Variations in ergosterol content and ornithine decarboxylase activity of ectomycorrhizal root-soil systems

Influences of soil P fertilization on temporal changes in ergosterol content and ornithine decarboxylase (E.C. 4.1.1.17, ODC) activity were monitored in rhizosphere soil, non-rhizosphere soil and Pinus contorta roots ectomycorrhizal with Hebeloma crustuliniforme grown in a loamy sand. With addition of mycorrhizal inoculum to loamy sand, ODC activity mg^-1 root increased between 10% and 2 fold within 21 weeks of pianting. Inoculation also decreased root mass per seedling. Inoculation increased mycelia mass per root mass by up to 2 fold but no differences were observed for total seedling mass until 35 weeks. Intramatrical mycelia were detrimental to early plant growth, but inoculated seedlings had 1.7 times more root mass and 1.3 times more shoot mass at 35 weeks. Rhizosphere soil contained up to 5 times more mycelia and up to 6 times greater ODC activity than non-rhizosphere soil. Inoculation increased rhizophere metabolic activity and intramatrical mycelia mass. Their sensitivity to fungal inoculation, P fertilization and temporal trends may make the methods useful in studies of rhizosphere ecology and root-microbe relationships.     

丛枝菌根化翅果油树幼苗根际土壤微环境

以我国二级濒危保护植物翅果油(Elaeagnus mollis)为供试植物, 通过温室盆栽试验, 研究接种丛枝菌根真菌对翅果油树幼苗根际土壤微生态环境的影响。试验设计分4个组: 摩西球囊霉(Glomus mosseae)单独接种组(GM)、脆无梗囊霉(Acaulospora delicata)单独接种组(AD)、混合接种组(GM + AD)、不接种的对照组(CK)。测定了菌根侵染率、生物量、根际微生物数量、土壤pH值、土壤酶活性及其对N、P营养的影响等指标。结果显示: 菌根真菌对3个接种组均有侵染, 其中, GM + AD的侵染率最大(90.5%), 生态学效应最好; 与对照组相比, 接种组的生物量均明显提高(p < 0.05), 其中GM + AD组生物量显著增加, 是CK组的2.2倍; AM菌根对根部微生物种群数量产生一定的影响, 主要是使根面上的细菌、放线菌、固氮菌的数量显著增加(p < 0.05); AM菌根使根际pH值降低, 与菌根侵染率呈显著负相关关系(p < 0.05); 接种组根际土壤磷酸酶、脲酶、蛋白酶的活性增加, 根际土壤的磷酸酶、蛋白酶的活性增加量与菌根侵染率呈极显著相关关系(p < 0.01); 接种组的根际土壤中, 可直接被植物吸收利用的N、P元素出现富集现象, 与菌根侵染率呈显著相关关系(p < 0.05)。研究表明: 丛枝菌根的形成改善了翅果油树幼苗的微生态环境, 提高了根际土壤肥力。     

Chemical alteration of the rhizosphere of the mycorrhizal-colonized wheat root

Plexiglass pot growth chamber experiments were conducted to evaluate the chemical alterations in the rhizosphere of mycorrhizal wheat roots after inoculation with Glomus intraradices [arbuscular mycorrhizal fungus (AMF)]. Exchange resins were used as sinks for nutrients to determine whether the inoculated plant can increase the solubility and the uptake of P and micronutrients. Treatments included: (1) soil (bulk soil); (2) AMF inoculation no P addition (I–P); (3) no inoculation with no P addition (NI–P); (4) AMF inoculation with addition of 50 mg P (kg soil)^–1 (I+P), and (5) no inoculation with addition of 50 mg P (kg soil)^–1 (NI+P). The AMF inoculum was added at a rate of four spores of G. intraradices (g soil)^–1. The exchange resin membranes were inserted vertically 5 cm apart in the middle of Plexiglass pots. Spring wheat (Triticum aestivum cv. Len) was planted in each Plexiglass pot and grown for 2 weeks in a growth chamber where water was maintained at field capacity. Rhizosphere pH and redox potential (Eh), nutrient bioavailability indices and mycorrhizal colonization were determined. Mycorrhizal inoculation increased the colonization more when P was not added, but did not increase the shoot dry weight at either P level. The rhizosphere pH was lower in the inoculated plants compared to the noninoculated plants in the absence of added P, while the Eh did not change. The decrease in pH in the rhizosphere of inoculated plants could be responsible for the increased P and Zn uptake observed with inoculation. In contrast, Mn uptake was decreased by inoculation. The resin-adsorbed P was increased by inoculation, which, along with the bioavailability index data, may indicate that mycorrhizal roots were able to increase the solubility of soil P.     

