Plant water status and hydraulic conductance during flowering in the southern California coastal sage shrub Salvia mellifera (Lamiaceae).

Premise of the Study: Plant water status during flowering is important for plant reproduction, but the physiology of floral water use is not well understood. We investigated plant water status in relation to leaf and floral physiology in naturally occurring individuals of a semiarid shrub, Salvia mellifera E. Greene. Methods: We measured stomatal (g(s)) and corollac (g(c)) onductance to water vapor, transpiration from leaves (E-leaf) and corollas (E-corolla), leaf-specific hydraulic conductance (K-H), bulk shoot water potential (psi(shoot)), and shoot water content on irrigated and control plants to analyze whether water was limiting to leaf and floral water use. Key Results: Experimental irrigation caused a 203% increase in soil moisture content, a 20% increase in predawn psi(shoot), a 29% increase in midday psi(shoot), and a 92% increase in K-H. Floral and leaf gas exchange did not respond significantly to water addition, indicating that rates were at seasonal maxima and not limited by water availability. Total daily water use by corollas was similar to 20% of total shoot water use. There were no significant differences in total daily shoot water use with water addition. Mean shoot water content (5.07 g) was close to mean daily shoot water use (6.71 g), indicating that the equivalent of total shoot water content turned over every 0.76 d. Conclusions: These results demonstrate that although irrigation improved whole-plant hydraulic conductance, gas exchange was not limited by water availability. Additionally, the high water use of flowers in this species might limit future flowering and reproductive success during dry years.