Universal trade-off between vessel size and number and its implications for plant hydraulic function

Area of Science:

• Plant physiology
• Xylem hydraulics
• Ecology

Background:

• