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Ecological Section

Goedhart, Christine [1], Pongetti, Greg [1], Nordenstahl, Marisa [2], Espino, Susana [1], Schenk, H. Jochen [1].

Hydraulic redundancy in shrubs along aridity gradients in North and South America.

Arid regions around the globe are dominated by shrubs of a unique growth form. These shrubs possess strongly segmented woody roots and stems that often split apart as the shrub matures, in many cases resulting in complete fragmentation of the plants. These species are often dominant in their native habitats and include Larrea tridentata and Ambrosia dumosa in North America, Zygophyllum dumosum and Artemisia herba-alba agg. in Israel, as well as numerous Artemisia species in the northern hemisphere. Many other species posses strongly fluted or segmented axes, but do not physically split apart.  In either case, morphological stem segmentation causes axial segmentation of the hydraulic system.  Previous research has shown that woody plants from dry environments often show a high degree of axial hydraulic segmentation of the water-conducting wood, even if they show no signs of morphological stem segmentation.  We postulate that axial hydraulic segmentation in its various forms introduces redundancy into the hydraulic system of plants, which increases the chances for survival of the whole genetic individual under water-limited conditions, but at the cost of loosing parts of the plants to drought-induced mortality. Based on this premise we hypothesized that the degree of hydraulic redundancy in shrubs will decrease along aridity gradients from arid to mesic conditions. To test this hypothesis, we documented the prevalence of morphological axis segmentation in shrubs from a variety of genera along North and South American aridity gradients located between 30° and 35° latitude.  Along the same gradients we also measured axial hydraulic segmentation at the anatomical level by mapping pathways of water transport in the xylem using injected dye tracers. The results support our hypothesis that the degree of hydraulic redundancy in shrubs decreases from arid to mesic environments.

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1 - California State University Fullerton, Department of Biological Science, PO Box 6850, Fullerton, California, 92834-6850, USA
2 - Facultad de Agronomía, University of Buenos Aires, Av. San Martín 4453, Buenos Aires, C1417DSE, Argentina

hydraulic segmentation
hydraulic redundancy
shrub ecology
climatic gradients
drought adaptations.

Presentation Type: Poster
Session: 33-36
Location: Salon C, D & E - Gov Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 12:30 PM
Abstract ID:185

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