PHOTOSYNTHESIS AND RESPIRATION OF ALPINE LICHENS

Phlotosynthetic and respiratory rates were studied in Cetraria islandica, C. nivalis, and Cladonia ranyiferina in the alpine zone of Mt. Washington, New Hampshire. Measurements were made in the field using an infrared gas analyzer; light, temperature, and thallus water content were varied. In all species, considerable reduction in photosynthesis and respiration occurred with drying, more rapidly in photosynthesis than respiration. Optimal photosynthetic rates in all 3 species occurred at 15-20 C with light levels of 1,600 ft-c. Light compensation points ranged from 200 to 350 ft-c. Optimal respiratory rates were attained at 13 C in the 2 species of Cetraria and at 20 C in Cladonia. The data indicate that these wide-ranging, arctic-alpine and arctic-temperate lichens on Mt. Washington are quite well adapted to a moist, foggv environment with cool temperatures and low light levels, conditions which predominate in summer. BECAUSE lichens occupy severe environments, they provide excellent material for physiological studies of their adaptations. \ [any of the studies have centered on water relations of thalli and on the influence of water content on photosynthetic and respiratory rates. AIuch of the early research on lichen physiology was reviewed by P'erez-Llano (1944), while more recent reviews include those of Stocker (1956), Quispel (1959, 1960), Stalfelt (1960), and Smith (1962). In many arctic and alpine environments, lichens, especially fruticose forms, constitute an important part of the vegetation. This is especially true for the Presidential Range, New Hampshire, where nearly all of the lichens are wide-ranging, arctic-alpine or arctic-temperate species. Bliss (1963, 1 96)44 ) has shown that the l'residential Range alpinie flora, vegetation, and microenvironments are in many respects more related to arctic thaii to western alpine tundra of the Rocky i\ lountains and Sierra Nevada, and an intensive study of energy relations of 9 vascular species again showed strong arctic affinities in 8 of the species (Hadley and Bliss, 1964). Three of the most important lichens (Cetraria islandica [L.] Ach., C. nivalis [L.] Ach., and Cladonia r-an gierina [L.] Web.) were studied to determine rates of CO2 exchange under different conditions of light and temperature, and with varying tlhallus moisture content, to determine, if possible, whether these plants, like many othei lichens, are well adapted to an environment of low temperature but high cloud cover and atmospheric moisture. All 3 of these species extend I Received for publication March 12, 1964. 2 This research was supported by a National Science Foundation grant 17864. Thanks are due Mr. Arthur Teague for providing living accommodations. 3 Present address: Department of Biology, Brookhaven National Laboratory, Upton, New York. 4Paper entitled "Plant productivity in alpine microenvironments on Mt. Washington, New Hampshire," submitted to Ecol. Monographs. farther southward than New Hampshire (lF'ink, 1960). However, nonie of the three is of ecological significance in a vegetation in the southerin part of its range. M1ETHODS-Al1 anialyses were made in the field at 1,840 m on the upper northwest exposure of Nit. Washington (710 18' W, 440 16' N). Clumps of lichens were removed from between rocks, carefully cleaned to remove soil an(d old thalli, and placed in a small, double-walled P'lexiglas chamber with a volume of I liter. A small quantity of water was added to prevent drying during each run. The chambers witere sealed wNith Apiezon "Q" and coonnected to a Beckman MIodel 15A infrared gas analyzer powered with a gasoline generator. An open system was used because of adequate air circulation and relatively constant ambient CO2 levels. Air flow through the chamber was maintained at 11 liters/hr or approximately 2 changes per minute. Each analysis ran for 1-2 hr, with alternate sampling of chamber CO2 for 15-20 min followed by ambient air for 5 min. Following each photosynthetic run, the chamber was covered with black cloth for a respiratory determination, after which the lichens were weighed, oven-dried at 80 C and reweighed. All data are expressed as mg C02/g dry wt/hr. Each determination is based on at least :replicates. Light levels presented are those inside the chamber. Light intensity was measured in foot candles (ft-c) with a Weston Illumination meter. Temperature was regulated (i 1 C) by circulating cold or hot water between the inner and outer jacket. Chamber temperature was measured every 1-2 min with a thermistor.5 Most determinations were made on plants at or near saturation with water, collected during or after prolonged periods of rain or heavy fog. However, a series was run at 5 For more detail on the analyzer, see Hadley and Bliss