Botany Blog Plants of the Northeastern U.S.

March 23, 2010

Mycorrizae and Sugar Maple

Filed under: Mycorrhizae — admin @ 02:51

I currently have an experiment in progress with the goal of testing if AM fungi aid in the establishment of seedlings that exhibit epicotyl dormancy. One of the experimental treatments involves planting a seed with that trait along with seedlings of Sugar Maple (Acer saccharum). The Sugar Maple is included as a carbon source in the symbiotic relationship. The reason I am using Sugar Maple is that it forms mycorrhizae with AM fungi, unlike most other trees which associate with ectomycorrhizae.

Unfortunately the germination rates for the Sugar Maple seeds have been very poor so the experiment is not likely to yield results that would survive peer review. However, those that have are already exhibiting what appears to be a significant difference in size between the treatments with AM fungi and those without.


The Maple seedlings on the right were treated with spores of several Glomus spp. shortly after germination. The seedlings on the left were grown in sterile media with no Glomus spp.  In a few months I plan to remove the seedlings, dry them and then weigh them. A portion of the roots will be saved and examined for the presence of aseptate hyphae.

February 28, 2010

Dark Septate Endophytes

Filed under: Mycorrhizae — admin @ 02:49

Dark septate endophytes (DSE) are a heterogenous group of conidial or sterile fungi (thought to be ascomycetes) with darkly-pigmented, septate hyphae that commonly colonize plant roots. Most DSE also produce intracellular structures called microsclerotia. It has been suggested that these microsclerotia may serve as dispersal structures (Currah et al., 1993), although the actual purpose appears to be unknown. Perhaps they serve a storage function for the fungi as do the vesicles of AM fungi?

The following images show septate hyphae of a DSE growing in and around a root of Eurybia divaricata. The first image shows net-like strands formed by the hyphae of a DSE:

DSE covering a root of White Wood Aster

 The next image depicts several hyphae ending in microsclerotia, which appear as grape-like clusters.

Dark septate hyphae and miscrosclerotia

Another  morphotype can be seen with a root of Maianthemum racemosum in the following image:

Microsclerotia in a root of False Solomon’s Seal

The taxonomy of this group is poorly understood and little is known of the role that DSE play in natural ecosystems (see review by Jumpponen and Trappe 1998). DSE are difficult to identify from field samples so many may not yet be known. A few of the species identified to date (mostly from bioassays) include Chloridium paucisporum, Leptodontidium orchidicola, Phialocephala dimorphosphora, Phialocephala fortinii, and Phialophora finlandia. Of these, Phialocephala fortinii appears to be the best studied. Unlike AM fungi, the DSE that have been studied to date do not require a plant host and many can be grown as pure cultures.

Available evidence suggests that DSE range from strongly pathogenic to non-pathogenic to mycorrhizal for plants. Some strains of DSE may be involved in host plant nutrient acquisition and it has been proposed that this may be a mutualistic, mycorrhiza-like relationship (Jumpponen and Trappe 1998). These relationships do not appear to be host specific (Jumpponen and Trappe 1998), with some strains forming ectendomycorrhizas but also associating with other hosts in ways not completely understood (Jumpponen 2001).

Although their mycorrhizal status is uncertain (Jumpponen and Trappe 1998), DSE are commonly associated with the roots of herbaceous and woody plants from alpine, boreal and northern temperate ecosystems (Haselwandter and Read 1980, Holdenrieder and Sieber 1992; O’Dell et al. 1993; Ahlich and Sieber 1996). To date, carbohydrate flow from a host plant to a DSE has not yet been demonstrated as it has for AMF (Jumpponen 2001). Despite their ubiquity in terrestrial ecosystems, the role of DSE in plant nutrient acquisition and plant community assemblage remains largely unknown. Given the ubiquity of DSE in many terrestrial ecosystems and their possible mycorrhiza-like relationships with plants, studying this group of fungi could increase our understanding of plant community assemblage.

Literature Cited:

Ahlich, K. and T.N. Sieber. 1996. The profusion of dark septate endophytic fungi in non-ectomycorrhizal fine roots of forest trees and shrubs. New Phytologist 132:259-270.

Currah, R.S., Tsuneda, A., and Murakami, S. 1993. Morphology and ecology of Phialocephala fortinii in roots of Rhododendron brachycarpum. Canadian Journal of Botany 71:1639-1644.

Haselwandter, K. and D.J. Read. 1980. Fungal associations of roots of dominant and sub-dominant plants in high-alpine vegetation systems with special reference to mycorrhiza. Oecologia 4:557-62.

