Localized application of sewage sludge improved plant nitrogen and phosphorus uptake by rhizobox‐grown spring wheat

Sewage sludge (SS) can be used as an alternative fertilizer in agriculture. It is normally broadcasted and plowed into soil, but it is not clear if it has a potential as a placement fertilizer. A rhizobox experiment was conducted to investigate the placement effect of SS and mineral nitrogen (N) fertilizer on shoot and root growth as well as nutrient uptake of spring wheat (Triticum aestivum L.). The treatments included localized SS, mixed SS, localized SS and ammonium, localized ammonium, and a control without addition of SS and ammonium to examine the effect of SS placement and, further, if ammonium co‐localization would enhance the placement effect. The results show that SS fertilization improved soil N and P availability, which significantly increased plant N and P uptake and enhanced shoot growth, while root length was significantly reduced compared to the control. Localized SS increased root proliferation in the placement region, resulting in enhanced uptake of P from the SS patch compared to homogenous application. However, co‐localized application of ammonium with SS significantly depressed plant shoot and root growth. Localized ammonium markedly restricted root proliferation in the placement region and reduced soil pH in both bulk soil and placement region, contributing to decreased nutrient uptake and plant growth.     

RESPONSE OF MAIZE GROWN IN AN ALFISOL OF SRI LANKA TO INOCULANTS OF PLANT GROWTH PROMOTING RHIZOBACTERIA

Field experiments were conducted to assess the ability of rhizobacterial inoculants to enhance growth and yield of maize. Performances of two phosphorus (P)-solubilizing bacteria in combination with a fertilizer mixture containing rock phosphate and triple super phosphate (PFM), and five diazotrophs combining either with 150 kg or 100 kg nitrogen (N) ha^?1 supplied as urea were compared with non-inoculated-fertilized controls. Shoot P and N and soil available P and N contents were assessed and shoot biomass and ear weights were recorded at harvest. Pseudomonas cepacia resulted in significantly higher available P (51 mg P kg^?1 soil), P accumulation (3.6 g kg^?1 dry matter) and 13% increase in shoot biomass over control. Azospirillum sp. and dual inoculant comprising Enterobacter agglomerans + Agrobacterium radiobacter led to significantly higher available N (74–94 mg kg^?1 soil) and 19 to 26% increase in shoot biomass over the control. However, inoculants did not increase the yield significantly.     

Soil‐solution speciation by MINEQL+4.6 model and plant uptake of Cd and Zn by barley (Hordeum vulgare L.) after application of different phosphate fertilizers

A greenhouse experiment was conducted to investigate the immediate effect of application of mono‐ammonium phosphate (MAP), single superphosphate (SSP), and triple superphosphate (TSP) fertilizers containing varying concentrations of Cd on (1) chemical speciation of Cd and Zn in soil solution by chemical‐equilibrium calculations (MINEQL+4.6 model), (2) growth of barley plants, (3) concentrations of Cd, P, and Zn in soil solution and plant tissue, as well as total plant accumulation of Cd, P, and Zn, and (4) monitoring pH and element changes during incubation periods following phosphate application. Results show that, in general, the pH of soil solution increased during the first 40 d of incubation, then declined. Also, at the end of incubation period, pH of soil solution was affected by fertilization source and fertilization rate. The concentration of Cd in soil solution changed with time. Phosphate fertilization (p < 0.05) or fertilizer source (p < 0.05) showed consistent effects. Also, the application of phosphate fertilizers with three rates significantly increased Zn concentrations in soil solution during the first half (0–30 d) of incubation period and then decreased but still more than in the control. In general, application of different sources of phosphate at 100 g kg^–1 did not change the dominant forms of Cd in soil solution during all incubation time intervals. Speciation of Zn in the control after 30 d of incubation had changed, in comparison to 10 d of incubation, and the dominant forms were Zn²⁺, ZnOH⁺, ZnHCO₃, ZnCO₃(aq), and Zn(OH)₂(aq). Adding phosphate fertilizer significantly increased both shoot and root dry weight compared to control, indicating P was a growth‐limiting factor in the control plants. The Zn concentrations in shoot and root were lower in the TSP‐ and SSP‐fertilizers treatment than those in the MAP and fertilizer treatments at all rates of fertilization. Adding phosphate increased the Cd : Zn and P : Zn ratios in the shoot and root tissue, with the effect being greater with increasing fertilization rate. Phosphate fertilization greatly increased the total accumulation of Cd of barley compared with the control plants (p < 0.001), with the effect being greater with increasing fertilization rate. Source and rate of fertilizers, and their interactions had significant effect (p < 0.05) on Cd accumulation in the whole plant.     

