PARENT SESSION
Oral Session # 60: Invasive Species V: Genetics; Chemical Cycling Effects.
Presiding: S Miao
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 204.
Biomass allocation, growth, and photosynthesis of native and introduced genotypes of an invasive tropical shrub.
DeWalt, Saara*,1, Denslow, Julie2, Hamrick, James3, 1 Louisiana State University, Baton Rouge, LA2 USDA Forest Service, Hilo, HI3 University of Georgia, Athens, GA
ABSTRACT- Exotic pest plants often grow to greater stature, become more abundant, and display increased shade tolerance in their introduced ranges than in their native ranges. We tested the hypothesis that genetic differences in growth, biomass allocation, or photosynthetic parameters between native and introduced genotypes of Clidemia hirta (Melastomataceae) contribute to differences in abundance and shade tolerance between its native and introduced ranges. We conducted a common garden experiment in a greenhouse with C. hirta grown from seed collected from four populations in part of its native range (Costa Rica) and four populations in part of its introduced range (Hawaiian Islands). Six-month old seedlings were placed in high (10.3-13.9 mol m-2 day1) or low (1.4-4.5 mol m-2 day-1) light treatments and grown for an additional six months. Our study provided little evidence that Hawaiian genotypes of C. hirta differed genetically from Costa Rican genotypes in ways that would contribute to the observed differences in habitat distribution and abundance. Hawaiian and Costa Rican genotypes displayed no differences in relative growth rates, maximal photosynthetic rates, or specific leaf areas in either light treatment. Some of the genetic differences that were apparent, such as greater allocation to stems and leaf area relative to whole plant biomass in Costa Rican genotypes and greater allocation to roots in Hawaiian genotypes, were contrary to predictions that genotypes from the introduced range would allocate more biomass to growth and less to storage than those from the native range. As predicted, however, Hawaiian genotypes allocated more biomass to reproductive parts than Costa Rican genotypes in the high light environment. We conclude that environmental differences, such as pest loads, between the native and introduced ranges likely play a greater role than genetic shifts in resource use or allocation in determining habitat distribution and abundance for this species.
Key words: common garden, Clidemia hirta, shade tolerance, invasive species