Spatio-temporal pattern of root exudation and enzyme activities in the rhizosphere

This thesis aims at studying the role of root hairs, benzoxazinoids, soil texture and drought on the spatio-temporal pattern of root exudates and enzyme activities in the rhizosphere of maize. The rhizosphere processes of soil organic matter decomposition and phosphorus mobilization were studied using non-destructive 2-D imaging methods. Thus, zymography, phosphor imaging, neutron radiography, planar optodes and diffusive gradients in thin films (DGT) we applied to visualize enzyme activity, 14C exudates, soil water, pH values and dissolved nutrients, respectively. The obtained images were then analyzed for colocalization of the measured parameters. In addition, soil samples were taken locally to measure enzyme kinetics and to conduct microbiome analysis using DNA sequencing. This multi-imaging approach coupled with co-localization analyses was applied for the first time in the laboratory in rhizobox experiments and in the field using root windows.

Root hairs enraged enzymatic rhizosphere extent of three-weeks-old maize grown in the rhizoboxes, but had no  effect at late growth stage under field conditions. Under drought, root hairs widen the rhizosphere to ensure better nutrient mining and water uptake. Soil texture play an important role on phosphorus mobilization processes. Despite more intensive processes detected in sand, a higher soil organic matter and better physico-chamical properties in loam combined with the presence  of root hairs provide better  plant phosphorus nutrition.Benzoxazinoids are secreted by roots to defend against pathogenic fungi, but may suppressed the activities of beneficial microorganisms.

Plant breeding towards increasing the content of benzoxazinoids and the presence of root hairs is a promising tool for better plant protection and improving nutrients acquisition, especially under drought and on sandy soils.





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