Phosphate solubilizing microorganisms isolated from rhizosphere of maize cultivated in an oxisol of the Brazilian Cerrado Biome

Many soil microorganisms are able to transform insoluble forms of phosphorus to an accessible soluble form, contributing to plant nutrition as plant growth-promoting microorganisms (PGPM). The objective of this work was to isolate, screen and evaluate the phosphate solubilization activity of microorganisms in maize rhizosphere soil to manage soil microbial communities and to select potential microbial inoculants. Forty-five of the best isolates from 371 colonies were isolated from rhizosphere soil of maize grown in an oxisol of the Cerrado Biome with P deficiency. These microorganisms were selected based on the solubilization efficiency of inorganic and organic phosphate sources in a modified Pikovskaya's liquid medium culture containing sodium phytate (phytic acid), soybean lecithin, aluminum phosphate (AlPO₄), and tricalcium phosphate (Ca₃(PO₄)₂). The isolates were identified based on nucleotide sequence data from the 16S ribosomal DNA (rDNA) for bacteria and actinobacteria and internal transcribed spacer (ITS) rDNA for fungi. Bacteria produced the greatest solubilization in medium containing tricalcium phosphate. Strains B17 and B5, identified as Bacillus sp. and Burkholderia sp., respectively, were the most effective, mobilizing 67% and 58.5% of the total P (Ca₃(PO₄)₂) after 10 days, and were isolated from the rhizosphere of the P efficient L3 maize genotype, under P stress. The fungal population was the most effective in solubilizing P sources of aluminum, phytate, and lecithin. A greater diversity of P-solubilizing microorganisms was observed in the rhizosphere of the P efficient maize genotypes suggesting that the P efficiency in these cultivars may be related to the potential to enhance microbial interactions of P-solubilizing microorganisms.     

Plant growth-promoting rhizobacteria alter rooting patterns and arbuscular mycorrhizal fungi colonization of field-grown spring wheat

The impact of plant growth-promoting rhizobacteria (PGPR) inoculants on the growth, yield and interactions of spring wheat with arbuscular mycorrhizal fungi (AMF) was assessed in field studies. The pseudomonad inoculants P. cepacia R55, R85, P. aeruginosa R80, P. fluorescens R92 and P. putida R104, which enhance growth and yield of winter wheat, were applied at a rate of ca. 10⁷–10⁸ cfu seed^-1 and plots established on pea stubble or summer fallow at two different sites in Saskatchewan. Plant shoot and root biomass, yield and AMF colonization were determined at four intervals. Plant growth responses were variable and dependent on the inoculant strain, harvest date and growth parameter evaluated. Significant increases or decreases were measured at different intervals but these were usually transient and final seed yield was not significantly affected. Harvest index was consistently increased by all pseudomonad inoculants; responses to strain R55 and R104 were significant. Root biomass to 60 cm depth was not significantly affected by inoculants except strain R104, which significantly reduced root dry weight. However, root distribution, root length and AMF colonization of roots within the soil profile to 60 cm were significantly altered by inoculants. Most of these responses were reductions in the assessed parameter and occurred at depths below 15 cm; however, strains R85 and R92 significantly increased root dry weight in the 0- to 15-cm zone. These results indicate that some PGPR inoculants may adversely affect mutualistic associations between plants and indigenous soil microorganisms, and suggest a possible reason as to why spring wheat growth was not consistently enhanced by these pseudomonad PGPR.     

