Desert plant bacteria reveal host influence and beneficial plant growth properties.

Deserts, such as those found in Saudi Arabia, are one of the most hostile places for plant growth. However, desert plants are able to impact their surrounding microbial community and select beneficial microbes that promote their growth under these extreme conditions. In this study, we examined the soil, rhizosphere and endosphere bacterial communities of four native desert plants Tribulus terrestris, Zygophyllum simplex, Panicum turgidum and Euphorbia granulata from the Southwest (Jizan region), two of which were also found in the Midwest (Al Wahbah area) of Saudi Arabia. While the rhizosphere bacterial community mostly resembled that of the highly different surrounding soils, the endosphere composition was strongly correlated with its host plant phylogeny. In order to assess whether any of the native bacterial endophytes might have a role in plant growth under extreme conditions, we analyzed the properties of 116 cultured bacterial isolates that represent members of the phyla Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. Our analysis shows that different strains have highly different biochemical properties with respect to nutrient acquisition, hormone production and growth under stress conditions. More importantly, eleven of the isolated strains could confer salinity stress tolerance to the experimental model plant Arabidopsis thaliana suggesting some of these plant-associated bacteria might be useful for improving crop desert agriculture.

[Effects of water stress on photosynthesis, biomass, and medicinal material quality of Tribulus terrestri].

A pot experiment was conducted to study the effects of water stress on the photosynthetic characteristics, biomass accumulation, and principal medicinal compositions of Tribulus terrestri. Water stress changed the diurnal variation of T. terrestri photosynthesis, decreased the net photosynthetic rate and transpiration rate significantly, weakened the plant photosynthetic and assimilative capability, and accordingly, hindered the dry matter accumulation and decreased the biomass. However, water stress promoted the accumulation of gross saponins in T. terrestri. In the treatments with irrigation amounts 150 and 450 mm, the gross saponins content was 13.26 and 12.47 mg x g(-1), respectively, being significantly different from that in the treatments with irrigation amounts 250 and 350 mm. The dynamic accumulation of gross flavonoids and gross saponins had an opposite tendency with that of biomass, namely, the contents of these principal medicinal compositions were the lowest when the biomass was the maximal. Correlation analysis showed that the biomass accumulation of T. terrestri was significantly correlated with outside environmental factors, while the contents of secondary metabolism products were affected not only by the outside environmental factors, but also by the inside factors such as biomass accumulation.