Der Einfluß von Bodenbearbeitung und N-Düngung auf die Verteilung von ¹⁴C-markierten Assimilaten auf Sproß und Wurzel sowie auf die Rhizodeposition bei Winterraps

Abstract

Rhizodeposition is considered to be an important source for soil organic carbon. Increased root turnover rates may be a mechanism employed by plants to respond to nutrient limiting conditions. Estimation of rhizodeposition for field-grown oilseed-rape plants (Brassica napus L.) using ¹⁴C-pulse labelling technique was the objective of our present work. Treatments consisted of two soil tillage systems (ploughing/surface tillage, ‘Horsch’) and two N rates (0 and 240 kg N/ha). Soil, roots, and shoot were sampled three weeks after labelling and also at the end of the growing season. Rhizodepostion was calculated from the decrease in ¹⁴C activity between the sampling dates. Under high N supply retranslocation of assimilates, an increase of root ¹⁴C-content which is incompatible with our methodical approach was observed. Therefore, a second experiment was conducted, combining pulse-labelling and ingrowth-core techniques to calculate the transfer of mobile ¹⁴C-labelled assimilates to newly formed roots. It is concluded that rhizodeposition accounted for up to 90% of total carbon allocation to the roots (high N supply and ploughing). N supply and soil tillage had pronounced effects on ¹⁴C partitioning within the shoot and also high N supply as well as ploughing resulted in reduced ¹⁴C allocation to generative organs.