L. Badalucco et al., PROTEASE AND DEAMINASE ACTIVITIES IN WHEAT RHIZOSPHERE AND THEIR RELATION TO BACTERIAL AND PROTOZOAN POPULATIONS, Biology and fertility of soils, 23(2), 1996, pp. 99-104
Protease and deaminase activities and population dynamics of bacteria
and protozoa were measured in the rhizosphere of wheat to study their
interactions with the mineralization of nitrogen. The experimental des
ign allowed the separation of roots and soil material by means of a ga
uze. The most pronounced ''rhizosphere effect'' was detected for all t
he measured variables in the soil closest to the gauze. The number of
bacteria was significantly higher in the presence than in the absence
of plants up to 4 mm away from the soil-root interface and the closer
to this interface the higher the number. Protozoan and bacterial popul
ation dynamics were positively correlated; generally, populations of f
lagellates and amoebae were comparable and their sum accounted for the
population of total protozoa. For both enzyme activities the rhizosph
ere effect extended up to 2 mm away from the soil-root interface. The
histidinase activity was of bacterial origin, while it is likely that
bacteria, protozoa and root hair all contributed to the overall casein
ase activity. Decomposition of root exudates and native organic matter
in the rhizosphere, reflected by a growing microbial population, is a
ssociated with nitrogen mineralization through increases in casein-hyd
rolysing and L-histidine-deaminating activities. The adopted soil-plan
t microcosm is suitable for the study of the rhizosphere effect over t
ime of incubation and distance gradient from the soil-root interface.