Microbial and hydrolase activity after release of indoleacetic acid and ethylene–polyamine precursors by a model root surface

Effects of indoleacetic acid (IAA) and ethylene (E) precursors on microbial biomass, respiration, and various hydrolase activities of the rhizosphere and bulk soil, were studied using a model system simulating this environment. The effects of IAA and E precursors were compared to those of glucose-C, N and S (GNS) applied at the same rate to soils. None of the treatments significantly affected respiration rates and ATP contents of soils. The IAA precursor significantly increased phosphatase, beta-glycosidase, urease and protease activities of the rhizosphere layer of both soils; the E precursor significantly increased phosphodiesterase, urease and protease activities of both soils. The GNS treatment did not significantly increase any hydrolase activity. The IAA precursor also stimulated the phosphatase activity of the bulk layer of the sandy soil after 7 d of incubation, possibly due to its diffusion from the rhizosphere to the bulk soil, whereas no stimulation in the bulk soil layer was observed in either E or GNS treatments. The increased hydrolase activities in the rhizosphere upon addition of both IAA and E precursors may be due to the role of these precursors as microbial metabolic activators, and may be involved in stimulation of plant growth through other processes involving IAA and E producing root associated microorganisms.