Effects of nitrogen supply on the source of nitrogen used for regrowth of laminae after defoliation of four grass species

Abstract

summaryPlants of Agrostis castellana, Festuca rubra, Lolium perenne and Poa trivials were grown in sand culture and supplied with a complete nutrient solution containing either 0.5 or 1.5 mol m−3 NH4NO3. Plants were clipped weekly to a height of 4 cm. At the time of the ninth clipping (day Q) the nutrient solution was replaced by one in which all nitrogen (N) was enriched with 15N to 5 atom %, but otherwise identical. Weekly destructive harvests were taken from day 0 to day 35. whilst unharvested plants continued to receive the weekly clipping. The 15N‐labelling allowed discrimination between remobilization within the plant from current root uptake in supplying N for laminae regrowth. For all four species a poor N supply reduced both N uptake by roots and the potential N available for remobilization, as welt as allocation of both these sources to laminae regrowth. Overall the N supply derived from root uptake was reduced by a greater extent, and the proportion of N in laminae regrowth derived from remobilization increased with low N supply. The rate of remobilization of the N which was accessible was slower with a reduced supply of N. The species order for increasing proportion of N for laminae regrowth being derived from remobilization was L. perenne < P. trivialis < A. castellana < F. rubra irrespective of N supply.