I K Mpanga
Universität Hohenheim, Germany
Title: Benefi ts of ammonium fertilization for plant-PGPM interactions
Biography
Biography: I K Mpanga
Abstract
Attempts to use soil microorganisms with potential for nutrient mobilization as inoculants to improve nutrient acquisition of
crops have a long history. However, a major limitation of these approaches is a frequently limited reproducibility of eff ects
under practical conditions. Testing a range of commercial products based on Bacillus, Pseudomonas, Trichoderma and Penicillium
strains, revealed that the expression of their plant growth promoting potential on maize was strongly dependent on the form of
nitrogen supply. Superior performance was recorded in combination with ammonium-based fertilizers, stabilized by nitrifi cation
inhibitors instead of nitrate dominated fertilization. A closer examination of the ammonium eff ects revealed a stronger stimulation
of root growth induced by the inoculants, associated with an ammonium-induced elongation of root hairs. Accordingly, ammoniumfertilized
maize plants showed higher endogenous auxin (IAA) levels and increased auxin-production potential was demonstrated for
Bacillus and Pseudomonas strains in presence of stabilized ammonium, both, on artifi cial growth media and aft er-isolation from the
rhizosphere. Higher root colonization of maize plants supplied with stabilized ammonium was recorded for a Trichoderma harzianum
strain. Moreover, the synergistic eff ect of microbial and ammonium-induced root growth promotion resulted in a larger root surface
area, involved in rhizosphere acidifi cation due to proton-extrusion in response to ammonium uptake, mediating the mobilization of
Ca-phosphates and micronutrients such as Zn and Mn. Finally, ammonium fertilization suppressed root infection by the seed-borne
pathogenic fungus Fusarium proliferatum. Th e fi ndings demonstrated that plant-PGPM interactions are strongly dependent on the
form of N fertilization off ering management options, which have been recently patented.