Ir. Fordyce et al., THE WATER RELATIONS OF ALLOSYNCARPIA-TERNATA (MYRTACEAE) AT CONTRASTING SITES IN THE MONSOONAL TROPICS OF NORTHERN AUSTRALIA, Australian Journal of Botany, 45(2), 1997, pp. 259-274
Allosyncarpia ternata S.T.Blake (Myrtaceae) is an evergreen tree, rest
ricted largely to rocky habitats on the Arnhem Land Plateau in the wet
-dry tropics of northern Australia. Allosyncarpia ternata grows in a w
ide range of habitats, including sites near permanent springs, where i
t forms a distinctive closed-canopy forest with an understorey of rain
forest plants, and sites on exposed cliffs and hilltops, where it occu
rs in open forest and woodland. Leaf water relations differ markedly b
etween these contrasting sites. During the dry season, trees at open s
ites show strong diurnal hysteresis in stomatal conductance (g(s)); af
ternoon depressions in g(s) coincide with regular afternoon increases
in vapour pressure deficit. Pressure-volume analyses indicate that A.
ternata maintains turgor down to leaf water potential values of about
-2.8 MPa, close to the minimum experienced by hilltop leaves late in t
he dry season. By contrast, trees on the ravine floor, with year-round
access to water, exhibit much smaller diurnal and seasonal variation
in stomatal conductance and little seasonal variation in leaf water po
tential. It is concluded that this flexible response in leaf water rel
ations to seasonally dry conditions is partly responsible for the abil
ity of A. ternata to occupy and dominate the vegetation in such a wide
variety of habitats. The near confinement of the species to the Arnhe
m Land Plateau is in part due to the water-holding capacity of the bed
rock.