HYDRAULIC ARCHITECTURE AND WATER-USE OF SELECTED SPECIES FROM A LOWERMONTANE FOREST IN PANAMA

Plant water relations of nine woody species were studied in a lower mo ntane rain forest in Panama. These data provide a partial test of the hypothesis that hydraulic architecture of lower montane species might limit transpiration and thus leaf size or nutrient transport (as sugge sted by J. Cavelier and E. G. Leigh, respectively). Diurnal variation in leaf transpiration was closely correlated with changes in net radia tion. Peak transpiration rates (7 x 10(-5) kg s(-1) m(-2)) were as hig h as peak transpiration rates from tropical lowland forests but mean d aily water use [0.39 +/- 0.08 (SEM) kg m(-2) day(-1)] were mostly lowe r than comparable data from tropical lowland forests. Thus transpirati on rates are sufficiently high for sufficiently long periods to make i t unlikely that nutrient transport is Limited by transpiration. Anothe r objective of this study was a comparison of two different methods to measure hydraulic conductance (K-h = flow rate per unit pressure grad ient) and leaf specific conductance of stem segments (K-L = K-h/leaf a rea distal to the segment). The results obtained with the traditional conductivity apparatus and the high pressure flow meter method, yielde d similar results in six out of seven cases.