© 1995 Heron Publishing—Victoria, Canada
Physiological responses to water stress and waterlogging in Nothofagus species
Osbert J. Sun (1, 2), Geoffrey B. Sweet (1), David Whitehead (3) and Graeme D. Buchan (4)
1. School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand / 2. New Zealand Forest Research Institute, Private Bag 4800, Christchurch, New Zealand / 3. Manaaki Whenua–Landcare Research, P.O. Box 69, Lincoln, Canterbury, New Zealand / 4. Soil Science Department, Lincoln University, Canterbury, New Zealand / Received December 13, 1994
Summary
Gas exchange and water relations were investigated in Nothofagus solandri var. cliffortioides (Hook. f.) Poole (mountain beech) and Nothofagus menziesii (Hook. f.) Oerst (silver beech) seedlings in response to water stress and waterlogging. At soil matric potentials (Ψsoil) above –0.005 MPa, N. solandri had significantly higher photosynthetic rates (A), and stomatal and residual conductances (gsw and grc), and lower predawn xylem water potentials (Ψpredawn) than N. menziesii. The relative tolerance of plants to water stress was defined in terms of critical soil matric potential (Ψcri) and lethal xylem water potential (Ψlethal). The estimated values of Ψcri and Ψlethal were –1.2 and –7 MPa, respectively, for N. solandri, and –0.7 and –4 MPa, respectively, for N. menziesii. Photosynthesis was sustained to a xylem water potential (Ψxylem) of –7 MPa in N. solandri compared with –4 MPa in N. menziesii.
Following rewatering, both A and Ψxylem recovered quickly in N. solandri, whereas the two variables recovered more slowly in N. menziesii. During the development of water stress, nonstomatal inhibition significantly affected A in both N. solandri and N. menziesii. Nothofagus menziesii was more susceptible to inhibition of A by waterlogging than N. solandri. However, the tolerance of N. solandri to severe waterlogging was also limited as a result of a failure to form adventitious roots, suggesting a lack of adaptation
to these conditions. The differences in tolerance to water stress and waterlogging between the two species are consistent
with the distribution patterns of N. solandri and N. menziesii in New Zealand.
Keywords:
gas exchange, geographical distribution, nonstomatal inhibition, Nothofagus menziesii, Nothofagus solandri var. cliffortioides, water relations, water stress.
