添加高粱根茬根际土对连作黄瓜生长和根际微生物的影响

为了分析添加高粱根茬根际土对连作黄瓜生长和根际微生物群落特征的影响,本研究通过盆栽试验,采用荧光定量PCR和高通量测序技术分析土壤细菌和真菌群落组成的差异.试验共设4个处理:CK(不施肥),T1(单施化肥),T2(优化施肥),T3(优化施肥+高粱根茬根际土).结果 表明:与其他处理相比,T3处理促进了黄瓜生长发育,提高...     

Effects of fertility management strategies on phosphorus bioavailability in four West African soils

Low phosphorus (P) in acid sandy soils of the West African Sudano-Sahelian zone is a major limitation to crop growth. To compare treatment effects on total dry matter (TDM) of crops and plant available P (P-Bray and isotopically exchangeable P), field experiments were carried out for 2 years at four sites where annual rainfall ranged from 560 to 850 mm and topsoil pH varied between 4.2 and 5.6. Main treatments were: (i) crop residue (CR) mulch at 500 and 2000 kg ha^–1, (ii) eight different rates and sources of P and (iii) cereal/legume rotations including millet (Pennisetum glaucum L.), sorghum [Sorghum bicolor (L.) Moench], cowpea (Vigna unguiculata Walp.) and groundnut (Arachis hypogaea L.). For the two Sahelian sites with large CR-induced differences in TDM, mulching did not modify significantly the soils' buffering capacity for phosphate ions but led to large increases in the intensity factor (C_P) and quantity of directly available soil P (E _1min). In the wetter Sudanian zone lacking effects of CR mulching on TDM mirrored a decline of E _1min with CR. Broadcast application of soluble single superphosphate (SSP) at 13 kg P ha^–1 led to large increases in C _P and quantity of E _1min at all sites which translated in respective TDM increases. The high agronomic efficiency of SSP placement (4 kg P ha^–1) across sites could be explained by consistent increases in the quantity factor which confirms the power of the isotopic exchange method in explaining management effects on crop growth across the region.     

不同作物轮作对连作高粱生长及其根际土壤环境的影响

以高粱连作5年为对照(CK),研究了高粱连作3年轮作苜蓿(T₁)和葱(T₂),对下茬高粱生长、根际土壤微生物及土壤酶活性的影响.结果表明:与CK相比,轮作改善了高粱地上部的生长;T₁增产16.5%,效果明显.轮作也促进了高粱根系的生长,T₁和T₂处理的高粱总根长是CK的1.3和1.4倍,根总表面积是CK的1.6和1.5倍,根体积是CK的2.2和1.6倍,根系生物量是CK的2.0和1.3倍,T₁促进了根系在10 cm以下土层中的分布.借助Biolog法对穗花期根际土壤微生物群落功能多样性分析表明,T₁和T₂处理根际土壤微生物活性显著高于CK,且Shannon多样性指数分别是CK的1.2和1.1倍;轮作提高了根际土壤蔗糖酶活性.综上,轮作苜蓿比轮作葱更能改善高粱根际土壤环境,提高土壤微生物活性和酶活性,控制高粱连作障碍,提高高粱产量.     

Fertilization effects on fineroot biomass, rhizosphere microbes and respiratory fluxes in hardwood forest soils

Fertilizer-induced reductions in CO(2) flux from soil ((F)CO(2)) in forests have previously been attributed to decreased carbon allocation to roots, and decreased decomposition as a result of nitrogen suppression of fungal activity. Here, we present evidence that decreased microbial respiration in the rhizosphere may also contribute to (F)CO(2) reductions in fertilized forest soils. Fertilization reduced (F)CO(2) by 16-19% in 65-yr-old plantations of northern red oak (Quercus rubra) and sugar maple (Acer saccharum), and in a natural 85-yr-old yellow birch (Betula allegheniensis) stand. In oak plots, fertilization had no effects on fine root biomass but reduced mycorrhizal colonization by 18% and microbial respiration by 43%. In maple plots, fertilization reduced root biomass, mycorrhizal colonization and microbial respiration by 22, 16 and 46%, respectively. In birch plots, fertilization reduced microbial respiration by 36%, but had variable effects on root biomass and mycorrhizal colonization. In plots of all three species, fertilization effects on microbial respiration were greater in rhizosphere than in bulk soil, possibly as a result of decreased rhizosphere carbon flux from these species in fertile soils. Because rhizosphere processes may influence nutrient availability and carbon storage in forest ecosystems, future research is needed to better quantify rhizo-microbial contributions to (F)CO(2).     

