The Role of Osmotic Adjustment in Thuja occidentals' Response to Drought Stress

• Published in: HortScience Vol. 30; no. 4; p. 837
• Main Authors: Edwards, D.R, Dixon, M.A
• Format: Journal Article
• Language: English
• Published: 01-07-1995
• ISSN: 0018-5345; 2327-9834
• DOI: 10.21273/HORTSCI.30.4.837A

Six-year-old trees were repeatedly conditioned by withholding irrigation until Ψ
pd
(predawn) thresholds of either –0.9 (“mild”) or –1.4 MPa (“moderate”) were attained. After conditioning, trees were exposed to severe drought (Ψ
pd
–2.0 MPa) and then to 10 days of well-watered conditions. Throughout the investigation, osmotic potential (Ψ
π
), leaf RWC, transpiration, and total water potential (Ψ
x
) were measured. Water stress was quantified by integrating Ψ
x
. Conditioning caused a significant, but modest, degree of osmotic adjustment (0.08 to 0.28 MPa), which persisted after a brief relief from stress and transpiration rates were reduced 35% to 50%. Osmotic adjustment was not significantly enhanced by more than one stress exposure or conditioning beyond the mild threshold of stress. During severe drought, the moderate group maintained less negative Ψ
x
and lower transpiration rates (38%). After prolonged stress relief, Ψ
x
was similar among all treatments and daily transpiration rates and Ψ
x
gradually recovered.
Thuja occidentalis
appears to rely on increased stomatal resistance more than osmotic adjustment to tolerate drought stress.