干旱区生态环境知识资源中心

We recently isolated a small green alga from a biological sand crust (BSC) in the NW Negev, Israel. Based on its 18S rRNA and rbcL genes, it is a close relative of Chlorella sorokiniana and of certain strains of C.vulgaris and C.variabilis, but differs substantially in many aspects from C.sorokiniana. Because the classification of Chlorellales is still not resolved, we designated this species as C.ohadii (Trebouxiophyceae) in honor of Professor Itzhak Ohad. Under controlled laboratory conditions, C.ohadii showed marked structural and photosynthetic performance changes, depending on the carbon source used during growth, as well as remarkable resistance to photoinhibition. CO2-dependent O-2 evolution was not affected even when exposed to a light intensity of 3500molephotonsm(-2)s(-1), over 1.5 times the maximal intensity reached at the BSC surface, whereas the variable fluorescence declined sharply. We briefly discuss the use of fluorescence to assess photosynthetic rate and the implications of this finding for the assessment of global BSCs activity.