Stem water storage capacity and efficiency of water transport: their functional significance in a Hawaiian dry forest

We investigated the contribution of internal water storage and efficiency o f water transport to the maintenance of water balance in six evergreen tree species in a Hawaiian dry forest. Wood-saturated water content, a surrogat e for relative water storage capacity, ranged from 70 to 105%, and was inve rsely related to its morphological correlate, wood density, which ranged be tween 0.51 and 0.65 g cm(-) (3). Leaf-specific conductivity (k(L)) measured in stem segments from terminal branches ranged from 3 to 18 mmol m(-1) s(- 1) MPa-1, and whole-plant hydraulic efficiency calculated as stomatal condu ctance (g) divided by the difference between predawn and midday leaf water potential (Psi(L)), ranged from 70 to 150 mmol m(-2) s(-1) MPa-1. Hydraulic efficiency was positively correlated with k(L) (r(2) = 0.86). Minimum annu al Psi(L) ranged from - 1.5 to - 4.1 MPa among the six species. Seasonal an d diurnal variation in Psi(L) were associated with differences among specie s in wood-saturated water content, wood density and k(L). The species with higher wood-saturated water content were more efficient in terms of long-di stance water transport, exhibited smaller diurnal variation in Psi(L) and h igher maximum photosynthetic rates. Smaller diurnal variation in Psi(L) in species with higher wood-saturated water content, k(L) and hydraulic effici ency was not associated with stomatal restriction of transpiration when soi l water deficit was moderate, but avoidance of low minimum seasonal Psi(L) in these species was associated with a substantial seasonal decline in g. L ow seasonal minimum Psi(L) in species with low k(L), hydraulic efficiency, and wood-saturated water content was associated with higher leaf solute con tent and corresponding lower leaf turgor loss point. Despite the species-sp ecific differences in leaf water relations characteristics, all six evergre en tree species shared a common functional relationship defined primarily b y k(L) and stem water storage capacity.