Deposition of 15N into Soil Layers of Different Proximity to Roots by Wheat Plants

Abstract

The translocation of root borne N compounds to different distances from the roots was studied by use of rectangular pots with three separated soil zones. Wheat plants were grown for 28 days (4 leaf stage) and subsequently pulse labelled by exposure to 15 ppm ¹⁵NH₃ (generated from (¹⁵NH₄)₂SO₄ with 95 at.-% ¹⁵N exc.) every other day with the rooting medium sealed from the atmosphere. Six pulses were applied in total.

The plants assimilated 65% of the label offered. The final ¹⁵N enrichment in the shoots was approx. 13 at.-% exc. and in the roots approx. 5 at.-% exc. These abundances were high enough to detect traces of ¹⁵N in soil approximately 1 cm distant from the roots. Most of the ¹⁵N recovered was retained in the shoots (about 90%), 5% were present in the roots and another 5% had been released into the rhizosphere. Considering the ¹⁵N released, 62% were found in the central root zone, 26% in the adjacent layer and 12% in the outer zone.