The relationship between density of Glomus mosseae propagules and the initiation and spread of arbuscular mycorrhizas in cotton roots

 The experiments aimed to determine the relationship between density of propagules in soil and initiation and spread of an arbuscular mycorrhizal fungus in the cotton roots. As few as 10 propagules of Glomus mosseae in approximately 95 g soil located in a band 25 cm below the soil surface established mycorrhizas in more than 80% of cotton roots at the point of inoculation within 36 days. Secondary spread was initiated 10–13 days after primary colonisation in treatments inoculated with one, 10 or 100 propagules. Spread of mycorrhizas within the root system was rapid from 100 propagules and was slower with fewer propagules. Accepted: 26 August 1999     

Localized elongation of roots of cotton follows establishment of arbuscular mycorrhizas

In an experiment to determine the influence of mycorrhizal colonization on root development, fertilized seedlings of cotton were grown in long tubular pots. Inoculation of soil with an isolate of Glomus mosseae at 10, 25 or 40 cm below the soil surface resulted in spread of arbuscular mycorrhizas up and down the root system, and localized elongation of roots following colonization. Specific root length was not influenced by colonization. Increases in local root density at the point of inoculation were observed, though total root mass in relation to shoot mass declined following initiation of mycorrhizas.     

Citrus root responses to localized drying soil: A new approach to studying mycorrhizal effects on the roots of mature trees

Because fine roots tend to be concentrated at the soil surface, exposure to dry surface soil can have a large influence on patterns of root growth, death and respiration. We studied the effects of arbuscular mycorrhizas (AM) formation on specific root length (SRL), respiration and mortality of fine roots of bearing red grapefruit (Citrus paradisi Macf.) trees on Volkamer lemon (C. volkameriana Tan. & Pasq.) rootstock exposed to drying soil. For each tree, the fine roots were removed from two woody lateral roots, the roots were surface sterilized and then each woody root was placed in a separate pair of vertically divided and independently irrigated soil compartments. The two split-pot systems were filled with sterilized soil and one was inoculated with arbuscular mycorrhizal fungi (Glomus etunicatum/G. intraradices). New fine lateral roots that emerged from the woody laterals were permitted to grow inside the pots over a 10-month period. Irrigation was then removed from the top compartment for a 15-week period. At the end of the study, roots inoculated with AM fungi exhibited about 20% incidence of AM formation, whereas the uninoculated roots were completely void of AM fungi. Arbuscular mycorrhizal roots exhibited lower SRL, lower root/soil respiration and about 10% lower fine root mortality than nonmycorrhizal roots after 15 weeks of exposure to dry surface soil. This study demonstrates the feasibility of examining mycorrhizal effects on the fine roots of adult trees in the field using simple inexpensive methods.     

The classification and frequency of ectotrophic mycorrhizas onPinus radiata D. Don. in New Zealand

Summary Eight subtypes and thirteen sub-subtypes of ectotrophic mycorrhizas were identified in New Zealand onPinus radiata. Subtype B occurred most frequently. The maximum occurrence of ectotrophic mycorrhizas was in New Zealand conditions at the end of winter and beginning of spring.     

Sebacinales are common mycorrhizal associates of Ericaceae

Previous reports of sequences of Sebacinales (basal Hymenomycetes) from ericoid mycorrhizas raised the question as to whether Sebacinales are common mycorrhizal associates of Ericaceae, which are usually considered to associate with ascomycetes. Here, we sampled 239 mycorrhizas from 36 ericoid mycorrhizal species across the world (Vaccinioideae and Ericoideae) and 361 mycorrhizas from four species of basal Ericaceae lineages (Arbutoideae and Monotropoideae) that do not form ericoid mycorrhizas, but ectendomycorrhizas. Sebacinales were detected using sebacinoid-specific primers for nuclear 28S ribosomal DNA, and some samples were investigated by transmission electron microscopy (TEM). Diverging Sebacinales sequences were recovered from 76 ericoid mycorrhizas, all belonging to Sebacinales clade B. Indeed, some intracellular hyphal coils had ultrastructural TEM features expected for Sebacinales, and occurred in living cells. Sebacinales belonging to clade A were found on 13 investigated roots of the basal Ericaceae, and TEM revealed typical ectendomycorrhizal structures. Basal Ericaceae lineages thus form ectendomycorrhizas with clade A Sebacinales, a clade that also harbours ectomycorrhizal fungi. This further supports the proposition that Ericaceae ectendomycorrhizas involve ectomycorrhizal fungal taxa. When ericoid mycorrhizas evolved secondarily in Ericaceae, a shift of mycobionts occurred to ascomycetes and clade B Sebacinales, hitherto not described as ericoid mycorrhizal fungi.     

