Ecophysiological studies in the genus Plecthranthus

Well-watered plants of Plectranthus marrubioides Benth., a crassulacean acid metabolism (CAM) species naturally inhabiting sun exposed succulent places, were grown at photosynthetically active photon flux densities (PPFD) of either 150 (LL) or 300 (HL) µmol m-2 s-1 in a controlled environment. Photosynhtesis of LL plants was saturated by irradiance of ca. 500 µmol m-2 s-1 while in HL plants saturation was not reached up to 1200 µmol m-2 s-1 and photosynthetic capacity was nearly 50 % higher than in the LL plants. However, maximum photon yield was 55 % lower and compensation irradiance was 25 % higher in LL plants.The former also had larger, more succulent leaves, i.e. they were morphologically more sun adapted. On the other hand, nocturnal accumulation of malic and citric acid, nighttime CO2 gain, and the low relative carbon recycling were independent of the prevailing PPFD. Furthermore, photosynthetically performance was flexibly and reversibly adjusted in HL plants after transfer to 600 or 150 µmol m-2 s-1 while nocturnal CO2 uptake was not influenced. Photosynthesis showed a high acclimation potential to high PPFD and patterns of gas exchange became more C3-like the higher the irradiance was, without a direct effect on CAM of P. marrubioides.

Drittmittelgeber:

Deutsche Forschungsgemeinschaft

Beteiligte Wissenschaftler:

Dr. W.B. Herppich, M. Herppich, Prof. Dr. D.J. von Willert

Veröffentlichungen:

Herppich, W.B.: Photosynthesis but not CAM responded flexibly to changes in irradiance in Plectranthus marrubioides (Lamiaceae). Photosynthetica 34, 1-12 (1997)

Herppich, W.B., M. Herppich, D.J. von Willert: Ecophysiolgical investigations on plants of the genus Plectranthus (Lamiaeae). Influence of environment and leaf age on CAM, gas exchange and leaf water relations in Plectranthus marrubioides Benth. Flora 193, 99-109 (1998)