Project Number: WVA00136
CRIS Number: 0177118
ECOTYPIC VARIATION IN ECTOMYCORRHIZAL FUNGI FROM SERPENTINE SOILS
Investigators: Cumming, J. R., Panaccione, D. G.
Performing Department: Plant & Soil Sciences -- 1825
Start Date: 09/01/1997
Termination Date: 08/31/2001
Reporting period: 09/01/1997 to 08/31/2001
Termination Report:
We established six research plots, three each on serpentine soils and non-serpentine clay "lenses," at the Soldiers Delight Natural Environmental Area in Owings Mills, MD. These soil types differ substantially in pH, Mg, and Ni concentrations, as well as in the availability of N and P. The serpentine soils also had a lower C:N ratio (10.7 versus 18.5), suggesting a greater pool of accessible N in the organic fraction. Virginia pine (Pinus virginiana) was the dominant tree species on the serpentine plots, whereas the non-serpentine plots contained mainly black oak (Quercus velutina), with fewer Virginia pine and miscellaneous other trees. We assessed ectomycorrhizal community biodiversity on these plots by three methods: (1) periodic basidiocarp counts; (2) trapping ectomycorrhizal fungi on roots of Virginia pine and subsequent classification of fungi in mycorrhizae by restriction fragment length polymorphism analysis of the internal transcribed spacer region of the ribosomal repeat (ITS-RFLP fingerprinting); and, (3) direct analysis of mycorrhizae collected from the field by ITS-RFLP fingerprinting. Collectively, basidiocarp, trap culture, and field mycorrhizal diversity data indicated that fungal species richness and community diversity were lower for serpentine compared to non-serpentine soils. A collection of isolates of one species common to both serpentine and non-serpentine plots, the imperfect ectomycorrhizal fungus Cenococcum geophilum, was assessed for genetic variation by ITS-RFLP fingerprinting and with additional polymorphic markers obtained from PCR-amplified beta-tubulin gene fragments. UPGMA analysis of the RFLP data indicated that the serpentine isolates of C. geophilum are genetically distinct when compared to isolates from local or distant non-serpentine sites. AFLP analyses, which sample a greater number of loci dispersed throughout the genome, provided an even more distinct separation of the serpentine isolates from non-serpentine isolates. The serpentine isolates also lacked a group I intron frequently found within the 18S ribosomal RNA gene in isolates of this species. Cultures of the C. geophilum isolates were grown axenically in media that was modified to screen responses to simulated serpentine soil factors (elevated Mg and Ni). There were two significant differences in physiology between the two soil ecotypes. First, isolates from serpentine soils exhibited two-fold greater acid phosphatase rates than isolates from non-serpentine sites. In addition, levels of malate exudation were 35-fold greater in serpentine than non-serpentine isolates. Interestingly, acid phosphatase activity and organic acid exudation have been associated with serpentine and other metal tolerances in higher plants.
Publications:
Panaccione, D.G., Sheets, N.L., Miller, S.P., and Cumming, J.R. 2001. Diversity of Cenococcum geophilum populations from serpentine and non-serpentine soil. Mycologia 93:645-652.
Cumming, J.R., Swiger, T.D., Kurnik, B.S., and Panaccione, D.G. 2001. Mechanisms of aluminum tolerance in Laccaria bicolor and Pisolithus tinctorius in vitro. Canadian Journal of Forest Research 31: 703-710.
Miller, S.P., and J.R. Cumming. 2000. Effects of serpentine soil factors on Virginia pine (Pinus virginiana Mill.) seedlings. Tree Physiology 20: 1129-1135.
Kurnik, B. 2000. Diversity of ectomycorrhizal fungi on two reclaimed surface mines differing in soil properties. Masters Thesis, West Virginia University, Morgantown, WV, 80 pp.
Impact:
Ectomycorrhizal fungi provide their tree hosts with numerous benefits, including tolerance of edaphic stresses. Our results indicate that serpentine soils contain isolates of ectomycorrhizal fungi that are genetically distinct from those of surrounding non-serpentine soils, and may be specialized for the soil in which they are found. These findings, particularly if shown to be true for other metal-rich soils, have implications for the re-forestation of disturbed soils.