Reproduction and growth in three species of West African fruit bats

This study outlines the reproduction periods of the African fruit bats Epomops buettikoferi, Epomophorus garnbianus , and Micropteropus pusillus at two West African savanna sites: a wet southern Guinea savanna and a drier southern Sudanese savanna. At both sites the two annual birth periods were timed such that both lactation by only one weaning period coincided with the rainy season peaks in fruit availability. On this basis we propose that lactation rather than weaning was the important determinant of the timing of reproduction. There was no evidence of cycling of testes size in males corresponding with the seasonal mating periods. E. buettikoferi and M. pusillus females mated at six months and gave birth at the age of 12 months. Males of the two species reached puberty by 11 months and seven months, respectively. Growth rates did not differ between cohorts growing through the wet and dry season and E. buettikoferi and M. pusillus grew at rates of 276 mg/day and 116 mg/day, respectively.     

Impact of legume versus cereal root residues on biological properties of West African soils

Many microbial turnover processes in acidic sandy subtropical soils are still poorly understood. In a 59-day pot and a 189-day laboratory incubation experiment with two West African continuous cereal soils, the effects of 2 mg g^?1 root residues were investigated on growth of sorghum seedlings, soil microbial biomass and activity indices, using cowpea, groundnut, pearl millet, maize and sorghum. The effects of root residues were compared with mineral P or mineral P + N treatments and with a non-fertilized control treatment. On the Alfisol (Fada, Burkina Faso), shoot dry mass was always significantly higher than on the Ultisol (Koukombo, Togo). Highest shoot dry mass was observed after application of mineral P + N on the Alfisol and after mineral P alone on the Ultisol. The application of legume root residues led to small and non-significant increases in dry mass production compared to the non-amended control, whereas the application of cereal root residues led to a decline, regardless of their origin (millet, maize or sorghum). Contents of microbial biomass C, microbial biomass N and ergosterol were 75 to 100% higher in the Alfisol than in the Ultisol, while ATP was only 36% higher. Organic amendments increased ergosterol concentrations by up to 145% compared to the control and mineral P application. Microbial biomass C and microbial biomass N increased by up to 50% after application of root residues, but ATP only up to 20%. After application of legume root residues, cumulative CO₂ production was similar in both soils with an average of 370?µg CO₂-C g^?1 over 189 days. After application of cereal root residues, cumulative CO₂ production was higher in the Alfisol (530?µg g^?1) than in the Ultisol (445?µg g) over 189 days.     

Fungitoxic effects of extracts from some West African plants

Extracts from five West African plants were evaluated in vitro for fungitoxicity against Ustilago maydis, Ustilaginoidea virens, Curvularia lunata and Rhizopus sp. Steam distillate from leaves of Cymbopogon citratus completely inhibited the growth of all four fungi, and hot water extracts from fresh leaves of Ocimum gratissimum and Chromoleana odorata, and dry fruits of Xylopia aethiopica, reduced radial growth by 10–60%. A hot water extract from dry fruits of Monodera myrstica was ineffective as a fungitoxicant.     

连作对白肋烟根际土壤细菌群落多样性的影响

以种植白肋烟1年、2年和4年的土壤为研究对象,采用末端限制性片段长度多态性(T-RFLP)技术分析根际土壤细菌群落的动态变化.结果表明:白肋烟根际土壤细菌群落香农指数和丰富度指数随着种植年限的增加呈现出先增后减的趋势,连作4年后细菌群落的多样性水平显著降低,细菌群落结构较单一.随着种植年限的增加,根际土壤细菌群落与对照的相似性指数逐渐降低.种植年限为1年、2年的土壤和对照土壤中放线菌门放线菌纲是优势类群,种植年限为4年的土壤中放线菌纲所占的比例下降,而厚壁菌门的芽孢杆菌纲成为优势类群.白肋烟连作使根际鞘氨醇单胞菌属和链霉菌属等益生菌数量减少、蜡状芽孢杆菌等潜在致病菌增加,破坏了烟草根际土壤微生物群落的平衡,使其微生态环境恶化.     

