PS 85-119 - Abiotic and biotic factors affecting first year seedling growth and survival of Acer grandidentatum

Friday, August 12, 2011
Exhibit Hall 3, Austin Convention Center
Terri Nelson Dickinson and Oscar Van Auken, Biology, University of Texas at San Antonio, San Antonio, TX

     Factors affecting growth and survival of first year Acer grandidentatum seedlings were considered.  A portion of the woody plant community at Lost Maples State Natural Area in the Edwards Plateau region of Central Texas was examined using the quadrat method.  Transects were established within a thirty year old deer exclosure and at two adjacent sites, one xeric and one mesic, and community composition was compared.  Fifteen first year seedlings were planted in the deer exclosure and fifteen in the xeric site.  Growth and survival rates were monitored for one year.  A full factorial greenhouse experiment compared the interaction of nutrient availability and competition with simulated herbivory.  Eighty plants were planted with high or low nutrients, with or without competition from the perennial grass Bouteloua curtipendula, and herbivory simulated by 0%, 25%, 50%, or 75% leaf tissue removal.  Growth and survival rates were recorded for one year.  Next, five seedlings each were grown at 20%, 40%, 60% and 100% of ambient light levels for six months. Survival, growth rates and dry mass were compared.  Photosynthetic rates of five full sun leaves and five shaded leaves of juvenile maples were measured in the field at varying light levels and photosynthetic parameters were calculated and compared. 


     In terms of density and basal area, the community within the exclosure was dominated by Quercus buckleyi, A. grandidentatum, and Juniperus asheii.  The mesic site was dominated by Platanus occidentalis, Diospyros texana, and Prunus serotina, while the xeric site contained primarily Juniperus asheii.  The exclosure had the highest density of seedlings, saplings, and mature A. grandidentatum.  Seedlings planted inside the exclosure survived at a greater rate than those outside the exclosure, though relative growth rates did not differ.   Greenhouse plants that experienced high nutrients, no competition, and 0% simulated herbivory had the highest relative growth rates and dry mass. Seedlings exposed to 40% ambient sunlight had the lowest mortality and attained the highest biomass, while those exposed to full sun had the highest mortality and the lowest biomass.  Photosynthetic light response curves were generated, identifying A. grandidentatum as intermediate between sun and shade tolerance and showing slightly higher rates for leaves in full sun.   Herbivory has the potential to affect seedling growth and succession both through direct damage and by altering abiotic conditions such as available light and competition, and seems to be a cause of A. grandidentatum recruitment failure in Central Texas.

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