Influence of varied soil microbial and inorganic nutrient conditions on the growth and vesicular-arbuscular mycorrhizal colonization of little bluestem [Schizachyrium scoparium (Michx.) Nash]

Summary A difference in biomass production between plants grown in autoclaved soil and non-autoclaved soil under N and base (Ca + Mg) treatments was probably caused by soil microbes other than vesicular-arbuscular mycorrhizal fungi. The plants were grown for 70 days in autoclaved soil, autoclaved soil with a vesicular-arbuscular mycorrhizal-free filtrate of non-autoclaved soil added, and non-autoclaved soil. The plants in each substrate received additional N, P, or Ca + Mg (base treatment) weekly. Control plants received no additional nutrients. The plant response to various substrates was a function of nutrient treatment. Colonization of roots by vesicular-arbuscular mycorrhizal fungi in non-autoclaved soil was lowest with the N and P treatments. There were significant negative correlations between vesicular-arbuscular mycorrhizal colonization and all plant growth variates. For all nutrient treatments, there were no differences in total biomass between plants grown in non-autoclaved soil and in the autoclaved-plus-filtrate substrate.     

Microbial population of ryegrass root surfaces: Influence of nitrogen and phosphorus supply

In three experiments perennial ryegrass (Lolium perenne) was grown in pots of soil, with the addition of soluble mineral nutrients to provide contrasting nitrogen and phosphorus supplies. After 7–10 weeks the plants were harvested and the bacteria on the root surface or in the outer cortex were investigated. In two experiments the bacteria of root-free soil were investigated, for comparison.Bacteria which were pleomorphic when cultured were more abundant than rods in the rhizoplane, especially when the plants had received a complete nutrient solution. Only about 1% of the bacteria which were cultured were pseudomonads. Only 6–10% of the rhizoplane bacteria could degrade pectin and no cellulose-degraders were isolated, suggesting that few rhizoplane bacteria can degrade mucigel.In general addition of N or P to the soil had little effect on the total numbers of bacteria in the rhizoplane or the composition of the population. The proportion of bacteria able to degrade chitin was reduced by nutrient addition, but starch and pectin-degraders were not affected, and the proportion able to grow with NH₄NO₃ as their N source changed only a little. These results appear to conflict with previous observations that growth of single bacterial species on L. perenne in sand culture is increased when P is deficient. In the present experiments rhizoplane fungi increased markedly when N or (especially) P was deficient. It is suggested that P deficiency results in increased supply of carbon substrate from the roots, but when mineral nutrients are in short supply fungi are more effective competitors than bacteria for this substrate.     

Micromycetes in the rhizosphere, the rhizoplane and the roots of wheat under conventional and zero tillage

The effects of different soil cultivation on the occurrence of micromycetes in the rhizosphere, at the root surface (rhizoplane) and in the root interior were investigated in a long-term field experiment on a chernozem soil at Hru?ovany u Brna, in an area of the corn production type. Cereals were grown as a monoculture with conventional and zero tillage.Soil cultivation had no significant effect on the total number of species of micromycetes. Zero tillage resulted in an increased number of colonies isolated from the rhizosphere and the rhizoplane. On the contrary, conventional tillage resulted in an increased number of isolates from the roots interior. The abundance of individual species of micromycetes varied somewhat in individual years, larger differences being observed with the saprophytic rather than with the parasitic (Gaeumannomyces graminis, Fusarium) species. In wheat roots, Gaeumannomyces graminis was more common under conventional tillage that under zero tillage, while the reverse was true of Fusarium.     

Quantification of Aluminum-Induced Changes in Wheat Root Architecture by X-ray Microcomputed Tomography

