Soil water availability and rooting depth as determinant of the hydraulic architecture in Patagonian woody species

BUCCI S.J. SCHOLZ F.G., GOLDSTEIN G, MEINZER F.C, ARCE ME

OECOLOGIA

Springer

Año: 2009 vol. 160 p. 631 - 641

0029-8549

 Adaptations of species to capture limiting resources is central for understanding structure and function of ecosystems. We studied the water economy of nine woody species differing in rooting depth in a Patagonian shrub steppe from southern-Argentina. Our main objective was to understand how soil water availability and rooting depth determine the hydraulic architecture of these species. Soil water content and potentials, leaf water potentials (YLeaf), water transport efficiency, wood density (rw), rooting depth, and specific leaf area (SLA) were measured during two summers. Water potentials in the upper soil layers during a summer drought ranged from -2.3 to -3.6 MPa, increasing to -0.05 MPa below 150 cm.  PredawnYLeaf was used as a surrogate of weighted mean soil water potential because no statistical differences in YLeaf were observed between exposed and covered leaves. Substantial species-specific differences in predawn YLeaf were observed which were consistent with rooting depths. Predawn YLeaf ranged from -4.0 MPa for shallow rooted shrubs to -1.0 MPa for deep rooted shrubs, suggesting that the roots of the latter have access to abundant moisture, whereas shallow rooted shrubs are adapted to use water deposited mainly by small rainfall events. Wood density was a good predictor of hydraulic conductivity and SLA. Overall, we found that shallow rooted species had low rw, efficient water transport, high SLA and minimum YLeaf that exhibited strong seasonal changes, whereas deeply rooted shrubs maintained similar minimum YLeaf throughout the year, had stems with high rw and low hydraulic conductivity and leaves with low SLA. These two hydraulic syndromes were the extremes of a continuum with several species occupying different portions of a gradient in hydraulic characteristics. It appears that the marginal cost for having an extensive root system (e.g.: high rw and root hydraulic resistance) result in low growth rates of the deeply rooted species.