PARENT SESSION
Oral Session #74: Plant Water Relations: Hydraulics and use.
Presiding: B. Engelbrecht
Thursday, August 8. 9:00 AM to 11:30 AM. Greenlee Meeting Room, TCC.
Hydraulic properties of rice.
Stiller, Volker*,1, Lafitte, Renee2, Sperry, John1, 1 University of Utah, Salt Lake City2 International Rice Research Institute (IRRI), Los Banos, Philippines
ABSTRACT- Drought stress is a major constraint to rice productivity (Oryza sativa L.), but little is known about the importance of xylem embolism in the rice drought response. In a field study at the International Rice Research Institute (IRRI, Los Banos, Philippines), we measured native embolism of leaves (PLC native) and leaf water potential (
leaf) in upland vs. lowland varieties of rice growing under well-watered vs. droughted conditions. Daily embolism was high (PLC native: 60-80%), even in well-watered controls. We plotted a native vulnerability curve from PLC native and leaf measurements and calculated the xylem pressure causing 50% loss of hydraulic conductivity (P50) in the leaves to be -1.6 MPa. There were no differences in P50s between varieties. In Utah, we measured the leaf vulnerability curve of one greenhouse-grown upland and lowland variety. As in the field study, there was no difference between varieties. However, the greenhouse plants were less vulnerable than field grown plants (P50: -1.9 MPa). In a second greenhouse experiment, plants were subjected to a drought-and-rewatering cycle, during which we continuously measured plant gas exchange, whole plant hydraulic conductance(Kh), and nightly root pressures that potentially refill embolized xylem. During 6 days of drought, the assimilation rate (A) and Kh decreased in linear proportion. Root pressures declined from 8.5±3.8 kPa to zero after 5 days. Plants were rewatered and then subjected to continuous light or darkness during the night. Plants rewatered in darkness recovered to pre-drought values of A and Kh, in association with large overnight root pressure that exceeded pre-drought values by over 7 fold (61.2±8.8 kPa). Plants kept in light showed no recovery in A and Kh and no root pressure. Results suggest that loss of hydraulic conductance during even mild drought may be an important limit on productivity, and that nightly root pressures and embolism reversal are essential for drought recovery.
KEY WORDS: rice (Oryza sativa L.), xylem embolism, hydraulic conductance, root pressure