Effects of Drought Stress and Species Variation on Carbon and Nitrogen Microbial Biomass and Β-Glucosaminidase Activity in the Rhizosphere of Grasses

Long-term drought effect is one of the main factors of global climate change, with consequences for soil biogeochemical cycling of carbon and nitrogen and the function of soil ecosystem under drought conditions. We hypothesized that 1) the Bromus inermis, Dactylis glomerata and festuca arundinacea species would differ in their rhizosphere responses to drought and 2) combined plant species and drought would have offsetting effects on the soil biological traits. We tested these hypotheses at the long-term drought field expreiment at the Lavark Farm of Isfahan University of Technology by analyzing soil microbial biomass carbon and nitrogen and activity of β-glucosaminidase in the rhizosphere of Bromus inermis, Dactylis glomerata and festuca arundinacea species. Soil microbial biomass carbon and nitrogen responses to drought depended on plant species, such that the highest MBC was recorded in the Bromus inermis rhizosphere, while the lowest was in the Dactylis glomerata rhizosphere, thereby suggesting the greater microbial sensitivity to drought in the Dactylis glomerata rhizosphere. Genotype variations (drought tolerate and sensitive) mostly affected the change in the β-glucosaminidase activity, but they were not significantly affected by drought treatment and plant species. In general, the positive effects of the plant genotype could offset the negative consequences of drought for soil microbial biomass and traits.