Ectomycorrhizal diversity by morphology and PCR-RFLP under global climate change.

KENDALL J. MARTIN¹, PAUL T. RYGIEWICZ², and ERIC A. DUBINSKY³.

¹Dynamac Inc., Corvallis, OR, 2U.S. Environmental Protection Agency, Corvallis, OR 97333 USA, and ³University of Pennsylvania, Philadelphia, PA 19104 USA.

During 1993-1997, we examined effects of elevated atmospheric CO₂ and temperature on ectomycorrhizal diversity. Naturally-inoculated Douglas-fir seedlings were grown in native forest soil that was reconstructed in controlled-climate terracosms. We first assessed diversity by morphotypes using gross morphological characteristics. We are sub-sampling these groupings to recategorize by PCR-RFLP. In order to analyze individual mycorrhizal tips, we developed a more sensitive nested-PCR system using ITS1F and three new primers. These broad-range fungal primers amplify both basidiomycete and ascomycete sequences, and were designed to discriminate against host plant sequences.
Percent colonization by the dominant Rhizopogon group is seasonally affected by elevated temperature, driving the seasonality in diversity: repeated measures analysis shows greater decreases in the Simpson's dominance (D) under elevated temperature in summer, and greater decreases under ambient temperature in winter. Cenococcum, an opportunistic species, formed more ectomycorrhizae under elevated temperature regardless of season. However, compared with ambient CO₂ treatments, increases in Cenococcum numbers under elevated CO₂ were greater in summer and less in winter. Numbers of tips in the Rhizopogon group were similarly affected by CO₂, reflecting carbon effects on host root development. Mean numbers of morphotypes per terracosm (richness) increased asymptotically from 4.2 in spring 1994 to 13.1 in fall 1996 and were generally steady thereafter. At the same time diversity (1/D) continued to increase, particularly under elevated temperature.