In situ and in vitro colonization of Cathaya argyrophylla (Pinaceae) by ectomycorrhizal fungi

Cathaya argyrophylla, a critically endangered conifer, is found to grow at four isolated areas located in subtropical mountains of China. To examine the involvement and usefulness of mycorrhizas for sustaining the population of this tree, we compared the root system, morphology, and structure of mycorrhizal roots of C. argyrophylla, which were collected from a natural stand and an artificial stand, each grown at a different location. More mycorrhizal roots were found for trees from an artificial stand. The presence of extramatrical mycelium, mantle, and Hartig net revealed that C. argyrophylla formed an ectomycorrhizal association in both sampling sites. Starch granules were found in mycorrhizal roots collected only from a natural stand. The aseptic synthesis of C. argyrophylla and Cenococcum geophilum was established for the first time in vitro. Typical ectomycorrhizas formed on seedlings on RM medium containing 0.1 g/l glucose, 5 weeks after inoculation. By light microscopy, the synthesized mycorrhizas showed a thin mantle from which emanated extramatrical hyphae and highly branched Hartig net. A simple, rapid, and convenient mycorrhiza synthesis system was developed, which facilitates further studies on ectomycorrhizal development of C. argyrophylla.     

贵州中部喀斯特山地不同植被生态系统细根生态特征及养分储量

为了解喀斯特生态系统退化过程中树木细根生物量和土壤养分的变化,选择贵州中部喀斯特山地乔木林、灌木林和灌草丛3种植被生态系统,比较分析不同深度(0～5 cm、5～10 cm和10～15 cm)土壤细根数量及其养分情况.结果表明:树木细根主要分布在0～10 cm土层,并随土层加深而减少.在0～10 cm土层中,乔木林、灌木林和灌草丛的活细根生物量分别占0～15 cm总细根生物量的42.78%、56.75%和53.38%,总活细根生物量的83.36%、86.91%和93.79%.不同植被下优势种植物细根生物量存在差异.0～5 cm土层乔木林活细根氮素和磷素储量均显著高于灌草丛和灌木林(P0.05),但灌木林和灌草丛间没有差异;5～10 cm土层乔木林活细根氮和磷储量显著高于灌草丛和灌木林(P0.05),灌木林下又显著高于灌草丛下(P0.05).0～10 cm土层的活细根生物量与植株地上部分生物量呈正相关,植物叶片氮、磷养分含量与细根比根长呈显著的负相关,说明细根的养分储量对地上生物量的建成和生态系统功能的发挥具有重要作用.     

Role of basidiospores as inocula of mycorrhizal fungi of birch

Summary Fruitbodies of sheathing mycorrhizal fungi collected under birch (Betula pendula andB. pubescens) were suspended over pots of soil and the resulting spore-supplemented soils were planted with sedlings ofB. pendula. Inocybe lacera, I. lanuginella, Hebeloma sacchariolens andH. leucosarx formed mycorrhizas readily.Lactarius pubescens andLeccinum roseofracta did not form mycorrhizas from basidiospore inocula, even after prolonged periods of seedling growth.Paxillus involutus gave equivocal results, perhaps because the soil was unsuitable for this species. Storage of the basidiospore-supplemented soils for 6 months in outdoor conditions or in a growth room at 18°C did not materially alter the results.The results are discussed in relation to the concept of mycorrhizal succession.     

Does liquid fertilization affect fine root dynamics and lifespan of mycorrhizal short roots?

