Sunsafe Bryophytes: Photoprotection from Excess and Damaging Solar Radiation

Abstract

Whilst light is essential for photosynthesis and development of plants, both excess photosynthetically active radiation and certain wavelengths (e.g. high energy ultraviolet-B) radiation can be damaging. Plants in general possess a suite of mechanisms that act to either prevent absorption of damaging and excess radiation or to mitigate against the damage that such radiation can cause once it is absorbed. Whilst bryophytes share many of these photoprotective mechanisms with the vascular plants, there are key differences in the photoprotection available to bryophytes. Some of these differences pertain to structural features, such as protective epidermal layers, that are available to vascular plants but not generally to bryophytes. Bryophytes thus have to invest more in cellular level photoprotection than vascular plants. In other respects bryophytes may retain mechanisms found in algal ancestors (e.g. thermal energy dissipation associated with the LHCSR protein) that have been lost during the evolution of vascular plants. Many bryophytes are able to manage light absorption during desiccation and rehydration and freezing and thawing, resulting in potentially novel mechanisms of energy dissipation. Given the high stress environments that many bryophytes inhabit, from hot or frozen deserts to alpine habitats with high incident UV-B radiation, it is unsurprising that they have a suite of photoprotective strategies.

Physiology of Photosynthetic Organisms Within Biological Soil Crusts: Their Adaptation, Flexibility, and Plasticity

“…Bryophytes and lichens show excellent protection against possible damage by high UVB and PAR Robinson and Waterman 2014). This protection seems to be constitutive, and when the plants are dry and inactive, chlorophyll fluorescence is near zero.…”

“…The light level required to saturate NP (PFD sat ) of biocrusts is almost always at, or above, about 700 μmol photons m À2 s À1 and, because of this, biocrusts have often been referred to as being similar to sun plants (Lange 2001), but they do not reach the NP max associated with such plants although they certainly have higher NP max than species from shadier habitats (Proctor 2014;Robinson and Waterman 2014). It is probable that the high PFD sat (and NPQ) provides protection against occasional high incident PFD.…”

The spatial structure of Antarctic biodiversity

“…Enhanced levels do occur on the Antarctic Peninsula, but there is evidence that the bryophytes at least can rapidly acclimate to changes in UV radiation (Newsham 2003, Newsham and Robinson 2009). Exposure does result in damage to biochemical constituents of cells (e.g., DNA and photosystems [Green et al 2000, George et al 2002, Lud et al 2002, Robinson and Waterman 2013), but these effects are transient. The dynamic behavior of the protective pigments, which are typically lost if the plants are shaded, suggests that there is a metabolic cost to their presence.…”

Functional Diversity of Subalpine Bryophyte Communities in an Oceanic Island (La Réunion)

“…However, because bryophytes are poïkilohydric organisms with varying degrees of desiccation tolerance, they also grow at high altitudes and their elevational ranges often exceed those of vascular plants. They are dominant in high altitude ecosystems (Theurillat et al, 2003;Robinson and Waterman, 2014), where they account for a large proportion of primary production. For instance, in alpine shrub meadows on the Tibetan plateau, bryophyte species contribute up to 35% of primary production (Li and Qi, 1993).…”