The plant growth‐promoting fungus Fusarium equiseti and the arbuscular mycorrhizal fungus Glomus mosseae stimulate plant growth and reduce severity of anthracnose and damping‐off diseases in cucumber (Cucumis sativus) seedlings

To alleviate the environmental contamination due to persistent chemical usage, approaches to integrated pest management were conceived. In this perspective, microbe–microbe interactions such as mycorrhizal relationships with other soil microbiota in the rhizosphere like the plant growth‐promoting fungi (PGPF) are particularly important. Better understanding of the interactions between beneficial microbial groups is imperative in the identification of possible synergistic or antagonistic effects to improve their practical usage as biocontrol agents or biofertilizers. In this study, the consequence of co‐inoculation of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae (Gm) and the PGPF Fusarium equiseti (isolates GF18‐3 and GF19‐1) in terms of plant growth enhancement, root and rhizosphere colonisation, and development of anthracnose (Colletotrichum orbiculare) and damping‐off (Rhizoctonia solani AG‐4) diseases in cucumber plants was investigated under controlled conditions. The amendment of either GF18‐3 or GF19‐1 singly or in combination with Gm indicated a general tendency to significantly enhance the shoot dry weight (SDW) of cucumber plants at 4 weeks after planting (WAP). Similarly, Gm alone significantly enhanced SDW at 4 WAP. Gm showed a tendency to depress root colonisation by F. equiseti but such antagonistic effect was not observed in the rhizosphere soil. Both GF18‐3 and GF19‐1 significantly reduced percent root colonisation of Gm. However, these general tendencies may vary with the inoculum densities of AMF and PGPF. Both F. equiseti and Gm inoculated singly significantly increased percent of protection against anthracnose, but the combined inoculation was more effective in controlling the disease compared to single inoculation. The inoculation of the cucumber seedlings with GF18‐3, GF19‐1 or Gm, 6 or 12 days prior to damping‐off pathogen inoculation, increased percent of protection against damping‐off disease. This study shows that the co‐inoculation of F. equiseti and Gm resulted in additive effect on the suppression of anthracnose disease in cucumber.     

Restoration of high altitude forests in an area affected by a wildfire: Polylepis australis Bitt. seedlings performance after soil inoculation

Key message

Outplanted Polylepis australis seedling growth, survival and mycorrhizal response were not influenced by inoculation with soil from different vegetation types. Seedling inoculation would not be essential for reforestation practices.

Abstract

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been recommended. To determine whether native soil inoculation could help in reforestation success, a field trial was set up to evaluate the response of outplanted P. australis seedlings to the inoculation with soils from three vegetation types (a grassland, a mature forest and a degraded forest) and a sterile soil, used as control. We evaluated seedlings performance: growth and survival for 18 months, root/shoot ratio, phosphorous content and arbuscular mycorrhizal fungal (AMF) colonization. To interpret performance patterns we evaluated the colonization potential of the three inoculum soils and the changes of the AMF community composition of the seedlings rhizosphere in relation to inoculation treatment and season. Our main results showed no significant differences in seedlings survival and growth between treatments. The colonization potential of grassland and degraded forest soils was ~25 times greater than mature forest soil and specific spore density of some morphospecies varied with season. However, AMF spore community of seedlings rhizosphere became homogenized after outplanting and was similar between treatments after 12 months. Therefore, we conclude that soil inoculation is not essential for outplanted P. australis survival and increase in height, and thus all the tested soils could be used as inocula, including grassland soils which in practice are the easiest to collect.     

