Outside-Xylem Vulnerability, Not Xylem Embolism, Controls Leaf Hydraulic Decline during Dehydration
Christine Scoffoni1,2,3,4,5,6, Caetano Albuquerque7,8,9,10,11,12, Craig R Brodersen7,8,9,10,11,12
1Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, 90095 (C.S., S.V.T., G.P.J., M.K.B., L.S.); cscoffoni@ucla.edu.
Plant Physiology
|January 5, 2017
Summary
During drought, leaf water transport decline is primarily caused by outside-xylem tissue vulnerability, not just xylem embolism. This finding highlights a key mechanism protecting plants from dehydration stress.
Area of Science:
- Plant Physiology
- Ecology
- Biophysics
Background:
- Leaf hydraulic conductance (Kleaf) is vital for CO2 uptake and plant growth.
- Drought causes Kleaf decline, leading to stomatal closure and leaf death.
- Previous research often attributed Kleaf decline to xylem embolism.
Purpose of the Study:
- To investigate the hydraulic vulnerability of xylem and outside-xylem pathways during leaf dehydration.
- To quantify the contribution of different pathways to the decline in plant water transport.
- To model the influence of outside-xylem tissues on Kleaf and plant water transport under drought.
Main Methods:
- In vivo x-ray microcomputed tomography (micro-CT) to visualize xylem conduit embolism in dehydrating leaves.
- Experimental measurements of Kleaf decline across multiple angiosperm species during dehydration.
- Spatially explicit and plant-scale modeling of water transport dynamics.
Main Results:
- Xylem embolism was minimal at the turgor loss point, increasing only under severe dehydration.
- Outside-xylem hydraulic vulnerability accounted for 75% to 100% of Kleaf decline from mild to severe dehydration.
- Modeling indicated reduced membrane conductivity in outside-xylem tissues and protection of xylem from embolism.
Conclusions:
- Outside-xylem tissues, not xylem embolism, are the primary drivers of Kleaf decline during drought.
- Outside-xylem hydraulic vulnerability plays a critical role in regulating plant water transport and protecting xylem.
- These findings identify outside-xylem tissues as a key control point for plant water status during drought.
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