Fungi constitute an essential component in forest and grassland ecosystems because of their roles as parasites of plants and animals, decomposers of organic matter, and mutualistic symbionts such as in lichens and mycorrhizae. Data on distribution patterns of macrofungi are important for understanding the evolution of fungi and the relationship between fungi and their associated plants.
Although the climatic and phytogeographical affinities between eastern Asia and eastern North America have been recognized since the time of Linnaeus (e.g., Boufford, 1994; Raven, 1972; Wu, Z.-Y., 1983), the possibility of a similar relationship between macrofungi of eastern Asia and eastern North America remains to be tested (Wu & Mueller, 1997). Basic questions such as the extent and level of similarity between the mycotas (fungal equivalent to flora and fauna) of the two regions have not been rigorously addressed. Two of the factors contributing to this situation are: 1) mycotas in many areas of the world, including Asia and North America, are not adequately known, and 2) a serious lack of interaction and information exchange between mycologists in Asia and North America. While the global occurrence and distribution of many macrofungi will remain unknown for many years, meaningful comparisons of the mycotas of eastern Asia and eastern North America can be made, and are the focus of this project.
This binational project has two scientific objectives: 1) obtain preliminary data on the occurrence, habitat and diversity of macrofungi in China, and compare these data to the mycota of eastern North America; 2) test several general biogeographic hypotheses by investigating genetic divergence among and within geographically isolated populations of species that have eastern Asia, eastern North America, and Central America disjunct distributions.
* Project Significance
We collect and analyze data directly relating to four important issues: 1) developing baseline information for studying changes in fungal communities, 2) assessing biodiversity, 3) investigating biogeographic relationships, and 4) detecting genetic divergence within and among allopatric populations.
Baseline information for studying changes in species composition of macrofungi: Microorganisms including fungi are crucial to many ecosystem process and thus the maintenance of biodiversity (Hawksworth & Ritchie, 1993), but they have received much less direct attention than plants and many groups of animals. Macrofungi (fungi forming conspicuous sporocarps) are mostly either ectomycorrhizal or saprobic. Ectomycorrhizal fungi form a mutually beneficial, often times obligatory, relationship with vascular plants and provide the plants with access to the key elements that are essential for plant growth (Read, 1991). Saprobic fungi are actively involved in nutrient recycling and vegetational succession in forest ecosystem. Therefore, knowledge of the diversity and ecology of macrofungi is crucial for forest management plans and conservation efforts, and they can also be used as a bioassay of ecosystem health.
A rapid decrease in the number and frequency of macrofungi has been documented in Europe, and many macrofungi are considered endangered species (Cherfas, 1991; Ing, 1993). Many studies have indicated that the decline of macrofungi is due to the effects of air pollution (Arnold, 1991; Fellner, 1993; Såstad & Jenssen, 1993) and/or soil disturbance (Termorshuizen & Schaffers, 1991; Arnolds & Jansen; 1992), and this decline has been found to precede a dramatic decline in forest health (Pegler et al., 1993). Currently these important trends are only well-documented for Europe and comparable data from other regions of the world are lacking. Quantitative data on fungal diversity are scant for North America (Ammirati et al., 1994; Bills et al., 1986; Cripps & Miller, 1993; O'Dell & Ammirati, 1994; Schmit & Mueller, 1995; Villeneuve et al., 1989; Walker et al., 1994). As part of this project, standard sampling of macrofungi communities in four study sites, two in China and two in U.S., have been initiated and preliminary data on macrofungal diversity are being gathered and compared.
