Phosphorus form-related metabolic responses in roots of Triticum aestivum and the impact of beneficial soil microorganisms

Phosphate fertilizers are a finite resource, thus sustainable crop production will most likely depend on the utilization of P sources naturally found in soil, in particular predominant organic P forms. To date we know little of the biochemical sensing and adaptation of crops to different organic and inorganic P that potentially affects its assimilation. Furthermore, the use of inoculants of beneficial soil microorganisms has become of increasing interest due to their ability to mobilize P from organic and inorganic sources naturally occurring in soil. However, many factors including nutrient type and status, plant species and the presence of other microbes have a positive or detrimental affect on microbial fitness and activity and as a result on crop P uptake and growth. Therefore, the aim of this PhD thesis was to improve our understanding of the biochemistry of phosphorus sensing, mobilization and uptake in wheat from various sources, and subsequently address the impact of mycorrhizal fungi as well as plant growth promoting rhizobacteria on these processes. Mesocosm studies provided detailed evidence that wheat root metabolism and the secretion of root exudates are sensitive to organic and inorganic P forms. In addition and with respect to P uptake and growth, wheat responsiveness to mycorrhizal fungi and plant growth promoting rhizobacteria colonization was highly dependent on the present P form. However, long-term changes in root metabolism were mainly driven by the P source. Based on these results, it is still necessary to ascertain if these metabolic changes are general responses of wheat or cultivar specific. Further, it is essential to link these responses to P uptake mechanisms and determine their effect on rhizosphere microorganisms in order to develop cultivars that not only have enhanced soil P exploitation and utilization capacities, but also positively respond to beneficial rhizomicroorganisms.