Alexander Levin*
*Oregon State University, Southern Oregon Research and Extension Center, 569 Hanley Rd., Central Point, OR 97502 (alexander.levin@oregonstate.edu)

The pressure chamber is a widely used tool for assessing water potential (Ψ) in plants and is commonly used as a tool in vineyard irrigation scheduling. Although it is regarded as the most robust method to assess plant water status in the field, there continues to be disagreement among users about proper technique for determining both midday leaf (Ψleaf) and midday stem (Ψstem) water potential. To resolve these discrepancies, three experiments were performed to understand how varied techniques affect either Ψleaf and Ψstem values: (1) Ψleaf response to the time interval between sample excision and pressurization; (2) Ψleaf response to sample preparation method (e.g., petiole re-cutting) prior to pressurization; and (3) Ψstem response to sample equilibration time. All experiments were performed by two operators using the same instrument. There were no significant effects of time interval or operator on Ψleaf at time intervals from 15 to 60 sec. Few significant differences were found in Ψleaf among sample preparation methods (experiment 2), and they depended on operator. Ψstem varied 5% when samples were allowed to equilibrate from 10 to 240 min prior to determination. The results show that time intervals of up to 60 sec between excision and pressurization were acceptable for accurate data, and petiole re-cutting did not substantively affect Ψleaf determination. Additionally, Ψstem equilibration times can be as short as 10 min. However, significant differences were observed between operators across all three experiments. Thus, the technical skill of the operator during pressurization may play a larger role in the outcome of the determination relative to the preparation of the sample prior to pressurization.

Funding Support: Agricultural Research Foundation, Oregon Wine Research Institute