Exploitation of glucose catabolic gene fusions to investigate in situ expression during Pseudomonas–plant interactions

Successful exploitation of bacterial inoculants in agriculture requires that the inoculant can colonize the crop rhizosphere and then express the gene(s) of interest. This study focuses on two glucose-metabolizing genes that are associated with the inorganic phosphate solubilization phenotype of Pseudomonas fluorescens: gcd, which encodes glucose dehydrogenase, and pqqB, which encodes a cofactor required for Gcd activity. Tn5-lux-gene fusions were created to assess the expression of these genes in situ on roots of two maize hybrids, DK315 and PR37Y15. Expression was compared to in vitro levels in the presence of root exudates and different carbon sources. Although root exudates from both varieties triggered similar levels of expression in in vitro cultures, there was a marked difference in situ, where significantly higher expression levels of both genes were observed on DK315 roots. This correlates with a higher level of rhizosphere colonization by the inoculant on this hybrid (over PR37Y15) and illustrates the importance of monitoring both colonization and expression levels in tandem. In addition to demonstrating expression of these important genes in the rhizosphere, this study also illustrates that variation can exist between cultivars or varieties and demonstrates a methodology to monitor the expression of genes of interest in the rhizosphere of the selected crop variety on which the inoculant is to be applied.     

Effect of microbial‐based inoculants on nutrient concentrations and early root morphology of corn (Zea mays)

Microbial‐based inoculants have been reported to stimulate plant growth and nutrient uptake. However, their effect may vary depending on the growth stage when evaluated or fertilizer applied. Thus, the objective of this study was to test the hypothesis that microbial‐based inoculants known to promote root growth and nutrient uptake will promote plant growth, enhance early root development, and increase nutrient concentrations of corn (Zea mays L.). Plants were evaluated at four different growth stages and in the presence of three different nitrogen (N) fertilizers. The microbial‐based treatments evaluated were: SoilBuilder™ (SB), a filtered metabolite extract of SoilBuilder™ (SBF), a mixture of four strains of plant growth‐promoting Bacillus spp (BM), and a water‐inoculated control. The experiment also included four fertilizer treatments: urea (U), urea‐ammonium nitrate (UAN), calcium‐ammonium nitrate (CAN), and an unfertilized control. Corn plants were evaluated at growth stages V2, V4, V6, and VT. Plant growth parameters for biomass, height, and SPAD readings were enhanced by the three microbial‐based treatments. A greater effect of microbial‐based treatments was observed when plants were evaluated at V6 and VT stages. Parameters of early root development such as total root length (TRL), root surface area (RSA), and length of fine roots were enhanced when microbial‐based treatments were applied. Concentrations of N, P, and K were also increased by microbial‐based treatments compared to the non‐inoculated control. Increases in plant N concentration due to microbial‐based treatments were on average 72% for CAN, 61% for UAN, 72% for urea, and 54% for the unfertilized control. Phosphorus concentration was increased most (138%) when BM was applied with CAN. In the same way, when CAN was present, K concentration was increased by 95% with BM and 65% when SB and SBF were applied. Overall, the results demonstrate that microbial‐based inoculants evaluated in this study can positively impact corn growth and nutrient concentration, especially during the late vegetative stages. Furthermore, the results indicate that the enhancement of nutrient concentrations (N, P, and K) in this case was related to the capacity of microbial‐based treatments to impact root morphology at early stages of corn growth.     

