Net Photosynthesis of Cladonia Mitis (Sand.) From Sun and Shade Sites on the Wisconsin Pine Barrens

The lichen Cladonia mitis (Sand.) from the Wisconsin Pine Barrens showed no significant differences in the light—dependence of net photosynthesis of sun— and shade—grown mats. Maximal net photosynthesis was 1.13 mg CO_2. g(—1) (air dry weight). hr(—1) at 3.88 x 105 ergs. cm(—2). sec(—1), 22.5 plus or minus 1.0 degrees,and near optimal thallus water content; the light compensation point was 0.36 x 105 ergs. cm2. sec(—1). After dormancy was broken by wetting the sun— and shade—grown C. mitis mats had comparable initial dark respiration rates of —0.47 and —0.48 mg CO2. g(—1). hr(—1), respectively, at high thallus relative water content (ca. 90% RWC). After drying to thallus RWC in the range 62—72%, the dark respiratory rates of the sun—and shade—grown C. mitis, respectively —0.33 and —0.25 mg CO_2. g(—1). hr(—1), differ significantly. The decreases in thallus RWC over 196 plus or minus 3.7 minutes of 37% and 29% for the sun— and shade—grown C. mitis, respectively, also differed significantly. The average annual growth rate of 5.2 plus or minus 0.2 mm. yr(—1) was the same for both sun— and shade—grown C. mitis. These characteristics of sun— and shade—grown C. mitis may be an important aspect of the physiological ecology of the plants.