The bias of a two‐dimensional view: comparing two‐dimensional and three‐dimensional mesophyll surface area estimates using noninvasive imaging

Abstract

Summary The mesophyll surface area exposed to intercellular air space per leaf area (Sm) is closely associated with CO2 diffusion and photosynthetic rates. Sm is typically estimated from two‐dimensional (2D) leaf sections and corrected for the three‐dimensional (3D) geometry of mesophyll cells, leading to potential differences between the estimated and actual cell surface area. Here, we examined how 2D methods used for estimating Sm compare with 3D values obtained from high‐resolution X‐ray microcomputed tomography (microCT) for 23 plant species, with broad phylogenetic and anatomical coverage. Relative to 3D, uncorrected 2D Sm estimates were, on average, 15–30% lower. Two of the four 2D Sm methods typically fell within 10% of 3D values. For most species, only a few 2D slices were needed to accurately estimate Sm within 10% of the whole leaf sample median. However, leaves with reticulate vein networks required more sections because of a more heterogeneous vein coverage across slices. These results provide the first comparison of the accuracy of 2D methods in estimating the complex 3D geometry of internal leaf surfaces. Because microCT is not readily available, we provide guidance for using standard light microscopy techniques, as well as recommending standardization of reporting Sm values.

Beyond Porosity: 3D Leaf Intercellular Airspace Traits That Impact Mesophyll Conductance

“…see Théroux-Rancourt et al, 2017), 350 this relationship could be used to estimate τ leaf based on 2D sections. Thus, τ leaf tends to 351 increase as porosity decreases, leading to a compounding effect on g IAS .…”

Drought‐introduced variability of mesophyll conductance in Gossypium and its relationship with leaf anatomy

“…B). Although S c /S was determined using two‐dimensional leaf sections, Théroux‐Rancourt et al () showed that the curvature correction factor method (Thain ) we used is the easiest to apply and produces reliable estimates by comparing four two‐dimensional methods and a three‐dimensional method. Those indicated that S c /S, to some extent, regulated the variability of g m .…”

“…The mesophyll and chloroplast surface area exposed to leaf intercellular air spaces per leaf area (S m /S and/or S c /S) were calculated as in Evans et al () and Syvertsen et al (). Although we estimated all of the anatomical structures on the basis of two‐dimensional methods, the curvature correction factor method (Thain ) we used is the easiest to apply and produces reliable estimates compared with other two‐dimensional and three‐dimensional methods (Théroux‐Rancourt et al ). According to the suggestion of Théroux‐Rancourt et al (), we measured curvature correction factors for each tissue.…”

“…Although we estimated all of the anatomical structures on the basis of two‐dimensional methods, the curvature correction factor method (Thain ) we used is the easiest to apply and produces reliable estimates compared with other two‐dimensional and three‐dimensional methods (Théroux‐Rancourt et al ). According to the suggestion of Théroux‐Rancourt et al (), we measured curvature correction factors for each tissue. The curvature correction factor ranged from 1.31 to 1.46 for spongy cells and from 1.41 to 1.51 for palisade cells according to the method of Thain ().…”

Margaret M. Barbour

“…My favourite recent paper is Théroux‐Rancourt et al . () because it is the first to reveal the leaf mesophyll anatomy we might have missed by looking at two‐dimensional cross‐sections. New techniques often open a path to new understanding.…”