Should I Stay or Should I Go? Roots Segregate in Response to Competition Intensity

Background and Aims Root segregation has been observed in a variety of species. Though it is usually attributed to a plant’s attempt to avoid below ground competition, a direct correlation of root distribution with the intensity of competition has never been shown. Methods The test species Hieracium pilosella L. was exposed to a gradient of competitive pressure using the closely related species Arabidopsis petraea (L.) V.I.D OROF ., Arabidopsis thaliana (L.) Heynh . , Capsella rubella Reut . and Cardamine hirsuta L. as neighbouring plants. Horizontal root distribution was quantified using a soil monolith method. Results The neighbour species could be ranked according to their competitive effect on the test species, identifying two weak ( A. thaliana and A. petraea ) and two strong competitors ( C. hirsuta and C. rubella ). The degree of root segregation correlated negatively with the competitive effect caused by the various neighbour species. Conclusions We conclude that root segregation is indeed a response to competitive pressure. Further factors such as root symbiotic relationships or root exuded allelochemicals are supposedly involved in the outcome of root interactions. We propose the use of screening experiments on root responses to various neighbours in order to quantify each factor’s relative influence on rooting patterns.