The Effect of Phosphorus and Potassium on Transpiration, Leaf Diffusive Resistance and Water-Use Efficiency in Sitka Spruce (Picea sitchensis) Seedlings

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Abstract
Sitka spruce seedlings were grown in horticultural peat supplied with either large or small amounts of P and of K. The effects of these treatments on the transpiration rate, leaf diffusive resistance and water-use efficiency were determined. K fertilization decreased the transpiration rate per unit needle weight; P fertilization had less effect. Neither P nor K fertilizer had much effect on the transpiration rate of dormant seedlings. Addition of K to deficient trees led to a marked reduction of transpiration over the subsequent 2 wk. Leaf diffuse resistance was positively related to leaf-air vapor pressure deficit but seedlings receiving both P and K showed the greatest sensitivity to an increase in vapor pressure deficit. Water-use efficiency of plants was greatest when K fertilizer was applied. The physiological response of the seedlings was probably attributable to effects on stomatal control.