Journal Article

Coordination of stem and leaf hydraulic conductance in southern California shrubs: a test of the hydraulic segmentation hypothesis

Alexandria L. Pivovaroff, Lawren Sack, Louis S. Santiago

2014

Overview

Coordination of water movement among plant organs is important for understanding plant water use strategies. The hydraulic segmentation hypothesis (HSH) proposes that hydraulic conductance in shorter lived, ‘expendable’ organs such as leaves and longer lived, more ‘expensive’ organs such as stems may be decoupled, with resistance in leaves acting as a bottleneck or ‘safety valve’. We tested the HSH in woody species from a Mediterranean-type ecosystem by measuring leaf hydraulic conductance (K leaf) and stem hydraulic conductivity (K S). We also investigated whether leaves function as safety valves by relating K leaf and the hydraulic safety margin (stem water potential minus the water potential at which 50% of conductivity is lost (Ψstem − Ψ50)). We also examined related plant traits including the operating range of water potentials, wood density, leaf mass per area, and leaf area to sapwood area ratio to provide insight into whole-plant water use strategies. For hydrated shoots, K leaf was negatively correlated with K S, supporting the HSH. Additionally, K leaf was positively correlated with the hydraulic safety margin and negatively correlated with the leaf area to sapwood area ratio. Consistent with the HSH, our data indicate that leaves may act as control valves for species with high K S, or a low safety margin. This critical role of leaves appears to contribute importantly to plant ecological specialization in a drought-prone environment.

• Publisher: New Phytologist Trust,Wiley Subscription Services, Inc
• Subject: Body organs / California / chaparral / Circadian Rhythm - physiology / Conductance / Coordination / Correlation / Drought / Dry seasons / hydraulic conductance / Hydraulic conductivity / hydraulic safety margin / Hydraulics / Hypotheses / Leaf area / leaf mass per area / Leaves / Mediterranean‐type ecosystem / Models, Biological / Organs / Plant Leaves - anatomy & histology / Plant Leaves - physiology / Plant organs / Plant Physiological Phenomena / Plant Stems - physiology / Plants / Resistance / Safety / Safety factors / Safety margins / Safety valves / Segmentation / Shoots / Shrubs / Species / Trees - physiology / Valves / Water - physiology / Water potential / water potentials / Water use / Wood - physiology / Wood density / Xylem