Stomatal conductance reduction tradeoffs in maize leaves: A theoretical study.

As the leading global grain crop, maize significantly impacts agricultural water usage. Presently, photosynthesis (Anet ${A}_{\text{net}}$) in leaves of modern maize crops is saturated with CO2 ${\text{CO}}_{2}$, implying that reducing stomatal conductance (gs ${g}_{{\rm{s}}}$) would not affect Anet ${A}_{\text{net}}$ but reduce transpiration (τ $\tau $), thereby increasing water use efficiency (WUE). While gs ${g}_{{\rm{s}}}$ reduction benefits upper canopy leaves under optimal conditions, the tradeoffs in low light and nitrogen‐deficient leaves under nonoptimal microenvironments remain unexplored. Moreover, gs ${g}_{{\rm{s}}}$ reduction increases leaf temperature (Tleaf ${T}_{\text{leaf}}$) and water vapor pressure deficit, partially counteracting transpiratory water savings. Therefore, the overall impact of gs ${g}_{{\rm{s}}}$ reduction on water savings remains unclear. Here, we use a process‐based leaf model to investigate the benefits of reduced gs ${g}_{{\rm{s}}}$ in maize leaves under different microenvironments. Our findings show that increases in Tleaf ${T}_{\text{leaf}}$ due to gs ${g}_{{\rm{s}}}$ reduction can diminish WUE gains by up to 20%. However, gs ${g}_{{\rm{s}}}$ reduction still results in beneficial WUE tradeoffs, where a 29% decrease in gs ${g}_{{\rm{s}}}$ in upper canopy leaves results in a 28% WUE gain without loss in Anet ${A}_{\text{net}}$. Lower canopy leaves exhibit superior tradeoffs in gs ${g}_{{\rm{s}}}$ reduction with 178% gains in WUE without loss in Anet ${A}_{\text{net}}$. Our simulations show that these WUE benefits are resilient to climate change. Summary statement: Reducing maize stomatal conductance boosts water use efficiency (WUE) by up to 26% in upper leaves and 170% in lower leaves, with minimal photosynthesis impact. However, higher leaf temperature could offset WUE gains by up to 16%. Stomatal conductance reduction tradeoffs are beneficial under diverse conditions and canopy leaf positions and are unaffected by climate change. [ABSTRACT FROM AUTHOR]

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