The effect of phosphorus and potassium on transpiration, leaf diffusive resistance and water-use efficiency in Sitka spruce (Picea sitchensis) seedlings.
Sitka spruce seedlings were grown in horticultural peat supplied with either large or small amounts of P and K. K decreased the transpiration rate per unit needle weight; P had less effect. Neither P nor K 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 next two weeks. Leaf diffusive resistance was positively related to leaf-air vapour pressure deficit but seedlings receiving both P and K showed the greatest sensitivity to an increase in vapour pressure deficit. Water-use efficiency of plants was greatest when K was applied. It is concluded that the physiological response of the seedlings was probably due to effects on stomatal control.