Variation among Soybean Cultivars in Mesophyll Conductance and Leaf Water Use Efficiency.

James Bunce

doi:10.3390/plants5040044

Abstract

Improving water use efficiency (WUE) may prove a useful way to adapt crop species to drought. Since the recognition of the importance of mesophyll conductance to CO2 movement from inside stomatal pores to the sites of photosynthetic carboxylation, there has been interest in how much intraspecific variation in mesophyll conductance (gm) exists, and how such variation may impact leaf WUE within C3 species. In this study, the gm and leaf WUE of fifteen cultivars of soybeans grown under controlled conditions were measured under standardized environmental conditions. Leaf WUE varied by a factor of 2.6 among the cultivars, and gm varied by a factor of 8.6. However, there was no significant correlation (r = −0.047) between gm and leaf WUE. Leaf WUE was linearly related to the sub-stomatal CO2 concentration. The value of gm affected the ratio of maximum Rubisco carboxylation capacity calculated from the sub-stomatal CO2 concentration to that calculated from the CO2 concentration at the site of carboxylation. That is, variation in gm affected the efficiency of Rubisco carboxylation, but not leaf WUE. Nevertheless, there is considerable scope for genetically improving soybean leaf water use efficiency.

Highlights

With increasing limitations on the amount of water available to support agriculture, increasing the water use efficiency (WUE) of crops—the ratio of crop dry mass gained to water consumed—is a reasonable objective
The cultivars differed significantly in gs, gm, leaf intrinsic WUE, sub-stomatal CO concentration (Ci), and the CO2 concentration at rubisco (Cc), but not in VCmCc (VCmax based on C2c), VCmCi (VCmax (Ci ), and the CO2 concentration at rubisco (Cc ), but not in VCm Cc (VCmax based on Cc ), VCm Ci (VCmax based on Cc), or A (Table 1)
The linear relationship between intrinsic leaf WUE and Ci was as expected, since Ca was constant across the measurements

Summary

Introduction

With increasing limitations on the amount of water available to support agriculture, increasing the water use efficiency (WUE) of crops—the ratio of crop dry mass gained to water consumed—is a reasonable objective. Selection for high leaf WUE in wheat improved yield in dry conditions [1]. WUE is often defined as the ratio of photosynthesis to transpiration. The rate of transpiration is directly related to the difference in water vapor pressure between the air inside and outside the leaf (the leaf to air vapor pressure difference, LAVPD), so the LAVPD during the measurement has a large impact on WUE. Comparisons of leaf WUE often use “intrinsic” water use efficiency [2], the ratio of photosynthesis to stomatal conductance

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Conclusion