Corner’s rules pass the test of time: little effect of phenology on leaf–shoot and other scaling relationships

Abstract

Background and Aims The twig cross-sectional area and the surface area of leaves borne on it are expected to be isometrically correlated across species (Corner’s rules). However, how stable this relationship remains in time is not known. We studied the interspecific and intraspecific twig leaf area–cross-sectional area (la–cs) and other scaling relationships, including the leaf–shoot mass (lm–sm) scaling relationship, across a complete growing season. We also examined the influence of plant height, deciduousness and the inclusion of reproductive buds in the stability of the scaling relationships, and we discuss results from a functional perspective. Methods We collected weekly current-year twigs of 6 Patagonian woody species that differed in growth form and foliar habit. We also used Embothrium coccineum’s (Proteaceae) prominent inflorescences to assess whether or not reproductive buds alter the la–cs isometric relationship. Mixed effects models were fitted to obtain parameter estimates and to test whether interaction terms were nonsignificant (invariant) for the scaling relationships. Key Results The slope of the la–cs scaling relationship remained invariant across the growing season. Two species showed contrasting and disproportional (allometric) la–cs scaling relationships (slope ≠ 1). Scaling relationships significantly varied across growth form and foliar habit. The lm–sm scaling relationship differed between reproductive- and vegetative-origin twigs in E. coccineum, which was explained by a significantly lower leaf mass per area in the former. Conclusions Although phenology during the growing season appeared not to change leaf–shoot scaling relationships across species, we show that scaling relationships departed from the general trend of isometry as a result of within-species variation, growth form, foliar habit and the type of twig. The identification of these functional factors helps to understand variation in the general trend of Corner’s rules.

Scaling the leaf length-times-width equation to predict total leaf area of shoots

“…For trees, a shoot is a fundamental unit of growth ( Sterck et al , 2005 ; Sterck and Schieving, 2007 ; Lecigne et al , 2021 ) and reproduction ( Chen et al , 2009 ; Scott and Aarssen, 2013 ; Miranda et al , 2019 ; Fajardo et al , 2020 ). Given its importance, allometric relationships of shoot size and total shoot leaf area have been important topics in plant ecophysiology ( Corner, 1949 ; White, 1983 ; Ackerly and Donoghue, 1998 ; Brouat et al , 1998 ; Westoby and Wright, 2003 ; Kleiman and Aarssen, 2007 ; Olson et al ., 2009 , 2018 ; Sun et al ., 2010 , 2020 ; Yan et al , 2013 ; Trueba et al , 2016 ; Fan et al , 2017 ; Smith et al , 2017 ; Zhu et al , 2019 ; Fajardo et al , 2020 ). However, most previous studies on leaf vs. shoot size allometry have focused on the relationship among shoot size, total shoot leaf area, total leaf number and/or mean individual leaf size on the shoot.…”

“… Koyama et al , 2012 ; Smith et al , 2017 ), this fact was not considered in most previous studies on leaf size – shoot size allometry (e.g. Sun et al ., 2006 , 2010 , 2017 , 2019 a , b , 2020 ; Kleiman and Aarssen, 2007 ; Ogawa, 2008 ; Yang et al ., 2008 , 2009 , 2010 ; Milla, 2009 ; Xiang et al , 2009 a , 2010 ; Whitman and Aarssen, 2010 ; Dombroskie and Aarssen, 2012 ; Scott and Aarssen, 2012 , 2013 ; Yan et al , 2013 ; Dombroskie et al , 2016 ; Trueba et al , 2016 ; Olson et al , 2018 ; Miranda et al , 2019 ; Zhu et al , 2019 ; Fajardo et al , 2020 ).…”

The intraspecific relationship between wood density, vessel diameter and other traits across environmental gradients

“…Knowing that WD negatively relates to MVD across the wateravailability gradient, we consequently expected an also negative , 1998;Fajardo, Mora, et al, 2020;Olson et al, 2018). With this in mind, several previous studies found a negative relationship between WD and LA when hundreds of species were compared (Baraloto et al, 2010;Wright et al, 2007).…”

“…Similarly, we can appeal to Corner's rules regarding leaf–shoot allometric scaling relationships to explain this negative WD‐MVD relationship. Corner's rules state that plants with large leaves tend to have thick twigs that branch sparingly, with wide piths, thick bark, low‐density, and flexible wood and bark; the opposite is true of plants with small leaves, which have slender twigs that branch intricately, with narrow piths, thin bark, and high‐density, stiff wood and bark (Ackerly & Donoghue, 1998; Fajardo, Mora, et al, 2020; Olson et al, 2018). With this in mind, several previous studies found a negative relationship between WD and LA when hundreds of species were compared (Baraloto et al, 2010; Wright et al, 2007).…”

Pith width, leaf size, and twig thickness

“…Due to hydraulic and biomechanical selective pressures coupled with leaf attachment requirements, small twigs cannot support large leaves (Shinozaki, 1964;Westoby et al, 2002). The observation that twig diameter increases with leaf size, referred to as Corner's rule of axial conformity (Corner, 1949), is well supported by data (White, 1983;Ackerly and Donoghue, 1998;Brouat et al, 1998;Cornelissen, 1999;Westoby and Wright, 2003;Fajardo et al, 2020). We investigated whether plants economize on these investments by constructing large-diameter twigs with thick cores of pith, a low density, and low cost tissue.…”