Visualized photosynthetic characteristics of the lichen Xanthoria elegans related to daily courses of light, temperature and hydration: a field study from Galindez Island, maritime Antarctica

Abstract

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 rock 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 colour images of FV/FM and quantum yield of photochemical processes in PS II (ΦII) distribution over the thallus could be taken over the course of a day. Simultaneously, microclimatic parameters of the habitat were recorded: air and thallus temperatures, relative air humidity, PPFR (photosynthetic photon fluence rate) and global radiation. Photosynthetic processes in X. elegans were activated by rainfall or water from melting snow. After thallus hydration, FV/FM and ΦII gradually decreased from their maximum values due to evaporation and progressive loss of water from the thallus. Chlorophyll fluorescence imaging showed that the thallus dehydration started from the margins and moved towards the central thicker thallus zones. These zones exhibited higher activity of PS II than the margins throughout the day. The rate of inhibition of photosynthetic processes in PS II was faster at the margins than in the centre of the thallus. Dependence of ΦII on thallus water potential (WP) was investigated during gradual dehydration under laboratory conditions. After a decrease in WP from zero to −7 MPa, X. elegans exhibited only a 13·8% decrease in ΦII from its maximal value. Within the range of WP of from −8 to −20 MPa, the ΦII decrease was more rapid reaching the critical point (ΦII=0) at WP of approximately −25 MPa. Chlorophyll fluorescence imaging and WP measurements showed that X. elegans is capable of maintaining 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 by rain or snowfall. It is suggested that chlorophyll fluorescence imaging is a powerful technique, transferable to field conditions and capable of visualizing heterogeneity of photosyntetic processes over a lichen thallus subjected to periodic dehydration.

Diurnal changes in photosynthetic activity of the biological soil crust and lichen: Effects of abiotic factors (Petuniabukta, Svalbard)

“…It is well comparable to the evidence from a wide variety of organisms (mainly lichens) investigated by a chlorophyll fluorescence approach, see e.g. Kappen et al 1995, Kappen et al 1996, Barták et al 2005, Barták et al 2007.…”

Changes in spectral reflectance of a foliar lichen Umbilicaria hirsuta during desiccation

“…Reflectance signal in the near infrared region (at 970 nm) has been found as the most reliable water status indicator for the tested lichen specimens. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or water potential > -1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually inhibited at much lower values of water potential than in leaves of vascular plants ( Barták et al 2000, 2005, Nash et al 1990, Kappen and Valladares 1999.…”

Interspecific differences in photosynthetic efficiency and spectral reflectance in two Umbilicaria species from Svalbard during controlled desiccation

“…Within last couple of years, the dependence of photosynthesis of numerous Arctic and Antarctic lichens on thallus dehydration expressed as water potential has been investigated in our laboratory (see e.g. Barták et al 2005). Representatives of genus Umbilicaria typically show substantial photosynthesis even at strong dehydration, i.e.…”