Stomatal conductance reduction tradeoffs in maize leaves: A theoretical study

As the leading global grain crop, maize significantly impacts agricultural water usage. Presently, photosynthesis ( $A_{\text{net}}$ ) in leaves of modern maize crops is saturated with ${\text{CO}}_2$ , implying that reducing stomatal conductance ( $g_s$ ) would not affect $A_{\text{net}}$ but reduce transpiration ( $\tau$ ), thereby increasing water use efficiency (WUE). While $g_s$ reduction benefits upper canopy leaves under optimal conditions, the tradeoffs in low light and nitrogen-deficient leaves under nonoptimal microenvironments remain unexplored. Moreover, $g_s$ reduction increases leaf temperature ( $T_{\text{leaf}}$ ) and water vapor pressure deficit, partially counteracting transpiratory water savings. Therefore, the overall impact of $g_s$ reduction on water savings remains unclear. Here, we use a process-based leaf model to investigate the benefits of reduced $g_s$ in maize leaves under different microenvironments. Our findings show that increases in $T_{\text{leaf}}$ due to $g_s$ reduction can diminish WUE gains by up to 20%. However, $g_s$ reduction still results in beneficial WUE tradeoffs, where a 29% decrease in $g_s$ in upper canopy leaves results in a 28% WUE gain without loss in $A_{\text{net}}$ . Lower canopy leaves exhibit superior tradeoffs in $g_s$ reduction with 178% gains in WUE without loss in $A_{\text{net}}$ . Our simulations show that these WUE benefits are resilient to climate change.