Root architectural traits are of fundamental importance for plant performance, especially under unfavorable soil conditions. This study examined the effect of aluminum (Al) toxicity in different growing media (nutrient solutions and soil) on root architecture of two wheat (Triticum aestivum L.) cultivars with different Al tolerances. Seedlings were grown in acidic and limed soil and in two contrasting nutrient solutions. Root systems of soil-grown plants were scanned using x-ray microcomputed tomography (µCT) while that of nutrient solution–grown plants were assesses using WinRhizo, 3 and 5 days after planting (DAP), respectively. Aluminum caused significant reduction of all examined root traits (number of seminal roots, root length, length of the longest seminal root, root surface area, and root volume). Growth in acidic soil caused significant reduction in root length, length of the longest seminal root, and root surface area at 5 DAP. Soil-grown plants produced a larger root system compared to plants grown in nutrient solutions. Aluminum toxicity–induced differences of root traits were also found between different nutrient solutions. Beside the well-known reduction of root length, Al toxicity had a profound effect on other root architectural traits. X-ray µCT has revealed root architectural changes under specific conditions of acidic, Al-toxic soil. Differences obtained in Al-induced effects on root architecture between different nutrient solutions as well as between different growing systems emphasize the need for further study of root architecture, especially under specific conditions of Al toxicity in acidic soils.     

Root growth,and microorganisms associated with the rhizoplane and root zone soil of a native C4 grass on burned and unburned sand prairies

We investigated the root growth of native Schizachyrium scoparium, little bluestem grass, and the seasonal abundance of rhizoplane and root zone soil microorganisms on burned and unburned sand prairies. Root growth and abundances of rhizoplane and root zone microorganisms were greater in burned than unburned sites. Microbe populations were nearly always higher on the rhizoplane than in the root zone soils, although they were not always significantly different. The seasonal dynamics of total bacteria, total fungi, fluorescent pseudomonads, and microorganisms that decompose chitin, cellulose, and protein varied between burned and unburned sites. Some microbial populations showed significant, though weak, relationships with root growth. Populations of most microorganisms were usually highest from June through August, when roots were being shed following the peak standing crop of root mass in May. The production of fine roots on burned sites early in the growing season and the consequent shedding of fine roots probably have an important effect on microbe population dynamics.     

六种水培的苋科植物对~(134)Cs的吸收和积累(英文)

对营养液栽培 42d后的 6种苋科植物用不同13 4 Cs比活度处理 ,1周后收获并分析13 4 Cs比活度。结果表明 ,不同植物组织的烘干重和最大生长高度存在差异。不同植物和同种植物不同器官间13 4 Cs积累量表现为显著差异 ,但差异取决于初始加入到营养液中的13 4 Cs比活度。放射性自显影结果表明 ,各种植物叶片积累的13 4 Cs比根茎积累的多。籽粒苋 (AmaranthuscruentusL .)较其它植物生物量高、根系密度大、生长速率快 ,虽然籽粒苋中13 4 Cs比活度较低 ,但其茎叶器官从13 4 Cs水培液中剔除的13 4 Cs明显高得多 ,且表现出很高的13 4 Cs去除速率。研究还发现 ,6种植物叶部含钾量与13 4 Cs比活度之间存在较弱的线性相关性。     

六种水培的苋科植物对134Cs的吸收和积累

对营养液栽培 42d后的 6种苋科植物用不同13 4 Cs比活度处理 ,1周后收获并分析13 4 Cs比活度。结果表明 ,不同植物组织的烘干重和最大生长高度存在差异。不同植物和同种植物不同器官间13 4 Cs积累量表现为显著差异 ,但差异取决于初始加入到营养液中的13 4 Cs比活度。放射性自显影结果表明 ,各种植物叶片积累的13 4 Cs比根茎积累的多。籽粒苋 (AmaranthuscruentusL .)较其它植物生物量高、根系密度大、生长速率快 ,虽然籽粒苋中13 4 Cs比活度较低 ,但其茎叶器官从13 4 Cs水培液中剔除的13 4 Cs明显高得多 ,且表现出很高的13 4 Cs去除速率。研究还发现 ,6种植物叶部含钾量与13 4 Cs比活度之间存在较弱的线性相关性。     

Relative importance of motility and antibiosis in the rhizoplane competence of a biocontrol agent Pseudomonas fluorescens MelRC2Rif