Bacterial inoculants for rice: effects on nutrient uptake and growth promotion

Beneficial soil bacteria are able to colonize plant root systems promoting plant growth and increasing crop yield and nutrient uptake through a variety of mechanisms. These bacteria can be an alternative to chemical fertilizers without productivity loss. The objectives of this study were to test bacterial inoculants for their ability to promote nutrient uptake and/or plant growth of rice plants subjected to different rates of chemical fertilizer, and to determine whether inoculants could be an alternative to nitrogen fertilizers. To test the interaction between putatively beneficial bacteria and rice plants, field experiments were conducted with two isolates: AC32 (Herbaspirillum sp.) and UR51 (Rhizobium sp.), and different nitrogen fertilization conditions (0%, 50%, and 100% of urea). Satisfactory results were obtained in relation to the nutrient uptake by plants inoculated with both isolates, principally when the recommended amount of nitrogen fertilizer was 50% reduced. These bacterial strains were unable to increase plant growth and grain yield when plants were subjected to the high level of fertilization. This study indicated that the tested inoculant formulations can provide essential nutrients to plants, especially when the levels of nitrogen fertilizers are reduced.     

Effects of ectomycorrhizal fungus <Emphasis Type="Italic">Boletus edulis</Emphasis> and mycorrhiza helper <Emphasis Type="Italic">Bacillus cereus</Emphasis> on the growth and nutrient uptake by <Emphasis Type="Italic">Pinus thunbergii</Emphasis>

The present greenhouse study was undertaken to evaluate the effects of co-inoculating the ectomycorrhizal (ECM) fungus Boletus edulis with the mycorrhiza helper bacterium Bacillus cereus HB12 or HB59 on the growth and nutrient uptake of Pinus thunbergii. The inoculation with mycorrhiza helper bacterium significantly (P?≤?0.05) increased the ectomycorrhizal colonization. Treatments with dual inoculum (the mycorrhiza helper bacterium plus mycorrhiza) significantly (P?≤?0.05) increased the P. thunbergii growth. Bacteria–mycorrhizae interactions resulted in a great utilization of phosphate and potassium. The single inoculation resulted in a higher root activity than the control while the co-inoculation led to the highest root activity. The 6-CFDA staining assay showed that B. cereus enhanced fungal activity in ectomycorrhizal symbiosis. The results conclusively suggest that B. cereus isolated from the rhizosphere of P. thunbergii can potentially be used as individual inoculant or co-inoculated with ECM fungi to increase the production in sustainable ecological systems. These results support the potential use of B. cereus (HB12 or HB59) and B. edulis as mixed inoculants stimulating growth of P. thunbergii.     

Growth and nutrient uptake of temperate perennial pastures are influenced by grass species and fertilisation with a microbial consortium inoculant

Background: The low fertility of sandy soils in South‐Western Australia is challenging for the establishment of temperate perennial pastures. Aims: To assess whether microbial consortium inoculant may improve plant growth by increasing nutrient supply, root biomass and nutrient uptake capacity. Methods: Five temperate perennial pasture grasses–cocksfoot (Dactylis glomerata L. cv. Howlong), phalaris (Phalaris aquatica L. cv. Atlas PG), tall fescue (Festuca arundinacea L. cv. Prosper), tall wheatgrass (Thinopyrum ponticum L. cv. Dundas), and veldt grass (Ehrharta calycina Sm. cv. Mission) were tested in a controlled environment on the growth and nutrition with the microbial consortium inoculant and rock mineral fertiliser. Results: Veldt grass produced the highest shoot and root growth, while tall fescue yielded the lowest. Rock mineral fertiliser with or without microbial consortium inoculant significantly increased root and shoot biomass production across the grass species. The benefit of microbial consortium inoculation applied in conjunction with rock mineral fertiliser was significant regarding shoot N content in tall wheatgrass, cocksfoot and tall fescue. Shoot P and K concentrations also increased in the five grass species by microbial consortium inoculation combined with rock mineral fertiliser in comparison with the control treatment. Arbuscular mycorrhizal (AM) colonisation decreased with rock mineral fertilisation with or without microbial consortium inoculant except in cocksfoot. Conclusions: The response to microbial consortium inoculation, either alone or in combination with rock mineral fertiliser, was plant species‐dependent, indicating its potential use in pasture production.     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

