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

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Abstract
Summary: Plants 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.

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