Displacement of an herbaceous plant species community by mycorrhizal and non-mycorrhizal Gmelina arborea, an exotic tree, grown in a microcosm experiment

Gmelina arborea Roxb. (Gmelina, Yemane) is a fast growing tree, native from India and considered as a potentially invasive woody plant in West Africa. Mycorrhizal inoculation of seedlings with Glomus intraradices was performed to study (1) the effect on the growth of G. arborea, (2) the impact on the catabolic diversity of soil microbial communities and (3) the influence on the structure of herbaceous plant species communities in microcosms. Treatments consisted of control plants, pre-planting fertilizer application and arbuscular mycorrhizal (AM) inoculation. After 4 months’ culture in autoclaved soil, G. arborea seedlings were either harvested for growth measurement or transferred into containers filled with the same soil but not sterilized. Other containers were kept without G. arborea seedlings. After 12 months’ further culture, effects of fertilizer amendment and AM inoculation on the growth of G. arborea seedlings were recorded. AM colonization was significantly and positively correlated with plant diversity. The substrate-induced respiration response to carboxylic acids was significantly higher in the absence of G. arborea and in the presence of G. intraradices as compared to the other treatments. The influence of AM symbiosis on plant coexistence and on allelopathic processes of invasive plants are discussed.     

Frankia inoculation,soil biota,and host tissue amendment influence Casuarina nodulation capacity of a tropical soil

The effects of soil biota, Frankia inoculation and tissue amendment on nodulation capacity of a soil was investigated in a factorial study using bulked soil from beneath a Casuarina cunninghamiana tree and bioassays with C. cunninghamiana seedlings as capture plants. Nodulation capacities were determined from soils incubated in sterile jars at 21 °C for 1, 7, and 28 days, after receiving all combinations of the following treatments: ± steam pasteurization, ± inoculation with Frankia isolate CjI82001, and ± amendment with different concentrations of Casuarina cladode extracts. Soil respiration within sealed containers was determined periodically during the incubation period as a measure of overall microbial activity. Soil respiration, and thus overall microbial activity, was positively correlated with increasing concentrations of Casuarina cladode extracts. The nodulation capacity of soils inoculated with Frankia strain Cj82001 decreased over time, while those of unpasteurized soils without inoculation either increased or remained unaffected. The mean nodulation capacity of unpasteurized soil inoculated with Frankia CjI82001 was two to three times greater than the sum of values for unpasteurized and inoculated pasteurized soils. Our results suggest a positive synergism between soil biota as a whole and Frankia inoculum with respect to host infection.     

溶磷细菌和丛枝菌根真菌接种对南方红豆杉生长及根际微生物和土壤酶活性的影响

以南方红豆杉实生苗为材料,采用盆栽实验探讨了高效溶磷细菌草木樨中华根瘤菌(Sinorhizobium meliloti)CHW10B与丛枝菌根真菌缩球囊霉(Glomus constrictum)单独和双接种条件下,其植株生长、根际土壤可培养微生物数量、土壤酶活和土壤微生物功能多样性变化,在微生态水平揭示接种对南方红豆杉生长的影响及其机制。结果表明:(1)各接种处理对南方红豆杉幼苗均有促生长作用,接种处理苗高、地径和生物量均较对照显著增加,并以双接种促进效果最好。(2)各接种处理提高了南方红豆杉根际土壤可培养细菌、真菌和放线菌含量,增加了土壤微生物碳源利用率,改变了土壤中物种的丰富度和均一度,增加了土壤中的生物多样性。(3)各接种处理促进了南方红豆杉根际重要土壤酶(酸性磷酸酶、脱氢酶、转化酶)活力的增加,且双接种的促进作用最为明显。可见,溶磷细菌(草木樨中华根瘤菌CHW10B)和丛枝菌根真菌(缩球囊霉)具有协同作用,两者同时接种可显著提高南方红豆杉根际土壤微生物数量及土壤酶活力,提高土壤微生物碳源利用率和土壤肥力,增加土壤中的生物多样性,从而达到间接促进宿主植物南方红豆杉生长的目的。     

A comparative study of aboveground biomass of three Mediterranean species in a post-fire succession

