Como variações nos atributos do xilema explica a distribuição de aspidosperma pyrifolium no semiárido brasileiro?

Abstract

Water availability variation may affect wood species distribution. Xylem plasticity allows adjustments in the hydraulic system that can favor the occurrence of the same species across environments with different aridity levels. Our goal was to verify the hypotheses that xylem plasticity may contribute to explain Aspidosperma pyrifolium distribution along an aridity gradient in the Brazilian semiarid. We examined anatomic traits: vessel density (N); vessel diameter (d) area occupied by vessels (Av), parenchyma (Ap), and fibers (Af); pit diameter (dpit); pit density (Npit), and hydraulic properties related to xylem: wood density (WD); saturated water content of wood (WCsat); potential hydraulic conductivity (Kp); vulnerability index (VI); implosion resistance (Ri) of five populations across this gradient. Our results showed that A. pyrifolium has xylem traits that are intrinsically safe (high vessel density, vestured pits with small diameter, and fiber associated to vessels). Although plasticity was low among populations, WCsat, d, and Af showed positive relationship with increasing water deficit. N and dpit decreased with increasing water deficit. Xylem plasticity allows the hydraulic transport of A. pyrifolium individuals along the aridity gradient, which may explain its wide distribution in the Brazilian semiarid. These results contribute to understand how adaptive xylem strategies may reflect on the distribution of species in semi-arid environments.