复合接种剂对三叶草生长特性和品质的影响

利用从兰州地区红三叶 (Trifolium pratense L.) 和白三叶（Trifolium repens L.）根际分离、 筛选获得的4株植物根际促生细菌（代号:A-Hsg、 B-ls1 3、 C-lhs11、 D-lhs14) 制作微生物接种剂,采用盆栽法测定不同接种剂处理对红三叶草生长特性及品质的影响。结果表明,本研究制作的接种剂符合《农用微生物菌剂》质量标准（GB 20287-2006）。复合接种剂处理AD对红三叶草株高、 根长促进作用显著 (P0.05),分别较对照增加33.62%和46.20%。AB和AD处理红三叶草地上植物量增重显著,较对照增加了101.69%和94.98%。BC和AD处理对地下植物量增加显著,增加了197.63%和151.18%。AC、 AD和BCD处理后红三叶草整株磷含量均高于对照,其中BCD处理较对照差异显著（P0.01）,磷含量较对照增加了15.38%。ABCD处理红三叶草整株的含氮量较对照达到了显著水平（P0.05）,较对照增加了14.77%。ABD、 BCD和ABCD处理均可提高红三叶草地上部分粗蛋白含量,其中处理ABCD粗蛋白含量较对照增加最多,增加了14.62%,达到了显著水平（P0.05）。复合接种剂AD、 AB、 BC、 AC、 ABD、 BCD和ABCD接种后,对红三叶草生长特性和品质的提高表现出良好的促进效果,可作为复合菌肥材料作进一步研究。     

Wirkung hoher Phosphatdüngung auf die Wachstumsrate,den Zinkgehalt und das P/Zn-Verhältnis in Weinreben (Vitis vinifera)

Effect of high phosphate fertilization on growth rate, zinc content and P/Zn ratio in grapevines (Vitis vinifera) In a 2 years' pot experiment with a soil low in available Zn, high doses of phosphate fertilizer induced Zn deficiency in grapevines (var. ?Riesling”? on 5 C root stock). This negative effect of phosphate fertilization could almost be prevented by simultaneous application of Zn to the soil. The negative effect of high phosphate fertilization on the Zn status of the soil was well reflected in both the content of available Zn as well as in the diffusion rate of Zn (⁶⁵Zn) in the soil. In young leaves of grapevines, Zn deficiency can be expected at Zn contents lower than 20 μg/g DM and P/Zn ratios larger than 170. These values, however, cannot be generalized as external factors modify them considerably. This latter holds true for the P/Zn ratio in particular. The most obvious Zn deficiency symptom was restricted elongation of the shoot due to shorter internodes. Typical for severe Zn deficiency were smaller leaves with intervenal chlorosis or even necrosis and the disappearance of the normally deeply lobed shape of the leaf blade. As a result of the growth inhibition of the shoot apex, growth of axillary buds had been enhanced and this led to a bushy shape of the Zn-deficient plants.     

植物根际微生物调控根系构型研究

植物根系构型即根系在其生长介质中的生长与分布,包括根系长度、根系分支和根系生物量等,能够将植物固定在土壤中并有效吸收水分和矿质养分,直接影响植物的生长和发育。根系构型受多种因素的影响,包括土壤水分、养分和根际微生物,传统方式主要依靠化学肥料增加土壤养分进而改善根系生长,但是化学肥料会对环境造成危害,根际微生物作为植物的“第二基因组”,能够改善初生根、侧根和根毛的发育,促进植物的生长和根际养分吸收,近年来基因组学−代谢组学、基因组学−转录组学等多组学关联技术的应用揭示了微生物的促生机制,为微生物菌剂的开发提供了新思路。基于该领域的研究现状,本文阐述了根际微生物（AMF、PGPR、根瘤菌）对根构型的调控机制包括激素调控、固氮、溶磷、释放挥发性有机化合物四个方面,并描述它们通过这四种机制增加植物根系长度、根系分支,促进根毛发育的调控效应,基于上述结论,植物根际微生物可以有效改善根系生长,但实际应用效果还有待研究,量化不同机制的相对贡献率以及提高微生物菌剂在实际应用中的稳定性是后续研究的重点。     

Influences of Potassium Chloride Fertilization on Mycorrhizal Formation in a Tropical Alfisol

