Elevated CO2 and nitrogen addition have minimal influence on the rhizospheric effects of Bothriochloa ischaemum

The influence of elevated CO₂ and nitrogen (N) addition on soil microbial communities and the rhizospheric effects of Bothriochloa ischaemum were investigated. A pot-cultivation experiment was conducted in climate-controlled chambers under two levels of CO₂ (400 and 800 μmol mol⁻¹) and three levels of N addition (0, 2.5, and 5 g N m⁻² y⁻¹). Soil samples (rhizospheric and bulk soil) were collected for the assessment of soil organic carbon (SOC), total N (TN), total phosphorus (TP), basal respiration (BR), and phospholipid fatty acids (PLFAs) 106 days after treatments were conducted. Elevated CO₂ significantly increased total and fungal PLFAs in the rhizosphere when combined with N addition, and N addition significantly increased BR in the rhizosphere and total, bacterial, fungal, Gram-positive (G⁺), and Gram-negative (G⁻) PLFAs in both rhizospheric and bulk soil. BR and total, bacterial, G⁺, and G⁺/G⁻ PLFAs were significantly higher in rhizospheric than bulk soil, but neither elevated CO₂ nor N addition affected the positive rhizospheric effects on bacterial, G⁺, or G⁺/G⁻ PLFAs. N addition had a greater effect on soil microbial communities than elevated CO₂, and elevated CO₂ and N addition had minor contributions to the changes in the magnitude of the rhizospheric effects in B. ischaemum.

Biological Activity of Autochthonic Bacterial Community in Oil-Contaminated Soil

Soil microbial communities play an important role in the biodegradation of different petroleum derivates, including hydrocarbons. Also other biological factors such as enzyme and respiration activities and microbial abundance are sensitive to contamination with petroleum derivates. The aim of this study was to evaluate the response of autochthonic microbial community and biological parameters (respiration, dehydrogenase and catalase activities, total microorganisms count) on contamination with car fuels and engine oils. The surface layer (0-20 cm) of Mollic Gleysol was used for the experiment. In laboratory conditions, soil was contaminated with the following petroleum substances: car fuels (petrol, diesel) and car engine oils (new and waste-after 10,000 km). The results demonstrated that, among the investigated hydrocarbon substances, petrol addition seemed to be the most toxic for the microbial activity of the investigated soil. The toxicity of the used hydrocarbon substances to microorganisms might be summarized as follows: diesel > new oil > waste oil > petrol. Species belonging to the genera Micrococcus and Rhodococcus were noted as the major autochthonic bacteria being present in soil contaminated with new automobile oil, whereas species of the genera Bacillus sp. and Paenibacillus sp. were identified in the combination treated with waste oil.