Cereal/legume rotations affect chemical properties and biological activities in two West African soils

A more widespread use of cereal/legume rotations has been suggested as a means to sustainably meet increasing food demands in sub-Saharan West Africa. Enhanced cereal yields following legumes have been attributed to chemical and biological factors such as higher levels of mineral nitrogen (N_min) and arbuscular mycorrhizae (AM) but also to lower amounts of plant parasitic nematodes. This study was conducted under controlled conditions to examine the relative contribution of AM, plant parasitic nematodes and increased nitrogen (N) and phosphorus (P) availability to cereal/legume rotation effects on two West African soils. Sample soils were taken from field experiments at Gaya (Niger) and Fada (Burkina Faso) supporting continuous cereal and cereal/legume rotation systems and analysed for chemical and biological parameters. Average increases in cereal shoot dry matter (DM) of rotation cereals compared with continuous cereals were 490% at Gaya and 550% at Fada. Shoot P concentration of rotation millet was significantly higher than in continuous millet and P uptake in rotation cereals was on average 62.5-fold higher than in continuous cereals. Rotation rhizosphere soils also had higher pH at both sites. For the Fada soil, large increases in Bray1-P and organic P were observed in bulk and rhizosphere soils. Plant parasitic nematodes in roots of continuous cereals were 60–80-fold higher than in those of rotation cereals. In both cropping systems mycorrhizal infection rates were similar at 37 days after sowing (DAS) but at 57 DAS AM infection was 10–15% higher in rotation sorghum than in continuous sorghum. This study provides strong evidence that cereal/legume rotations can enhance P nutrition of cereals through improved soil chemical P availability and microbiologically increased P uptake.     

Long-term rice-rice-rape rotation optimizes 1,2-benzenediol concentration in rhizosphere soil and improves nitrogen-use efficiency and rice growth

Plant and Soil - Allelopathy is an ecological phenomenon consisting of both positive and negative effects between organisms determined by the release of secondary metabolites into the environment....     

轮套作对黄瓜根际土壤细菌种群的影响

以黄瓜为试材,采用PCR-DGGE技术研究了小麦、大豆、毛苕子、三叶草和苜蓿与黄瓜轮作及大蒜、毛葱与黄瓜套作对黄瓜根际土壤细菌种群的影响.结果表明:轮套作对黄瓜根际土壤细菌种群的种类、数量和黄瓜产量具有一定的影响,提高了土壤细菌种群多样性指数、均匀度指数和黄瓜产量.对DGGE条带进行测序的结果表明,它们大多与不可培养的细菌种属具有较高的同源性,大多为鞘氨醇杆菌属（Sphingobacterium）和变形细菌纲（Proteobacteria）, High bacterium G+C只在以毛葱为套作作物的黄瓜根际中出现.不同轮套作中细菌种群多样性随黄瓜生育期的变化而变化,在盛瓜期达最高值.以小麦为轮作作物和以毛葱为套作作物的黄瓜轮套作栽培模式最佳.     

Comparison of non-linear growth models to describe the growth curve in West African Dwarf sheep

The objectives of this study were to compare the goodness of fit of four non-linear growth models, i.e. Brody, Gompertz, Logistic and Von Bertalanffy, in West African Dwarf (WAD) sheep. A total of 5274 monthly weight records from birth up to 180 days of age from 889 lambs, collected during 2001 to 2004 in Betecoucou breeding farm in Benin were used. In the preliminary analysis, the General Linear Model Procedure of the Statistical Analysis Systems Institute was applied to the dataset to identify the significant effects of the sex of lamb (male and female), type of birth (single and twin), season of birth (rainy season and dry season), parity of dam (1, 2 and 3) and year of birth (2001, 2002, 2003 and 2004) on the observed birth weight and monthly weight up to 6 months of age. The models parameters (A, B and k), coefficient of determination (R²), mean square error (MSE) were calculated using language of technical computing package Matlab®, 2006. The mean values of A, B and k were substituted into each model to calculate the corresponding Akaike’s Information Criterion (AIC). Among the four growth functions, the Brody model has been selected for its accuracy of fit according to the higher R², lower MSE and AIC. Finally, the parameters A, B and k were adjusted in Matlab®, 2006 for the sex of lamb, year of birth, season of birth, birth type and the parity of ewe, providing a specific slope of the Brody growth curve. The results of this study suggest that Brody model can be useful for WAD sheep breeding in Betecoucou farm conditions through growth monitoring.     

