Disturbance and intraspecific variation in the clonal morphology of salt marsh perennials

While considerable interest has focused on interspecific differences in dispersal and colonizing ability, the relationship between disturbance and intraspecific differences in colonizing ability has received less study. Here, we examined the relationship between wrack-burial disturbance and intraspecific variation in clonal morphology of a fugitive clonal species, Distichlis spicata, and a competitively dominant species, Spartina parens. We tested three hypotheses: 1) clones invading gaps exhibit greater mobility (i.e., displacement) than clones within dense swards, 2) clones invading gaps within infrequently disturbed marshes exhibit greater mobility than clones invading gaps within frequently disturbed marshes, and 3) rhizome connections to ramets of D. spicata inside gaps enable the ramets to tolerate hypersaline and highly-reduced soils within lower-lying gaps. Clones of D. spicata from gaps had greater growth rates, produced longer rhizomes, and exhibited greater mobility than clones from dense swards. The magnitude of this difference in mobility was greatest in an infrequently disturbed marsh and lowest in a frequently disturbed marsh. In contrast, we did not observe significant differences in clonal dispersal between clones of S. patens from gaps and swards. The effect of severing rhizomes initialing D. spicata ramets within gaps in the Juncus gerardi zone was more detrimental to survival al lower elevations, where salinity was highest and redox was lowest. Our results suggest that intraspecific variation in clonal morphology of marsh perennials can be strongly affected by disturbances but also show that disturbance effects can be species- and site-specific. Our results also suggest that invasion of hypersaline and highly reduced soils within gaps by ramets of D. spicata may be facilitated by physiological integration with ramets located outside gaps.