Embolized Stems Recover Overnight in : The Role of Soil Water, Root Pressure, and Nighttime Transpiration.

It is not currently well-understood how much xylem conductance is lost in maize plants during the day, if conductance is recovered during the night, or what soil water conditions are required for recovery to take place. To answer these questions we designed a greenhouse experiment whereby two genetically dissimilar maize genotypes were subjected to a level of water stress commonly experienced in the field (Ψ ∼-2 MPa). We then measured the loss of stem-specific conductivity associated with this level of stress, as well as the overnight recovery following three re-watering treatments: Ψ ∼ 0 MPa, Ψ ∼-0.40 MPa, and Ψ ∼-1.70 MPa. Mid-day leaf water potentials of -1.98 MPa resulted in stem-specific conductivity (K) values that were 31.5% of maximal (i.e., 68% loss). Returning soils to field capacity (Ψ ∼ 0 MPa) overnight allowed for the significant recovery of K (76% of maximal), whereas partial watering (Ψ ∼-0.40 MPa) resulted K values that were 51.7% of maximal values, whereas not watering resulted in no recovery (35.4% of maximal; Ψ ∼-1.7 MPa). Recovery of K was facilitated by the generation of root pressure and low rates of nighttime transpiration.