Faculty Profiles

Mary Ann McLean

Assistant Professor of Life Sciences

General Education Committee, College of Arts and Sciences, 2005-2008

Ph.D., The University of Calgary

Office telephone: 812-237-2425
Office: Science Building room 280
E-mail: lsmclean@isugw.indstate.edu

Research Interests: microbial ecology; soil mycology; soil ecology; community and ecosystem ecology; disturbance ecology; invasion of exotic species.

I am a soil ecologist interested in the community dynamics of soil microfungi and soil invertebrates (including earthworms and microarthropods), their interactions, and the implications of their interactions for ecosystem processes.

Soils, the "poor man's tropical rainforest", especially those of mature forests, have greater phylogenetic diversity than any habitat except coral reefs. It has been estimated that 80-90 % of annual net primary production enters the soil decomposer food web, where fungi are the major decomposers. Although soil processes such as organic matter decomposition and nutrient cycling are performed by soil fungi and bacteria, they are regulated by the soil fauna (eg. microarthropods such as mites and Collembola, and earthworms) which graze on them. These mostly microscopic arthropods are abundant but relatively unstudied. Conservative estimates of the diversity of oribatid mites (only one of several suborders of mites) suggest that there are probably 30,000 species, of which about 20 % have been seen. Not studied. Merely seen. Even earthworms, the largest of the soil fauna, are poorly known. In North America many areas have not been surveyed for earthworms, but about 150 species have been recorded, of which about 30% are exotics. This diversity of life in the soil and its critical importance for the maintenance of terrestrial ecosystem processes has led me to investigate the impacts of disturbance on these organisms and the processes they mediate as well as the significance of microfungal diversity to soil processes. I am particularly interested in the effects of anthropogenic disturbances on soil organisms and processes.

Urbanization impacts on soil organisms and ecosystem processes
A current project focuses on the abiotic and biotic alterations in ecosystems surrounded by urban land uses and the impacts of these alterations on soil microbial communities and the ecosystem processes they mediate such as decomposition and nutrient cycling. Urban ecosystems differ from their rural counterparts in several ways: urban sites experience increased temperatures, higher atmospheric nitrogen deposition and larger nitrate pools, and more often contain exotic earthworms. Microbes, which are critical to decomposition of recalcitrant substrates such as chitin or lignin, are most active under particular environmental, chemical and physical conditions. What happens to these microbes and the processes they mediate when soil temperatures increase several degrees? Recent research in my lab indicates that at least some soil fungi do adapt to grow faster at higher temperatures. We will be following this up with several studies to determine i) how widespread these adaptations are; ii) how changes in chitinolytic fungal community structure alters chitinolytic activities and nutrient cycling at the ecosystem level; iii) how quickly these microbes adapt to these urban conditions; and iv) the mechanism behind these adaptations, e.g. alterations in the enzyme systems involved. The changes that we see in the microbial community and its enzyme activity under the increased temperatures in urban areas will also allow us to predict the impact of global warming on these soil processes.

Impacts of coal production on soil organisms and ecosystem processes. Coal is an important source of energy in the Indiana, and surface mining has impacted tens of thousands of hectares in Indiana. Prior to coal mining, the topsoil is removed and stockpiled, and during reclamation, a thin (often only 4-8" thick) layer of topsoil is replaced over the waste materials. The resulting soils have a low pH, low levels of nutrients and soil organic matter, and high levels of trace elements (e.g. As B, Cd, Cr, Mo, Ni, Pb, Se, V, Zn). Preliminary data from a local reclaimed mine showed that Solidago uptake of Pb, Th and U was very high although these element concentrations were relatively low in soil and water at this site. To determine how general this pattern is, undergraduate students in my lab, in conjunction with Dr S. Brake (Department of Geography, Geology and Anthropology) and Dr S. Wolf (Department of Chemistry) are currently investigating the trace element uptake in a variety of plants at this reclaimed site.

