Photosynthesis of terrestrial cyanobacteria under light and desiccation stress as expressed by chlorophyll fluorescence and gas exchange

Terrestrial mats of cyanobacteria with other associated microscopical cryptogams were obtained from various sites in the tropics, i.e. rocks of mountains and rock-outcrops and bare soil surfaces, a valley in the Austrian Alps and a glasshouse. Species diversity of each sample was analysed qualitatively. The samples came from very different light climates. Responses to light and desiccation stress were studied using the saturation pulse method for recording chlorophyll fluorescence variables as well as by measuring net CO2 and O2 exchange in order to confirm results by independent methods. Under light stress, shade and high-light, samples showed a reduction of gas exchange and of the fluorescence variables photochemical fluorescence quenching coefficient (qp), potential quantum yield of photosystem II (FvIFm) and effective quantum yield (ΔFIFm) and recovery to different degrees. Short-term desiccation led to suppression of variable fluorescence yield and inhibition of gas exchange, but recovery occurred rapidly within 1 h after rewetting. It is concluded that together with the well-known ability for assimilation of atmospheric dinitrogen, desiccation tolerance of terrestrial cyanobacteria mats is the major reason for their success as pioneers on bare substrata. In addition, the capacity to produce sun and shade forms adapted to a very wide range of light intensities appears to be important.