Recent advances in sequencing technologies have allowed researchers to describe microbial richness in very fine resolution. Typically sequences are categorized into OTUs (operational taxanomic units) based on 95%, 98%, or 99% similarity between sequences. For example, Zimmerman and Vitousek found 4063 fungal endophyte OTUs (95% cutoff) on the leaves of one species of tree (Metrosideros polymorpha) at 13 sites (10 trees per site). Even with a tremendous number of OTUs, this and other microbial genetic surveys conclude that sampling may be insufficient as is evident by the lack of asymptotic response of rarefaction curves. What is the “usefulness” of this number of OTUs from an ecological perspective, in other words what does this number of species “do” for the system? To this end it might be useful to assign functionality to groups of OTU’s so that functional diversity could be incorporated into these studies. This thought led me to a review of fungal endophytes function by Rodriguez et al. 2009 in the New Phytologist. As a fungal neophyte (not endophyte) I found the review helpful.
Here are a few highlights:
Clearly, before functional diversity is assigned to OTU groups for ecological comparisons, a great deal of work needs to be done to determine the roles of the highly diverse fungal endophyte groups.
Lisa Marrack
Here are a few highlights:
- All plants in natural ecosystems are symbiotic with fungal endophytes.
- Fungal endophytes may increase plant fitness by boosting stress tolerance, increasing biomass and decreasing water consumption, or decrease fitness by altering resource allocation.
- C-endophytes are found in grass species. C-endophytes produce toxins that deter grazing by many insect and even mammal species. For example, sleepy grass (Achnatherum robustum) contains an endophyte that causes horses who eat small quantities of the grass to sleep up to 3 days. When the horses recover they will avoid the plants. This type of grass-endophyte mutualism is seen worldwide. There is evidence that some C-endophytes may improve water and nutrient uptake as well as protect grasses from other fungal infections but this depends on species specific interactions.
- NC-endophytes are highly diverse and found in most plants. Despite a large number of studies(1000+ since 1970) few have examined the functional roll of NC-endophytes. There are three functional groups of NC-endophytes. Class 2 - Colonize roots, stems and leaves; vertically or horizontally transmitted; broad host range. They increase plant and shoot biomass as well as confer tolerance to abiotic and biotic stresses such as disease, drought, desiccation, heat and salinity. Class 3 – Colonize above ground tissues; horizontally transmitted; broad host range. Include the hyper diverse endophytic fungi associated with leaves of tropical trees and above ground tissues of many plants worldwide. Ecology and function are not well understood. Science may need to look at wider microbial community ecology. Class 4 - Colonize roots; horizontally transmitted; broad host range
Clearly, before functional diversity is assigned to OTU groups for ecological comparisons, a great deal of work needs to be done to determine the roles of the highly diverse fungal endophyte groups.
Lisa Marrack
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