Geographic variation in shoot structure in association with fruit size in an evergreen woody species.

Takuma Goto,Noriyuki Osada

doi:10.1093/aobpla/plab023

Abstract

The generality of scaling relationships between multiple shoot traits, known as Corner’s rules, has been considered to reflect the biomechanical limits to trees and tree organs among the species of different leaf sizes. Variation in fruit size within species would also be expected to affect shoot structure by changing the mechanical and hydraulic stresses caused by the mass and water requirement of fruits. We investigated the differences in shoot structure and their relationship with fruit size in Camellia japonica from 12 sites in a wide geographic range in Japan. This species is known to produce larger fruits with thicker pericarps in more southern populations because warmer climates induce more intensive arms race between the fruit size and the rostrum length of its obligate seed predator. We found that, in association with the change in fruit size, the diameter and mass of 1-year-old stems were negatively associated with latitude, but the total mass and area of 1-year-old leaves did not change with latitude. Consequently, the length of 1-year-old stems and the total mass and area of 1-year-old leaves at a given stem diameter were positively associated with latitude in the allometric relationships. In contrast, the allometric relationships between stem diameter and total mass of the 1-year-old shoot complex (the leaves, stems and fruits that were supported by a 1-year-old stem) did not differ across the trees of different latitudes. Thus, natural selection on fruit size is considered to influence the other traits of Corner’s rules in C. japonica, but all of the traits of Corner’s rules do not necessarily change in a similar manner across latitudinal gradients.

Highlights

A shoot is a fundamental unit of growth in woody plants, and the shoot structure has multiple functions and develops under multiple selection pressures (Pearcy et al 2005; Valladares and Niinemets 2007)
In C. japonica, the negative relationship between fruit size and latitude has been attributed to the intensification of co-evolutionary arms races between the fruit size and the rostrum length of specific weevils in the regions of warm climate (Toju and Sota 2006; Toju et al 2011)
We found that the structure of fruiting shoots differed between C. japonica trees at different latitudes, and this difference was related to the latitudinal gradient of fruit size (Figs 3–7)

Summary

Introduction

A shoot is a fundamental unit of growth in woody plants, and the shoot structure has multiple functions and develops under multiple selection pressures (Pearcy et al 2005; Valladares and Niinemets 2007). Interspecific differences in the shoot structure of woody plants have been studied intensively in association with variations in leaf size (Corner 1949; White 1983; Ackerly and Donoghue 1998; Brouat et al 1998), leaf size/number trade-off (Kleiman and Aarssen 2007; Milla 2009) and light interception efficiency (Falster and Westoby 2003; Osada and Hiura 2017) These studies found clear coordination of the shoot structure among species, known as Corner’s rules; the species with thicker stems have fewer and larger leaves (Corner 1949; White 1983; Ackerly and Donoghue 1998; Brouat et al 1998). Such pattern deviates among the species of different habitats; the mass and area of leaves deployed by a stem of given diameter (or cross-sectional area) are Received: 19 October 2020; Editorial decision: 13 April 2021; Accepted: 6 May 2021

Methods

Results

Conclusion