Morphological and moisture availability controls of the leaf area-to-sapwood area ratio: Analysis of measurements on Australian trees

Abstract

<p>1 The leaf area-to-sapwood area ratio (<i>LA:SA</i>) is a key plant trait that links photosynthesis to transpiration. The pipe model theory states that the sapwood cross-sectional area of a stem or branch at any point should scale isometrically with the area of leaves distal to that point. Optimization theory further suggests that <i>LA:SA</i> should decrease toward drier climates. Although acclimation of <i>LA:SA</i> to climate has been reported within species, much less is known about the scaling of this trait with climate among species.</p> <p>2 We compiled <i>LA:SA</i> measurements from 184 species of Australian evergreen angiosperm trees. The pipe model was broadly confirmed, based on measurements on branches and trunks of trees from one to 27 years old. Despite considerable scatter in <i>LA:SA</i> among species, quantile regression showed strong (0.2 < <i>R1</i> < 0.65) positive relationships between two climatic moisture indices and the lowermost (5%) and uppermost (5–15%) quantiles of log <i>LA:SA</i>, suggesting that moisture availability constrains the envelope of minimum and maximum values of <i>LA:SA</i> typical for any given climate.</p> <p>3 Interspecific differences in plant hydraulic conductivity are probably responsible for the large scatter of values in the mid-quantile range and may be an important determinant of tree morphology.</p>