Changes in root hydraulic conductance (KR) of Olea oleaster seedlings following drought stress and irrigation

Quasi‐steady‐state measurements of root hydraulic conductance ( K R ) of Olea oleaster Hoffmgg. et Link potted seedlings were performed using a pressure chamber with the aim of: ( a ) measuring the impact of different water‐stress levels on a K R ; ( b ) measuring the kinetics of K R recovery several days after soil rewetting; ( c ) relating changes in K R to changes in root anatomy and morphology. Increasing water‐stress was applied in terms of ratio of leaf water potential (Ψ L ) measured at midday to that at zero turgor (Ψ TLP ), i.e. Ψ L /Ψ TLP =0·5, 1·0, 1·2, 1·6; K R was measured initially and at 24, 48, 72, 96 h after irrigation. Values of K R in seedlings stressed to Ψ L /Ψ TLP =1·2 increased for 48 h after irrigation from 0·23 to 0·97×10 −5 kg s −1 m −2 MPa −1 i.e. from 16% to 66% of that measured in unstressed seedlings. A marked shift of the x ‐axis intercept of the straight line relating flow to pressure (zero flow at non‐zero pressure) was recorded initially after irrigation and persisted up to 48 h. Recovery of K R occurred within 24 h after irrigation in seedlings at Ψ L /Ψ TLP =0·5 and 48 h later in those at Ψ L /Ψ TLP =1·0. Severe drought stress (Ψ L /Ψ TLP =1·6) caused anatomical changes to roots which formed a two‐layered exodermis with thicker suberized walls and a three‐ to four‐layered endodermis with completely suberized tangential walls. Recovery of K R in these roots required resumed growth of root tips and emergence of new lateral roots.