Chlorophyll fluorescence of desiccation-tolerant cyanobacterial crusts of sub-tropical inselberg rocks in southern China: 1. Drought stress responses
Zeng, Xue-Qin; Hou, Yu-Jia; Yang, Zhi-Cong; Evelin, Pèli; Nie, Lei; Peng, Chang-Lian
Desiccation-tolerant cyanobacterial crusts of sub-tropical inselberg rocks in Guangdong province, China, were collected with their original rock substratum during the dry season. Following rehydration, changes in photosynthetic efficiency as measured by chlorophyll fluorescence and water content of samples were studied during subsequent dehydration under different light intensities and temperature treatments in the laboratory condition. Dehydration behaviour over time under all laboratory conditions showed the same pattern. Maximal PSII quantum yield (Fv/Fm) remained stable for a long time with minor fluctuations. A sudden decline to zero was observed at critical water content before the samples completely dried. Specifically, Fv/Fm values of samples incubated at 5°C exhibited this threshold at 110-115 min, while those samples incubated at 30°C declined abruptly at 50-65 min. A 8-20% water content in this type of terrestrial cyanobacteria crusts represented a threshold for the loss of photosynthetic efficiency. The consistent relationship supports the observations that terrestrial cyanobacterial crusts are resistant to desiccation and can adapt well to dehydration in a wide range of light-temperature conditions.