In lichens, each symbiotic partner cooperates for the survival of the symbiotic association.
The protection of the susceptible photosynthetic apparatus is essential for both participants.
The mycobiont and photobiont contribute to the protection against the damaging effect
of excess light by various mechanisms. The present study investigated the effect of
seasonality and microhabitat exposure on photoprotection and photoacclimation in the
photo- and the mycobiont of six lichen species with different thallus morphology in
inland dune system in the Kiskunság region (Hungary) with shaded, more humid and exposed,
drier dune sides. High-Performance Liquid Chromatography, spectrophotometry, chlorophyll
a fluorescence kinetic technique were used, and micrometeorological
data were collected. The four years data series revealed that the north-east-facing
side was characterized by higher relative humidity and lower light intensities compared
to the south-west-facing drier and more exposed sides. The south-west facing side
was exposed to direct illumination 3–4 hours longer in winter and 1–2 hours shorter
in summer than the north-east facing side of the dune, influencing the metabolism
of sun and shade populations of various species. Because rapid desiccation caused
short active periods of lichens during bright and drier seasons and on exposed microhabitats,
the rapid, non-regulated non-photochemical quenching mechanisms in the photobiont
had a significant role in protecting the photosynthetic system in the hydrated state.
In dehydrated conditions, thalli were mainly defended by the solar screening metabolites
produced by the mycobiont and curling during desiccation (also caused by the mycobiont).
Furthermore, the efficacy of light use (higher chlorophyll and carotenoid concentration)
increased because of short hydrated periods. Still, a lower level of received irradiation
was appropriate for photosynthesis in dry seasons and on sun exposed habitats. In
humid seasons and microhabitats, more extended active periods lead to increased photosynthesis
and production of solar radiation protectant fungal metabolites, allowing a lower
level of photoprotection in the form of regulated non-photochemical quenching by the
photobiont. Interspecific differences were more pronounced than the intraspecific
ones among seasons and microhabitat types.
