University of Natural Resources and Life Sciences, Vienna (BOKU) - Research portal
Gewählte Master / Diploma Thesis:
Rainer Franz Mühlbacher
(2015):
Where do roots leak phosphorus?
An Inquiry on Root Phosphorus Efflux into the Rhizosphere.
Master / Diploma Thesis - Institut für Bodenforschung (IBF),
BOKU-Universität für Bodenkultur,
pp 71.
UB BOKU
obvsg
FullText
- Abstract:
- Phosphorus is of particular importance in plant nutrition. As P-fertilizers have to be made from declining workable rock phosphorus deposits, P dynamics and uptake kinetics in the soil and in the rhizosphere are of great interest. After findings of phosphorus hotspots within the rhizosphere of rape seed plants using diffusive gradients in thin films technique (DGT) ferrihydrite gels and laser ablation inductively coupled plasma mass spectrometry a possible connection between root phosphorus efflux and those hotspots was hypothesized. Here those experiments were repeated with maize plants using also radiophosphorus and digital autoradiography. Maize seedlings grown in P-fertilized and non-fertilized acidic and alkaline soils as well as in agarose gels were labeled with 33P and DGT strips were applied for a period of 48 hours. After this the DGT strips were removed from the root surface and exposed to autoradiography screens for 48 hours and scanned afterwards. The experiments resulted in the detection of phosphorus hotspots in the rhizosphere of maize plants and in clear evidence that phosphorus in the rhizosphere is released by the plant roots in a spatially very heterogeneous way. Phosphorus efflux mainly occurs at the root tips whereas efflux along root axes is very small. Overall mean relative quantification of root phosphorus efflux shows a mean axis-to-tip ratio of 0.003, i.e. only 0.30% of total efflux occurs along main axes. Similar results were obtained in the other treatements. According to clear evidence obtained by the experiments, efflux quantifications relating to root mass, root surface area, root length, etc. are inappropriate and future quantifications should relate mainly to root tips. We show that the Michaelis-Menten model as it has been applied in previous studies is inaccurate as it describes uptake rates for the entire root system where (almost) only root tips should be taken into account.
- Beurteilende(r): Wenzel Walter
- 1.Mitwirkender: Santner Jakob