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

Agnew, M. L., Carrow, R. N.
Agronomy journal 1985 v.77 no.6 pp. 878-884
Poa pratensis, soil compaction, soil water content, water stress, leaf water potential, stomatal conductance, canopy, temperature
In 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 pratensis L. ‘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, Rₛ remained low for 2 days and then increased over a 5-day period for all treatments, even though Ψ₁ did not change until the fifth day after irrigation (DAI). By DAI 9, Rₛ declined but then increased between DAI 10 to 13 as soil water potential (Ψₛ) and Ψ₁ decreased. 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.