Horizontal and vertical distribution of root absorption zones of four common grass species in a mountain grassland

Horizontal distance between shoots and the place of nutrient absorption as a function of depth of the absorption zone was studied using a pointwise application of a non-radioactive tracer (strontium). The tracer was applied to three different soil depths in a mountain grassland and the biomass was sampled at the fine-scale. Vertical distribution of absorption zones differed between the species; in Deschampsia flexuosa, Festuca rubra and Anthoxanthum alpinum the amount of strontium absorbed decreased with increasing application depth; no such decrease took place in Nardus stricta. The horizontal distance of maximum strontium concentration from the application point increased with increasing depth of application in Festuca and, to a lesser extent, in Anthoxanthum. The absorbing zone therefore had essentially a conical shape, widening with increasing depth. No similar increase in horizontal-uptake distance with depth occurred in Nardus or Deschampsia; their absorption zones were more cylindrical. This indicates that shapes of root absorption zones differ between the component grass species. The differences in shapes of root absorption zones can be attributed to different gross morphologies of roots and rhizomes. The horizontal extent of root absorption zones is large relative to the grain of interspecific spatial pattern in the grassland.