Clonal and seasonal differences in leaf osmotic potential and organic solutes of five hybrid poplar clones grown under field conditions

• Published in: Tree physiology 1998-10, Vol.18 (10), p.645-652
• Main Authors: Gebre, G.M, Tschaplinski, T.J, Tuskan, G.A, Todd, D.E
• Format: Article
• Language: English
• Subjects: carbohydrates; chemical constituents of plants; clonal variation; clones; diurnal variation; drought tolerance; free amino acids; genetic variation; hybrids; leaves; measurement; organic compounds; osmotic pressure; Populus balsamifera subsp. trichocarpa; Populus deltoides; Populus nigra; quantitative analysis; seasonal variation; solutes
• ISSN: 0829-318X; 1758-4469
• DOI: 10.1093/treephys/18.10.645

Leaf osmotic potential at full turgor (leaf osmotic potential) and the major solutes that contribute to osmotic potential were characterized in five hybrid poplar clones of Populus trichocarpa Torr. & Gray x P. deltoides Bartr. (TD) and P. deltoides x P. nigra L. (DN), growing under field conditions at two sites in eastern Washington and Oregon, USA. Trees were drip irrigated with 46, 76 or 137 cm of supplemental irrigation during each growing season. Trees at Wallula, WA, which were in their third growing season in 1994, were sampled twice a year for two years (1994 and 1995), and trees at Boardman, OR, which were in their second growing season in 1994, were sampled once a year or three years (1994-1996). At Wallula, the TD and DN clones exhibited lower predawn leaf water potentials in the 46-cm treatment than in the 137-cm treatment (-1.2 versus -0.7 MPa) during a hot, dry period in July 1994. Clone TD had a lower leaf osmotic potential than Clone DN (-1.67 versus -1.56 MPa) during the same period and the difference was also evident in 1995 (-1.81 versus -1.72 MPa) when trees were in their fourth growing season. There was also a significant treatment effect on leaf osmotic potential in Clone TD, with trees in the 46-cm treatment having lower leaf osmotic potential than trees in the 137-cm treatment in July 1994. At Boardman, leaf osmotic potential was generally high with no treatment differences during the 1994-96 samplings. The TD clones had significantly lower leaf osmotic potential than the DN clones in 1994 (-1.44 versus -1.36 MPa) and 1996 (-1.72 versus -1.54 MPa), but there was no difference between clones in 1995 (-1.40 versus -1.43 MPa). In 1995, at Wallula, osmotic adjustment in Clone TD was largely accounted for by an increase in sucrose, which constituted 70% of total organic solutes. Although the total concentration of free primary amino acids in this clone was 28% higher in trees in the 46-cm treatment than in trees in the 137-cm treatment, amino acids constituted only a small fraction of the total solute pool. Sixty-two percent of total solutes were inorganic ions in Clone TD compared to 52% in Clone DN, and potassium was the main ion constituting about 30% of total solutes and 50% of total ions. However, the clonal difference in leaf osmotic potential was not fully accounted for by the difference in solute concentration. Osmotic potential at full turgor declined over the growing season and with age. We conclude that, because the extent of