Genotypic and Phenotypic Diversity of Cyanobacteria in Biological Soil Crusts of the Succulent Karoo and Nama Karoo of Southern Africa

Biological soil crusts (BSCs) are communities of cryptogamic organisms, occurring in arid and semiarid regions all over the world. Based on both morphological identification and genetic analyses, we established a first cyanobacterial inventory using the biphasic approach for BSCs within two major biomes of southern Africa. The samples were collected at two different sites in the Succulent Karoo and one in the Nama Karoo. After cultivation and morphological identification, the 16S rRNA gene was sequenced from the cyanobacterial cultures. From the soil samples, the DNA was extracted, and the 16S rRNA gene sequenced. All the sequences of the clone libraries from soil and cultures were compared with those of the public databases. Forty-five different species were morphologically identified in the samples of the Succulent Karoo (observatories of Soebatsfontein and Goedehoop). Based on the genetic analyses, 60 operational taxonomic units (OTUs) were identified for the Succulent Karoo and 43 for the Nama Karoo (based on 95% sequence similarity). The cloned sequences corresponded well with the morphologically described taxa in cultures and sequences in the public databases. Besides known species of typical crust-forming cyanobacterial genera (Microcoleus, Phormidium, Tolypothrix and Scytonema), we found sequences of so far undescribed species of the genera Leptolyngbya, Pseudanabaena, Phormidium, Oscillatoria, Schizothrix and Microcoleus. Most OTUs were restricted to distinct sites. Grazed soils showed lower taxa numbers than undisturbed soils, implying the presence of early successional crust types and reduced soil surface protection. Our combined approach of morphological identification and genetic analyses allowed both a taxa inventory and the analysis of species occurring under specific habitat conditions

Nitrogen input by cyanobacterial biofilms on an inselberg into a tropical rainforest in French Guiana

Inselbergs are isolated rock outcrops displaying high heterogeneity in both soil formation and microclimatic condition with high variation in plant biodiversity. Vegetation patterns on inselbergs in the humid tropics range from rocks covered with dense biofilms predominated by cyanobacteria to high forest on deep soils. Along a similar transect, we investigated N supply to the vegetation using element and isotopic analyses of soil and biofilm samples from an inselberg in French Guiana. An increase in N content related to total dry weight (N%) in soils from the inselberg peak to surrounding habitats was related to changes in stable isotope composition (delta N-15). At the inselberg peak cyanobacterial biofilms on bare rocks and soils within small vegetation islands had similar delta N-15 values of -1.9 parts per thousand and - 1.3 parts per thousand while delta N-15 of soils progressively increased towards the primary rainforest up to 6 parts per thousand. From the peak towards the base of the inselberg, the density of higher plants and soil depth increased. Hence, soil N cycling and N losses to the environment resulted in a progressive increase of soil delta N-15. The distribution of N%, delta N-15 and delta C-13 values suggest that the main N supply for soils at and nearby the inselberg is derived from cyanobacterial N-2 fixation through leaching processes. (c) 2007 Elsevier GmbH. All rights reserved