PARENT SESSION
Poster Session #9: Water Relations.
Monday, August 6, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Environmental effects on xylem cavitation in Phaseolus vulgaris (common bean).

HOLSTE, ELLEN¹, MATZNER, STEVEN¹, ¹

ABSTRACT- Xylem cavitation induced by water stress reduces plant hydraulic conductance and can be an important limitation to stomatal conductance and carbon gain. Resistance to xylem cavitation may be influenced by environmental factors that affect either xylem size or structure (or both). The objectives of this study were to study the effects of various environmental factors on resistance to xylem cavitation in Phaseolus vulgaris (common bean). Beans were grown from seed in a growth chamber and exposed to reduced light levels, reduced moisture levels, reduced phosphorus nutrition or increased soil particle size compared with controls. A centrifuge was used to spin stem sections to specific tensions and measurements of hydraulic conductance were made at 0, -0.3, -0.6, -1.0, and -1.4 MPa. For all treatments, conductance was between 10-20 % of maximum at -1.4 MPa. Low moisture, low light, and the larger particle size soil all increased drought tolerance (greater cavitation resistance), causing a negative shift in the 50 % loss in conductance point of 0.15-0.25 MPa. In contrast, low phosphorus nutrition decreased drought tolerance, as shown by a positive shift in the 50 % loss in conductance point of 0.3 MPa. The results of this study indicate that environmental factors can have a significant effect on cavitation resistance within a species. Understanding the relationships between these factors and cavitation resistance may enable us to predict and perhaps even manipulate drought tolerance in plants.

KEY WORDS: xylem, cavitation, drought, beans