Comparison of the chemical changes in the rhizosphere of the nickel hyperaccumulator Alyssum murale with the non-accumulator Raphanus sativus

Changes in pH and redox potential were studied in the rhizosphere soil of a nickel hyperaccumulator plant (Alyssum murale) and of a crop plant, radish (Raphanus sativus). Differences in rhizosphere pH and reducing activity were found between the lateral and the main roots of both species, but the pH changes in the rhizosphere were similar in both species. Changes in pH were associated with the relative uptakes of cations and anions; whether the concentrations of heavy metals in the growth medium did not have any effect on the rhizosphere pH. The source of nitrogen (ammonium or nitrate) was the major factor determining the pH of the rhizosphere of both species. The redox potential of the rhizosphere was influenced by both the N-source and the concentrations of heavy metals. When heavy metals were not present in the growth medium, and nitrate was the N-source, the reducing capacity of A. murale roots was enhanced. However, the reducing activity of A. murale was always smaller than that of radish. Therefore, the mechanism of metal solubilization by the hyperaccumulator plant does not involve either the reduction of pH in the rhizosphere or the release of reductants from roots. The acidification and reducing activity of the roots of A. murale was always smaller than that of R. sativus.     

Effects of ammonium sulphate application on the rhizosphere,fine-root and needle chemistry in aPicea abies (L.) Karst. stand

Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation pattern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatments started in 1988. Current year needles, one-year-old needles and cylindrical core samples of the LFH-layer and the mineral soil layers were sampled in 1988, 1989 and 1990. Compared to the control plots, pH decreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO₄-S concentration increased significantly. Aluminium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0–10 cm depths, both in 1989 and 1990. Calcium, Mg and K concentrations also increased after treatment with ammonium sulphate. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar trend was found in the needles. Ca concentrations in fine roots were significantly lower in the NS plots in the LFH layer in 1990 and the same pattern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots. It was suggested that NS treatment resulted in displacement of Mg, Ca and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

艾比湖湿地芦苇根际土壤氨氧化古菌的多样性和群落结构

【目的】旨在揭示耐盐植物芦苇根际与非根际土壤AOA群落结构间的差异,为深入研究盐生植物根际土壤微生物与耐盐性之间的关系提供理论基础。【方法】应用高通量测序技术以氨单加氧酶基因(amoA)为分子标记,对新疆艾比湖湿地荒漠生态系统不同季节(春、夏、秋)芦苇根际与非根际土壤氨氧化古菌(AOA)的多样性和群落结构进行研究。【结果】结果表明,不同季节芦苇根际土壤AOA多样性和丰富度存在差异,相比非根际土壤,夏季和秋季芦苇根际土壤AOA多样性较低丰富度较高,春季多样性较高丰富度较低。芦苇根际土壤中AOA的多样性为春季夏季秋季。AOA群落组成分析表明,土壤样品中AOA群落主要集中在泉古菌门(Crenarchaeota)和奇古菌门(Thaumarchaeota),其中泉古菌门为主要优势菌门。RDA分析表明,含水量(SM)、有机质(SOM)、总氮(TN)和pH是影响芦苇根际土壤AOA群落多样性和丰富度的主要环境因子。【结论】不同季节芦苇根际土壤AOA多样性及丰富度存在差异,相比非根际土壤,芦苇根际土壤AOA更丰富。     

Fertilisation practice changes rhizosphere microbial community structure in the agroecosystem

Rhizosphere microbial community is important for the acquisition of soil nutrients and closely related to plant species. Fertilisation practice changed soil quality. With the hypothesis of stronger rhizosphere effect of plant on rhizosphere microbial community than fertilisation management, we designed this research based on a long‐term field experiment (1982–present). This study consists of no fertilisation (NF), mineral fertilisers (NPK), mineral fertilisers plus 7,500 kg/ha of wheat straw addition (WS) and mineral fertilisers plus 30,000 kg/ha of cow manure (CM). After analysing, we found that fertilisation management not only elevated crop yield but also affected crop rhizosphere microbial community structure. The influence of fertilisation practice on wheat rhizosphere microbial structure was stronger than that of wheat. For wheat rhizosphere bacterial community, it was significantly affected by soil water content (SWC), nitrogen (TN), phosphorus (TP), pH, available phosphorus (AVP) and nitrogen (AVN), dissolved organic nitrogen (DON) and carbon (DOC). Besides SWC, pH, AVP, AVN, TN, TP and DOC, the wheat rhizosphere fungi community was also significantly affected by soil organic matter (SOM) and available potassium (AVK). Moreover, compared to rhizosphere bacterial community, the influences of soil physiochemical properties on rhizosphere fungal community was stronger. In conclusion, fertilisation practice was the primary factor structuring rhizosphere microbial community by changing soil nutrients availabilities in the agroecosystem.     