The aboveground biomass of three woody species (Cistus albidus, Quercus coccifera and Pinus halepensis) in two early successional stages (3- and 10-year old) of a post-fire Mediterranean ecosystem was investigated. Among these three species, which belong to the successional series of holm oak (Quercus ilex), C. albidus and Q. coccifera are two dominant shrub species in the garrigue ecosystem and P. halepensis is a pioneer tree species widely represented in the Mediterranean area. The results obtained showed that in monospecific stands, C. albidus and Q. coccifera had a high recovery potential. In the 3-year-old stands, the cover of P. halepensis was only 19.8% for a total biomass of 0.75 ± 0.21 t ha^–1, while the plant cover of C. albidus and Q. coccifera was, respectively, 26% and 85.5% and biomass was 4.72 ± 1.09 and 11.5 ± 0.16 t ha^–1. Only 10 years after fire, the plant cover of C. albidus and Q. coccifera was, respectively, 55% and 100% and total biomass 13.2 ± 1.7 and 35.8 ± 4.7 t ha^–1. The greatest increase in biomass was noted for P. halepensis (29.7 t ha^–1). If mean annual biomass increments are considered, it appears that there was a significant decrease with the stand age for the two shrub species although the tree species showed an increase in productivity. These differing patterns in biomass and productivity of shrub and tree species with stand age provide information on biomass accumulation rates of pioneer species in a Mediterranean succession and their importance in the vegetation dynamics.     

Effects of water stress, organic amendment and mycorrhizal inoculation on soil microbial community structure and activity during the establishment of two heavy metal-tolerant native plant species

Our aim was to examine the effect of water stress on plant growth and development of two native plant species (Tetraclinis articulata and Crithmum maritimum) and on microbial community composition and activity in the rhizosphere soil, following the addition of an organic amendment, namely sugar beet residue (SBR), and/or the inoculation with an arbuscular mycorrhizal (AM) fungus, namely Glomus mosseae, in a non-sterile heavy metal-polluted soil. The AM inoculation did not have any significant effect on plant growth of both species. In T. articulata, SBR increased shoot growth, foliar P, total phospholipid fatty acids (PLFA), fungi-related PLFA, AM fungi-related neutral lipid fatty acid, bacterial gram-positive/gram-negative PLFA ratio and the β-glucosidase and dehydrogenase activities. SBR and AM inoculation increased phosphatase activity in T. articulata plants grown under drought conditions. In both plants, there was a synergistic effect between AM inoculation and SBR on mycorrhizal colonisation under drought conditions. In C. maritimum, the increase produced by the SBR on total amounts of PLFA, bacterial gram-positive-related PLFA and bacterial gram-negative-related PLFA was considerably higher under drought conditions. Our results suggest that the effectiveness of the amendment with regard to stimulating microbial communities and plant growth was largely limited by drought, particularly for plant species with a low degree of mycorrhizal colonisation.     

Effects of liming and mycorrhizal colonization on soil phosphate depletion and phosphate uptake by maize (Zea mays L.) and soybean (Glycine max L.) grown in two tropical acid soils

The effects of liming and inoculation with the arbuscular mycorrhizal fungus, Glomus intraradices Schenck and Smith on the uptake of phosphate (P) by maize (Zea mays L.) and soybean (Glycine max [L.] Merr.) and on depletion of inorganic phosphate fractions in rhizosphere soil (Al-P, Fe-P, and Ca-P) were studied in flat plastic containers using two acid soils, an Oxisol and an Ultisol, from Indonesia. The bulk soil pH was adjusted in both soils to 4.7, 5.6, and 6.4 by liming with different amounts of CaCO₃.In both soils, liming increased shoot dry weight, total root length, and mycorrhizal colonization of roots in the two plant species. Mycorrhizal inoculation significantly increased root dry weight in some cases, but much more markedly increased shoot dry weight and P concentration in shoot and roots, and also the calculated P uptake per unit root length. In the rhizosphere soil of mycorrhizal and non-mycorrhizal plants, the depletion of Al-P, Fe-P, and Ca-P depended in some cases on the soil pH. At all pH levels, the extent of P depletion in the rhizosphere soil was greater in mycorrhizal than in non-mycorrhizal plants. Despite these quantitative differences in exploitation of soil P, mycorrhizal roots used the same inorganic P sources as non-mycorrhizal roots. These results do not suggest that mycorrhizal roots have specific properties for P solubilization. Rather, the efficient P uptake from soil solution by the roots determines the effectiveness of the use of the different soil P sources. The results indicate also that both liming and mycorrhizal colonization are important for enhancing P uptake and plant growth in tropical acid soils.     

