NITROGEN LOSSES FROM PERENNIAL GRASS SPECIES

Nitrogen losses from plants may occur through a variety of pathways, b ut so far, most studies have only quantified losses of nutrients by ab ove-ground litter production. We used N-15 pulse labelling to quantify total nitrogen losses from above- and below-ground plant parts. Using this method we were able to include also pathways other than above-gr ound litter production. To test the hypothesis that species from nutri ent-poor habitats lose less nitrogen than species from more fertile so ils, six perennial grasses from habitats with a wide range of nutrient availability were investigated: Lolium perenne, Arrhenatherum elatius , Anthoxanthum odoratum, Festuca rubra, F. ovina and Molinia caerulea. The results of an experiment carried out in pots in greenhouse at two fertility levels show that statistically significant losses occur thr ough pathways other than aboveground litter production. In the low fer tility treatment, most (70%) losses from L. perenne occurred by litter production, but in Ar. elatius, F. rubra, F. ovina and M. caerulea, m ore than 50% of labelled N losses took place by root turn-over, leachi ng or exudation from roots, When nutrient supply increased, the N-15 l osses in aboveground dead material increased in all species and in Ar. elatius, A. odoratum and F. rubra the N-15 losses via other pathways decreased. Ranked according to decreasing turnover coefficient the seq uence of species was: L. perenne, A. odoratum, F. rubra, F. ovina, Ar. elatius, M. caerulea. These results suggest that species adapted to s ites with low availability of nutrients lose less nitrogen (including above- and below-ground losses) than species adapted to more fertile s oils.