Influence of Celery on the Remediation of PAHs-contaminated Farm Soil

Polycyclic aromatic hydrocarbons (PAHs) contamination has been considered as one of the major environmental concerns for farmland soil all over the world including China. Due to small per capita land area, to find crops or vegetable, which could not only degrade the PAHs contaminants but also would not concentrate PAHs, was particularly important. Celery was selected as the phytoremediator in this experiment, and the soil enzyme activity, PAHs-degrading microorganisms, and the speciation of PAHs in soil were studied. The results showed that celery could significantly enhance the remediation of PAHs compared with the controlled experiment after 90 days (p< 0.01), and the removal efficiency were 31.29%, 30.79%, and 50.21% in the soil, non-rhizosphere soil, and rhizosphere soil, respectively. The soil enzyme activity and PAHs-degrading microorganisms significantly increased in rhizosphere soil compared with non-rhizosphere soil (p< 0.05), and the bioaccessibility of PAHs in soil could have been enhanced in the presence of celery root exudates. Those would help the bioremediation of PAHs by soil microorganisms. Meanwhile, the concentration of PAHs in the edible portion of celery was only 17.13 ± 1.24 μg/kg, and the bioconcentration factors in the aboveground part of celery were only 0.025. This study provides a potential in-site farmland soil phytoremediation technology that could have practical utility.     

苹果根际自毒物质降解菌的筛选鉴定及降解特性研究

【目的】从苹果根际土壤筛选苹果根系自毒物质降解细菌,并探究分离菌株对根皮苷、邻苯二甲酸、对羟基苯甲酸以及焦性没食子酸的降解能力。【方法】分别采用邻苯二甲酸、焦性没食子酸为唯一碳源富集并筛选其降解菌株。通过对分离菌株的生理生化特征测定及16S r RNA基因序列分析,采用MEGA 5构建系统发育树,进行菌株鉴定。采用紫外分光光度法和高效液相色谱法测定分离菌株对4种自毒物质的降解能力。【结果】共分离5株有降解能力的细菌,编号为BL1、BL2、BL3、BJ1和BJ2,经鉴定BL1为钩虫贪铜菌Cupriavidus necator,BL2为生脂固氮螺菌Azospirillum lipoferum,BL3为氧化烃微杆菌Microbacterium hydrocarbonoxydans,BJ1为Paenibacillus phyllosphaerae,BJ2为Ochrobactrum cytisi。BL1、BL2、BL3菌株对邻苯二甲酸、对羟基苯甲酸、根皮苷、焦性没食子酸的降解率均高于50%。其中BL2菌株的降解效果最好,分别达到66%、72%、84%和84%。【结论】首次发现钩虫贪铜菌、生脂固氮螺菌和氧化烃微杆菌对4种自毒物质均具有很好的降解能力,对缓解自毒物质引起的连作障碍具有潜在的应用价值。     

Effect of potassium nutrition of rice on rhizosphere redox status

With four soils differing in K supplying power and with four rice cultivars (Oryza sativa L.) differing in K uptake kinetic parameters, the relationship between K fertilizer application and soil redox status in rhizosphere and; the distribution of ferrous iron and other toxic substances on the root surface and in the rhizosphere; and the effect of K supply on uptake of reduced iron by rice plants have been studied.The results show that K application on K-deficient soils reduced the content of active reducing substances and ferrous iron in the soil, raised the soil redox potential in the rhizosphere, increased the Eh value of rice roots and lowered the content of iron in the rice plants. These effects of K varied with different rice cultivars. When no K fertilizer was applied, active reducing substances and ferrous iron in rhizosphere soils were decreased more by the rice cultivars absorbing K strongly (e.g. Shanyou 64) than by cultivars absorbing K weakly (e.g. Zhongguo 91). Therefore, the diminution of the toxic substances by K application in the weakly K-absorbing cultivars was more significant.The observation of a rhizobox separated by a nylon screen showed that appreciably more iron oxides, compared with the control, were deposited at or adjacent to the root surfaces of the rice plant supplied with K fertilizer, fully demonstrating the relationship between K nutrition and the total oxidizing power of rice plants. According to the distribution of active reducing substances and ferrous iron, the oxidizing range of the rice root extended in K application treatment a few centimeters away from the root plane. K application to rice affected the soil redox status in rhizosphere in many ways. The main effect was an increase of the oxidizing power of the rice root. As a result, the value of soil Eh was increased, the contents of active reducing substances and ferrous iron were lowered, as well as the number of oxygen consuming microorganisms.     