This study examines the influence of different amounts of potassium chloride (KCl) fertilization on plant growth, nutrient accumulation and content, nutrient ratios, and root colonization by indigenous arbuscular mycorrhizal (AM) fungi in maize (Zea mays L.). KCl was applied at the rate of 0, 0.25, 0.50, 1.00, 1.50, and 1.75 mg/kg of soil. Effect of KCl on indigenous AM formation and function was evaluated in terms of the extent of root length colonization, plant growth, and nutrient uptake. Increasing concentration of KCl fertilization proportionately limited the total root length colonized by AM fungi as well as the root length with different AM fungal structures. Maize plants raised on soils amended with different concentrations of KCl were significantly taller than those raised on unamended soils. KCl application also significantly increased the total root length and root dry weight. Nevertheless, KCl fertilization did not significantly alter the root/shoot ratios. Higher concentrations of nitrogen (N), phosphorus (P), and potassium (K) were evident in shoot and root tissues of maize (except shoot N) raised on KCl-amended soils. Phosphorus concentrations in shoots and roots significantly influenced mycorrhization and root length colonized by different AM fungal structures, and such an effect was evident for root N. KCl fertilization increased the efficiency of N and P accumulation. No significant change was evident in the K:N ratios of shoots or roots, whereas the K:P ratios were significantly altered in shoots or roots in response to KCl application.     

The acquisition of phosphate by higher plants: Effect of carboxylate release by the roots. A critical review.

Phosphorus is one of the most limiting macronutrients for plant productivity in agriculture worldwide. The main reasons are the limited rock phosphate reserves and the high affinity of phosphate (P) to the soil solid phase, restricting the P availability to the plant roots. Plants can adapt to soils low in available P by changing morphological or/and physiological root features. Morphological changes include the formation of longer root hairs and a higher root : shoot ratio both parameters increasing the root surface which provides the shoot with P. This may be successful if the P availability in soil, i.e., the P concentration of the soil solution is not extremely low (> 1–2 µM P). If the P concentration of the soil solution is lower, the diffusive flux to the root surface will be very low and may not satisfy the P demand of the shoots. Under these conditions plants have developed strategies to increase the rhizosphere soil solution concentration by secreting mobilizing agents. The most effective way of P mobilization is the release of di‐ and tricarboxylic acid anions, especially oxalate and citrate. Citrate can accumulate in the rhizosphere up to concentrations up to 80 µmol g^?1 soil. Cluster root formation is an efficient way of carboxylate accumulation in the cluster root rhizosphere improving P mobilization. Cluster roots strongly improve the acquisition of the mobilized P. Considering a single root, around 80–90% of the mobilized P diffuses away from the root. From the rhizosphere of cluster roots, most of the mobilized P is taken up by the cluster roots. Both, the strong accumulation of carboxylates in and the effective P uptake from the cluster‐root rhizosphere are the basis of the unique ability of P acquisition by cluster root‐forming plants. Plants that do not form cluster roots, e.g., red clover, can also accumulate carboxylates in the rhizosphere. Red clover accumulates high quantities of citrate in the rhizosphere soil. Model calculations show that the release of citrate by red clover roots and its accumulation in the rhizosphere strongly improve P acquisition by this plant species in various soils. Similar results are obtained with alfalfa. In sugar beet, oxalate release can strongly contribute to P acquisition. In summary, P acquisition can be strongly improved by the release of carboxylates and should be taken as a challenge for basic and applied research.     