We studied effects of nitrogen, other nutrients and water (liquid fertilization; LF) on fine root dynamics (production, mortality) and life span of mycorrhizal short roots in a Norway spruce stand, using minirhizotrons. Data were collected and analyzed during a two-year period at depths of 0–20 cm, 21–40 cm and 41–85 cm, six years after the start of treatment. Relative to control (C), root production was lower in LF plots at depth 0–20 cm. Root production increased significantly at depth 41–85 cm. Fine root mortality in LF plots was higher at all depths. Life span of mycorrhizal short roots in LF plots was significantly lower than C plots and at the end of the study no mycorrhizal short roots were alive. It is suggested that the water and nitrogen input lower longevity of mycorrhizal short roots and promote fine root production at deeper soil layers.     

伪潜育土季节性滞水条件下大冷杉(Abies grandis Lindl.)毫根动态的研究

本文对一个25年生大冷杉林在伪潜育土至45cm矿质土壤里,从1987年晚秋滞水期至1988年生长旺盛期的毫根量动态及化学组成变化进行了研究。滞水期土壤中死根量(5558kg Ds／ha)显著高于活根量(3594kg DS／ha)。生长旺盛期初,括根量增加约50％,死根量降低约27％。经过夏季至生长旺盛期末,活根量仍略有增加,死根量继续降低。毫根化学组成分析显示,滞水期活根中K、Mg及Zn九离子含量显著低于生长旺盛期,Mn离子含量则明显高于生长旺盛期。这一结果表明,除了与季节性相关的生长节奏因素外,大冷杉毫根生物量的变化主要是由滞水状况所致。     

Comparative study of mycorrhizal susceptibility and anatomy of four palm species

A morphological and anatomical study of the root systems of the palm species Brahea armata S. Watson, Chamaerops humilis L., Phoenix canariensis Chabaud and Phoenix dactylifera L. has been carried out to determine possible mycorrhizal colonization sites. Furthermore, the arbuscular mycorrhizal (AM) anatomical types formed by the four palm species in association with Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe have been examined. The presence of a continuous sclerenchymatic ring in the outer cortex and aerenchyma in the inner cortex that are anatomical indicators of mycorrhizal nonsusceptibility in all four palm species is observed. The root systems of B. armata and C. humilis present only one group of third-order roots, while the third-order roots of P. canariensis and P. dactylifera may be divided into five different groups: short thick roots, mycorrhizal thickened roots, fine short roots, fine long roots, and pneumatorhizas. Third-order and some second-order roots of B. armata and C. humilis are susceptible to colonization by AM fungi, while only the mycorrhizal thickened roots form mycorrhizas with arbuscules in the Phoenix species. The root system of the Phoenix species also presents AM colonization in fine roots with only intraradical hyphae and spores, but without arbuscules, and pseudomantles of spores anchored in the pneumatorings of the second-order roots, which are described for the first time. The mycorrhizas formed by the four palm species are of an intermediate type, between the Arum and the Paris types, and are characterized by intercalary arbusculate coils and not only by intracellular but also by intercellular fungal growth. Our study suggests that a different degree of adaptation may exist among palm mycorrhizas toward the slow growth of palms and low spore numbers in the soil where they grow.     

Tissue-Specific and Development-Dependent Accumulation of Phenylpropanoids in Larch Mycorrhizas

The tissue-specific and development-dependent accumulation of secondary products in roots and mycorrhizas of larch (Larix decidua Mill.; Pinaceae) was studied using high-performance liquid chromatography and histochemical methods. The compounds identified were soluble catechin, epicatechin, quercetin 3-O-[alpha]-rhamnoside, cyanidin- and peonidin 3-O-[beta]-glucoside, 4-O-[beta]-hydroxybenzoyl-O-[beta]-glucose, 4-hydroxybenzoate 4-O-[beta]-glucoside, maltol 3-O-[beta]-glucoside, and the wall-bound 4-hydroxybenzaldehyde, vanillin, and ferulate. In addition, we partially identified a tetrahydroxystilbene monoglycoside, a quercetin glycoside, and eight oligomeric proanthocyanidins. Comparison between the compounds accumulating in the apical tissue of fine roots, long roots, and in vitro grown mycorrhizas (L. decidua-Suillus tridentinus) showed elevated levels of the major compounds catechin and epicatechin as well as the minor compound 4-hydroxybenzoate 4-O-[beta]-glucoside specifically in the root apex of young mycorrhizas. The amounts of wall-bound 4-hydroxybenzaldehyde and vanillin were increased in all of the mycorrhizal sections examined. During the early stages of mycorrhization the concentrations of these compounds increased rapidly, perhaps induced by the mycorrhizal fungus. In addition, studies of L. decidua-Boletinus cavipes mycorrhizas from a natural stand showed that the central part of the subapical cortex tissue and the endodermis both accumulate massive concentrations of catechin, epicatechin, and wall-bound ferulate compared with the outer part of the cortex, where the Hartig net is being formed.     

