losses were not influenced by either crop type, time of sowing or sowing density, because potential evaporation and hence evapotranspiration was low during the period when drainage losses occurred. The total drainage loss measured in each season was different, with losses ranging from 20.1 to 22.2 mm in 1990, from 40.4 to 46.7 mm in 1991 and from 49.4 to 66.6 mm in 1992. The increase in drainage loss from 1990 to 1992 was a result of progressively more seasonal rainfall in 1990, 1991 and 1992. It was concluded that there was little scope to increase water use and decrease deep drainage through crop management for sites with climatic conditions where winter rainfall exceeds potential evaporation. This revised version was published online in June 2006 with corrections to the Cover Date.     

阿拉善荒漠灌木根际中、微量元素含量特征

探讨了阿拉善干旱荒漠区霸王、白刺、红砂、沙冬青、沙木蓼、梭梭和驼绒藜7种旱生灌木根际与非根际土壤Ca、Mg、Fe、Mn、Zn、Cu的含量特征.结果表明:(1)除梭梭根际pH值高于非根际之外,其余6种灌木根际土壤均表现出不同程度的酸化作用.(2)7种灌木根际全钙和交换性钙的含量均低于非根际.除沙木蓼和驼绒藜外,其余5种灌木根际全镁含量均高于非根际,白刺的富集率最高,为43.04%;除沙木蓼外,其余灌木根际交换性镁的含量均有所富集,梭梭的富集率最高,为26.52%.(3)7种灌木根际全铁、全锰、全锌含量总体上小于非根际,但是根际有效铁、有效锰、有效锌含量均大于非根际,表现出明显的富集效应,沙木蓼根际有效铁、有效锰、有效锌的富集率最高,分别为:29.76%、20.92%、86.99%.(4)沙木蓼根际全铜和有效铜含量略高于非根际.梭梭根际全铜含量低于非根际,但梭梭根际有效铜含量却有富集的趋势.其余五种灌木根际全铜和有效铜含量均低于非根际.(5)根际及非根际土壤各养分性状之间,存在复杂的相关性.     

不同植物对黄顶菊根际土壤微生物和土壤养分的影响

[目的] 不同植物对外来入侵植物的抵御能力不同,研究不同植物对入侵植物根际土壤生态的影响可为筛选入侵植物的竞争替代植物提供科学依据。[方法] 利用同质园试验,以入侵植物黄顶菊为研究对象,设置黄顶菊单种、黄顶菊与不同植物（地肤、苘麻、苏丹草、反枝苋）混种处理,采用磷脂脂肪酸分析方法来研究不同植物对黄顶菊根际土壤微生物群落结构的影响,并结合土壤养分的变化探究不同植物对黄顶菊根际土壤生态的影响。[结果] 与黄顶菊单种相比,地肤和苘麻降低了黄顶菊根际微生物的总含量,改变了黄顶菊根际微生物群落结构。地肤、苘麻能竞争性抑制黄顶菊对铵态氮的吸收,从而抑制黄顶菊的生长。[结论] 不同植物的抵御能力与其土壤生态有关,替代植物通过改变黄顶菊根际土壤微生物,抑制黄顶菊对氮的吸收,从而抑制黄顶菊的生长,实现对黄顶菊的替代控制。     

库布齐沙地两种植被恢复类型根际土壤微生物和土壤化学性质比较研究

油蒿(Artemisia ordosica)与中间锦鸡儿(Caragana intermedia)是库布齐沙地分布广泛的优良固沙植被类型,在植被恢复过程中受到关注。以库布齐沙地自然恢复的油蒿群落与人工种植的中间锦鸡儿群落为研究对象,以流动沙地为对照,采用野外调查、室内生化实验与统计分析相结合的方法,分析两种植被恢复类型根际与非根际土壤微生物、土壤化学性质的差异,研究土壤微生物与土壤化学性质间的相关关系,并运用综合指数法评价两种植被恢复类型对土壤生态系统的恢复效果,为库布齐沙地植被恢复与重建提供科学依据。主要结论如下:(1)与流沙对照相比,两种植被恢复类型根际、非根际土壤微生物数量、微生物生物量碳、氮含量均有不同程度的提高,其中,自然恢复的油蒿群落根际土壤微生物总数、细菌数量、微生物量碳和氮含量均显著高于中间锦鸡儿根际,真菌和放线菌数量分布表现为中间锦鸡儿油蒿;(2)两种植被恢复类型根际、非根际土壤有机质、全氮、全磷、速效氮、速效钾含量均比流动沙地有不同程度地提高,其中,油蒿根际、非根际土壤有机质、全氮、速效氮含量显著高于中间锦鸡儿;(3)影响油蒿和中间锦鸡儿群落土壤微生物数量、生物量碳和氮的土壤因子是有机质、p H值、全氮、速效氮、速效钾、速效磷,其中,对两种植被恢复类型土壤微生物数量和生物量有正向促进作用的主要因子是土壤有机质、速效钾和全氮含量;(4)运用综合指数法计算出基于14个土壤指标的土壤质量综合指数(SQI),SQI值排序为:油蒿根际中间锦鸡儿根际油蒿非根际中间锦鸡儿非根际流沙对照。自然恢复的油蒿群落对土壤质量的改良效果显著优于人工种植的中间锦鸡儿群落,是库布齐沙地生态恢复的适合途径之一。     

