PARENT SESSION
Poster Session # 15: Plant Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Influence of variation in spatial and temporal light distribution on the dynamics of leaf area biomass and nitrogen of woody plants and their relationship to community dominance in subtropical savanna.
Zitzer, Stephen*,1, Archer, Steve2, 1 Desert Research Institute, Las Vegas, NV, USA2 University of Arizona, Tucson, AZ, USA
ABSTRACT- Leaf area biomass and nitrogen relationships can vary greatly within and between species occurring in the same plant community. Determining environmental factors that affect these leaf relationships and the amplitude of variation may suggest mechanisms for ecological success. We tested the hypothesis that species with the greatest plasticity in leaf area biomass and nitrogen characteristics will be the most successful in terms of having the greatest frequency within the plant community. Leaves of the seven dominant woody growth-forms from a south Texas subtropical savanna were collected from four canopy positions within vertical transects of four landscape types in summer and in winter. We measured specific leaf area (cm2 leaf area/g dry weight leaf), mean leaf biomass (mg dry wt/leaf), mean leaf size (cm2 area/leaf) and leaf nitrogen as a function of leaf area and weight. Zanthoxylum fagara, a drought-deciduous evergreen with compound coriaceous leaves, had the greatest leaf plasticity and the greatest frequency. Conversely, evergreen sclerophyllous Mahonia trifoliolata and evergreen coriaceous Schaefferia cuneifolia had the least leaf plasticity and the lowest frequencies. Among the intermediate species, leaf plasticity decreased from Prosopis glandulosa, through Celtis pallida, Condalia hookeri and Diospyros texana and was also correlated with decreasing frequency. The data did not suggest a significant relationship between leaf phenology and genetic plasticity. Canopy position, season and landscape type were equally important relative to significantly affecting leaf characteristics across all species. Specific leaf area, mean leaf nitrogen content and specific leaf nitrogen had the most variation, while leaf nitrogen concentration was the most stable characteristic. Understanding dynamics in leaf biomass and nitrogen relationships is prerequisite to estimating dynamics in foliar biomass at the ecosystem level.
Key words: subtropical savanna, woody plants, leaf plasticity, light distribution