Occurrence of arbuscular mycorrhizal fungi in a phosphorus-poor wetland and mycorrhizal response to phosphorus fertilization

The presence of arbuscular mycorrhizas in fens has received little attention, but because fen plants are often phosphorus limited, the plant-fungus interaction could be an important factor in plant competition for phosphorus. In this field study, we determined mycorrhizal colonization rates for 18 fen plant species. Also in the field, we examined the effect of four different forms of phosphorus on the percentage colonization for one fen plant species, Solidago patula. We found that in a species-rich, phosphorus-poor wetland both mycorrhizal and nonmycorrhizal species were common. Nine of ten dicotyledonous species examined formed arbuscular mycorrhizas, while all monocotyledonous species were at most very weakly mycorrhizal. A morphological explanation for this pattern is that the monocots in our study have more extensive aerenchyma, especially in coarse roots. Therefore, monocots are able to transport oxygen to their roots more effectively than dicots. In the organic wetland soil, additional oxygen in the rhizosphere promotes phosphorus mineralization and availability. Two of the monocot species (Typha latifolia and Carex lasiocarpa), which have been described previously as mycorrhizal in other wetland types, are surprisingly nonmycorrhizal in our phosphorus-poor study site, suggesting that a mycorrhizal association would not offer improved phosphorus nutrition to these species. In contrast, our field phosphorus addition decreased mycorrhizal colonization in S. patula, suggesting that one benefit to S. patula of the mycorrhizas is phosphorus uptake.     

Arbuscular mycorrhizal colonization delays nucleus senescence in leek root cortical cells

Arbuscular mycorrhizas are a widespread symbiosis between soil fungi and plant roots. Flow cytometry, after DNase I partial digestion and DAPI staining, and light and electron microscopy were used to analyse chromatin condensation and nuclear conditions in mycorrhizal and control roots of Allium porrum . The 2C peak, detected by flow cytometry, split into two peaks representing two populations of nuclei, one more resistant and one more susceptible to the enzyme action. The microscopic analyses showed the presence of pyknotic and chromatolytic nuclei, two typical features of senescence. In order to quantify the senescing process, a terminal deoxynucleotidyl transferase assay was performed on extracted nuclei, later analysed by flow cytometry. The numbers of senescing nuclei and their DNA cleavage were higher in control plants. Our results show the existence of senescing nuclei in cortical cells of the bulbous monocotyledon A. porrum and the delaying effect of arbuscular mycorrhizas on senescence.     

Impact of <Emphasis Type="Italic">Heterobasidion</Emphasis> root-rot on fine root morphology and associated fungi in <Emphasis Type="Italic">Picea abies</Emphasis> stands on peat soils

