Root contact responses and the positive relationship between intraspecific diversity and ecosystem productivity.

High species and functional group richness often has positive effects on ecosystem function including increasing productivity. Recently, intraspecific diversity has been found to have similar effects, but because traits vary far less within a species than among species we have a much poorer understanding of the mechanisms by which intraspecific diversity affects ecosystem function. We explored the potential for identity recognition among the roots of different Pseudoroegneria spicata accessions to contribute to previously demonstrated overyielding in plots with high intraspecific richness of this species relative to monocultures. First, we found that when plants from different populations were planted together in pots the total biomass yield was 30 % more than in pots with two plants from the same population. Second, we found that the elongation rates of roots of Pseudoroegneria plants decreased more after contact with roots from another plant from the same population than after contact with roots from a plant from a different population. These results suggest the possibility of some form of detection and avoidance mechanism among more closely related Pseudoroegneria plants. If decreased growth after contact results in reduced root overlap, and reduced root overlap corresponds with reduced growth and productivity, then variation in detection and avoidance among related and unrelated accessions may contribute to how ecotypic diversity in Pseudoroegneria increases productivity.