Biodiversity issues: Floristic studies have suggested that China has a richer biodiversity than North America (Pei, 1984; Shetler & Skog, 1981). However, this has not been verified in fungi. The number of documented fungal species in China is only 8,000, in contrast to 12,700 for U.S.A. (Tai, 1979; Zhuang, 1993). However, fungi in the U.S.A. have been much more intensively sampled than in China. The Fanjing Mtn. range in southwestern China, for example, is an area uniquely rich in plant species. Floristic data showed that the Fanjing Mtn. range houses about 1,550 vascular plant species, with tropical and temperate elements as well as Sino-Himalayan and Sino-Japanese elements (Zhou, 1990). Villeneuve et al. (1989) showed that the average ratio of the number of macrofungi vs. the number of vascular plants in boreal forests of Quebec, Canada is 1.8. This is similar to the later estimate put forth by Hawksworth and Ritchie (1993). If we use Villeneuve et al's ratio of 1.8 to estimate, there may be over 2,700 species of macrofungi in Fanjing Mtn. range. Currently, there are only about 400 species (i.e. 15%) recorded from Fanjing Mtn. (Wu, X. -L., 1990). The commonly accepted hypothesis for the richer plant diversity in Asia is that Asian flora was less affected by Pleistocene glaciation, which caused great extinction of species in eastern North America (Graham, 1972). Comparative data of fungal biodiversity may give us insights on the correlation between biogeographic history and fungal diversity.
Fungal biodiversity also may be related to other geographical elements (e.g., latitude, climate, etc.) as suggested by data on animals and plants (Schluter & Ricklefs, 1993). Villeneuve et al. (1989) surveyed the mycota in boreal Canada and showed that: 1) differences in frequency and diversity of ectomycorrhizal and saprobic fungi existed between deciduous and coniferous forests, and between open and closed stands; 2) species richness decreased toward the north and with increasing altitude; 3) the diversity of saprobic fungi was related to that of vascular plants, while the diversity of ectomycorrhizal fungi was related mainly to the percent cover of ectomycorrhizal hosts. Other studies showed that variation also occurred in relation to sample size, time, year, and degree of disturbance (Ammirati et al., 1994; Bills et al., 1986; Cripps & Miller, 1993; O'Dell & Ammirati, 1994; Villeneuve et al., 1989; Walker et al., 1994). Currently, there are several ongoing efforts by Field Museum researchers and collegues to further investigate macrofungal biodiversity in North and Central America (http://www.nybg.org/bsci/res/hall/costaric.html; http://archive.fieldmuseum.org/candr/botany/botany_sites/sniif/localfungi.htm)
This study is designed to compare the fungal diversity of two disjunct continents along south to north gradients. Results from this study will make it possible to compare data from other areas and to understand basic patterns of fungal diversity in the north temperate zone. Quantitative studies focusing on the occurrence and diversity of macrofungi corresponding to vegetation types, geographic gradients, climate, and ecological elements such as our study are crucial to understanding the global pattern of fungal diversity.
Biogeographic relationships: An affinity between the mycotas of eastern North America and eastern Asia has been suggested due to a number of taxa that presumably occur in both areas, including several that are reported to have disjunct distributions. However, this hypothesis has never been tested.
In a previous study (please see the publications page), we calculated the Simpson Coefficient of Similarity (Simpson, G. G., 1960) for the four north temperate regions (i.e. eastern Asia, Europe, western North America and eastern North America) for four distinct groups, i.e. genera Amanita, Lactarius, and Ramaria, and the family Boletaceae. While mycotas from different areas on the same continent generally are more similar than mycotas separated by oceans, the similarity between eastern North America and eastern Asia can be quite high. Values range from relatively low to a value that is comparable to or higher than that between eastern and western North America. These results provided a gross estimate of the relationship between the mycotas of eastern Asia and eastern North America on the basis of documented taxonomic treatments. However, an important weakness of such studies is that many European and North American fungal names were used to describe the fungi found in areas of eastern Asia, but these studies were conducted by mycologists who had virtually no experience with the mycotas of Europe and North America. Similarly, North American mycological studies rarely deal with the Chinese mycota. Clarifying the taxonomy and distribution of selected fungi in both eastern North America and China is an important focus of this project.
