Mycoheterotrophy

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Introduction

Monotropastrum humile

The obligate mycoheterotroph Epipogium roseum

Sarcodes sanguinea

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Mycoheterotrophy is the process by which plants, either wholly or partially achlorophyllous, sustain a heterotrophic metabolism via a fungal partner that provides a source of carbon and mineral nutrients. Mycoheterotrophic plants are considered parasites of their fungal hosts, which are often--but not invariably--associated with the roots of a fully autotrophic plant.

Plants are often obligately mycoheterotrophic, with stunted root systems, degenerated vascular tissue, little or no photosynthetic capacity, and "dust-seeds" that contain a fungal inocula but little or no carbon reserves. The mycoheterotrophic plant-fungal relationship is unique inasmuch as in mutualistic mycorrhizal associations plants are the carbon source while the fungi provide mineral nutrients (primarily phosphorus and nitrogen).

While the effects of obligate mycoheterotrophs are not usually measured on the ecosystem scale, some evidence exists that adult plants can facilitate the recruitment of proximal conspecific seedlings by supplementing their carbon demand through a common mycelial network (i.e., the "wood-wide web"). This process of positive-feedback is thought to be responsible for the establishment of monoculture forest patches dominated by ectomycorrhiza plant species, even within a diverse matrix of surrounding forest. This transitive dependence on an external carbon source is termed mixotrophy.

Mycoheterotrophic plants occur in a diverse and unclustered group of plants, which include liverworts, ferns, and monocot (ex. in the order Orchidales) and some dicot (ex. in the family Monotropideae) angiosperms. The fungal hosts include highly specific functional groups of ectomycorrhiza from the orders Basidiomycota and Ascomycota, sometimes called monotropid and orchid mycorrhizas, as well as some arbuscular mycorrhizas from the order Glomeromycota.

Note that mycoheterotrophy is distinct from the direct plant-plant parasitism that results when plant parasites (ex. mistletoe) develop haustorium that tap directly into a host plant's vascular tissue.

Biological interaction

A plant family tree displaying taxa with mycoheterotrophic individuals with a dashed line. From Bidartondo (2005).

The earliest known drawing of a mycorrhizal fungus (left, from 1888), showing the sheathing of hyphae along the root epidermis and a layer of dead plant cells. An electron micrograph (right) of the infected roots of the mycoheterotrophic afrothismisa from 2005 shows the same thing in three-dimensions (see Dr. Hans Christian Weber's research profile).

Provide details of the symbiosis or biological interaction. Is this a specific or general interaction? How do these interactions influence the host or other microbial populations, and their activities? How do these interactions influence other organisms (positive or negative influences)? What is the outcome of this interaction? Are there ecological consequences? Describe biological interactions using as many sections/subsections as you require. Look at other topics available in MicrobeWiki. Create links where relevant.

Niche

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Microbial processes

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Key Microorganisms

Bidartondo (2005)

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Microbial processes

What microbial processes are important for this microbial interaction? Does this microbial interaction have some ecosystem-level effects? Does this interaction affect the environment in any way? Describe critical microbial processes or activities that are important in this interaction, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.

Current Research

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References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by <your name>, a student of Angela Kent at the University of Illinois at Urbana-Champaign.