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Community Dynamics of Ectomycorrhizal Fungi Following the Vision Fire

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Community Dynamics of Ectomycorrhizal Fungi 33Thomas D. Bruns, Jacqueline Baar, Paul Grogan, Thomas R. Horton, Annette M. Kretzer, Dirk Redecker, Jenny Tan, and D. Lee TaylorDepartment of Plant and Microbial BiologyUniversity of California BerkeleyIntroductionMany people that read this chapter may be aware of mammals, birds, and maybe even plant species that are common at Point Reyes, and may have witnessed or have been aware of the ways that these organisms responded to the Vision fi re of 1995. Few will be familiar with fungal species at Point Reyes, and even fewer may have noticed their response to the fi re. This is un for tu nate, be cause fungi play many critical roles in structuring and maintaining plant (and therefore also animal) communities at Point Reyes. It is un der stand able, however, because even those of us that study fungi for a living know less about them than plant or animal biologists typically know about their or gan isms. There are several reasons for our collective ignorance. Fungi can be diffi cult to identify, so reliable species records are rare. For most of their lives, fungi are microscopic and hidden in soil or plant parts; this makes it diffi cult to observe their basic life histories and ecology. Finally, relatively few people study fungi, especially when one considers that there are roughly six species of fungi for every plant species on the planet (Hawksworth 1990). The good news is that there is much to learn, and the Vision fi re provided an exceptional oppor-tunity to do exactly that. Getting to the root of Point Reyes plant communitiesThe goal of this chapter is to heighten aware-ness of the role of ectomycorrhizal fungi and to relate what we have learned about this group from the Vision Fire. To start this process it is important for the reader to understand that in nature fi ne roots of most plants are not simply plants. Instead, they are colonized by fungi in mutualistic interactions known as mycorrhizae. This symbiosis is a way that plants “con tract-out” the specialized function of collecting min-eral nutrients from soil. They pay their fungal partners with sugar, and in return fungi provide phosphorus, nitrogen, and other mineral nutri-ents to plants. The vast majority of land plants are nor mal ly my c or rhizal, and some plants, such as pines and oaks, require these fungi for normal growth. Similarly, most fungi involved in mycorrhizal sym bi o ses, require plants.At Point Reyes, and elsewhere, there are three main types of my c or rhizal in ter ac tions. Diff er-ent groups of fungi are involved with each, and plants are generally restricted to one of these three groups (Table 1). For a pine seedling to grow and compete, it must encounter an ecto-mycorrhizal fungus within the fi rst few months. There are two basic forms of fungi that an uncolonized pine root can encounter: spores and sclerotia, or mycelium. Spores and sclero-tia are roughly microscopic equivalent of seeds and tubers, respectively, in plants, and they can be dispersed in various ways to new locations. Myce li um (Fig 1a) is the growing body of a fungus. It is made up of thread-like hyphae. Mycelium can spread locally from a colonized root to a new uncolonized root of a seedling. Note that this latter type of col o ni za tion can only work if living roots of a plant, that uses the same general type of my c or rhizal fungi, are in the im me di ate neighborhood. For example, fungi found on roots of coyote bush and pines are diff erent, and, there fore, pine cannot rely on coyote bush as a reservoir for its fungi. In Community Dynamics of Ectomycorrhizal Fungi Following the Vision FireTable 1: The three main Mycorrhizal types found at Point Reyes Mycorrhizal Type Examples of Plants Examples of FungiEctomycorrhizae bishop pine, Dou glas-fi r, tanbark Basidiomycetes: mushrooms, boletes,(EM or Ecto) oak, live oak, manzanita, madrone, alder chanterelles, false- truffl es, crusts; and Ascomycetes: cup fungi, and true truffl es. Ericoid mycorrhizae huckleberry, salal Ascomycetes: particularly Hymenoscyphus ericae, and close relatives.Arbuscular mycorrhizae Most plants: coyote bush, California Glomalean fungi: microfungi(AM, VAM, or endo) lilac, poison oak, bay laurel, grasses, (e.g. Glo mus, Acaulospora, Gigaspora) ferns, herbs34 Vision Fire - Lessons Learned from the 1995 fi recontrast, Douglas-fi r and pine, or coyote bush and poison oak, share many of the same fungi, and so one plant may in ad vert ent ly supply its neighbor with fungi.There is a genetic diff erence between spores and mycelium. Spores are pro duced in fruiting bodies such as mushrooms or truffl es, and they are usually the prod uct of a sexual recom-bination (i.e., they are products of mei o sis); therefore each spore is genetically unique. This is diff erent from mycelial growth or sclerotia which are vegetatively (i.e. mitotically) produced and therefore result in the spread of identical fungal genotypes. Understanding this point is important, because later in this chap ter we use knowledge of fungal gen o types to infer whether fungi spread primarily by spores or veg e ta tive growth. The pre-fi re ectomycorrhizal communityWe have studied mycorrhizal fungi associated with Bishop pine in the Limantour road area of Point Reyes since 1991. We have done this in two ways. First, we have collected mushrooms, truffl es, and other fruiting bodies of fungi of interest. Second, we have examined roots of Bishop pine trees or seedlings and used molecular-based identifi cation methods to catalogue fungi present and to quantify their frequencies and abundance (Table 2).This work has revealed several interesting features of mycorrhizal community associated with Bishop pine. One of the most unexpected fi ndings of our early work was that some species that exhibit the most abundant fruit- ing were rare or low abundance species on roots, and conversely, some spe cies that were dominant colonizers of roots,


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