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Turgor Potential and Osmotic Constituents of Kentucky Bluegrass Leaves Supplied with Four Levels of Potassium

Agronomy Dep., Univ. of Maryland, College Park, MD 20742

^* Corresponding author.

Solute accumulation is one mechanism by which plants are able to sustain positive leaf turgor potentials (_t). Potassium, the cation most often found in greatest concentration in Kentucky bluegrass (Poa pratensis L.), can influence accumulation of solutes. A 2-yr glasshouse study was conducted to determine the effect of K availability on accumulation of six osmotically active solutes and ₁ within leaves of Kentucky bluegrass. Four nutrient solutions containing 0, 10, 100, or 124 mg K L^–1 were applied three times weekly to plants grown in silica sand. Small increases in K (0 to 10, or 100 to 124 mg L^–1) had no effect on _t, but increasing K from 0 or 10, to 100 or 124 mg L^–1 increased leaf _t 0.19 to 0.35 MPa. Increasing K from 10 to 100 mg L^–1 caused leaf osmotic potential (yn) to decline by 0.17 to 0.23 MPa. Potassium was the only measured osmotically active solute that could account for most of the decline in . When the supply of K was increased from 10 to 100 mg L^–1, the resulting increase in leaf K concentration caused the calculated contribution of K alone to depress leaf , by 0.29 to 0.31 MPa. Conversely, the combined calculated osmotic contribution of Ca, Mg, glucose, fructose, and sucrose increased leaf by 0.12 to 0.13 MPa when K was increased from 10 to 100 mg L^–1. The calculated osmotic contribution of all six osmolytes accounted for 46 to 60% of the measured . Increasing Kentucky bluegrass K tissue concentration appears to have a small but positive influence in increasing leaf turgor.

Received for publication September 30, 1993.