Mutants defective in motility or antibiotics production were obtained by Tn5 mutagenesis of a biocontrol agent Pseudomonas fluorescens MelRC2Rif (wt). Tomato or melon seeds were co-inoculated with a Tn5 mutant and wt in a 1:1 ratio and then grown in soil for 10 days. There was no change in ratios of Tn5 mutants defective in antibiosis to wt in the process of rhizoplane colonization, suggesting little contribution of in vitro antibiosis to the rhizoplane competence of P. fluorescens MelRC2Rif. Similar results were also obtained when seeds treated with bacteria were planted in soil artificially infested with fungal pathogens. In contrast, ratios of Tn5 mutants defective in motility to wt significantly decreased, suggesting the contribution of motility to the rhizoplane competence of this bacterium. When a non-motile Tn5 mutant and wt were co-inoculated into soil at a matric potential of pF 2.3 (–20 kPa) and plants were then grown, there was no change in the ratio in rhizoplane colonization, suggesting that motility might have a role in the movement along roots but an insignificant role in the movement from bulk soil towards roots. When they were co-inoculated into 0.2% water agar (WA) instead of soil, a remarkable decline in ratios was detected. Thus it was soil structure that hindered the efficiency of motility. Time course enumeration of rhizoplane colonization of tomatoes grown in WA revealed that motility was an important means of movement towards and/or along roots rather than the multiplication on roots. Received: 8 July 1996     

Effect of variety on nutrient composition of field corn

Abstract

Significant varietal differences in plant nutrient content have been reported in the literature which would make extremely difficult the interpretation of plant analysis results for diagnosing plant nutritional problems. This investigation was conducted to analyze a relatively large number of uniformly fertilized commercially grown corn (Zea mays) varieties for possible differences in N, P, K, Ca, and Mg concentrations. Whole young plants 60 to 90 cm tall and ear leaves collected at tassel ling were chemically analyzed.

Varietal differences in the concentrations of N, P, K, and Ca in field corn were statistically significant. Varietal differences in Mg concentrations were significant in three out of the six sets of data.

In spite of statistical significance, plant nutrient concentrations were found to be within expected limits for the morphological parts and growth stages examined except for ear leaf P levels in two varieties. These varieties (P.A.G. SX 29 and Pioneer 3304) apparently were capable of accumulating high levels of P, but only when ear leaf P concentrations were generally high for all varieties indicating excessive soil P levels.

The majority of corn varieties tested contained relatively uniform nutrient levels and were not significantly different from one another. The usual bell‐shaped frequency distribution curves indicated normal distributions of plant nutrient contents. Varietal differences in nutrient concentrations were generally not found to be large enough to interfere with interpretation of plant analysis results (except possibly for P accumulation in the two varieties mentioned above). But, there was no indication that critical phosphorus levels were higher in P accumulating varieties than in other varieties.     

Hormonal interactions in the rhizosphere of maize (Zea mays L.) and their effects on plant development

The phytohormones indole acetic acid (IAA), abscisic acid (ABA), isopentenyladenosine (iPA), dihydrozeatin riboside (DHZR), and zeatinriboside (ZR) were determined quantitatively using monoclonal antibodies by an enzyme immunoassay in the following samples: a) culture filtrates of known bacterial species, growing naturally in close, loose or without contact with higher plants; b) culture filtrates of heterogeneous populations of microorganisms, isolated from the rhizoplane and rhizosphere of maize as well as from root-free soil; c) sterile and nonsterile maize root exudates; d) in the rhizosphere of field-grown maize plants and in soil fractions distant from the roots (bulk soil). ABA was not detected in the culture filtrates of bacteria and ZR was not found in bulk soil and rhizosphere soil of field-grown maize. All phytohormones were present in the other samples analyzed. Bacterial cultures with cell concentrations roughly equal to those in the rhizosphere of field-grown maize may produce under optimal laboratory conditions phytohormone concentrations comparable to those measured in the rhizosphere of field-grown maize. During the whole vegetation period there was a steep phytohormone gradient in the first centimeter of soil around a maize root in the field. Inoculation of maize seedlings growing in nutrient solution with rhizosphere bacteria resulted in a synergistic increase in phytohormone concentration in comparison to the sum of hormone production by sterile plant roots and by bacteria cultures. Using regression analysis, the relationship between phytohormone concentration changes in the rhizosphere and different morphological characteristics of the maize plant were shown to be highly significant.     

