CONICET | Buscador de Institutos y Recursos Humanos

Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Most stem traits including wood density (ñwood), the xylem water potential at 50% loss of hydraulic conductivity (P50), sapwood area specific hydraulic conductivity (Ks), and leaf area specific hydraulic conductivity (Kl) did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (Kleaf) and its related trait leaf capacitance (C) tended to be higher in savanna species. Predawn leaf water potential (Øpd), a variable reflecting plant rooting depth and therefore related to patterns of carbon allocation, and leaf mass per area (LMA) was higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday Kleaf values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of leaf hydraulic conductance (P50leaf) or to the turgor loss points (ð0), suggesting that savanna species were more buffered from changes in leaf water potential. The results suggested that the relative success of savanna over forest species in the savanna-forest boundary is related in part to their larger biomass allocation to roots and that their ability to cope with soil and atmospheric drought is determined more by leaf than by stem hydraulic traits.

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