We examined differences in fine root morphology, mycorrhizal colonisation and root-inhabiting fungal communities between Picea abies individuals infected by Heterobasidion root-rot compared with healthy individuals in four stands on peat soils in Latvia. We hypothesised that decreased tree vitality and alteration in supply of photosynthates belowground due to root-rot infection might lead to changes in fungal communities of tree roots. Plots were established in places where trees were infected and in places where they were healthy. Within each stand, five replicate soil cores with roots were taken to 20 cm depth in each root-rot infected and uninfected plot. Root morphological parameters, mycorrhizal colonisation and associated fungal communities, and soil chemical properties were analysed. In three stands root morphological parameters and in all stands root mycorrhizal colonisation were similar between root-rot infected and uninfected plots. In one stand, there were significant differences in root morphological parameters between root-rot infected versus uninfected plots, but these were likely due to significant differences in soil chemical properties between the plots. Sequencing of the internal transcribed spacer of fungal nuclear rDNA from ectomycorrhizal (ECM) root morphotypes of P. abies revealed the presence of 42 fungal species, among which ECM basidiomycetes Tylospora asterophora (24.6 % of fine roots examined), Amphinema byssoides (14.5 %) and Russula sapinea (9.7 %) were most common. Within each stand, the richness of fungal species and the composition of fungal communities in root-rot infected versus uninfected plots were similar. In conclusion, Heterobasidion root-rot had little or no effect on fine root morphology, mycorrhizal colonisation and composition of fungal communities in fine roots of P. abies growing on peat soils.     

Mycorrhizal colonization of transgenic aspen in a field trial

Mycorrhizal colonization of genetically modified hybrid aspen (Populus tremula x P. tremuloides Michx.) was investigated over 15 months in a field experiment. The aspen carried the rolC gene from Agrobacterium rhizogenes under control of either the constitutive cauliflower mosaic virus 35S promoter or the light-inducible rbcS promoter. Arbuscular mycorrhizas (AMs) were rare in all root samples, while fully developed ectomycorrhizas (EMs) were found in all samples. No significant differences in the degree of mycorrhizal colonization between aspen lines were seen with either AMs or EMs. The EM community on the release area was dominated by four fungal species that formed more than 90% of all mycorrhizas, while eleven EM types were found occasionally. Mycorrhizal diversity did not differ between transgenic and non-transgenic trees. The structure of mycorrhizal communities was similar for most aspen lines. The sole significant difference was found in the abundance and development of one of the four common EM morphotypes, which was rare and poorly developed on roots from the transgenic aspen line Esch5:35S-rolC-#5 compared with non-transgenic controls. This effect is clone specific as the formation of this EM type was not affected by the transgene expression in the other transgenic line, Esch5:35S-rolC-#1. This is the first demonstration of a clonal effect influencing the ability of a transgenic plant to form a mycorrhizal symbiosis with a potential fungal partner.     

The concept of succession in relation to the spread of sheathing mycorrhizal fungi on inoculated tree seedlings growing in unsterile soils

Summary Repeated annual assessments of the toadstools (fruitbodies) of mycorrhizal fungi associated with a mixed stand ofBetula spp. indicated that they were produced in a pattern ordered in time and space, suggesting a succession with identifiable early-and late-stage fungi. This concept is supported by below-ground observations of mycorrhizas which, however, need to be augmented.Both early- and late-stage mycorrhizal fungi form mycorrhizas on seedlings growing in axenic (aseptic) conditions. In contrast, only early-stage fungi seem able to trigger mycorrhizal formation on seedlings growing in unsterile soils.During axenic propagation, the early-stageHebeloma sacchariolens and the late-stageAmanita muscaria formed similar numbers of mycorrhizas per root system. After being transplanted to a range of unsterile field soils,A. muscaria failed to keep pace with the spread of the developing root system: no moreA. muscaria mycorrhizas were formed. On the other hand the continued development ofH. sacchariolens mycorrhizas precluded, during the first season after transplanting, the development of mycorrhizas by fungi naturally occurring in field soils. In the second season, however, the development ofH. sacchariolens mycorrhizas was restricted in acid peat but not in three other types of soil.The development ofLaccaria mycorrhizas after inoculating Sitka spruce with this fungus was associated, irrespective of soil type, with accelerated tree growth; with heights at the end of the first season being doubled.     

