Root morphological plasticity and nutrient acquisition of perennial grass species from habitats of different nutrient availability

We studied the root foraging ability and its consequences for the nutrient acquisition of five grass species that differ ill relative growth rate and that occur in habitats that differ widely in nutrient availability. Foraging responses were quantified, based on the performance of the plants in homogeneous and heterogeneous soil environments of the same overall nutrient availability. Although all species tended to produce a significantly higher root length density in a nutrient-rich patch, this response was significant only for the faster-growing species. The increased root length density resulted from small, though not significant, changes in root biomass and specific root length. The effectiveness of root proliferation was determined by quantifying the total amount of nutrients (N and P) accumulated by the plants over the course of the experiment. Plants acquired more N in a heterogeneous environment than in a homogeneous environment, although the total nutrient availability was the same. The ability to acquire nutrients (N or P) in the heterogeneous environment was not related to the ability of species to increase root length density in response to local nutrient enrichment. In contrast to other studies, our results suggest that the role of morphological plasticity of roots in acquiring patchily distributed resources is limited. Possible reasons for this discrepancy are discussed.