Xylem root and shoot hydraulics is linked to life history type in chaparral seedlings (Rhamnaceae)Functional Ecology (2009)
Abstract1. Shrubs in ﬁre prone chaparral communities have evolved different life history types in response to ﬁre. A key to understanding the evolution of life history type differences is to understand how physiological traits are linked to differences in life history type. Vascular adaptations are important for delivering an efﬁcient and stable water supply to evergreen chaparral shrub leaves. This study tested for a link between vascular physiology and life history type in chaparral shrubs. 2. Chaparral shrub species along the south-western coast of North America survive wildﬁre by three different life histories. Non-sprouters are killed by ﬁre and re-establish exclusively through germination of ﬁre-stimulated seeds, facultative sprouters re-establish by a combination of vegetative sprouting and ﬁre-stimulated seeds, and obligate sprouters re-establish exclusively by vegetative sprouting because their seeds do not survive ﬁre. Non-sprouters and facultative sprouters establish seedlings in the open canopy post ﬁre environment, whereas obligate sprouters establish seedlings in the shady understory of the mature chaparral canopy. 3. Seedlings of nine species (Rhamnaceae) representing three each of the different life history types were grown in deep containers in a common garden under treatments of sun and shade. Hydraulic conductance was measured using a high-pressure ﬂow meter for all organs, and a vacuum technique was used to measure conductance of ﬁne and woody roots. We predicted that non-sprouters would exhibit greater hydraulic efﬁciency than the sprouting species, and that facultative sprouters would be more efﬁcient than the shade tolerant obligate sprouters. 4. Non-sprouters had the greatest hydraulic conductance per unit leaf and sapwood area at the whole seedling level, whereas facultative and obligate sprouters were not different. Comparing hydraulic conductance across major organs (from ﬁne roots to leaves) showed that the hydraulic system was well coordinated. At the whole seedling level, the root system was more of a bottleneck than the shoot system. This pattern was consistent with high resistance extraxylary pathways in roots and differences in root architecture. 5. The greater hydraulic efﬁciency of the non-sprouter life history type is attributed to its post-ﬁre pioneering habit and may partially explain the relatively high speciation in the nonsprouters. Lower hydraulic efﬁciency is associated with a sprouting life history and greater shade tolerance. The seedling root systems represent a hydraulic bottleneck that may place roots under especially intense selection.
Citation InformationR. B. Pratt, Gretchen North, A. L. Jacobsen, F. W. Ewers, et al.. "Xylem root and shoot hydraulics is linked to life history type in chaparral seedlings (Rhamnaceae)" Functional Ecology (2009)
Available at: http://works.bepress.com/gretchen_north/3/