Sanio’s laws revisited. Size‐dependent changes in the xylem architecture of trees

Abstract

Early observations led Sanio [Wissen. Bot., 8, (1872) 401] to state that xylem conduit diameters and lengths in a coniferous tree increase from the apex down to a height below which they begin to decrease towards the tree base. Sanio's law of vertical tapering has been repeatedly tested with contradictory results and the debate over the scaling of conduit diameters with distance from the apex has not been settled. The debate has recently acquired new vigour, as an accurate knowledge of the vertical changes in wood anatomy has been shown to be crucial to scaling metabolic properties to plant and ecosystem levels. Contrary to Sanio's hypothesis, a well known model (MST, metabolic scaling theory) assumes that xylem conduits monotonically increase in diameter with distance from the apex following a power law. This has been proposed to explain the three-fourth power scaling between size and metabolism seen across plants. Here, we (i) summarized available data on conduit tapering in trees and (ii) propose a new numerical model that could explain the observed patterns. Data from 101 datasets grouped into 48 independent profiles supported the notions that phylogenetic group (angiosperms versus gymnosperms) and tree size strongly affected the vertical tapering of conduit diameter. For both angiosperms and gymnosperms, within-tree tapering also varied with distance from the apex. The model (based on the concept that optimal conduit tapering occurs when the difference between photosynthetic gains and wall construction costs is maximal) successfully predicted all three major empirical patterns. Our results are consistent with Sanio's law only for large trees and reject the MST assumptions that vertical tapering in conduit diameter is universal and independent of rank number.

Linking phloem function to structure: Analysis with a coupled xylem–phloem transport model

“…This vertical tapering and developmental changes may be similar to those already documented for the xylem (e.g. Anfodillo et al, 2004;Mencuccini et al, 2007;McCulloh et al, 2003;West et al, 1999), at least partially. In the xylem, conduit tapering is predicted to reduce the adverse effects of growing transport distance on the whole xylem pathway conductance (West et al, 1999).…”

Testing the packing rule across the twig–petiole interface of temperate woody species

“…For example, previous studies typically report ontogenetic (and thus intraspecific) changes in conduit dimensions (e.g. Petit et al 2008;Anfodillo et al 2006;Weitz et al 2006;Mencuccini et al 2007) that are nevertheless, by in large, consistent with theoretical predictions (e.g. Preston et al 2006;Sperry et al 2008;McCulloh et al 2010;Savage et al 2010).…”

Leaf Extraction and Analysis Framework Graphical User Interface: Segmenting and Analyzing the Structure of Leaf Veins and Areoles

“…For example, there is a long history of measurements of components of the aboveground structure of xylem networks. Extensive measurements have been made of vein length distributions (Tyree and Zimmerman, 1983), width and scaling of xylem (Anfodillo et al, 2006;Weitz et al, 2006;Coomes et al, 2007;Mencuccini and Holtta, 2007), and even relative hydraulic resistance across distinct components of trees (Tyree and Sperry, 1989;Turcotte et al, 1998;McCulloh et al, 2003). In addition, there is a growing interest in describing detailed root network structure, largely applied to Arabidopsis (Arabidopsis thaliana) as well as to crop plants (French et al, 2009;Iyer-Pascuzzi et al, 2010;Le Bot et al, 2010).…”