Ecophysiology of five subalpine Acaena species in relation to habitat
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The ecophysiology of five subalpine Acaena species: A. Caesiiglauca, A. Fissistipula, A. Glabra, A. inermis and A. Profundeincisa, was examined in relation to their habitats at Porters Pass. All five species except A. profundeincisa had distinct habitat preferences. Experimental comparisons of their seed ecology, adaptations to water stress, growth responses and interference potential were used to examine how each species is adapted to its preferred habitat. A. caesiiglauca has a distinct preference for grassland/scrub habitats. Its absence from drier sites is attributable to its inability to tolerate desiccation. A. fissistipula is restricted to streamside habitats because it is unable to tolerate desiccation. Its low interference potential excludes it from grassland/scrub habitats. A. glabra and A. inermis, due to their poor interference potential, are limited to sites with high evaporating conditions where few other species grow. However they have adapted to these environments in different ways. A. glabra has developed an extensive transpiration system to provide an efficient cooling system. It has therefore made a compromise between closing stomata to resist desiccation and maintaining open stomata for continued photosynthesis. In contrast, A. inermis attempts to minimize water loss by having a low stature with extensive branching to form mats. Its leaves are also more physiologically tolerant of desiccation. A. profundeincisa has no distinct habitat preference. Optimum germination occurs at a lower temperature than the other species which is reflected by its higher altitudinal distribution. It is relatively tolerant of water stress and has a high interference potential, which enables it to inhabit a variety of habitats.