Soil Compaction and Moisture Stress Preconditioning in Kentucky Bluegrass. II. Stomatal Resistance, Leaf Water Potential, and Canopy Temperature1

Abstract

AbstractIn this greenhouse study we investigated the effects of soil compaction and moisture stress preconditioning on stomatal diffusive resistance (Rs), leaf water potential (Ψ1), and canopy minus air temperatures (ΔT) of Kentucky bluegrass (Poa pratensisL. ‘Ram I’). The compaction treatments were: (i) NC = no compaction, (ii) LT = long‐term compaction over a 99‐day period, and (iii) ST = short‐term compaction for 9 days. The compactive treatment was equivalent to 720 J energy. Irrigation regimes were initiated at the same time as LT compaction and were: (i) well‐watered = irrigation at −0.045 MPa and (ii) water‐stressed = irrigation at −0.400 MPa. Ninety‐nine days after initiation of preconditioning treatments, a dry‐down cycle was started by watering each treatment to saturation. At this time, we monitored on a daily basis Rs, Ψ1, and ΔT. Under low soil O2, Rsremained low for 2 days and then increased over a 5‐day period for all treatments, even though Ψ1did not change until the fifth day after irrigation (DAI). By DAI 9, Rsdeclined but then increased between DAI 10 to 13 as soil water potential (Ψs) and Ψ1decreased. As soil water deficits increased, plants preconditioned to LT compaction or water‐stressed exhibited lower Ψ1(0.2 to 0.4 MPa), higher Rs, and higher Δ (1 to 2°C) compared with uncompacted or well‐watered plants. Regardless of the cause for higher Rs(i.e., low soil O2, LT compaction or water‐stress preconditioning), the result would be lower photosynthesis and greater high‐temperature stress.