Survival and escape of Agrobacterium tumefaciens in triploid hybrid lines of Chinese white poplar transformed with two insect-resistant genes

Two partly modified insect-resistant genes (BtCryI Ac gene [Bt gene toxin against Lepidopterean insects] and API gene [arrowhead proteinase inhibitor]) were transferred to the triploid hybrid of Chinese white poplar ((Populus tomentosa Carr. × Populus bolleana Louche) × Populus tomentosa Carr.) mediated by A. tumefaciens. The survival of Agrobacterium in transgenic plants was examined during the processes of transplanting and subculturing on the nutrient medium. The results suggested that 80% of the plants, which were obtained by repeated selection on media added with 50 mg/L kanamycin and 300 mg/l carbenicillin, showed positive reactions after examination using molecular methods. The ELISA test indicated that the Bt toxoprotein was expressed in seven of the transgenic sub-clones. Leaves, stems, and roots of all the 28 transgenic plants were cultured on the YEB medium added with 50 mg/L kanamycin, and it was found that Agrobacterium survived in three sub-clones (33, 37, 5) and could have existed for 24 months in the bottle. These three transgenic sub-clones were transplanted and cultivated for one month in the room, and then the target Agrobacterium was found in rhizosphere of the sub-clone 33.     

Effect of organic and conventional farming on soil bacterial diversity of pecan tree (Carya illinoensis K. Kosh) orchard across two phenological stages

We described the bacterial diversity of walnut grove soils under organic and conventional farming. The bacterial communities of rhizospheric and nonrhizospheric soils of pecan tree (Carya illinoensis K. Koch) were compared considering two phenological stages (sprouting and ripening). Sixteen operational taxonomic units (OTUs) were identified significantly more abundant according to the plant development, only one according to the farming condition, and none according to the soil origin. The OTUs specificaly abundant according to plant development included Actinobateria (2) and Betaproteobacteria (1) related OTUs more abundant at the sprouting stage, while at the fruit ripening (FR) stage the more abundant OTUs were related to Actinobacteria (6), Alphaproteobacteria (6), and unclassified Bacteria (1). The Gaiellaceae OTU18 (Actinobacteria) was more abundant under conventional farming. Thus, our study revealed that the plant development stage was the main factor shaping the bacterial community structure, while less influence was noticed for the farming condition. The bacterial communities exhibited specific metabolic capacities, a large range of carbon sources being used at the FR stage. The identified OTUs specifically more abundant represent indicators providing useful information on soil condition, potential tools for the management of soil bacterial communities.     

Effect of Bacillus mesonae H20-5 Treatment on Rhizospheric Bacterial Community of Tomato Plants under Salinity Stress

Plant growth-promoting bacteria improve plant growth under abiotic stress conditions. However, their effects on microbial succession in the rhizosphere are poorly understood. In this study, the inoculants of Bacillus mesonae strain H20-5 were administered to tomato plants grown in soils with different salinity levels (EC of 2, 4, and 6 dS/m). The bacterial communities in the bulk and rhizosphere soils were examined 14 days after H20-5 treatment using Illumina MiSeq sequencing of the bacterial 16S rRNA gene. Although the abundance of H20-5 rapidly decreased in the bulk and rhizosphere soils, a shift in the bacterial community was observed following H20-5 treatment. The variation in bacterial communities due to H20-5 treatment was higher in the rhizosphere than in the bulk soils. Additionally, the bacterial species richness and diversity were greater in the H20-5 treated rhizosphere than in the control. The composition and structure of the bacterial communities varied with soil salinity levels, and those in the H20-5 treated rhizosphere soil were clustered. The members of Actinobacteria genera, including Kineosporia, Virgisporangium, Actinoplanes, Gaiella, Blastococcus, and Solirubrobacter, were enriched in the H20-5 treated rhizosphere soils. The microbial co-occurrence network of the bacterial community in the H20-5 treated rhizosphere soils had more modules and keystone taxa compared to the control. These findings revealed that the strain H20-5 induced systemic tolerance in tomato plants and influenced the diversity, composition, structure, and network of bacterial communities. The bacterial community in the H20-5 treated rhizosphere soils also appeared to be relatively stable to soil salinity changes.