Abstract
This study, conducted on
Acacia
species (
Acacia
ehrenbergiana
Hayne and
Acacia tortilis
subsp.
raddiana
(Savi) Brenan) to determine their adaptive capacity to tolerate drought and suitability for reforestation, revealed that leaf water potential (ψ) decreased in both the species with increase in drought intensity. With increase in the intensity of drought, vessel diameter increased in
A. ehrenbergiana,
causing a significant decline in vessel frequency mm
−2
of the transverse wood surface, while it decreased in
A. tortilis,
leading to a crowded vessel population. Vessel-wall thickness, in conjunction with inter-vessel pit membrane thickness, showed a positive correlation with drought stress in both the species. Ray dimensions generally decreased in
A. ehrenbergiana
but increased in
A. tortilis
under increasing degree of drought. The transverse fiber-wall area decreased in
A. ehrenbergiana,
thus lowering the density (
r
= 0.996) and enhancing the vulnerability of wood (
r
= −0.979) under the drought stress, but increased in
A. tortilis,
causing a high density (
r
= −0.979) and low vulnerability of wood (
r
= 0.869), under the same set of conditions. Correlation of wood density with vulnerability index was stronger in
A. ehrenbergiana
(
r
= −0.993) than in
A. tortilis
(
r
= −0.753). Diameters and thickness of inter-vessel pit membrane were linearly correlated with increasing intensity of drought in both the species, but its area fraction per vessel segment increased due to water stress in
A. ehrenbergiana
and decreased in
A. tortilis
. This study indicated that, on the whole,
A. tortilis
has a greater capacity to tolerate the harshness of drought than
A. ehrenbergiana.