Effects of gamma irradiation on Holcus lanatus (Yorkshire fog grass) and associated soil microorganisms.

An investigation was conducted to determine the impact of acute doses of gamma radiation on the microbial community structure of a Holcus lanatus dominated grassland soil. Mesocosms containing soil and established grass were irradiated using a sealed (137)Cs source (7.0 Gy min(-1)). Doses ranged from 5 to 160 Gy, analyses were conducted on the day of irradiation, then 7 and 30 days later. Plant growth and arbuscular mycorrhizal fungal colonisation of roots were reduced by irradiation. Gram-negative bacteria, and microbial metabolic capacity were also negatively affected by treatment. Microbial biomass measured by phospholipid fatty acid (PLFA) analysis, showed an increase at doses above 20 Gy, 7 and 30 days after treatment. Proportions of Gram-positive bacterial and fungal PLFAs fluctuated inversely to each other, in response to both sampling time and radiation dose. We hypothesise that many of the observed soil microbial responses are indirect effects mediated by the influence of ionising radiation on the plants in this system.