Functional reactivation of photosystem II in lichen soil crusts after long-term desiccation

As an important successional stage of biological soil crusts, lichen soil crusts (LSCs) are often in the dry and inactive state in desert environments, so it is vital for their survival and development in these areas to reactivate the photosynthetic systems during a rehydration event. In this study, the reactivation patterns of light-harvesting complexes (LHCs) and reaction centres of photosystem (PS) II in the long-term desiccated LSCs (approximately 10 months) were monitored using chlorophyll a fluorescence technique. For the long-term desiccated LSCs, PS II reaction centres could recover their activity gradually in the light after rehydration, whereas no obvious recovery occurred in the dark (0.1 < Fv/Fm < 0.2). After experiencing prior rehydration/desiccation (R/D) cycle(s) in the light, the PS II reaction centres could rapidly recover their activity following rehydration both in the light and dark. Even the most reactivation (76 % of the PSII centers) was independent on the synthesis of new proteins. In addition, compared with reaction centres, LHCs of PS II could recover their activity faster both in the light and dark, and prior R/D cycle(s) also accelerated the recovery of LHC II. It is concluded that prior R/D cycles strongly accelerated LSC recovery process of photosynthetic systems and removed the dependence on light in subsequent hydration events. This characteristic is essential for LSCs to survive and develop in desert environments because it facilitates more carbon fixation during transient rehydration.As an important successional stage of biological soil crusts, lichen soil crusts (LSCs) are often in the dry and inactive state in desert environments, so it is vital for their survival and development in these areas to reactivate the photosynthetic systems during a rehydration event