Exclusion of root competition increases competitive abilities of subordinate plant species through root-shoot interactions

Questions
What is the importance of root competition in the competitive abilities of dominant and subordinate species?

Location
Pair-wise greenhouse experiment based on field data from a semi-natural grassland community in the Swiss Jura Mountains (Col du Marchairuz, Switzerland).

Methods
The dominance hierarchy from a mountain wood-pasture ecosystem was used to identify five dominant and three subordinate species. These species were grown in pair-wise combinations under full competition and in the absence of root competition, enabling us to calculate indices of competitive effect and response and overall asymmetry.

Results
Root competition exclusion led to a decrease in the competitive abilities of dominants, whereas subordinates became overall more competitive. Total asymmetry also decreased, indicating reduced competition between the two species groups. The exclusion of root competition increased both below-ground and above-ground growth of subordinates, whereas for dominants below-ground growth was unaffected and above-ground growth decreased.

Conclusions
We demonstrate that root competition through root–shoot competition interactions is an important factor driving the competitive dominance of species and the structure of grazed grassland communities. Locally, reduction of root competition involved in gap creation might explain persistence of subordinate species within the vegetation community and lead to an aggregated spatial pattern of subordinates involved in species co-existence in grasslands.