Effect of dehydration on spectral reflectance and photosynthetic efficiency in Umbilicaria arctica and U. hyperborea

Abstract

In many polar and alpine ecosystems, lichens of genus Umbilicaria represent dominant species forming community structure. Photosynthetic and spectral properties of the lichens may change rapidly according to an actual hydration status of their thalli. In this study, we investigated responses of photochemical reflectance index (PRI), normalized difference vegetation index (NDVI), effective quantum yield of photosynthetic efficiency of photosystem (PS) II (Φ PSII ), and several photosynthetic parameters derived from fast induction kinetics of chlorophyll fluorescence (OJIP) to controlled dehydration. We used U. arctica and U. hyperborea collected close to Nuuk, Greenland. In both the species, PRI showed a curvilinear increase with dehydration, i.e., a decreasing water potential ( w ). The increase was apparent within  w range of 0 to -10 MPa. The PRI increase was less pronounced in U. arctica than in U. hyperborea. NDVI decreased with a progressive thallus dehydration in both the species, however, throughout  w range of 0 to -30 MPa, U. hyperborea had lower NDVI values than U. arctica. The relationship between Φ PSII and  w resulted in a typical S curve. A critical  w at which photosynthetic processes were fully inhibited was -30 MPa in both the species, however, species-specific differences in the S curve shape were found. Analyses of photosynthetic parameters derived from OJIPs revealed that the absorption of radiation energy and a trapping rate increased with dehydration in active reaction centres of PS II, the number of which decreased with a more pronounced lichen thallus dehydration. It is concluded that U. arctica and U. hyperborea possess effective physiological mechanisms to maintain an effective photosynthesis when partly dehydrated (the  w range of 0 to -15 MPa). In spite of similar ecological niches that these two lichens occupy in nature, their spectral and photosynthetic properties differred.

Affecting Factors and Recent Improvements of the Photochemical Reflectance Index (PRI) for Remotely Sensing Foliar, Canopy and Ecosystemic Radiation-Use Efficiencies

“…Similar findings were also reported for Salix viminalis trees [112], eggplant [88] and oak and beech trees [86], where the sizes of the pigment pools contributed to most of the PRI variability and thus limited its use for RUE estimation on long timescales. Changes in pigment concentrations due to water stress, however, could also potentially affect the seasonal variability of PRI [118][119][120], but these changes varied between species such as Umbilicaria arctica and U. hyperborean [118]. PRI clearly differentiated between normal and stressed holm oaks but was not very informative under a severe drought [121], and could generally detect the physiological status of water-stressed plants but was not useful for the drought-tolerant species Elaeagnus umbellate [122].…”

Desiccation‐induced changes in photochemical processes of photosynthesis and spectral reflectance in Nostoc commune (Cyanobacteria, Nostocales) colonies from polar regions

“…Thus, in higher plants, PRI decreases with desiccation (Sun et al ) because of involvement of protective mechanisms including increased de‐epoxidation of carotenoids. In contrast to higher plants, an increase in PRI with dehydration is reported in some lichens (Barták et al ). In cyanobacteria, PRI in response to desiccation could not relate to dehydration‐induced activation of the xanthophyll cycle, since cyanobacteria lack it.…”

Short-term responses of primary processes in PS II to low temperature are sensitively indicated by fast chlorophyll fluorescence kinetics in Antarctic lichen Dermatocarpon polyphyllizum

“…In lichens, OJIP is used to evaluate the responses of thalli to rehydration at different temperatures (Oukarroum et al 2012, Barták et al 2015b, photoinhibition (Balarinová et al 2014), ultraviolet radiation (Medina et Avalos-Chacon 2015), and fast reoxidation of PS I (Ilík et al 2006). In this study, we applied fast chlorophyll fluorescence transients to evaluate the response of Dermatocarpon polyphyllizum, an Antarctic chlorolichen, to a short-term decrease in thallus temperature.…”