Effects of root wrenching on the growth and water relations of Prunus avium and Castanea sativa seedlings in nursery beds and after outplanting

The roots of wild cherry (Prunus avium L.) and sweet chestnut (Castanea sativa Mill.) seedlings grown in a nursery bed at the same density (110 plants/m2) were cut by passing a wedge-shaped blade horizontally through the soil (wrenched) at 20 cm depth on 10 July (early) or 12 August (late) or on both dates. Shoot growth was reduced, and this coincided with lower final leaf areas for both species. Leaf water potential (y) and leaf conductance to water vapour (gl) of each were reduced immediately after the root wrenching treatments, but recovered within 1 month. Prunus avium seedlings that were late root wrenched suffered more severe drought stress than C. sativa seedlings wrenched at the same time. This was indicated by a larger reduction in y and shedding of leaves. Seedlings of P. avium that were wrenched early suffered less drought stress when wrenched a second time (late). Late root wrenching caused greater stress in P. avium than C. sativa, which is ascribed to the smaller quantity of their roots above the depth of wrenching. Early wrenching increased the total shoot growth of both species in the first 2 years after outplanting.