亚热带人工林乔灌草根际土壤氮矿化特征

为了探讨人工林内优势乔木和林下灌草根际土壤氮矿化特征, 明确乔灌草根际土壤氮转化差异, 该研究以江西泰和千烟洲站区典型人工杉木(Cunninghamia lanceolata)、马尾松(Pinus massoniana)和湿地松(Pinus elliottii)林为对象, 在植被生长季初期(4月)和旺盛期(7月)分析3种人工林内乔木、优势灌木(檵木(Loropetalum chinense)、杨桐(Adinandra millettii)、格药柃(Eurya muricata))和草本(狗脊蕨(Woodwardia japonica)、暗鳞鳞毛蕨(Dryopteris atrata))根际土壤的净氮矿化速率、土壤化学性质及土壤微生物特征。结果发现: 1)物种、林型和取样季节显著影响了根际土壤净氮矿化速率(N_min)、净铵化速率(N_amm)和净硝化速率(N_nit)。马尾松和湿地松林内林下灌草根际土壤净氮矿化的季节敏感性高于乔木: 4月乔木根际土壤N_min和N_amm显著高于大多数林下灌草, 而7月林下灌草根际土壤N_min和N_amm显著提高, 与乔木不再具有显著差异, 与主成分综合得分方差分析的结果一致。一般情况下, 杉木林N_min和N_nit显著高于马尾松林和湿地松林。7月净氮矿化显著高于4月。2)土壤铵态氮、硝态氮、全氮及土壤微生物量氮含量是影响根际土壤净氮矿化的主要因素。土壤化学性质对人工林根际土壤净氮矿化变异的贡献率为29.2%, 显著高于土壤微生物的解释率。充分考虑不同季节林下植被根际土壤的净氮矿化及其关键影响因素可为准确评估人工林生态系统养分循环状况提供重要支撑。     

Effect of genetically modified Pseudomonas fluorescens introduced into soil contaminated with copper (II) on microbial community diversity in the soil and rhizosphere

When genetically altered strains of Pseudomonas fluorescens were introduced into soil contaminated with copper in a laboratory study, they did not affect the phenotypic diversity (eco-physiological index) of indigenous microflora in the rhizosphere and bulk soil. Soil contamination with copper also did not cause shifts in the distribution of bacterial classes within the total community of heterotrophic or Gram-negative bacteria.     

The dynamics of soil redistribution and the implications for soil organic carbon accounting in agricultural south‐eastern Australia

Anthropogenically induced change in soil redistribution plays an important role in the soil organic carbon (SOC) budget. Uncertainty of its impact is large because of the dearth of recent soil redistribution estimates concomitant with changing land use and management practices. An Australian national survey used the artificial radionuclide caesium‐137 (¹³⁷Cs) to estimate net (1950s–1990) soil redistribution. South‐eastern Australia showed a median net soil loss of 9.7 t ha^?1 yr^?1. We resurveyed the region using the same ¹³⁷Cs technique and found a median net (1990–2010) soil gain of 3.9 t ha^?1 yr^?1 with an interquartile range from ?1.6 t ha^?1 yr^?1 to +10.7 t ha^?1 yr^?1. Despite this variation, soil erosion across the region has declined as a likely consequence of the widespread adoption of soil conservation measures over the last ca 30 years. The implication of omitted soil redistribution dynamics in SOC accounting is to increase uncertainty and diminish its accuracy.     

