The Effect of Temperature Preconditioning on the Temperature Sensitivity of Net CO2 Flux in Geographically Diverse Populations of the Moss Polytrichum Commune

Abstract

Gametophytes of five geographically diverse populations of the moss Polytrichum commune ranging from Barrow, Alaska (71°N), to Gainesville, Florida (29°N), were grown under constant temperatures of 5° and 20°C with 16 h of light each day. The net CO2 exchange of the shoot tissue produced under these conditions was subsequently studied in relation to temperature. The following patterns were noted. (1) The maximum net photosynthetic rate decreased in P. commune populations from sites along a gradient of increasing latitude, except that highest rates were found in the temperature St. Hilaire population; the difference in photosynthetic rates between the extreme values was about sevenfold, (2) Cool growth conditions resulted in low maximum net CO2 uptake rates. (3) The growth temperature affected the maximum net photosynthetic rate of low—latitude populations more than high—latitude populations. (4) The optimum temperatures for photosynthesis were equal to or higher than the growth temperatures. (5) The temperature at the center of the estimated optimal range for net CO2 uptake was correlated with both preconditioning temperature and the latitude of origin. (6) The upper temperature compensation points, which were unusually high for bryophytes, were correlated positively with the preconditioning temperature and negatively with the latitude of origin. (7) Northern populations had dark—respiration rates which were equal to or lower than those of southern populations. (8) After low—temperature acclimation, the dark respiration increased only in the southernmost population.