Holdenrieder, O. and T.N. Sieber. 1992. Fungal associations of serially washed healthy non-mycorrhizal roots of Picea abies. Mycological Research 96:151-156.

Jumpponen, A. and J.M. Trappe. 1998. Dark septate endophytes: a review of facultative biotrophic root-colonizing fungi. New Phytologist 140:295-310.

Jumpponon, A. 2001. Dark septate endophytes – are they mycorrhizal? Mycorrhiza 11:207-211.

O’Dell, T.E., H.B. Massicotte and J.M. Trappe. 1993. Root colonization of Lupinus latifolius Agardh. and Pinus contorta Dougl. By Phialocephala fortinii Wang & Wilcox. New Phytologist 124:93-100.

November 29, 2009

Mycorrhizae of False Solomon’s Seal

Filed under: Mycorrhizae — admin @ 02:53

This image shows the pattern of mycorrhization in a root of Maianthemum racemosum (False Solomon’s Seal), a plant of rich, mesic forests in the northeastern USA.

AM Fungi

In eastern deciduous forests, 60-74% of herbaceous plants regularly exhibit colonization by arbuscular mycorrhizal fungi (AMF) (McDougall and Liebtag 1928; Brundrett and Kendrick 1988). Mycorrhizal symbioses improve plant assimilation of phosphorus (P) and nitrogen (N) (e.g. Baylis 1959; Holevas 1966; Johansen et al. 1992; Frey and Schüepp 1993; Van der Heijden et al. 1998; Hodge et al. 2001).

Many woodland herbs form air channels in the roots to improve gas exchange and these structures are also thought to facilitate colonization by AMF (Brundrett and Kendrick 1988). Often these plants have soft, thick roots that either lack root hairs or have short, sparse root hairs (magnolioid-type) and are thus more dependent on AMF for P uptake in mature forest soils (Baylis 1975).

As seen in the image above, an external hypha gives rise to a structure call an appressorium (Ap) which penetrates a short cortical cell and forms a hyphal coil (C). From there the fungus eventually enters air channels and spreads along length of root. The fungus can produce lipid-rich structures called vesicles (V) to store energy. Examination of fungal features in plant roots is facilitated by first clearing them in a solution of KOH (potassium hydroxide). The roots can then stained using Chlorozal Black E to improve contrast (Brundrett et al. 1996).

The seedlings of False Solomon’s Seal (below) exhibit epicotyl dormancy (a type of double-dormancy); following the first winter, the radicle emerges and the seedlings establishes a modest root system and a small shoot tip during the first growing season. The shoot does not emerge until the following spring, which means that for the first year of growth no photosynthesis takes place in the seedling.

Seedlings of False Solomon’s Seal

Literature cited:

Baylis, G.T.S. 1959. Effect of vesicular-arbuscular mycorrhizas on growth of Griselinia littoralis (Cornaceae) New Phytologist 58(3):274-280.

Brundrett, M.C. and B. Kendrick. 1988. The mycorrhizal status, root anatomy, and phenology of plants in a sugar maple forest. Canadian Journal of Botany 66:1153-1173.

Brundrett, M.C., N. Bougher, B. Dell, T. Grove and N. Malajczuk. 1996. Working with mycorrhizas in forestry and agriculture. The Australian Centre for International Agricultural Research. Monograph, Canberra, Australia. 375p.

Frey, B. and H. Schüepp. 1993. The role of vesicular–arbuscular (VA) mycorrhizal fungi in facilitating inter-plant nitrogen transfer. Soil Biology and Biochemistry 25:651-658.

Hodge, A., C.D. Campbell and A.H. Fitter. 2001. An arbuscular mycorrhizal fungus accelerates decomposition and acquires nitrogen directly from organic material. Nature 413:297-299.

Holevas, C.D. 1966. The effect of a vesicular-arbuscular mycorrhizal on the uptake of soil phosphorus by strawberry (Fragaria sp. var. Cambridge Favorite). Journal of Horticultural Science 41:557-64.

Johansen, A., I. Jakobsen and E.S. Jensen. 1992. Hyphal transport of N-15-labeled nitrogen by a vesicular-arbuscular mycorrhizal fungus and its effect on depletion of inorganic soil-N. New Phytologist 122:281-288.

McDougall, W.B. and C. Liebtag. 1928. Symbiosis in a Deciduous Forest. III. Mycorhizal Relations. Botanical Gazette 86(2):226-234.

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