Responses by iron-efficient and inefficient oat cultivars to inoculation with siderophore-producing bacteria in a calcareous soil

Rhizosphere bacteria may enhance plant uptake of Fe by producing siderophores that chelate sparingly soluble Fe³⁺ in calcareous soils. To evaluate the extent to which plants benefit from colonization of the roots by prolific siderophore-producing bacteria, we inoculated two oat cultivars with six strains of bacteria that produced high concentrations of siderophores under Felimiting conditions in vitro. Oat cv Coker 227, an Fe-efficient cultivar, which produces the phytosiderophore avenic acid, and cv TAM 0-312, and Fe-inefficient cultivar, which does not produce the phytosiderophore, were grown in a calcareous soil (Weswood silt loam) on a light bench in the laboratory. Half of the plants were fertilized with a nutrient solution containing 5 mM Fe and half with a nutrient solution containing no Fe. After 6 weeks of growth, we compared colonization of the roots by the inoculant bacteria and the dry weight and Fe content of roots and shoots. Three species of Pseudomonas colonized the roots of both oat cultivars in high numbers (10⁶ cells g^-1 root dry weight), whereas the remaining bacteria colonized the roots in substantially lower numbers (10⁴ cells g^-1 root dry weight). Plants fertilized with 5 mM Fe were larger and supported greater numbers or rhizosphere bacteria per gram of root than plants not supplied with Fe. Comparisons of the Fe content and dry weight of roots and shoots revealed few significant differences between inoculated and uninoculated plants, or among the plants inoculated with the different strains of siderophore-producing bacteria. The differences that were observed revealed no consistent response to inoculation. We conclude that inoculation of the roots of the two oat cultivars with bacteria that produce high concentrations of siderophores in response to an Fe deficiency had little or no effect on Fe acquisition by the plants.     

酸性红壤上玉米不同部位固氮微生物群落丰度和组成特征

[目的]发挥微生物固氮功能可降低农田化学氮肥的投入,对于缓解土壤酸化具有重要意义.固氮微生物广泛存在于植物体的各个部位,了解酸性土壤上作物不同部位固氮微生物群落特征,为挖掘其功能潜力提供数据支撑和理论基础.[方法]选择性状差异较大的耐铝玉米品种先玉335和铝敏感品种Mo17为试验材料,在酸性红壤上种植1个月后,收集玉米...     

Effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize (Zea mays) and barley (Hordeum vulgare)

Summary The addition of sugars or amino acids to the soil gave rise to the development of different groups of microorganisms. The increase in the number of different groups of microorganisms in the soil had an influence on the microbiota in the rhizoplane and endorhizosphere of maize and barley grown in that soil. Furthermore, growth of maize and barley decreased with increasing microbial activity and density in soil. This effect could be counteracted effectively by the rhizopseudomonad strain 7NSK2. The beneficial effect of the strain 7NSK2 correlated inversely with the microbial activity, as measured by soil respiration, in the bulk-pretreated soil.The effect of seed inoculation with the rhizopseudomonad strain 7NSK2 on the root microbiota of maize and barley was evaluated. The strain 7NSK2 was capable of colonizing the rhizoplane and endorhizosphere of the maize cultivar Beaupré and barley cultivar Than very effectively and of considerably altering their composition. The number of total bacteria, fungi, pseudomonads and coliform bacteria in the rhizoplane and endorhizosphere of both plants was strongly reduced by inoculating the seeds with the strain 7NSK2.     

Influence of rhizosphere bacteria on morphological characteristics of maize seedlings (Zea mays L.)

The effect of a rhizosphere microflora on some morphological and physiological plant characteristics was studied with maize seedlings grown for five days in a mineral nutrient solution. In the presence of the microorganisms the root dry weight is lower than that of axenically grown plants due to a smaller diameter of the primary root. In addition, the root content of some vitamins and sugars is affected. Pure cultures of rhizosphere bacteria were isolated and their influence on morphological characteristics of the maize plant was classified. Whereas one culture retards the overall plant development, the remaining nine cultures exert a significant influence only on specific morphological parameters. These results are discussed as an indication of the participation of phytohormones in interactions between roots and bacteria.     

