Natural ultraviolet radiation exposure alters photosynthetic biology and improves recovery from desiccation in a desert moss

Abstract

Plants in dryland ecosystems experience extreme daily and seasonal fluctuations in light, temperature, and water availability. We used an in-situ field experiment to uncover the effects of natural and reduced levels of UV on maximum PSII quantum efficiency (Fv/Fm), relative abundance of photosynthetic pigments and antioxidants, and the transcriptome in the desiccation-tolerant desert moss Syntrichia caninervis. We tested the hypotheses that: (1) S. caninervis plants undergo sustained thermal quenching of light (non-photochemical quenching; NPQ) while desiccated and after rehydration, (2) a reduction of UV will result in improved recovery of Fv/Fm, but (3) one year of UV removal will de-harden plants and increase vulnerability UV damage to photosynthetic efficiency. All field-collected plants had extremely low Fv/Fm after initial rehydration but recovered over eight days in lab-simulated winter conditions. UV-filtered plants had lower Fv/Fm during recovery, higher concentrations of photoprotective pigments and antioxidants such as zeaxanthin and tocopherols, and lower concentrations neoxanthin and chlorophyll b than plants exposed to near natural UV levels. Field-grown S. caninervis underwent sustained NPQ that took days to relax and for efficient photosynthesis to resume. Reduction of solar UV radiation adversely affected recovery of Fv/Fm following rehydration.

Sex Differences in Desiccation Tolerance Varies by Colony in the Mesic Liverwort Plagiochila porelloides

“…Recently, a study found that ultraviolet light resulted in an increase in desiccation tolerance in Syntrichia caninervis Mitt. [27]. While UV light was not measured in this current study, the pattern of light measures of C3 vs. C1 and C2 translates to more direct light and thus more UV light for C3.…”

“…In fact, few studies have tested for intraspecific differences in desiccation [15] (and references therein). For example, the percentage of canopy openness (exposure) was related with increased male water stress tolerance [24] and UV light was positively associated with tolerance [27]. Identifying and quantifying environmental associations to desiccation tolerance will provide insight into selection drivers or their correlates.…”

Transcriptomic Effects of Acute Ultraviolet Radiation Exposure on Two Syntrichia Mosses

“…In its natural desert habitat, this species experiences prolonged periods of desiccated quiescence seasonally, where it dissipates excess solar radiation as heat (Ekwealor et al, 2021). Since UV-B radiation varies substantially seasonally, relative to other regions of the spectrum (Robson et al, 2019), UV-B can act as a phenological cue for plants.…”

“…As this protein is uncharacterized, the role it is playing in UVR response can only be speculated upon, but given the high level of desiccation tolerance in this species, the functional annotation is intriguing. In fact, UVR has been implicated in desiccation tolerance in S. caninervis, where removal of natural levels of UVR from a field setting hindered recovery of photosynthetic efficiency from desiccation (Ekwealor et al, 2021). By T 30 , abundance of this transcript had increased again to nearly an LFC of −1 (Figure 4).…”

“…Based on their occurrence in open, exposed habitats (Mishler and Oliver, 1991;Oliver et al, 1993;Bowker et al, 2000), they are presumed to be UVR tolerant (UVT), too. In fact, wild-grown S. ruralis and S. caninervis plants are unaffected by UV-B radiation, based on chlorophyll fluorescence (Takács et al, 1999;Csintalan et al, 2001;Ekwealor et al, 2021). Syntrichia ruralis occupies a wide range of elevations and aridities ranging from arid to mesic (Oliver et al, 1993).…”