A recent phylogenetic study on the biogeography of the mushroom genus Pleurotus conducted by Vilgalys & Sun (1994) has shown that the earlier evolving species groups have a broad distribution while more recently evolved groups are mainly restricted within the Northern Hemisphere. In addition, recent species radiations may have occurred within the Northern Hemisphere in that genus. These data documented the utility of phylogenetic analyses in understanding fungal biogeographical relationships. We are conducting a phylogenetic study of several disjunct macrofungi species based on DNA sequencing data. Results from these analyses are being used to test the presumed relationship of the mycotas of China and eastern North America.
Genetic divergence: Many widely distributed macrofungi that have previously been viewed as a single species are now found to be morphologically and genetically divergent. For example, the fungus Heterobasidion annosum (Fr.) Bref. was believed to be homogeneous and occur in temperate and boreal forests throughout the northern hemisphere. However, enzyme and DNA data have shown that genetic divergence exists among allopatric populations (Garbelotto et al., 1993; Otrosina et al., 1992). Similar cases can be found in Armillaria mellea (Vahl.: Fr.) Kummer sensu lato (Anderson & Ullrich, 1979; Andersen et al., 1980, 1987), Collybia dryophila (Vilgalys, 1991), Laccaria laccata and L. bicolor complex (Gardes et al., 1991; Mueller, 1992), and Pleurotus species (Vilgalys et al., 1993; Vilgalys & Sun, 1994).
Wu's previous studies on the wood-rooting fungus, Clavicorona pyxidata (Pers: Fr.) Doty, indicated that genetic divergence existed between eastern Asian and eastern North American populations (Wu, Q. X., 1991). This coral fungus has been reported from eastern North America, Europe and China. Morphological variation among collections from different geographical areas is either not recognized or considered minor. Collections from North America, Europe and China are completely intercompatible. However, variation in enzyme extracellular laccase electrophoretic mobility suggests that populations from China are genetically different from populations of North America and Europe (Wu et al., 1995). The genetic differentiation may be an indication of lack of recent gene exchange due to significant geographical and ecological barriers. Further studies to assess genetic divergence within disjunct taxa at the molecular level are therefore a primary goal of this study.
* Methodology and Work Plan
This research has two major components: 1) field work to determine the generic and species composition for each study site and to obtain material for the DNA analyses, and 2) laboratory work to investigate genetic divergence among allopatric populations using DNA analysis techniques. Both field and laboratory parts are essential to reach the goals of this project.
Study sites: Four study sites are being sampled for comparison of the North American and Chinese mycotas and for investigating biogeographic relationships. These are: 1) Highlands Biological Station, North Carolina, U.S.A., 2) the Huron Mtn. Reserve, Michigan, U.S.A. 3) Changbai Mtn., Jilin, China, 4) a site in southwestern China that is yet to be determined. Geographic and vegetation information of the sampling plots is shown in the Study Sites page. In addition, in the western hemisphere two other study sites have been established. One is a temperate site, i.e. Indiana Dunes National Lakeshore, Indiana, and the other is a montane neotropical site at San Gerardo de Dota, Costa Rica. Mycological surveys in both areas are funded through ongoing projects of Greg Mueller and his collaborators. Information on macrofungi from these sites are available for comparisons with data obtained during this project.
Field work: Each of the study sites described above are represented by two sampling plots. The plot location are determined based on forest maturity, stand size, absence of disturbance and edge effects, and accessibility. The total sampling area of each plot is 1000 square meters. The occurrence of macrofungi in each sampling plot are surveyed one to two times each year. A list of fungal and vascular plant species are being recorded for each plot, as well as information on the surrounding habitat and substrate association. Macrofungi occurring outside of the plots are also collected to document species richness and to obtain samples for the DNA analyses.
Identification: Macrofungi are a collective term for fungi that form conspicuous sporocarps. They are mostly members of Agaricales, Aphyllophorales, and Gasteromycetes, as well as some species of Auriculariales, Dacrymycetales, Tremellales, and Ascomycetes. Determination of these fungi is based on sporocarp macro- and micromorphological characters, cultural features, and chemical reactions. Currently, there are no comprehensive taxonomic treatments for either North American or Chinese macrofungi. Published monographs and/or local treatments and diagnostic keys are used as identification references.
