Photosynthesis and Respiration of Forest and Alpine Populations of Polytrichum juniperinum

Abstract

Apparent photosynthesis was measured as a function of light intensity, temperature, and CO, concentration in alpine and forest populations of Polytrichum juniperinum Hedw. The forest population showed light saturation at lower light intensities, sustained apparent photosynthesis at higher temperatures, and showed a greater response to elevated CO, concentration than did the alpine population. The achlorophyllous margins of the leaves in the alpine plants are disproportionately large compared to those in forest plants. The differences in physiology and morphology can be interpreted as adaptations to the respective habitats of alpine and forest populations. The moss Polytrichum iuniperinum Hedw. is a widely distributed species in North America. It occupies diverse habitats ranging from the alpine zone, e.g. in the New England mountains, to fairly dry scrub oak forests on sandy soils. Species of such a wide range may consist of ecologically distinct races genetically adapted to their environments or they may possess wide tolerance limits that allow them to thrive under various environmental conditions. In phanerogams both conditions occur and are very well documented. In the bryophytes, studies on ecotypic differentiation are limited. Tallis (1959) reported that Rhacoamitrium lanuginosum has variable morphology according to the site variation, and that growth rates vary with altitude, being highest at 80 m and lowest at 720 m. Forman (1964) found that leaf morphology of Tetraphis pellucida varies with temperature, being wider relative to its length at lower temperatures. In another study (Forman, 1968) he found that there was an inverse correlation in caloric values of mosses with the altitudes at which they grow. Polytrichum juniperinum from the alpine zone of Mt. Washington gave the lowest value (3951 cal) of the alpine mosses studied. There are other reports indicating that some bryophytes are able to occupy diverse habitats because of their wide tolerances. For example, Rastorfer and Higinbotham (1968) showed that Bryum sandbergii has the capacity of net photosynthesis over a wide range of temperatures and light intensities. They explain its presence in all vegetation zones of the Pacific Northwest intermountain area on the basis of its wide tolerances. Szweykowski and Vogel (1966) found that populations of Geocalyx graveolens collected at two totally different 1 This study was performed at the Department of Botany, University of Illinois, Urbana. Support for the work was furnished in part by NSF GB-6520. We also acknowledge Dr. J. S. Boyer, who furnished the gas analyzer for our use. 2 Department of Botany, University of Illinois, Urbana, Illinois 61801. 3 Section of Genetics, Development, and Physiology, Cornell University, Ithaca, New York 14850. 4 Department of Botany, University of Vermont, Burlington, Vermont 05401. This content downloaded from 157.55.39.177 on Sat, 19 Nov 2016 04:38:54 UTC All use subject to http://about.jstor.org/terms 580 THE BRYOLOGIST [Volume 73 habitats showed no significant morphological differences when grown under the same environmental conditions. For this paper we studied two populations of P. juniperinum from contrasting habitats, measuring their patterns of CO2 exchange at various temperatures, light intensities, and carbon dioxide concentrations. In addition leaf morphology and turgor movements were studied to elucidate possible relationships with the environ-