Anatomical determinants of gas exchange and hydraulics vary with leaf shape in soybean

Authors: TAMANG, BISHAL - University Of Illinois; ZHANG, YANQUN - China Institute Of Water Resources And Hydropower Research; ZAMBRANO, MICHELLE - University Of Illinois; Ainsworth, Elizabeth - Lisa

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2022
Publication Date: 9/16/2022
Citation: Tamang, B., Zhang, Y., Zambrano, M., Ainsworth, E.A. 2022. Anatomical determinants of gas exchange and hydraulics vary with leaf shape in soybean. Annals of Botany. 131(6):909-920. https://doi.org/10.1093/aob/mcac118.
DOI: https://doi.org/10.1093/aob/mcac118

Interpretive Summary: Soybeans show large variation in leaf shape, which can alter the light penetration to lower leaves in the canopy and impact photosynthesis. This work tested the anatomical determinants and physiological consequences of variation in leaf shape in soybean. Using a selection of soybean lines from the USDA germplasm collection, we measured cross-sections of leaves, photosynthesis of leaves and hydraulic conductance of leaves. We discovered that narrow soybean leaves were thicker and had a greater proportion of spongy mesophyll. Narrow and thicker leaves also had higher rates of photosynthesis and greater stomatal conductance per unit area. Our results suggest that selecting for narrow leaf varieties could improve photosynthetic performance in soybean.

Technical Abstract: Leaf shape in crops can impact light distribution and carbon capture at the whole plant and canopy level. Narrow leaves can allow a greater fraction of incident light to pass through to lower canopy leaves potentially increasing canopy-scale photosynthesis. Soybean has natural variation in leaf shape which can be utilized to optimize canopy architecture. However, the anatomical and physiological differences underlying variation in leaf shape are largely unexplored. In this study, we selected 28 diverse soybean lines with leaf length to width ratios (leaf ratio) ranging between 1.1 and 3.2. We carried out leaf cross-sectional, gas exchange, vein density, and hydraulic measurements and studied their interrelationships among these lines. Our study show that narrow leaves tend to be thicker with ~30 µm increase in leaf thickness for every unit increase in leaf ratio. Interestingly, thicker leaves had a greater proportion of spongy mesophyll while the proportions of palisade and paraveinal mesophyll decreased. In addition, narrow and thicker leaves had greater photosynthesis and stomatal conductance per unit area along with greater leaf hydraulic conductance. Our results suggest that selecting for narrow leaves can improve photosynthetic performance and potentially provide a yield advantage in soybean.