Photosynthetic characteristics of foliose lichens in response to light, temperature and water status of thallus
| Authors | |
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| Year of publication | 2004 |
| Type | Article in Proceedings |
| Conference | Book of Abstracts. 5th IAL Symposium |
| MU Faculty or unit | |
| Citation | |
| Field | Botany |
| Keywords | lichen; chlorophyll fluorescence imaging; stress physiology |
| Description | Introduction Majority of lichens are capable to cope with extremes and rapid fluctuations in environmental factors, availability of water, light, and air temperature in particular. Photosynthesis in lichens is controlled by these factors and actual rate of photosynthetic processes reflects their interactive effect. Material and Methods To study lichen photosynthesis both in situ (mainly maritime Antarctica) and in a laboratory, fluorometric and gas exchange methods were used. In addition, spectral reflectance, photosynthetic pigments and antioxidants analyses, oxymetric evaluation of photosynthesis in photobionts, anatomic studies were applied in Lasallia pustulata, Umbilicaria hirsuta, U. antarctica, and U.decussata. Results and discussion Temperature response curves revealed that primary processes of photosynthesis (Fv/Fm - capacity of photochemical reactions in photosystem II, FII - quantum yield of PS II) had optimum at 18-22 oC, and hold high level (about 80 % of maximum) within the range of -5 to 18 oC. Temperature minimum was found at -20 to -15 oC. Hydration response curves showed that maximum values of Fv/Fm, FII retained to water saturation deficit (WSD) of 50-60 % and then decreased rapidly with desiccation. In most species, critical WSD was 70-80 % which corresponds to water potential (WP) of - 35 to -25 MPa. In situ measurements of net photosynthesis (Pn) showed Pn of 1-2 mmol (CO2) m-2 s-1 for well-hydrated U.antarctica. When exposed to high light in wet state in a laboratory, thalli showed decrease in Fv/Fm, FII and consequent recovery in dark. Chlorophyll fluorescence imaging showed intrathalline differences in the sensitivity of U. antarctica to photoinhibition. During photoinhibion, non-photochemical quenching (NPQ) and zeaxanthin formation increased simultaneously. Photosynthetic processes (FII)were linearly related to oxygen evolution rate in non-stressed symbiotic algae. Under osmotic stress, however, FII to OEC relation was curvilinear. |
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