Soil‐plant hydraulics explain stomatal efficiency‐safety tradeoff

AbstractThe efficiency‐safety tradeoff has been thoroughly investigated in plants, especially concerning their capacity to transport water and avoid embolism. Stomatal regulation is a vital plant behaviour to respond to soil and atmospheric water limitation. Recently, a stomatal efficiency‐safety tradeoff was reported where plants with higher maximum stomatal conductance (gmax) exhibited greater sensitivity to stomatal closure during soil drying, that is, less negative leaf water potential at 50% gmax (ψgs50). However, the underlying mechanism of this gmax‐ψgs50 tradeoff remains unknown. Here, we utilized a soil‐plant hydraulic model, in which stomatal closure is triggered by nonlinearity in soil‐plant hydraulics, to investigate such tradeoff. Our simulations show that increasing gmax is aligned with less negative ψgs50. Plants with higher gmax (also higher transpiration) require larger quantities of water to be moved across the rhizosphere, which results in a precipitous decrease in water potential at the soil‐root interface, and therefore in the leaves. We demonstrated that the gmax‐ψgs50 tradeoff can be predicted based on soil‐plant hydraulics, and is impacted by plant hydraulic properties, such as plant hydraulic conductance, active root length and embolism resistance. We conclude that plants may therefore adjust their growth and/or their hydraulic properties to adapt to contrasting habitats and climate conditions.