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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.