PARENT SESSION
Oral Session #43: Soil Ecology: Mycorrhizae and Roots. Presiding: W. Stock.
Wednesday, August 8, 2001. 8:00 AM to 12:15 PM. Hall of Ideas F.
Pinus edulis stand stress impacts ectomycorrhizal colonization and community structure: Implications for global climate change.
Swaty, Randy1, Gehring, Catherine1, Koch, George1, Whitham, Thomas1, 1
ABSTRACT- The mutualism between ectomycorrhizal fungi and plants may be particularly important in stressful areas or during stressful times, yet few studies have examined ectomycorrhizal dynamics in association with severe drought. In 1996, northern Arizona experienced a record drought that caused extreme mortality of pinyon pine (Pinus edulis) in some locations, while nearby populations experienced little mortality. To investigate ectomycorrhizal responses to stress, we assessed pinyon roots for ectomycorrhizal colonization and ectomycorrhizal community analysis through morphotyping at three paired sites with high (up to 70% mortality) and low mortality (0-5% mortality). We also measured pre-dawn water potentials and growth rates as indicators of tree stress. Water potentials were significantly different between sites. Levels of ectomycorrhizal colonization were significantly lower at the high mortality sites compared to low mortality sites (mean colonization = 28% vs. 40%). We observed ten distinct ectomycorrhizal morphotypes, six of which occurred in both high and low mortality sites. Non-metric multi-dimensional scaling ordination analysis revealed that the morpho-communities at the high mortality sites were significantly different from the morpho-communities at the low mortality sites. These data suggest that while ectomycorrhizal colonization may increase under moderately stressful conditions, it declines with extreme stress. Furthermore, some ectomycorrhizal fungal associates appear to be better suited for life in hotter and drier environments. Such shifts in ectomycorrhizal fungal dynamics could become increasingly important if predictions for more frequent and intense droughts in semi-arid systems are accurate.
KEY WORDS: ectomycorrhiza, mortality, stress, community structure