Photosynthetic and Respiratory Capacity of Foliose Lichen Lobaria pulmonaria throughout the Annual Cycle

Lichens are unique phototrophic organisms whose physiology of stress tolerance attracts much attention. Parameters of photosynthetic and respiratory activities of the epiphytic large-leaved lichen Lobaria pulmonaria were investigated with an aim to reveal physiological responses to seasonal changes in environmental conditions. The highest accumulation of chlorophylls in thalli (2.3 mg/g dry wt) was noted in autumn (October); the amount of green pigments decreased 2.5 times in spring (April). The chlorophyll/carotenoid ratio varied from 3.1 to 4.4. The extent of deepoxidation of xanthophyll cycle pigments equaled 34% in winter but it was two times as low in summer. When L. pulmonaria thalli were hydrated and acclimated shortly under standard laboratory conditions, they exhibited a relatively high photochemical activity and were able to assimilate CO 2 throughout the entire annual cycle. The rate of net CO 2 uptake by thalli under optimal irradiance and temperature ranged from 3 to 5 µmol CO 2 /m 2 s and the highest values were recorded in spring. No significant seasonal changes were observed in the total respiration rate of thalli. The proportions of various respiratory pathways were altered in spring and autumn, and metabolic heat production was accelerated due to the activation of an energetically low-efficient alternative respiratory pathway. The results provide evidence that the functional adaptation of photo- and mycobionts in the lichen is implicated in resistance of this complete system to seasonal changes in environmental conditions.