Plant species affect the concentration of free sugars and free amino acids in different types of soil

Substantial amounts of low molecular weight organic compounds (LMWs) such as sugars and amino acids are transferred from plant roots into soil. These substances are released due to decomposition processes or leaching (exudation). Afterwards they can be metabolized by soil microorganisms into different compounds, or they can be partially re‐absorbed by the plants. The aim of this study was to clarify the influence of five wild plant species on the composition and pool sizes of LMWs extractable from three different soils. Four of the five species caused significant changes in soil LMW pools. In Chernozem, the sugar concentrations of soil with plants were up to 60 % higher than those of the bulk reference soil, and amino acids increased by as much as 207 %. The relative abundance of free amino acids in roots did not correlate with the relative abundance of amino acids in soil after six weeks of plant growth. The relative abundance of soil amino acids, that increased after plant growth, was strongly dependent on the type of soil and on the plant species present. We suggest that rather than rhizodeposition being dependent on soil type, it reflects differential microbial metabolization of amino acids in the respective soils.     

Extracellular phosphomono- and phosphodiesterase associated with and released by the roots of barley genotypes: a non-destructive method for the measurement of the extracellular enzymes of roots

Genotypes of spring barley (Hordeum vulgare L. cvs. Alexis and Regatta) and winter barley (Hordeum vulgare L. cvs. Marina and Sonate) grown under sterile and non-sterile conditions were compared with regard to the activity of root- and rhizoplane-microorganism-associated and -released phosphatases. A method is described of growing plants individually under sterile and non-sterile conditions and assaying of the enzyme activities of intact roots and rhizoplane microorganisms. The results of the experiments presented in this paper indicate that all the genotypes showed significantly (P<>;0.01) higher actitivity of extracellular phosphomonoesterase than that of phosphodiesterase both associated with and released by their roots. There were no significant differences (P<>;0.05) between the sterile and non-sterile root and its surrounding solutions in the activity of extracellular phosphomonoesterase. The contribution of rhizoplane microorganisms to the root total activity of extracellular phosphomonoesterase was estimated to be 3%. Generally, the activity of the enzymes associated with the roots was 20–80 times higher than the activity of those released by the roots to the surrounding nutrient solution. However, a close correlation was found between the activity of extracellular phosphomonoesterase associated with and that released by the roots. Received: 3 April 1996     

Comparison of root system architecture and rhizosphere microbial communities of Balsas teosinte and domesticated corn cultivars

The progenitor of maize is Balsas teosinte (Zea mays subsp. parviglumis) which grows as a wild plant in the valley of the Balsas river in Mexico. Domestication, primarily targeting above-ground traits, has led to substantial changes in the plant's morphology and modern maize cultivars poorly resemble their wild ancestor. We examined the hypotheses that Balsas teosinte (accession PI 384071) has a) a different root system architecture and b) a structurally and functionally different rhizosphere microbial community than domesticated cultivars sweet corn (Zea mays subsp. mays accession PI 494083) and popping corn (Zea mays subsp. mays accession PI 542713). In a greenhouse experiment, five plants from each corn variety were grown in individual pots containing a Maury silt loam – perlite (2:1) mixture and grown to the V8 growth stage at which rhizosphere bacterial and fungal community structure was assessed using terminal restriction fragment length polymorphism and fatty acid methyl ester analysis. Functional characteristics of the rhizosphere were assayed by examining the potential activity of seven extracellular enzymes involved in carbon, nitrogen and phosphorus cycling. Root system architecture was characterized by root scans of sand grown plants at the V5 growth stage. Compared to the control the sweet corn rhizosphere had different bacterial and fungal community structure, decreased fungal diversity and increased bacterial abundance. Teosinte caused a significant change in the rhizosphere bacterial and fungal community structure and increased bacterial abundance, but no significant decrease in bacterial or fungal diversity where the former was found to be significantly greater than in the sweet corn rhizosphere. Popping corn did not trigger significant changes in the bacterial or fungal diversity and bacterial abundance in the soil. The individual popping corn plants changed the bacterial and fungal communities in different directions and the overall effect on community structure was significant, but small. Of the enzymes analyzed, potential N-acetylglucosaminidase (NAG) activity was found to contributed most to the differentiation of teosinte rhizosphere samples from the other corn varieties. The teosinte root system had proportionally more very fine (diameter < 0.03 mm) roots than popping corn and sweet corn and it developed the highest root to shoot dry weight ratio, followed by popping corn. Sweet corn had significantly lower average root diameter than popping corn and teosinte and grew proportionally the least below-ground dry mass. The results allude to functional and structural differences in the rhizosphere microbial communities of the corn varieties that, with additional research, could lead to useful discoveries on how corn domestication has altered rhizosphere processes and how plant genotype influences nutrient cycling.     

