Ecophysiology of microcolonial fungi and lichens on rocks in northeastern Oregon

Abstract

SUMMARYIn this study of rocks in eastern Oregon, air and rock temperatures and moisture were monitored, along with the abundance and distribution of micro‐colonial fungi (MCF) and lichens, for 2 yr. Conditions were suitable for MCF growth during all but the winter months with the most favorable conditions occurring in spring and autumn. In these seasons moisture was frequent and the absorption of solar irradiation by rocks increased the surface temperatures considerably above the very cool air temperatures.Distributions of MCF and lichens were studied in detail on ten granite rocks at one site. While MCF were most numerous on southern rock exposures, this appeared to be because this exposure was least favorable for lichen growth. MCF appeared to precede lichens in colonizing recently fractured, exposed rock surfaces. The ability of the MCF to grow in the dark as well as the light may be an important factor favouring growth of MCF relative to lichens, especially in the summer when daytime air and rock temperatures were too high to permit growth. However, conditions on some areas of the rocks were especially favourable for lichen growth and in these places lichens effectively dominated the MCF for surface area. A list of lichen species observed at this and nearby locations is provided. 14CO2 release from [14C]acetate was used as a measure of MCF activity at 10–12 °C and 25 °C under different conditions of moisture. Moderate respiration was found at 10–12 °C and respiration occurred with a 2 h period of air drying. In contrast, MCF on rocks air dried for several weeks and subsequently dried for 18 h over H2SO4 did not become active during incubation for 2 h following wetting.