Responses of Rhizosphere Microbial Communities in The Drought-Sensitive and -Tolerant Genotypes of Bromus inermis, Dactylis glomerata and Festuca arundinacea Species to Water Stress

Root exudates and morphological root traits play an important role in plant species’ response to drought. However, the functional consequences of these drought-induced changes for rhizosphere microbial communities are unknown. We hypothesized that drought-sensitive and -tolerant grass genotypes widely differ in the quality of root exudates, growth strategies, and root systems, which may affect rhizosphere microbial communities. Therefore, we examined microbial biomass carbon and nitrogen in the rhizosphere of drought-sensitive and -tolerant genotypes of Bromus inermis, Dactylis glomerata, and Festuca arundinacea species under four years water stress treatments at Lavark Farm of the Isfahan University of Technology. Responses of the rhizosphere microbial communities to the water stress varied by the plant genotypes. Water stress increased rhizosphere microbial biomass carbon in the drought-sensitive and -tolerant genotypes of Bromus inermis species. In contrast, water stress treatment significantly reduced microbial biomass in the rhizosphere of Dactylis glomerata genotypes. The effect of water stress on rhizosphere microbial biomass carbon was positive in the drought-sensitive genotypes of Festuca arundinacea species, while conversely, this effect was negative in the drought-tolerant genotypes. We found a similar pattern across two drought-sensitive and -tolerant genotypes of Bromus inermis species to the water stress, which could be an evolutionary strategy to overcome drought conditions through the stimulation of microbial biomass and activity and the subsequent mineralization of nutrients. Higher microbial biomass carbon in the rhizosphere soils relative to those in the control (bulk soil) were observed, regardless of the moisture treatment. Under the water stress, microbial biomass carbon were almost simillar in the rhizosphere of drought-sensitive and -tolerant genotypes but were higher in the drought-tolerant genotypes without the stress.