Ecophysiological traits of various genotypes of a green key alga in biological soil crusts from the semi-arid Colorado Plateau, USA

Biological soil crusts (BSCs) represent a micro-ecosystem consisting of various microorganisms including algae in drylands worldwide. The green algal genus Klebsormidium is a typical member of such communities, and because of its filamentous morphology and sticky cells, it plays an ecological key role in the stabilization of soil surfaces. In the present study, we investigated for the first time the phylogeny and ecophysiological performance of five BSC Klebsormidium strains from the semi-arid Colorado Plateau, USA. The molecular phylogeny of rbc L sequences showed that these strains belong to two subclades, which have been described before from mainly humid habitats. During controlled dehydration, the effective quantum yield of photosystem II decreased during 370–430 min of exposure. After controlled rehydration, all strains recovered between 32.9 and 97.6% of the control, but with significant differences depending on the genetic lineage. All five isolates grew between 18.1 and 27.9 °C, with isolate-specific optimal growth temperatures. Similarly, all strains were grown under increasing photon fluence rates from 4 to 110 μmol photons m −2 s −1 with optima under the higher tested light levels. Two strains showed inhibition at higher photon fluence rates and hence low light requirements for growth. Photosynthesis under increasing photon fluence rates up to 314 μmol photons m −2 s −1 indicated again low light requirements, but with no photoinhibition. All results underline a pronounced plasticity of the ecophysiological traits of the investigated Klebsormidium strains, which allow these terrestrial algae to exploit the environmental gradients within BSCs in arid regions.