P and N deficiency change the relative abundance and function of rhizosphere microorganisms during cluster root development of white lupin (Lupinus albus L.)

We studied microbe-plant interactions of white lupin, a cluster root-forming plant, under low P and N conditions to examine increased nutrient acquisition by plants either by a shift to a more specialized microbial community or changes in microbial enzyme production. White lupin plants were grown in rhizoboxes filled with either P- or N-deficient soil; fertilized soil was used as control. After cultivation of plants in a glasshouse for 41 d, plant growth (shoot and roots) and P and N accumulation in shoots were measured. Microbial functions were analyzed by P- and N-cycling enzymes. The microbial community structure was estimated by fingerprinting (denaturing gradient gel electrophoresis) and sequencing techniques. P deficiency induced the released citrate and acid phosphomonoesterases from cluster roots and stimulated the production of microbe-derived alkaline phosphomonoesterase in the rhizosphere. P deficiency decreased microbial diversity in the cluster root rhizosphere. Increased relative abundance of Burkholderiales in the rhizosphere of P deficient plants might be responsible for the degradation of different organic P fractions such as phytates. N deficiency induced an increase of the number of nodules and P concentration in shoot as well as roots of white lupin. We clarified that high release of citrate from cluster roots might be the preferred mechanisms to meet the P demand of nodulated plants under N deficiency. In addition, the high abundance of Rhizobiales and Rhodospirillales in the rhizosphere of cluster roots showed that the importance of N-fixing microorganisms under N deficiency. The contribution of rhizosphere microorganisms due to similar activities of N-cycling enzymes under the two different N treatments is less important for N nutrition of plants. Further understanding of the regulation of cluster roots under N-deficiency will provide new information on the interactions between P and N nutrition.     

Effect of combined nitrogen supply and nodulation on nitrate reductase activity and growth of pea plants

Nitrate reductase activity (NRA; EC 1.6.6.1) was measured in leaves, stems and roots of Pisum sativum cv. Lincoln supplied with different nitrate concentrations and inoculated with selected Rhizobium leguminosarum strains. As a control, noninoculated plants were grown in the same nutrient medium. NRA was determined by an in vivo‐nitrate assay. Although differences in tissue NRA were mainly related to nitrate concentration in the growing medium, nodulation much affected the NRA in the different plant organs, especially in root. An increased proportion of total plant NRA occurred in the leaves and stems as nitrate concentration was increased. Nitrate accumulation in leaves, stems and roots was correlated with the concentration of this ion in the nutrient solution. Nodulation also affects the nitrate accumulation in the different plant organs.     

Soil protozoa and forest tree growth: non-nutritional effects and interaction with mycorrhizae

Mycorrhizal (Lactarius rufus Fr.) and non-mycorrhizal Norway spruce seedlings (Picea abies Karst.) were grown in a sand culture and inoculated with protozoa (naked amoebae and flagellates) extracted from native forest soil or with protozoa grown on agar cultures. A soil suspension from which the protozoa were eliminated by filtration or chloroform fumigation was used as a control. After 19 weeks of growth in a climate chamber at 20–22°C, the seedlings were harvested. Protozoa reduced the number of bacterial colony-forming units extracted from the rhizoplane of both non-mycorrhizal and mycorrhizal seedlings and significantly increased seedling growth. However, concentrations of mineral nutrients in needles were not increased in seedlings with protozoan treatment. It is concluded that the increased growth of seedling was not caused by nutrients released during amoebal grazing on rhizosphere micro-organisms. The protozoa presumably affected plant physiological processes, either directly, via production of phytohormones, or indirectly, via modification of the structure and performance of the rhizosphere microflora and their impact on plant growth. Mycorrhizal colonization significantly increased the abundance of naked amoebae at the rhizoplane. Our observations indicate that protozoa in the rhizosphere interact significantly with mycorrhizae.