Biodiversity data analysis: The concept of biodiversity incorporates two components: richness in number of species and relative abundance of these species (Whittaker, 1972). Richness can be measured by the number of species present in a specified sample. Lists of macrofungal species that occur in each site are being generated, and species richness data are being compared using coefficients of similarity with data from other studies by means of normalization. Frequency data are used to represent relative abundance of a species.
Assessing genetic divergence: The internal transcribed spacer (ITS) region contains two spacer regions each about 300 bp long and the 5.8S rDNA that is subtended by the spacers. Most species level phylogenies within the fungi have been based on ITS and/or partial lsrDNA. Direct sequencing of the ITS region of rDNA has also been shown to be appropriate for understanding patterns of geographic speciation of macrofungi (Vilgalys & Sun, 1994). In this study, representatives from each population of selected disjunct species are being selected for sequencing of the ITS regions.
Computerization: Specimen information are being entered into Field Museum's databases and will be made available to both the U.S. and Chinese mycological community. Geographical coordinates, altitude, and other precise locality fields are included to facilitate incorporating the data into Geographical Information Systems.
* Scientific Benefits
The main products of the project will include establishing permanent sampling plots, joint scientific publications and databases, complementary collections of specimens and cultures, and enhanced collaboration between U.S. and Chinese mycologists, and the conservation and forest management communities of U.S. and China. This study is generating baseline information for maintaining forest ecosystems in subtropical and temperate regions and is providing new evidence for understanding biogeographic relationships. It is increasing our knowledge on speciation and gene flow in macrofungi. The participants are also gaining firsthand experience on the fungi of each country and establishing an infrastructure for continued cooperation between the Chinese and U. S. mycological community.
China is an ideal choice for studies on biodiversity in the Northern Hemisphere and for studies on relationships of macrofungi between eastern Asia and eastern North America. Conserving the biodiversity of China is to preserve an important sample of the world's biodiversity. This is especially challenging and urgent because of the rapid growth of the economy and the Chinese population at the present time. One of our primary study sites, Chang Bai Mtn., is internationally recognized as an important resource of biodiversity and is designated as a Man and the Biosphere Preserves. Information on biodiversity is important for effective long-term management of the forest preserve.
* U.S. - China Cooperation
The combined expertise of the U.S. and Chinese participants are necessary for the successful completion of this project. Principle investigators, Drs. Qiuxin Wu and Gregory M. Mueller (The Field Museum of Natural History, Chicago, USA) work closely with three Chinese participants, Drs. Jiangchun Wei and Shoyu Guo (Institute of Microbiology, Chinese Academy of Sciences, Beijing, China), and Mr. Sha Meng (Chief, Wildlife Management Division, Ministry of Forestry). Another Chinese mycologist, Dr. Yongqing Huang, also from the Institute of Microbiology, has recently joined our project. His research is funded by a grant from the World Bank entitled "Biodiversity Research and Information Management Project" in China. The personnel, information resources and their commitment to mycology programs of both the Institute of Microbiology and the Field Museum are well suited for this binational cooperative project (for more information, see Links).
For the Chinese participants, this project provides assistance in developing protocols for biodiversity surveys in China, information on current advances and concerns in mycological research of the United States, and opportunities for observing the vegetation and fungi of North America. For the U.S. participants, this project provides opportunities of hands-on experience with the Chinese fungi, complimenting our current research activities in North and Central America, and increasing the accessibility by U.S. mycologists to the herbarium and collection information systems of China.
In addition, this project has an education component in which one U.S. college student is funded each year to join our field trips in China. This program exposes the U.S. students not only to mycological research but also to a different culture. Aleksa Kosinski, a graduate from the University of Illinois at Chicago, participated in the program in 1996. David Quist, a graduate from the University of Washington, joined us in 1997.