Summary The relationships between bacterial community diversity and stability were investigated by perturbing soils, with naturally differing levels of diversity, to equivalent toxicity using copper sulfate and benzene. Benzene amendment led to large decreases in total bacterial numbers and biomass in both soils. Benzene amendment of an organo‐mineral/improved pasture soil altered total soil bacterial community structure but,...

The effect of CO 2 concentration on plant growth and the size of the rhizosphere denitrifier population was investigated for ryegrass grown at 3 different soil pH values (pH 4.3, 5.9 and 7.0). Soil microcosms were planted with ryegrass and maintained under constant growth conditions at either ambient (450ppm) or elevated (720ppm) CO 2 concentration. At harvest, the rhizosphere soil was collected and subjected to a potential de...

Direct effects of increased above‐ground CO 2 concentration on soil microbial processes are unlikely, due to the high pCO 2 of the soil atmosphere in most terrestrial ecosystems. However, below‐ ground microbial processes are likely to be affected through altered plant inputs at elevated CO 2 . A major component of plant input is derived from litter fall and root turnover. Inputs also derive from rhizodeposition (loss of C‐com...