TURGOR POTENTIAL AND OSMOTIC CONSTITUENTS OF KENTUCKY BLUEGRASS LEAVES SUPPLIED WITH 4 LEVELS OF POTASSIUM

Solute accumulation is one mechanism by which plants are able to susta in positive leaf turgor potentials (psi(t)). Potassium, the cation mos t often found in greatest concentration in Kentucky bluegrass (Pea pra tensis L.), can influence accumulation of solutes. A 2-yr glasshouse s tudy was conducted to determine the effect of K availability on accumu lation of six osmotically active solutes and psi(t) within leaves of K entucky bluegrass. Four nutrient solutions containing 0, 10 100, of 12 4 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 e ffect on psi(t) but increasing K from 0 or 10, to 100 or 124 mg L(-1) increased leaf psi(t) 0.19 to 0.35 MPa. Increasing K from 10 to 100 mg L(-1) caused leaf osmotic potential (psi(pi)) to decline by 0.17 to 0 .23 MPa. Potassium was the only measured osmotically active solute tha t could account for most of the decline in psi(pi). When the supply of K was increased from 10 to 100 mg L(-1), the resulting increase in le af K concentration caused the calculated contribution of K alone to de press Leaf psi(pi) by 0.29 to 0.31 MPa. Conversely, the combined calcu lated osmotic contribution of Ca, Mg, glucose, fructose, and sucrose i ncreased leaf psi(pi) 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 osmol ytes accounted for 46 to 60% of the measured psi(pi). Increasing Kentu cky bluegrass K tissue concentration appears to have a small but posit ive influence in increasing leaf turgor.