Plant and rhizosphere processes involved in phytoremediation of metal-contaminated soils

This paper reviews the recent advances in understanding of metal removal from contaminated soils, using either hyperaccumulator plants, or high biomass crop species after soil treatment with chelating compounds. Progress has been made at the physiology and molecular level regarding Zn and Ni uptake and translocation in some hyperaccumulators. It is also known that natural hyperaccumulators do not use rhizosphere acidification to enhance their metal uptake. Recently, it has been found that some natural hyperaccumulators proliferate their roots positively in patches of high metal availability. In contrast, non-accumulators actively avoid these areas, and this is one of the mechanisms by which hyperaccumulators absorb more metals when grown in the same soil. However, there are few studies on the exudation and persistence of natural chelating compounds by these plants. It is thought that rhizosphere microorganisms are not important for the hyperaccumulation of metals from soil. Applications of chelates have been shown to induce large accumulations of metals like Pb, U and Au in the shoots of non-hyperaccumulators, by increasing metal solubility and root to shoot translocation. The efficiency of metal uptake does vary with soil properties, and a full understanding of the relative importance of mass flow and diffusion in the presence and absence of artificial chelates is not available. To successfully manipulate and optimise future phytoextraction technologies, it is argued that a fully combined understanding of soil supply and plant uptake is needed.     

甘肃省中部沿黄灌区轮作和连作马铃薯根际土壤真菌群落的结构性差异评估

甘肃省中部沿黄灌区是西北地区乃至全国重要的加工型马铃薯生产基地,然而因集约化种植带来的连作障碍问题已经严重影响到当地马铃薯种植业的可持续发展。采用大田试验与PCR-DGGE(Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis)技术相结合的方法,并通过真菌的18S r DNA序列分析,评估轮作(未连作)和连作条件下马铃薯根际土壤真菌群落在组成结构上的差异,以期为甘肃省中部沿黄灌区马铃薯连作的土壤障碍机理研究提供新证据。结果表明,同轮作相比,连作显著降低了马铃薯块茎产量和植株生物量,并且随着连作年限的延长,连作障碍也愈加严重。长期连作(6a)也导致马铃薯根冠比显著增加和植株收获指数的显著下降。在根际土壤真菌的种群数量和多样性上,连作和轮作间无显著差异,但在群落组成结构上差异明显。真菌18S r DNA测序分析进一步表明,马铃薯连作较轮作相比增加了Fusarium sp.和Fusarium solani以及Verticillium dahliae的种群或个体数量,而这些真菌是导致马铃薯土传病害的主要致病菌类型。根际土壤真菌群落组成结构的改变特别是与土传病害有关的致病菌滋生可能是导致当地马铃薯连作障碍的重要原因。     

Response characteristics of Scirpus trioueter and its rhizosphere to pyrene contaminated soils at different growth stages

Scirpus triqueter (Triangular club-rush), a typical wetland species, is used to study the response characteristics to pyrene. A pot experiment was conducted to investigate the growth parameters (height, diameter, shoot number, total volume, underground biomass, above-ground biomass and total biomass), and enzymes (catalase and superoxide dismutase) of S. triqueter. The characteristics of soil enzymes (catalase and polyphenol oxidase) and microorganisms (bacteria and fungi) were also assessed after pyrene treatment. Elevated pyrene concentration (80 mgkg(-1)) in the soil reduced the shoot number and biomass significantly, especially at the early growth stage. In root tissue, the enzyme catalase was activated at 80 mgkg(-1) of pyrene. Compared to roots, shoots had higher enzyme activities. Catalase activities in the rhizosphere increased throughout the growth period of S. triqueter. Polyphenol oxidase activities in the rhizosphere were higher than those in the bulk soil and unplanted soil. The populations of bacteria (total bacteria, pyrene-tolerant bacteria, and actinomyces) and fungi decreased under the stress of high pyrene concentration, while that of pyrene-tolerant bacteria increased with the increasing pyrene concentration. The presence of pyrene did not benefit the growth of S. triqueter. S. triqueter and soil enzymes varied within the growth stages. The presence of S. triqueter could improve the activity of soil enzymes and facilitate the propagation of microorganisms which could help eliminate pyrene contamination.     

Aluminum stress on sorghum growth and nutrient relationships

Summary Sorghum plants were grown in the greenhouse in modified Steinberg nutrient solution containing ten Al rates (0 to 297 μM) and harvested 28 days after transplanting. Top and root dry weight were not affected by added Al up to 74 μM; but decreased sharply at concentration of 148 μM and greater. Aluminum concentrations in blade 1 (recently matured blade) and plants remained constant from 0 to 297 μM added Al. Root Al concentration increased as added Al increased. No correlation existed between top dry weight and Al concentration in blade 1 or in plant. Root Al concentration was related to top dry weight and root dry weight to estimate the Al critical toxicity level. The Al critical toxicity levle in the root was 54 mmol kg⁻¹ root dry weight basis for either top or root dry weight. In blade 1 Cu concentration negatively correlated with Al while Fe and P were positively correlated. In roots Ca, Mg, Mn and Fe concentrations were negatively correlated with Al while Zn, Cu, P, and K were positively correlated with Al concentration.