Genetic variation and bidirectional gene flow in the riparian plant Miscanthus lutarioriparius,across its endemic range: implications for adaptive potential

Miscanthus lutarioriparius is an endemic species that grows along the middle and lower reaches of the Yangtze River and is a valuable source of germplasm for the development of second‐generation energy crops. The plant that propagates via seeds, stem nodes, and rhizomes shows high phenotypic variation and strong local adaptation. Here, we examined the magnitude and spatial distribution of genetic variation in M. lutarioriparius across its entire distributional range and tested underlying factors that shaped its genetic variation. Population genetic analyses were conducted on 644 individuals from 25 populations using 16 microsatellite markers. M. lutarioriparius exhibited a high level of genetic variation (H_E = 0.682–0.786; A_r = 4.74–8.06) and a low differentiation (F_ST = 0.063; D_est = 0.153). Of the total genetic variation, 10% was attributed to the differences among populations (df = 24, P < 0.0001), whereas 90% was attributed to the differences among individuals (df = 619, P ≤ 0.0001). Genetic diversity did not differ significantly across longitudes and did not increase in the populations growing downstream of the Yangtze River. However, significant associations were found between genetic differentiation and spatial distance. Six genetic discontinuities were identified, which mostly distributed among downstream populations. We conclude that anthropogenic factors and landscape features both contributed to shaping the pattern of gene flow in M. lutarioriparius, including long‐distance bidirectional dispersal. Our results explain the genetic basis of the high degree of adaptability in M. lutarioriparius and identify potential sources of new germplasm for the domestication of this potential second‐generation energy crop.     

Carbon flow in an upland grassland: effect of liming on the flux of recently photosynthesized carbon to rhizosphere soil

The effect of liming on the flow of recently photosynthesized carbon to rhizosphere soil was studied using ¹³CO₂ pulse labelling, in an upland grassland ecosystem in Scotland. The use of ¹³C enabled detection, in the field, of the effect of a 4‐year liming period of selected soil plots on C allocation from plant biomass to soil, in comparison with unlimed plots. Photosynthetic rates and carbon turnover were higher in plants grown in limed soils than in those from unlimed plots. Higher δ¹³C‰ values were detected in shoots from limed plants than in those from unlimed plants in samples clipped within 15 days of the end of pulse labelling. Analysis of the aboveground plant production corresponding to the 4‐year period of liming indicated that the standing biomass was higher in plots that received lime. Lower δ¹³C‰ values in limed roots compared with unlimed roots were found, whereas no significant difference was detected between soil samples. Extrapolation of our results indicated that more C has been lost through the soil than has been gained via photosynthetic assimilation because of pasture liming in Scotland during the period 1990–1998. However, the uncertainty associated with such extrapolation based on this single study is high and these estimates are provided only to set our findings in the broader context of national soil carbon emissions.     

Relative contributions of soil chemistry, plant physiology and rhizosphere induced changes in speciation on Ni accumulation in plant shoots

The aim of this study is to rank the relative importance of soil properties, root uptake and root-to-shoot redistribution on the transfer of the trace element nickel from soil to the shoots of non hyperaccumulatings plants. Two contrasting soils and seven plant species have been studied using the radioactive isotope, ⁶³Ni. Shoots and roots were analysed separately and the specific activity of each plant has been measured. The isotopic exchange properties of rhizosphere soil where compared with control non rhizosphere soil. Possible changes in Ni speciation in the rhizosphere have been assessed by comparing the isotopic exchange properties of the rhizosphere and control soil and by comparing the specific activities of Ni in each plant. The capacity of soil to immobilise added radiotracer largely determines root uptake, leading to between a 4- and 40-fold difference between soils for a given species. The redistribution of nickel from roots to shoots was fairly constant for plants grown on the rendzina, but varied strongly between species for the acid soil. This variation enhanced the contrast between species of the soil-to-shoot transfer factor. Root action significantly enhanced immobilisation of added nickel in an acid soil due to the modification of speciation of initially non exchangeable soil nickel, but had little effect on a neutral rendzina. Changes in rhizosphere pH were similar on the two soils. In the acid soil, these pH changes were accompanied by changes in Ni speciation but a causative link has not been established. In the neutral soil pH changes may have modified root uptake properties.     

Carbon translocation to the rhizosphere of maize and wheat and influence on the turnover of native soil organic matter at different soil nitrogen levels

Wheat and maize were grown in a growth chamber with the atmospheric CO₂ continuously labelled with ¹⁴C to study the translocation of assimilated carbon to the rhizosphere. Two different N levels in soil were applied. In maize 26–34% of the net assimilated ¹⁴C was translocated below ground, while in wheat higher values (40–58%) were found. However, due to the much higher shoot production in maize the total amount of carbon translocated below ground was similar to that of wheat. At high N relatively more of the C that was translocated to the root, was released into the soil due to increased root respiration and/or root exudation and subsequent microbial utilization and respiration. The evolution rate of unlabelled CO₂ from the native soil organic matter decreased after about 25 days when wheat was grown at high N as compared to low N. This negative effect of high N in soil was not observed with maize.