Effects of nutrient depletion on growth of Holcus lanatus L. and Festuca ovina L. and on the ability of their roots to absorb nitrogen at warm and cool temperatures.

To examine the ecological relevance of slow growth for survival in unproductive environments, responses to nutrient depletion were compared between two ecologically contrasted grasses with reference to their ability to utilize a nutrient flush. Dry weight growth, ability of roots to absorb nitrogen and subsequent distribution between root and shoot were determined for Holcus lanatus L. and Festuca ovina L. before and after subjecting them to nutrient depletion at warm and cool temperatures. Initially, the relative growth rates (RGR) of H. lanatus were much higher than those of F. ovina, but after 21 days of nutrient depletion, F. ovina attained higher RGR. During nutrient depletion, F. ovina maintained higher shoot N concentrations than H. lanatus, mainly due to lower rates of dry matter accumulation in F. ovina. Maintenance of N concentrations in F. ovina may contribute to sustaining of the shoot activity under N-depleted conditions. Nutrient depletion caused an increase in the proportion of N allocated to roots relative to shoots, but F. ovina exhibited less plasticity than H. lanatus. Following nutrient depletion, the ability of roots to absorb nitrate declined markedly in H. lanatus and to a much lesser extent in F. ovina. The ability to absorb ammonium was also reduced at warm temperatures, while at cool temperatures it was unchanged in H. lanatus, but increased in F. ovina. These results suggest that F. ovina has a greater potential to exploit 'nutrient flushes' than H. lanatus under unproductive conditions, especially at cool temperatures.