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 roof anatomy and morphology. Increasing water-stress was applied in terms of ratio of leaf water potential (Psi(L)) measured at midday to that at zero turgor (Psi(TLP)), i.e.Psi(L)/Psi(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 Psi(L)/Psi(TLP) = 1.2 increased for 48 h after irrigation from 0.23 to 0.97 x 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 Psi(L)/Psi(TLP) = 0.5 and 48 h later in those at Psi(L)/Psi(TLP) = 1.0. Severe drought stress (Psi(L)/Psi(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.