N transfer from white clover to perennial ryegrass, via exudation of nitrogenous compounds

The nitrogen isotope N-15 was used to quantify and determine the direction of nitrogen transfer between white clover ( Trifolium repens L.) and perennial ryegrass ( Lolium perenne L.). A micro-lysimeter system allowed the determination of the nature of the compounds exuded. During N privation, transfer was one-way from clover to ryegrass and was mainly explained by the large amounts of ammonium exuded by clover. N compound exudation by legume followed by uptake by companion grass is a highly significant pathway for inter-specific N transfer between young plants. Ammonium was the major N compound exuded. Amino acids were released in lower amounts, serine and glycine being the most abundant in leachates. In the micro-lysimeter, the amounts of ammonium, serine and glycine in the exudate were not altered by the presence of bacteria, providing evidence of the plant origin of these compounds.