Studies on lichen-dominated systems. XXIII. The control of seasonal rates of net photosynthesis by moisture, light, and temperature in Cladonia rangiferina

• Published in: Canadian Journal of Botany
• Main Authors: Tegler, B., Kershaw, K. A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1980
• Subjects: Plant Science; Cladonia rangiferina
• Online Access: http://dx.doi.org/10.1139/b80-214; http://www.nrcresearchpress.com/doi/pdf/10.1139/b80-214

The net photosynthetic response matrix to four light levels combined with four temperatures and for a full range of thallus hydration has been defined for a Cladonia–woodland population of Cladonia rangiferina in midsummer and early winter. Maximum rates of net photosynthesis are generated between 150 and 200% thallus water content by weight between 15 and 25 °C with low rates being generated at 5 and 35 °C. Light saturation occurs above 600 μE∙m −2 ∙s −1 . There is no evidence of acclimation of photosynthetic optima to temperature but with the onset of early winter there is a marked decrease of respiration rate. An examination of the sensitivity of Cladonia rangiferina in an air-dry state to heat stress shows a rapid decline of net photosynthesis under 45 °C daytime stress. Although 35 °C initially reduces the level of net photosynthesis to some extent, over a 3-week experimental period no further decline is observed. It is suggested that this population of Cladonia rangiferina, which is markedly restriced to a position under the shade of Ledum shrubs, is protected there from the otherwise excessive heat load which occurs on the open Cladonia stellaris surface and which typically reaches 40 °C under full radiation conditions in summer.