Protein patterns and superoxide dismutase activity in non-mycorrhizal and arbuscular mycorrhizalPisum sativum L. plants

There are few reports in relation to the role of specific proteins in the mycorrhizal symbiosis. Among the changes in the protein expression as a consequence of the arbuscular mycorrhizal symbiosis, only one case related to changes in superoxide dismutase (SOD; EC 1.15.1.1) activity has been reported in the red clover-Glomus mosseae symbiosis.In this paper, the symbiotic system formed by a leguminous plant,Pisum sativum, and the fungusGlomus mosseae is studied in terms of protein patterns and SOD activity in both mycorrhizal and non-mycorrhizal roots. Our results show that among the differential polypeptides separated by SDS-PAGE, one with a molecular weight of 32.0 kDa, and a protein with an isoelectric point of pI 4.9 appeared strongly expressed in mycorrhizal roots. A partial purification of the related polypeptide could be achieved by DEAE-cellulose chromatography. A higher SOD activity was also detected in mycorrhizal pea roots, although both mycorrhizal and non-mycorrhizal roots showed the same isoenzymatic pattern for SODs: two Mn-SODs (I and II) and two Cu,Zn-SODs (I and II) were detected, Cu,Zn-SOD I being the most abundant isozyme in both types of roots. A similar pattern of SOD isozymes (Mn-SODs I and II, and Cu,Zn-SODs I and II) was also found in nodules of mycorrhizal and non-mycorrhizal pea roots. However, in nodules Mn-SOD II was the main isozyme. The bacterial nature of this isozyme is postulated in this report.Dr. Justo Arines died on the 15th November, 1993 in Dijon (France), while he was attending a molecular biology course on mycorrhizas.     

Epiphytic and terrestrial mycorrhizas in a lower montane Costa Rican cloud forest

The epiphyte community is the most diverse plant community in neotropical cloud forests and its collective biomass can exceed that of the terrestrial shrubs and herbs. However, little is known about the role of mycorrhizas in this community. We assessed the mycorrhizal status of epiphytic (Araceae, Clusiaceae, Ericaceae, and Piperaceae) and terrestrial (Clusiaceae, Ericaceae) plants in a lower montane cloud forest in Costa Rica. Arbuscular mycorrhizas were observed in taxa from Araceae and Clusiaceae; ericoid mycorrhizas were observed in ericaceous plants. This is the first report of intracellular hyphal coils characteristic of ericoid mycorrhizas in roots of Cavendishia melastomoides, Disterigma humboldtii, and Gaultheria erecta. Ericaceous roots were also covered by an intermittent hyphal mantle that penetrated between epidermal cells. Mantles, observed uniquely on ericaceous roots, were more abundant on terrestrial than on epiphytic roots. Mantle abundance was negatively correlated with gravimetric soil water content for epiphytic samples. Dark septate endophytic (DSE) fungi colonized roots of all four families. For the common epiphyte D. humboldtii, DSE structures were most abundant on samples collected from exposed microsites in the canopy. The presence of mycorrhizas in all epiphytes except Peperomia sp. suggests that inoculum levels and environmental conditions in the canopy of tropical cloud forests are generally conducive to the formation of mycorrhizas. These may impact nutrient and water dynamics in arboreal ecosystems.     

Effect of soil temperature on nutrient allocation and mycorrhizas in Scots pine seedlings

We studied the effect of soil temperature on nutrient allocation and mycorrhizal development in seedlings of Scots pine (Pinus sylvestris L.) during the first 9 weeks of the growing season. One-year-old seedlings were grown in Carex-peat from a drained and forested peatland at soil temperatures of 5, 9, 13 and 17 °C under controlled environmental conditions. Fourteen seedlings from each temperature treatment were harvested at intervals of three weeks and the current and previous year's parts of the roots, stems and needles were separated. Mineral nutrient and Al contents in all plant parts were determined and the tips and mycorrhizas of the new roots were counted. Microbial biomass C and N in the growth medium were determined at the end of the experiment. None of the elements studied, except Fe, were taken up from the soil by the seedlings during the first three weeks. Thereafter, the contents of all the elements increased at all soil temperatures except 5 °C. Element concentrations in needles, stems and roots increased with soil temperature. Higher soil temperature greatly increased the number of root tips and mycorrhizas, and the numbers of mycorrhizas increased more than did the length of new roots. Cenococcum geophilum was relatively more abundant at lower soil temperatures (5 and 9 °C) than at higher ones (13 and 17 °C). A trend was observed for decreased microbial biomass C and N in the peat soil at higher soil temperatures at the end of the experiment.