Abstract The diazotrophic communities in a rice paddy
field were characterized by a molecular polyphasic
approach including DNA/RNA-DGGE fingerprinting,
real time RT-PCR analysis of nifH gene and the
measurement of nitrogen fixation activities. The investigation
was performed on a diurnal cycle and comparisons
were made between bulk and rhizosphere / root
soil as well as between fertilized / unfertilized soils.
Real time RT-PCR showed no significant difference in
the total quantity of nifH expression under the
conditions investigated. The functional diversity and
dynamics of the nifH gene expressing diazotroph
community investigated using RT-PCR-DGGE
revealed high diurnal variations, as well as variation
between different soil types. Most of the sequence
types recovered from the DGGE gels and clone
libraries clustered within nifH Cluster I and III