Responses to severe competitive stress in a clonal plant: Differences between genotypes

The rhizomatous perennial grass (Amphibromus scabrivalvis) has the ability to be phalanx-like and guerrilla-like in its growth form, producing new ramets both from the base of established ramets (phalanx) and spread out along elongated rhizomes (guerrilla). Changes in clonal growth and allocation patterns of A. scabrivalvis in response to severe competitive stress induced by a background of Lolium perenne, a phalanx species, were studied. Eleven genotypes of A. scabrivalvis were divided into ramets and planted into pots in the glasshouse alone or into a background of dense L, perenne. Plants were harvested after 27 wk. Competitive stress was severe, with relative competition intensity for the genotypes ranging from 0.89 to 0.97. Both ramet production and mean interramet distances were significantly depressed by competition. Under competition, A. scabrivalvis showed a much higher allocation to roots and rhizomes compared to the control. This may serve to increase storage under competitive conditions. Genotypes producing a large number of ramets with high interramet distances in the control were more strongly affected by competition than genotypes producing fewer ramets with low interramet distances. This suggests that a more phalanx-like growth strategy may be selectively favored under severe competitive stress from a phalanx species in A. scabrivalvis. In communities dominated by perennial plants, general growth strategy, as exemplified by clone architecture, may be a critical determinant of population development and maintenance under highly competitive conditions.