Freezing temperature effects on photosystem II in Antarctic lichens evaluated by chlorophyll fluorescence

Abstract

This study explores and compares the limits for photosynthesis in subzero temperatures of six Antarctic lichens: Sphaerophorus globosus, Caloplaca regalis, Umbilicaria antarctica, Pseudephebe minuscula, Parmelia saxatilis and Lecania brialmontii combining linear cooling and chlorophyll fluorescence methods. The results revealed triphasic S-curves in the temperature response of the maximum quantum yield (FV/FM) and effective quantum yield of photosystem II (ΦPSII) for all species. All investigated species showed a high level of cryoresistance with critical temperatures (Tc) below −20 °C. However, record low Tc temperatures have been discovered for L. brialmotii (−54 °C for FV/FM and −40 °C for ΦPSII) and C. regalis (−52 °C for FV/FM and −38 °C for ΦPSII). Additionally, the yield differentials (FV/FM − ΦPSII) in functions of temperature revealed one or two peaks, with the larger one occurring for temperatures below −20 °C for the above-mentioned species. Finally, Kautsky kinetics were measured and compared at different temperatures (20 °C, 10 °C, 0 °C and −10 °C and then −10 °C after 1 h of incubation). This research serves as a foundation for further developing investigations into the biophysical mechanisms by which photosynthesis is carried out at subzero temperatures.