Belowground zone of influence in a tussock grass species

Belowground plant competition is strong and mediated by resource depletion as well as by high variety of exudates. Both factors contribute to active root segregation, affecting neighbours’ growth. In field and greenhouse experiments we investigated the belowground zone of influence of Stipa tenacissima, a tussock-forming grass which is the dominant species in many semiarid communities of the western Mediterranean Basin. Sometimes tussocks show a fringe nearly devoid of annual plants, most likely caused by competition or interference. Fringe size was a function of water availability, so that the more water available the smaller the fringe and vice-versa. Aboveground mass of annual plants was higher in gaps than in the fringe, but root mass was higher in the fringe. More species emerged in soils from gaps than in soils from the fringe, and productivity was ten times higher in soils from gaps than in soils from the fringe. Growth of barley plants was inhibited in the vicinity of S. tenacissima tussocks. S. tenacissima produced a belowground zone of influence around the tussock through resource depletion, particularly water, but also likely through root exudates. Both mechanisms might inhibit the establishment of other annual and grass species within the fringe. Fringe area has important effects for plant establishment, influencing population and community dynamics in these semiarid environments.