披碱草根际促生菌筛选及其接种剂的促生作用

【目的】体外促生能力是衡量微生物菌株作用的一个重要指标,测定获取的植物根际促生菌并明确其对披碱草的促生效果,可为其在生产中的应用提供依据。【方法】2014年9月从西藏阿里地区采集披碱草根系及根际土壤,以常规方法分离出其中的溶磷菌、 固氮菌和分泌3-吲哚乙酸(IAA)细菌的10株菌株。测定其溶磷量、 固氮酶活性及分泌生长素能力,并将其制成植物根际接种剂,测定接种剂对披碱草生长的影响及其在根际的定殖能力。【结果】菌株PWXZ10溶磷能力较好,达40.89 mg/L; 菌株003PWXZ6固氮酶活性较强,达421.21 nmol/(mL·h); 菌株NXP17分泌生长素能力较强,达31.33 μg/mL。与对照菌株(Pseudomonas sp. Jm92)相比,菌株003PWXZ6和NXP17制备的接种剂可显著增加披碱草株高、 地上生物量和地下生物量(P0.05),但两者之间差异不显著(P0.05); 接种剂003PWXZ6对披碱草根总长、 根表面积、 根体积、 根直径、 含磷量、 含氮量和粗蛋白含量增加显著(P0.05),分别较对照菌株(Pseudomonas sp. Jm92)增加了330%、 199%、 118%、 187%、 70%、 15%和19%,并且该菌株在根际定殖能力很强。 【结论】植物根际促生菌003PWXZ6和NXP17对披碱草具有良好促生效果,可为开发经济环保的生物肥料提供了菌种资源。     

解磷细菌、磷酸岩和化肥对玉米和小麦轮作及其经济收入的影响

A two-year field study was conducted to test the effects of two phosphate-solubilizing bacteria (PSB), Pantoea cypripedii (PSB-3) and Pseudomonas plecoglossicida (PSB-5), inoculated singly or together with rock phosphate (RP) fertilization on maize and wheat cropping cycle by comparing with chemical P fertilizer (diammonium phosphate, DAP), mainly in the crop yield, soil fertility and economic returns. Inoculation of PSB together with RP fertilization increased the crop growth in terms of shoot height, shoot and root dry biomass, grain yield and total P uptake in both maize and wheat crops compared to the other treatments. Soil fertility in the context of available P, enzyme activities and PSB population in both maize and wheat crops was significantly improved with PSB inoculation together with RP fertilization compared to DAP treatment. The combined use of PSB inoculation and RP fertilization was more economical due to minimal cost and maximum returns. These results suggested that PSB inoculation along with RP fertilization would be an appropriate substitute for chemical phosphate fertilizer application in sustainable agriculture systems.     

Nutrient status of rhizosphere and phosphorus response of radish

Radish (Raphanus sativus L.) exhibits a high efficiency in the utilization of sparingly‐soluble phosphates. A greenhouse experiment was designed to investigate the growth response of radish to different phosphorus (P) sources and the nutrient status of the rhizosphere associated with radish growth and nutrient absorption. Radish plants were grown in pots with the roots confined in rhizobags, in such a manner that the concentration of roots was very high within the rhizobag. The rhizosphere soils and non‐rhizosphere soils were analyzed separately for active silicon (Si), aluminum (Al), iron (Fe), and manganese (Mn) using Tamm's solution and for “available”; P using the Bray P1 extraction reagent. The radish growth response was mostly attributable to phosphate amount and availability, and the lime level used in the experiment. Concentrations of active Fe, Si, Al, and Mn were reduced in the rhizosphere, especially when lime and rock phosphate (Ps) were added. Available soil P was accumulated in the rhizosphere under lime and Ps addition, whereas its concentration was reduced with the zero lime treatment. Phosphorus utilization, characterized by P accumulation in shoots, was in accordance with the concentration pattern for “available”; P in the rhizosphere, but not with the growth response of radish itself. The calcium (Ca) concentration of the shoot followed the same trend as the radish growth. There was an antagonism between potassium (K) and Ca absorption as well as between Ca and magnesium (Mg) absorption. With the addition of P, shoot Mn concentration increased, while shoot Fe and Al concentrations increased with no lime addition but decreased with lime addition. The high P efficiency of radish is discussed from the view of rhizosphere chemistry. The high Mn efficiency of radish may be influenced by the same rhizosphere processes that are involved in its high P efficiency. It was concluded that rhizosphere processes and the status of nutrients determined the nutrient efficiency of radish and thus influenced its growth response and nutrient uptake.