1 Utilization of carbon sources by culturable soil bacteria can be assessed
with BIOLOG microtiter plates (contain 31 C sources). We used this techniq
ue to investigate bacterial community structure at various levels of plant
diversity. Plant diversity levels were replicated and we investigated the i
nfluence of three plant functional groups, grasses, legumes and non-legumin
ous herbs, as well as the influence of individual plant species.
2 Catabolic activity and catabolic diversity of culturable soil bacteria we
re used to estimate their density (abundance) and functional diversity, res
pectively. Both increased linearly with the logarithm of plant species numb
er and with the number of plant functional groups in experimental grassland
ecosystems. These effects may have been caused by an increased diversity a
nd quantity of material and energy flows to the soil. They may also have be
en mediated by increased diversity of soil microhabitats via a stimulation
of the soil fauna.
3 The presence of particular plant species or functional groups in the diff
erent experimental communities stimulated the activity and functional diver
sity of the culturable soil bacteria in addition to their contribution via
plant diversity. The legume Trifolium repens had the strongest effect and m
ay be regarded as a keystone species with regard to plant-microbial interac
tions in the systems studied.