Functional ecology, ecophysiology, and convergent evolution of dwarf shrub and cushion plant growth forms.

摘要

This work involves the comparison of morphology and ecophysiology between several species of dwarf shrubs and cushion plants in three geographically distinct regions. The overall goal is to understand the environmental cues that maintain these growth forms and to determine the specific adaptations that such growth forms confer.; The Bodega Head Natural Reserve in Sonoma County is the first field site. Three native shrubs dominate this temperate coastal prairie: Eriophyllum stachaedifolium, a cushion shrub, Lupinus arboreus, and Baccharis pillularis, both noncushion forming shrubs. Morphology, environmental parameters, water stress and, photosynthesis were measured. The cushion growth form of E. stachaedifolium is best adapted to windy bluffs, but seedlings in a greenhouse did not maintain a cushion growth form, indicating that the cushion growth form for this species is not genetically constrained and is maintained by wind trimming.; The second field site is an arid tropical alpine zone in the Andes of northern Chile, Parque Nacional Lauca, which represents a region known as puna, and is 4000 m above sea level. The morphology, ecophysiology and size class distribution for a large dense cushion plant, Azorella compacta , were investigated. Very low wind speeds recorded in this region indicate that for A. compacta, the cushion growth form is an adaptation to low temperature or water stress. Analysis of water stress confirmed that both stresses have an effect in maintaining the cushion form of A. compacta.; The final field site is at the White Mountain Research Station in the White Mountains of California. For the dwarf shrub, Chrysothamnus viscidiflorus ssp. viscidiflorus, morphology and ecophysiology of two populations, a lower altitude site at (3094 m above sea level) and a higher altitude site (3850 m a.s.l.), were compared. Also, 60 seedlings from each population were taken to UCLA where seedlings were assigned to one of four treatments: increased wind, cold nighttime temperature, drought, or control. The cold nighttime temperature treatment showed the most cushion like growth form.; Although many hypotheses exist for why dwarfism and cushion growth forms occur in plants, this project shows that no single environmental cue is responsible for these growth forms in each environment.