Will climate warming exceed lethal photosynthetic temperature thresholds of lichens in a southern African arid region?

Abstract

Predicted elevated temperatures and a shift from a winter to summer rainfall pattern associated with global warming could result in the exposure of hydrated lichens during summer to more numerous temperature extremes that exceed their thermal thresholds. This hypothesis was tested by measuring lethal temperature thresholds under laboratory and natural conditions for four epilithic lichen species (Xanthoparmelia austro-africana, X. hyporhytida, Xanthoparmelia sp., Xanthomaculina hottentotta) occurring on quartz gravel substrates at a hot arid inland site two epigeous lichen species (Teloschistes capensis, Ramalina sp.) occurring on gypsum-rich topsoil at a warm humid coastal site. Extrapolated lethal temperatures for photosynthetic quantum yield under laboratory conditions were up to 4°C higher for lichens from a dry inland site than those from a humid coastal site. Lethal temperatures extrapolated for photosynthetic quantum yield at a saturating photosynthetic photon flux density of ≥11,000 lmol photons m -2 s -1 under natural conditions were up to 6°C higher for lichens from the dry inland site than the more humid coastal site. It is concluded that only under atypical conditions of lichen exposure in a hydrated state to temperature extremes at high midday solar irradiances during summer could lethal photosynthetic thresholds in sensitive lichen species be potentially exceeded, but whether the increased frequency of such conditions with climate warming would lead to increased likelihood of lichen mortality is debatable.

Can Antarctic lichens acclimatize to changes in temperature?

“…As a consequence, lichen net photosynthesis has an optimal temperature above which further increases in respiration depress net carbon gain, and it has been shown that net CO 2 exchange can become negative at moderately elevated temperatures (Green & Lange, 1994). Lethal temperatures for photosynthesis in active, hydrated lichens are not high, usually around 30-35°C (Chiarucci, Calderisi, Casini, & Bonini, 2008;Lange, 1965;Maphangwa, Musil, Raitt, & Zedda, 2014;Smith, 1981).…”

Effect of thallus melanisation on the sensitivity of lichens to heat stress

“…However, the resistance to heat stress certainly depends on lichen species. For example, in lichens from the arid region of South Africa, the lethal temperature ranged between 44.1 and 48.1 °C 48 . In contrast, Marin et al .…”

Regionally Varying Habitat Relationships in Lichens: The Concept and Evidence with an Emphasis on North-Temperate Ecosystems

“…We found that most within-species variation in lichen habitat relationships revealed plastic adaptation to available combinations of ecological factors, rather than evolutionary lineages. This highlights regional ecosystem integrity, resilience, and related risk assessments (long-term trends; disasters; novel threats) as a major approach for lichen conservation (e.g., [ 266 , 267 , 268 ]), for which sensitive species might serve as indicators [ 269 ].…”