Microbial inoculation influences arbuscular mycorrhizal fungi community structure and nutrient dynamics in temperate tree restoration

Soil microbial communities have a profound influence on soil chemical processes and subsequently influence tree nutrition and growth. This study examined how the addition of a commercial inoculum or forest‐collected soils influenced nitrogen (N) and phosphorus (P) dynamics, soil microbial community structure, and growth in Liriodendron tulipifera and Prunus serotina tree saplings. Inoculation method was an important determinant of arbuscular mycorrhizal fungi (AMF) community structure in both species and altered soil N dynamics in Prunus and soil P dynamics in Liriodendron. Prunus saplings receiving whole forest soil transfers had a higher rhizosphere soil carbon/nitrogen ratio and ammonia content at the end of the first growing season when compared to unmanipulated control saplings. Inoculation with whole forest soil transfers resulted in increased inorganic phosphorus in Liriodendron rhizosphere soils. The number of AMF terminal restriction fragments was significantly greater in rhizosphere soils of Liriodendron saplings inoculated with whole forest soil transfers and Prunus saplings receiving either inoculum source than control saplings. Forest soil inoculation also increased AMF colonization and suppressed stem elongation in Liriodendron after 16 months; conversely, Prunus AMF colonization was unchanged and stem elongation was significantly greater when saplings were inoculated with whole forest soil transfers. Longer term monitoring of tree response to inoculation will be essential to assess whether early costs of AMF colonization may provide long‐term benefits. This study provides insight into how practitioners can use microbial inoculation to alter AMF community structure and functioning, subsequently influencing tree growth and nutrient cycling during the restoration of degraded lands.     

Root biomass distribution in a moist tropical montane forest

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.     

Comparison of Organic and Chemical Soil Amendments Used in the Reforestation of a Harsh Sierra Nevada Site

Abstract A comparison of a composted organic amendment, a controlled‐release fertilizer, and induced mycorrhizal inoculation as affecting the establishment and nutrition of bareroot Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was conducted on a Sierra Nevada surface mine. The soil amendments were applied at outplanting to the backfill of augered planting holes, with a low rate of 8 g and a high rate of 16 g per seedling for the fertilizer, Gromax 21‐6‐2 + Minors, whereas a single rate of 2.0 L was used for organic matter. Colonization by Pisolithus tinctorius (Pers.) Coker & Couch was induced by coating the root systems with basidiospores suspended in a gel carrier. The organic amendment especially, but also mycorrhizal inoculation, caused substantial seedling mortality, whereas survival was unaffected by controlled‐release fertilization. Gromax applied at the high rate produced a 74% increase in shoot volume after three growing seasons, whereas the organic amendment reduced volume by 28%. Growth was unaffected by mycorrhizal treatment. The growth response to the 16‐g Gromax application probably reflected enhanced N, P, and K nutrition and decreased concentrations of potentially toxic metallic elements, including Mn and Al among others, as revealed through foliar analysis. Because they were accompanied by growth reduction, nutritional responses to the organic amendment, which involved both macronutrients and trace elements, were of little consequence. Impaired water relations may account for the poor response to this amendment. Likewise, nutritional responses to mycorrhizal inoculation produced no discernible benefit in terms of seedling performance. An inoculation procedure that failed to induce substantially greater P. tinctorius colonization in inoculated than uninoculated seedlings, and that may have also impaired water relations, likely explains this result. Overall, these findings indicate that further research is needed before either the organic amendment or the mycorrhizal inoculation procedure used here can be used in forest restoration efforts on dry sites.     

