The Middle East and North Africa (MENA) comprises some of the largest sandy deserts in the planet, which includes the Sahara (in Northern Africa) and the Rub' al Khali (or Empty Quarter; in the Arabian Peninsula, encompassing areas of Saudi Arabia, Oman, the United Arab Emirates and Yemen). The DARWIN21 project was launched some years ago to generate a global knowledge base of the biodiversity of the Arabian desert rhizosphere and to study their potential use for sustainable agricultural systems in arid lands. DARWIN21 is an initiative by the King Abdullah University of Science and Technology with partners such as the International Center for Biosaline Agriculture in the United Arab Emirates and academic institutions in Europe.
The bacterial composition of the rhizosphere of four plants, including a desert grass (Panicum turgidum) and three Zygophyllaceae species (Tribulus terrestris, Tribulus pentandum and Zygophyllum simplex), and of a soil sample of the Jizan desert (southern Saudi Arabia) was analyzed in a recent study. More than 3,500 operational taxonomic units (OTUs) were found – in Biology, an OTU defines a cluster of closely related individuals based on DNA similarity. In the plant samples, the most abundant organisms belonged to the Proteobacteria and Bacteroidetes phyla, while in the soil sample displayed an abundance of organisms from the Firmicutes phylum, particularly Bacillus. This study was further expanded to include the microbial composition not only of the rhizosphere (soil close to the root surface) but also the root endosphere (within root tissues) of desert plant samples in the Jizan area and in the Al Wahbah crater (Western Saudi Arabia). Actinobacteria and Proteobacteria dominated both the rhizosphere and endosphere of all samples, but the bacterial distribution from the Jizan and Al Wahbah areas were significantly different. The authors went on to cultivate more than 100 of bacterial isolates from these samples and observed that there were substantial differences in nutrient acquisition, hormone production and growth under stress conditions. More importantly, eleven of the isolated strains helped the plant model Arabidopsis thaliana to tolerate high salt conditions, suggesting a potential utilization of these microbes as natural enhancers of agriculture yield in the desert. Similar beneficial effects for various crop traits of alfalfa were observed for root-adhering bacteria isolated from the rhizosphere of plants from Hada Al Sham in Saudi Arabia. In the Al Jouf region (Northern Saudi Arabia), an Actinobacteria was obtained from the rhizosphere of a desert grass that was able to alleviate the effects of drought stress on maize. Finally, a recent study has determined that there is a considerable fungal biodiversity in sand samples from Saudi Arabia and Jordan deserts, which included culturable species from the genera Fusarium, Chaetomium and Albifimbria. These are simply some examples; similar examinations of the soil biodiversity (mainly bacterial diversity) of the Arabian desert have been conducted.
Interesting facts: Plant growth promoting rhizobacteria (PGPR) are a group of naturally-occurring bacteria that proliferate in the plant rhizosphere and stimulate plant physiological processes and biomass production. This includes enhancing plant growth, remediating degraded wastelands, controlling pesticide pollution, nitrogen, and phosphorous runoff, and increasing resistance to pathogens. For example, PGPR found in the desert soil are evolutionarily well adapted to the harsh abiotic conditions of those ecosystems and help plants to thrive in the extreme conditions. Thus, these organisms have been applied as “biofertilizers” in agricultural settings to enhance productivity.
Photograph courtesy of John A. Kelly, USDA-NRCS