Publication details
Visualized photosynthetic characteristics of the lichen <i>Xanthoria elegans</i> related to daily courses of light, temperature and hydration: a field study from Galindez Island, maritime Antarctica.
| Authors | |
|---|---|
| Year of publication | 2005 |
| Type | Article in Periodical |
| Magazine / Source | The Lichenologist |
| MU Faculty or unit | |
| Citation | |
| web | available at the Lichenologist web page: |
| Field | Botany |
| Keywords | chlorophyll fluorescence imaging; dehydration; photosynthesis; quantum yield of PS II |
| Description | Diurnal courses of photosystem II (PS II) activity of Xanthoria elegans were continuously monitored using a novel technique of chlorophyll fluorescence imaging in the field (maritime Antarctica) over a period of 7 days. The lichen specimens grew on stone surfaces in a North-facing coastal area of Galindez Island (Argentine Islands). A portable fluorometer FluorCam equipped with a CCD camera and image analysis software was placed over a thallus so that false color images of FV/FM and quantum yield of photochemical processes in PS II (śII) distribution over the thallus could be taken in the course of a day. Simultaneously, microclimatic parameters of the habitat were recorded: air and thallus temperature, relative air humidity, PAR (photosynthetically active radiation) and global radiation. Photosynthetic processes in X. elegans were activated by rainfall or water from melting snow. After thallus hydration, FV/FM and śII gradually decreased from their maximal values due to evaporation and progressive loss of water from the thallus. Chlorophyll fluorescence imaging showed that the thallus dehydration started from margins and moved towards central thicker thallus parts that exhibited higher activity of PS II than margins throughout a day. The rate of inhibition of photosynthetic processes in PS II was faster in marginal than in central thallus parts. Dependence of śII on thallus water potential (WP) was investigated during gradual dehydration under laboratory conditions. After decrease of WP form zero to ĄV7 MPa, X. elegans exhibited only 13.8 % decrease in śII from its maximal value. Within the range of WP of from ĄV8 to ĄV20 MPa, śII decrease was more rapid reaching critical point (śII = 0) at WP about ĄV25 MPa. Chlorophyll fluorescence imaging and WP measurements documented that X. elegans is capable to maintain detectable photosynthetic activity even at extremely low WP. Based on our microclimatological data, X. elegans may be photosynthetically active under field conditions for several hours after being wetted from rain or snowfall. It is suggested that chlorophyll fluorescence imaging is a powerfull technique, transferable to field conditions and capable to visualize heterogeneity of photosyntetic processes over a lichen thallus subjected to periodic dehydration. |
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