Nitrogen-use efficiency in six perennial grasses from contrasting habitats

1. We studied the nitrogen-use efficiency (NUE) in six perennial grasses adapted to a wide range of nutrient availability. The glasshouse experiment was carried out in pots containing nutrient solution, with two fertility treatments. Nitrogen-use efficiency was considered as the product of nitrogen productivity and mean residence time of the nitrogen in the plant (calculated using ¹⁵N pulse labelling).
2. The species investigated are characteristic of habitats ranging from very nutrient rich to extremely nutrient poor, in the following order: Lolium perenne, Arrhenatherum elatius, Festuca rubra, Anthoxanthum odoratum, Festuca ovina and Molinia caerulea .
3. Lolium perenne (adapted to nutrient-rich habitats) had higher nitrogen productivity ( A ) than M. caerulea (species adapted to nutrient-poor habitats) but lower than that of F. rubra (from habitats with an intermediate availability of nutrients).
4. In the low fertility treatment, species with the lowest nitrogen-use efficiency had the lowest N productivity and the highest mean nitrogen residence time (MRT); however, although species with the highest nitrogen use efficiency had the highest N productivity they did not have the lowest MRT. In all species the nitrogen-use efficiency decreased with increasing N supply. The two components of the NUE ( A and MRT) are inversely correlated along gradients of nutrient availability, but not at very high levels of nutrient availability.
5. The nitrogen-use efficiency of species at constant levels of nutrient supply tends to increase with increasing nutrient availability in their preferred habitat, according to the Clausman nutrient index, up to a certain nutrient availability and then decreases. The results support the contention that species from nutrient-poor sites are not necessarily adapted by a high nitrogen-use efficiency, but by low nutrient loss rates (high mean residence time of N in the plant).