Thermotolerance Generated by Plant/Fungal Symbiosis

All plants studied in natural ecosystems are symbiotic with fungi (1), which obtain nu-trients while either positively, negatively, or neutrally affecting host fitness (2). Plant adaptation to selective pressures is consid-ered to be regulated by the plant genome (3). To test whether mutualistic fungi con-tribute to plant adaptation, we collected 200 Dichanthelium lanuginosum plants from geothermal soils at 10 sites in Lassen Volcanic (LVNP) and Yellowstone (YNP) National Parks. These soils have annual temperature fluctuations ranging from about 20 ° to 50°C (4). Plants and their roots were removed and as-