Irradiance prior to and during desiccation improves the tolerance to excess irradiance in the desiccated state of the old forest lichen Lobaria pulmonaria

Abstract

Hydrated thalli of the lichen Lobaria pulmonaria were either preconditioned to dim irradiance (DI, 5 µmol m -2 s -1 ) or medium irradiance (MI, 200 µmol m -2 s -1 ) for 6 h. After this 6 h period, the thalli were allowed to desiccate under the two respective irradiances. Thereafter, these dry lichens were exposed to high irradiance (HI, 1 000 µmol m -2 s -1 ) for 60 h. After this HI treatment, the maximal photochemical quantum yield (F V /F M ) and the de-epoxidation state of xanthophyll cycle pigments (DEPS) were highest in thalli preconditioned to MI. Hence irradiance in the last hydrated period before sampling is significant for the physiological state of lichens. A standardized irradiance pre-treatment before start of experiments is recommended.

Unravelling the roles of desiccation-induced xanthophyll cycle activity in darkness: a case study in Lobaria pulmonaria

“…These processes may lead to the overexcitation of photosynthetic apparatus, which is exacerbated when photosynthetic organisms desiccate upon sun exposure (Heber et al 2006). Under such conditions, the de-epoxidation of the xanthophyll cycle protects desiccation-tolerant organisms against photooxidation, as has been shown in lichens (Kranner et al 2003;Stepigova et al 2008). Not only during desiccation, but also during the rehydration process, the photoprotective mechanisms play a crucial role, since the formation of ROS in mitochondria and chloroplast are a cause of damage when the hydrated conditions return (Kranner et al 2008).…”

“…It does not exclude a protective role of Z in the desiccated state of the lichen, mainly considering the detrimental eVects of illumination in these conditions (Gauslaa and Solhaug 2000). In fact, Stepigova et al (2008) proved that irradiance prior to desiccation favours Z synthesis and enhances light tolerance during the dry state in the same species. Furthermore, the modest, but signiWcant, V de-epoxidation maintained during the desiccated state could also be eVective in engaging the mechanism of NPQ of absorbed energy during rewatering, since only a few Z molecules per reaction centre are suYcient to permit eYcient light dissipation (Bukhov et al 2001).…”

“…In the case of L. pulmonaria, strong seasonal modiWcations of photosynthetic components (MacKenzie et al 2001;SchoWeld et al 2003), together with instantaneous morphological and physiological responses to drying Barták et al 2006;Heber et al 2010), allow the photobionts (Dictyochloropsis reticulata) to maintain the functionality of the photosynthetic apparatus for many years (SchoWeld et al 2003). The activation of xanthophyll de-epoxidation induced by light seems to improve the desiccation tolerance of this species (Stepigova et al 2008). Thus, the dark synthesis of zeaxanthin reported in the present study, acting as antioxidant, membrane stabiliser or mediating downregulation of photosynthetic eYciency, probably adds a new piece to the complex set of protective mechanisms in L. pulmonaria.…”

“…Its natural occurrence and growth are strongly inXuenced by the availability of light and the risk of desiccation (Gauslaaa et al 2006). Photosynthetic responses have been deeply characterised in relation to desiccation and light-damage processes in this species Gauslaa and Solhaug 2000;Kranner 2002;Barták et al 2006;Gauslaaa et al 2006;Hájek et al 2006;Stepigova et al 2008;Heber et al 2010). These studies have highlighted the plasticity of the photosynthetic apparatus of this lichen as well as the importance of thallus morphology, antioxidant metabolism, conformational changes leading to energy dissipation and xanthophyll cycle operation during desiccation in lightexposed thalli.…”

Can partial‐cut harvesting be used to manage terrestrial lichen habitat? A review of recent evidence

“…Gauslaa et al (2012) noted that a rapid transition to high light exposure in desiccated lichens (this in work on Lobaria pulmonaria) resulted in chlorophyll degradation, an interaction that was exacerbated under low relative humidity conditions. This same high light exposure while the lichens were desiccated gradually, however, triggered changes in the photochemistry of the lichens that improved their tolerance of excess irradiance in the desiccated state (Stepigova et al, 2008).…”