Survival of Xanthoria parietina in simulated space conditions: vitality assessment and spectroscopic analysis

Abstract

Xanthoria parietina is a widespread foliose lichen growing on barks and rocks showing a broad spectrum of tolerance to air pollutants such as NOX and heavy metals, and resistance to UV-radiation because of the screening properties provided by the secondary metabolite parietin. The aim of this study was to evaluate the ability of this lichen species to survive in the following simulated space conditions, UV-radiation in N2 atmosphere and UV-radiation in vacuum. The efficiency of the photosynthetic apparatus was used as an indicator of vitality, and was expressed in terms of chlorophyll a fluorescence (FV/FM) and Normalized Difference Vegetation Index (NDVI), which were measured within 72 h from the exposure. Additionally, during the irradiation, the IR reflectance spectrum of the lichen was monitored in situ to assess changes in spectral bands. The results showed significant differences in physiological recovery trends between the treatments, highlighting that UV-radiation in vacuum causes stronger effects on FV/FM values. The IR analysis revealed several spectral band changes in the fingerprint region. The most visible variation was the 5200 cm−1 water band that disappeared in the overtone region. Nevertheless, X. parietina was able to survive UV-radiation in N2 atmosphere and in vacuum, and for this reason it may be considered a candidate for further evaluations on its survival capacity in extreme conditions.

Survivability of the lichen Xanthoria parietina in simulated Martian environmental conditions

“…Specimens were dehydrated for 24 h at room temperature (25 °C) and stored at − 18 °C until treatment, as this procedure ensures that thalli remain healthy for later experiments and physiological analyses 29 . Three days before the pre-exposure analyses, specimens were allowed to slowly recover their normal metabolic conditions in a growth chamber at 25 °C, with 12 h dark and 12 h light at 50 μmol m -2 s −1 PAR photons, daily sprayed with distilled water 28 , 30 , 31 . On the third day, photoefficiency measurements were performed to assess proper thalli reactivation.…”

“…On the third day, photoefficiency measurements were performed to assess proper thalli reactivation. They were dehydrated for 24 h and cut to obtain 12 samples of 1 cm 2 in size for the next analyses 28 . The size was determined by the aluminum sample holders adopted for the exposure (Fig.…”

“…The post-exposure analyses consisted of the Raman spectroscopy, after which the FM and DM samples were rehydrated for the recovery phase. During this last phase, the FM, DM and external control samples were kept in the growth chamber at 25 °C, with 12 h dark and 12 h light at 50 μmol m −2 s −1 PAR photons, wetted daily for 8 days 28 , 31 . Every day of the recovery phase—with exception of the weekend—the FM, DM and external control samples were measured with the Imaging PAM to assess photosynthetic activity and verify their recovery over time.…”

“…Rusavskia elegans ascospores showed the highest survivability and X. parietina showed a remarkable germination rate of the irradiated ascospores too. At INAF—Astrophysical Observatory of Arcetri (Florence), X. parietina was exposed in two extremely dehydrating conditions—UV-radiation in N 2 atmosphere and UV-radiation in vacuum 10 0 –10 −2 Pa (both 1.34 MJ m −2 final dose) and for the first time, in situ IR spectroscopic analyses were performed on the exposed lichen species 28 . The recovery capability was evaluated assessing chlorophyll a (Chl a ) fluorescence, showing a full recovery in N 2 exposed thalli and a 50% recovery in vacuum-exposed samples, after 72 h from the treatment 28 .…”

“…At INAF—Astrophysical Observatory of Arcetri (Florence), X. parietina was exposed in two extremely dehydrating conditions—UV-radiation in N 2 atmosphere and UV-radiation in vacuum 10 0 –10 −2 Pa (both 1.34 MJ m −2 final dose) and for the first time, in situ IR spectroscopic analyses were performed on the exposed lichen species 28 . The recovery capability was evaluated assessing chlorophyll a (Chl a ) fluorescence, showing a full recovery in N 2 exposed thalli and a 50% recovery in vacuum-exposed samples, after 72 h from the treatment 28 . As X. parietina was able to survive these conditions, it was considered an optimal candidate for further evaluations on its survival capacity in extreme conditions.…”