Stimulated saprotrophic fungi in arable soil extend their activity to the rhizosphere and root microbiomes of crop seedlings

Saprotrophic fungi play an important role in ecosystem functioning and plant performance, but their abundance in intensively managed arable soils is low. Saprotrophic fungal biomass in arable soils can be enhanced with amendments of cellulose-rich materials. Here, we examined if sawdust-stimulated saprotrophic fungi extend their activity to the rhizosphere of crop seedlings and influence the composition and activity of other rhizosphere and root inhabitants. After growing carrot seedlings in sawdust-amended arable soil, we determined fungal and bacterial biomass and community structure in roots, rhizosphere and soil. Utilization of root exudates was assessed by stable isotope probing (SIP) following ¹³CO₂-pulse-labelling of seedlings. This was combined with analysis of lipid fatty acids (PLFA/NLFA-SIP) and nucleic acids (DNA-SIP). Sawdust-stimulated Sordariomycetes colonized the seedling's rhizosphere and roots and actively consumed root exudates. This did not reduce the abundance and activity of bacteria, yet higher proportions of α-Proteobacteria and Bacteroidia were seen. Biomass and activity of mycorrhizal fungi increased with sawdust amendments, whereas exudate consumption and root colonization by functional groups containing plant pathogens did not change. Sawdust amendment of arable soil enhanced abundance and exudate-consuming activity of saprotrophic fungi in the rhizosphere of crop seedlings and promoted potential beneficial microbial groups in root-associated microbiomes.     

AM真菌对采煤沉陷区黄花菜生长及根际土壤养分的影响

于陕北黄土沟壑采煤沉陷区内布设试验小区,对黄花菜(Hemerocallis citrina Baroni)接种丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)—摩西管柄囊霉菌,通过测定黄花菜光合性能、植株生长、抗逆性、土壤养分含量、根际微生物数量等,揭示AM真菌对黄花菜生长和土壤养分的影响。结果表明,黄花菜种植3—5个月后,接种AM真菌显著提高了黄花菜株高、冠幅及其根系菌根侵染率、菌丝密度。与不接种对照区相比,接种AM真菌后黄花菜叶片的光合速率、可溶性糖含量和过氧化氢酶活性分别提高了51%、12%、79%。接种AM真菌处理区黄花菜根际土壤的电导率、有机质、碱解氮和速效钾含量等均显著高于对照区,细菌数量和磷酸酶活性的菌根贡献率分别达77%和24%。表明采煤沉陷区扰动土壤接种AM真菌具有增强土壤微生物活性、改善土壤肥力和提高黄花菜植株抗逆性的作用,对促进陕北黄土沟壑采煤沉陷区经济作物生长和提高土壤质量具有重要现实生态意义。     

Mycorrhizas on nursery and field seedlings of Quercus garryana

Oak woodland regeneration and restoration requires that seedlings develop mycorrhizas, yet the need for this mutualistic association is often overlooked. In this study, we asked whether Quercus garryana seedlings in nursery beds acquire mycorrhizas without artificial inoculation or access to a mycorrhizal network of other ectomycorrhizal hosts. We also assessed the relationship between mycorrhizal infection and seedling growth in a nursery. Further, we compared the mycorrhizal assemblage of oak nursery seedlings to that of conifer seedlings in the nursery and to that of oak seedlings in nearby oak woodlands. Seedlings were excavated and the roots washed and examined microscopically. Mycorrhizas were identified by DNA sequences of the internal transcribed spacer region and by morphotype. On oak nursery seedlings, predominant mycorrhizas were species of Laccaria and Tuber with single occurrences of Entoloma and Peziza. In adjacent beds, seedlings of Pseudotsuga menziesii were mycorrhizal with Hysterangium and a different species of Laccaria; seedlings of Pinus monticola were mycorrhizal with Geneabea, Tarzetta, and Thelephora. Height of Q. garryana seedlings correlated with root biomass and mycorrhizal abundance. Total mycorrhizal abundance and abundance of Laccaria mycorrhizas significantly predicted seedling height in the nursery. Native oak seedlings from nearby Q. garryana woodlands were mycorrhizal with 13 fungal symbionts, none of which occurred on the nursery seedlings. These results demonstrate the value of mycorrhizas to the growth of oak seedlings. Although seedlings in nursery beds developed mycorrhizas without intentional inoculation, their mycorrhizas differed from and were less species rich than those on native seedlings.     