In the US, coal combustion produces millions of tons of solid waste (fly ash) each year. Disposal of this material is a concern. Fly ash has potential for use as a soil amendment since it contains high levels of Ca, S, B, Mo and Se. However, it also may contain high levels of trace elements (e.g. As, B, Cd, Cr, Pb, Ni, V, Zn). Plants grown in soil amended with fly ash may take up toxic levels of these trace elements. Earthworms consume organic and mineral materials in the soil and egest them as casts. During earthworm gut passage profound chemical alteration of ingested organic and mineral materials occurs. This can result in the complexing of minerals or elements onto clays or organic matter, thus reducing bioavailability. In conjunction with Drs Brake and Wolf, an undergraduate student in my lab is currently testing the possibility that earthworm activities result in significant complexing and increased immobilization of trace elements from fly ash.

Fungal synergisms. While exploring whether urban chitinolytic fungi traded off competitive ability with enhanced growth at higher temperatures, we observed that many of the interactions between pairs of chitinolytic fungi were synergistic. There was no evidence of a tradeoff with competitive ability. On the contrary, there was evidence that growth of these fungi was dependent on their ability to cooperate with other chitinolytic fungi to degrade chitin, irrespective of their growth response to temperature. For example, urban isolates of Penicillium bilaii appeared to take advantage of synergisms with other chitinolytic fungi. Its growth was enhanced by other species relative to that of rural isolates, but it enhanced the growth of other species less than that of rural isolates. These data suggest that fungal synergisms may be common during the degradation of complex substrates. How widespread are these synergisms? Do they impact community level enzymatic activity and nutrient cycling? We are currently exploring the idea that synergisms are more common during degradation of complex substrates than during degradation of labile substrates.

Graduate student opportunities in my lab
I will be accepting 1 to 3 graduate students to begin August 2005. Potential projects could include the study of the fungal community and ecosystem level consequences of increased nitrate availability and increased disturbance due to exotic earthworms associated with urbanization, and the study of fungal synergisms under disturbance conditions (urban or coal reclamation etc). Applicants with interests in soil ecology, mycology and ecosystem processes are encouraged to apply. Experience with fungi or soil nutrient or enzyme analysis is a definite plus. For more information please email me at: lsmclean@isugw.indstate.edu

Send resume, names, phone numbers and email addresses of 3 references to: Dr. M.A. McLean, Department of Life Sciences, Science 280, Indiana State University, Terre Haute, IN 47809. Phone: (812) 237-2425.

Undergraduate student opportunity for summer 2005
A position is available for an undergraduate student researcher for 16 weeks (30 h/week) from May to August 2005. The student will collaborate with students in GGA and Chemistry and with Dr Brake (GGA) and Dr Wolf (Chem). The students will set up research plots, sample plants and soils and analyze samples for trace element contamination at an acid mine drainage seep. The project will assess 1) the suitability of different plant species for use in low pH, contaminated sites and 2) the utility of crushed limestone application in increasing pH and decreasing trace element mobility in plants and soils. For more information please email Dr M.A. McLean at lsmclean@isugw.indstate.edu or phone me at (812) 237-2425.

Publications

Reprints for some publlications are available as PDF files. By accessing the PDF file, the user agrees to abide by all copyright laws and education fair-use regulations.

McLean, M.A., S. Migge and D. Parkinson. Earthworm invasion of ecosystems devoid of earthworms: effects on soil microbes. Invited review, Biological Invasions, Accepted

Migge, S., M.A. McLean, J. Maerz and L. Heneghan. Influence of invasive earthworms on indigenous fauna previously uninhabited by earthworms. Invited review, Biological Invasions, Accepted

McLean, M.A., M.J. Angilletta Jr. and K.S. Williams. If you can't stand the heat stay out of the city: thermal adaptation by chitinolytic soil fungi. Journal of Thermal Biology, In Press

Parkinson, D., M.A. McLean, and S. Scheu. 2004. Impacts of earthworms on other biota in forest soils, with some emphasis on cool temperate montane forests. In: Earthworm Ecology. 2nd edition., C.A. Edwards, ed. Soil and Water Conservation Society, Ankeny, Iowa. pp. 241-259. ( PDFDownload PDF - 551 kB)

