Root exposure effects on water relations of Eucalyptus nitens nursery stock

Bare-root seedlings of Eucalyptus nitens frequently exhibit water stress af ter planting resulting in leaf lamina damage and reduced leaf area. Two tri als examined effects of root exposure and desiccation between lifting and t ransplanting on post-planting water relations, leaf retention and root grow th. Plants with roots exposed on a glasshouse bench initially lost water ra pidly. In one trial psi(1) declined to around -2.0 MPa within 2.5 h, after which there was no further change with exposure up to 7.5 h. In the second trial, the initial decline in psi(1) was more rapid, reaching below -2.0 MP a in the first hour, before remaining stable with continuing exposure up to 4.5 h. A further decline then continued to -4.0 MPa after 7.5 h. Two days after transplanting into potting mix, day - time leaf water potent ials in all desiccation treatments had declined to near -2.0 MPa. Hydraulic resistivity, measured as leaf specific resistivity two days after transpla nting, increased following exposure for greater than 2.5 h, but there was n o further increase between 4.5 and 7.5 h. The increase in resistivity corre sponded with leaf water potential declining below -2.0 MPa during exposure. In the second trial, increasing root exposure time resulted in decreased le af area due to lamina necrosis. Root growth, measured three weeks after pla nting, was also reduced. and there was also a positive curvilinear relation ship between leaf area remaining at three weeks and new root growth. The re sults are discussed in terms of hardiness and the management of E. nitens s eedlings from nursery to plantation.