Rhizodeposition and C-partitioning of Lolium perenne in axenic culture affected by nitrogen supply and defoliation

This study investigated the effects of N-supply and partial defoliation on C-partitioning, root morphology and soluble rhizodeposition, for Lolium perenne grown in axenic sand culture systems percolated with nutrient solution. Plants were grown for 36 d in nutrient solutions with differing N concentrations (4 mM or 0.02 mM NH4+NO3-), and effects of repeated defoliation to 4 cm were determined. The 'low N' supply reduced (P < 0.05) dry matter accumulation, with proportionately increased partitioning to the root systems. Root morphology was also altered at 'low N', with development of a finer root system, manifest as increased (P < 0.05) specific root length. Concurrent with these effects on growth of L. perenne, 'low N' increased (P < 0.05) exudation of C-compounds from roots on a per g root basis. Defoliation was found to increase exudation (P < 0.05) of soluble compounds for periods of 3-5 d following each cut, at both N-supply rates. The effects of N-supply and defoliation are of importance in understanding the coupling of plant productivity to nutrient cycling in soils with differing N availabilities and for grassland systems which are subject to grazing.