Bohlen, P.J., Scheu, S., Hale, C.M., McLean, M.A., Migge, S., Groffman, P.M. and Parkinson, D. 2004. Non-native invasive earthworms as agents of change in northern temperate forests. Frontiers in Ecology and the Environment 2(8): 427-435 ( PDFDownload PDF - 650 kB)

Setälä, H. and McLean, M.A. 2004. Decomposition rate of organic substrates in relation to the species diversity of soil saprophytic fungi. Oecologia 139(1): 98-107 ( PDFDownload PDF - 211 kB)

McLean, M.A. and V. Huhta. 2002. Microfungal community structure in anthropogenic birch stands in central Finland. Biology & Fertility of Soils. 35: 1-12 ( PDFDownload PDF - 340 kB)

McLean, M.A. and V. Huhta. 2000. Temporal and spatial fluctuations in moisture affect microfungal community structure in microcosms. Biology & Fertility of Soils. 32: 114-119 ( PDFDownload PDF - 151 kB)

McLean, M.A. and D. Parkinson. 2000. Introduction of the epigeic earthworm Dendrobaena octaedra changes the oribatid community and microarthropod abundances in a pine forest. Soil Biology & Biochemistry. 32: 1671-1681 ( PDFDownload PDF - 217 kB)

McLean, M.A. and D. Parkinson. 2000. Field evidence of the effects of the epigeic earthworm Dendrobaena octaedra on the microfungal community in pine forest floor. Soil Biology & Biochemistry. 32: 351-360 ( PDFDownload PDF - 234 kB)

Parkinson, D. and M.A. McLean. 1998. Impacts of earthworms on the community structure of other biota in forest soils. In: Earthworm Ecology. C.A. Edwards, ed. Soil and Water Conservation Society, Ankeny, Iowa. pp. 213-226.

Kaneko, N., M.A. McLean, and D. Parkinson. 1998. Do mites and Collembola affect litter fungal biomass and microbial activity? Applied Soil Ecology. 9: 209-213 ( PDFDownload PDF - 230 kB)

McLean, M.A. and D. Parkinson. 1998. Impacts of the epigeic earthworm Dendrobaena octaedra on microfungal community structure in pine forest floor: a mesocosm study. Applied Soil Ecology. 8: 61-75 ( PDFDownload PDF - 582 kB)

McLean, M.A. and D. Parkinson. 1998. Impacts of the epigeic earthworm Dendrobaena octaedra on oribatid community diversity and microarthropod abundances in pine forest floor: a mesocosm study. Applied Soil Ecology 7: 125-136 ( PDFDownload PDF - 405 kB)

McLean, M.A. and D. Parkinson. 1997. Soil impacts of the epigeic earthworm Dendrobaena octaedra on organic matter and microbial activity in lodgepole pine forest. Can. J. For. Res. 27: 1907-1913

McLean, M.A. and D. Parkinson. 1997. Changes in structure, organic matter and microbial activity in a pine forest soil following the introduction of Dendrobaena octaedra (Oligochaeta, Lumbricidae). Soil Biol. Biochem. 29: 537-540

McLean, M.A., D.U. *Kolodka and D. Parkinson. 1996. Survival and growth of Dendrobaena octaedra (Savigny) in pine forest floor materials. Pedobiologia 40: 281-288

McLean, M.A., N. Kaneko and D. Parkinson. 1996. Do mites and collembola affect litter fungal community structure? Pedobiologia 40: 97-105

Kaneko, N., M.A. McLean and D. Parkinson. 1995. Grazing preference of Onychiurus subtenuis (Collembola) and Oppiella nova (Oribatei) for fungi inoculated on pine needle litter. Pedobiologia 39: 538-546

Seifert, K.A., J.C. Frisvad and M.A. McLean. 1994. Penicillium kananaskensis, a new species from Alberta soil. Can. J. Bot. 72: 20-24

Scheu, S. and M.A. McLean. 1993. The earthworm (Lumbricidae) distribution in Alberta (Canada). Megadrilogica 4(11): 175-180.