Effects of mycorrhizae and chitin-hydrolysing microbes on Vicia faba

The effect of Streptomyces albovinaceus (S-22) and Bacillus sp. (B1) on the growth response, nodulation, nutrition and nitrogenase activities of faba bean (Vicia faba) varieties infected with Glomus mosseae under pot conditions in sterile soil amended with chitin was studied. The growth, nodulation, nutrients content and nitrogenase activity of mycorrhiza-treated plants of Giza-667 were significantly increased compared to untreated ones. Such increases were related to the increase in mycorrhizal root infection. Amendment of soil with chitin alone reduced the growth, nodulation, total nitrogen contents and nitrogenase activities of mycorrhiza-treated faba bean plants (Giza-667) compared to untreated plants. Inoculation of plants with S. albovinaceus or Bacillus sp. significantly increased the level of mycorrhizal roots infection, but addition of chitin to the soil in combination with Bacillus sp. reduced the mycorrhizal infection of faba bean roots. Highest phosphorus contents of faba bean Giza-667 were recorded after G. mosseae inoculation in the presence of all treatments. Similar results were observed for the other varieties. The microbial populations were significantly increased in rhizospheres amended with chitin. Such increases were not in response to the mycorrhizal inoculation. Generally, the microflora of faba bean rhizospheres was increased after treatment with G. mosseae in the absence of chitin amendment alone compared with non-mycorrhizal rhizospheres.     

Root symbioses ofAlnus glutinosa (L.) gaertn. and their possible role in alder decline: A preliminary study

During the last few years alder has declined in South Bohemia. The possible role of mycorrhizal and actinorhizal symbioses is reviewed and some of the preliminary results from experiments testing the influence of these symbioses on alder growth and the influence of eutrophication on the development of these symbioses are reported. Seedlings ofAlnus glutinosa were inoculated with arbuscular mycorrhizal (AM) fungi and the actinomyceteFrankia in experiment 1, and with rhizosphere soil collected from field sites with different degrees of alder damage in experiment 2. In both experiments, a solution containing nitrate, ammonia and phosphorus in concentrations simulating eutrophic waters, was applied. Both symbioses markedly promoted the growth of the seedlings in experiment 1. The plants inoculated with the rhizosphere soil microflora in experiment 2 were larger than the control plants. Response of the seedlings to the inoculation with the soil from the rhizosphere of damaged alder trees from six field sites differs, even though no correlation was found relating growth to the health status of the trees. Nutrient treatment did not have any effect on the growth of seedlings in either experiment. The dry weight ofFrankia was greater in mycorrhizal plants compared to nonmycorrhizal plants and mycorrhizal colonization is reduced inFrankia inoculated plants supplemented with phosphorus in experiment 1. Nitrogen enhanced mycorrhizal colonization in nodulated plants which were not supplemented with phosphorus no effect of nitrogen on actinorhiza was observed.     

Effect of seed inoculation,mycorrhizal infection and organic amendment on wheat growth

Summary The effect of seed inoculation withAzotobacter spp. orAzospirillum spp., and garbage amendment (0.5%), on the growth of wheat was studied in a field experiment under sub-tropical conditions. Two levels of N fertilizer were applied, the usual field rate (150 kg N ha^–1) and half this amount. Tillering of plants, dry matter contents and nitrogenase activity were determined 30, 60 and 90 days after sowing. At the end of the experimental period, spore numbers and percentage of mycorrhizal infection were observed in the rhizosphere and root systems of plants. Straw and grain yields were also determined. The results of this study showed that seed inoculation and/or organic amendment stimulated plant growth, nitrogenase activity and mycorrhizal infection. This was more noticeable withAzotobacter than withAzospirillum. Inoculation withAzotobacter together with 1/2 N dose and organic amendment was the most effective application (19.75 and 10.70 t ha^–1 were recorded for straw and grain yield, respectively).