Comparisons of Mycorrhizal Properties from Two Host Tree Species

ABSTRACT

In this lab experiment, students learn about ectomycorrhizal (ECM) fungal properties associated with two host tree species to better under understand symbioses in general and gain experience using soil sampling and mycorrhizal field methods. Students will learn in more depth about terms and concepts related to symbioses (e.g. mutualisms, coevolution, host specificity) and about specific experimental methods. Two labs and 2-4 preceding lectures are required. In the first lab, students make field observations to form a hypothesis about ECM fungal colonization, record images of sporocarps, and extract roots. In the second, students process their roots and describe ECM fungi. They then analyze data, test their hypothesis, and summarize their findings and interpretations of lab content/concept questions in written and oral assessments.

AUTHORS

Gregory D. Turner

Department of Biology, West Chester University of Pennsylvania, West Chester, PA, 19383; gturner@wcupa.edu

CLASS TIME

Two lab and 2-4 preceding lecture sessions each are required. Students spend one hour in the field and two hours in the lab in the first lab session and three lab hours in the second. Note that the field location should be close enough to the location where the following lab is held to allow for the estimated two hour first day lab session. Two-four, one-hour, lecture sessions (or two longer ones) should be held prior to the labs in order to cover content related to symbioses and mycorrhizae as described in the abstract.

OUTSIDE OF CLASS TIME

Students need about 4-6 hours to identify sporocarps found, analyze and summarize data, and prepare their assessments.

STUDENT PRODUCTS

A written group Lab Data Analysis (Guidelines & Rubric Word file) and group PowerPoint based Lab Report Presentation (Guidelines & Rubric Word file).

SETTING

Field and lab. The field component can be conducted in any natural area where sporocarps and trees occur. Forests and wooded field edges are ideal, but single trees from campus grounds can also be used. The field component should ideally be conducted in the early fall or late spring, and within a week or so of a rain event, when soil conditions are most likely to support sporocarp production and ECM fungal root colonization. The lab component can be conducted in any lab with adequate sink, water, and dissecting microscope availability. Given that 18-24 students are best suited for the lab, with students working in groups of three, a maximum of 6-8 scopes are all that are needed.

COURSE CONTEXT

The lab could best be used in a mycology, fungal ecology, or other upper level ecology course that covers mycorrhizae and soil ecology topics on some level, regardless of the instructor’s knowledge of mycology, and could be modified for partial use for lower level ones (see “Transferability” below). Inclusion of at least some lab portions in lower level courses is encouraged given that mycology and soil ecology topics are often not covered in introductory biology courses and that few programs require mycology in their curricula. The lab can also serve to guide undergraduate research projects. It has been used effectively in undergraduate and graduate content and research courses. A class of 18 students is ideal, but 24 can be facilitated.

INSTITUTION

Public regional university with bachelors and masters programs.

TRANSFERABILITY

The lab is best fit for mycology and fungal ecology courses, and for upper level ecology elective courses (e.g. community or plant ecology), where students should have some basic knowledge of mycorrhizae and familiarity with field and microscopy methods. However, it can be adapted for lower level majors courses. Adaptations could employ a number of approaches. One is to remove the entire root-sampling portion to focus on sporocarp identification and counts, but include an augmentation of it by showing colonized root samples retrieved by the instructor in the lab. Links between sporocarps and mycorrhizal roots could then be made to illustrate physical interaction between sporocarps, roots, and mycorrhizal fungi. In addition, a second approach might be to keep both the sporocarp and mycorrhizal description portions, but to remove most quantitative measurements. This would be similar to the first approach, but would allow students to still gain some experience with root sampling, prepping, and morphotyping to describe ECM morphotypes (i.e. unidentified species). Quantification of colonized and uncolonized root tips could be kept to give students at least some familiarity with measuring mycorrhizal colonization. The t-test could be conducted to test for differences in colonization as originally planned, or it too could be omitted. All other quantitative measures including percent colonization by morphotype (needed to construct community composition profiles), total colonization, and Shannon diversity could be omitted completely (or partially at the discretion of the instructor). Such modifications should not greatly alter the key experiment goals, which are to increase student knowledge of mycorrhizal ecology, to authenticate an understanding of symbioses, and give students exposure to ECM and soil ecology methods. Based on these and any other modification, the homework, lab data analysis, and oral presentation would need modification to accommodate such changes. Instructors should be able to do that. Finally, whether modified or not, access to wooded habitats that are flat and accessible to ALL students is ideal, but any wooded area can be used.

Overall, whether intended for Mycology or Fungal Ecology courses, or modified for use in related lower-level courses, what follows is a list of the essential background concepts and terms that instructors should know and be able to teach to students to ensure that they can answer questions related to explaining their results:

• Symbioses (e.g. mutualisms) as a key type of species interactions
• Community composition and diversity as ecological concepts
• Common measures of ECM fungal diversity (i.e., Shannon diversity index)
• ECM vegetative (i.e. root tip mantles) and reproductive (e.g. sporocarps) morphology, including some common representative taxa from the study region
• ECM root tip colonization as a proxy for abundance
• The influence of host specificity and size, and abiotic factors (e.g. soil moisture and nutrient availability) on ECM root tip and sporocarp abundance and diversity

DOWNLOADS

• Full Article Text [doc], [pdf]

Description of other Resource Files:

• Lab overview [doc]
• Data collection table [xlsx]
• Example data and calculations [xlsx]
• Analysis guidelines and rubric [docx]
• Presentation guidelines and rubric [docx]

ACKNOWLEDGMENTS

I first learned how to use elements of this experiment as a middle school science teacher, but gained more formal guidance on mycorrhizal methods from my doctoral advisor, Dr. James Lewis, at Fordham University. I was encouraged to further develop the experiment by Drs. Bob Pohlad and Carolyn Thomas, Ferrum College, for use by the Collaboration through Appalachian Watershed Studies.

CITATION

Gregory D. Turner. 10 November 2013, posting date. Comparisons of Mycorrhizal Properties from Two Host Tree Species. Teaching Issues and Experiments in Ecology, Vol. 9: Experiment #3 [online]. http://tiee.esa.org/vol/v9/experiments/turner/abstract.html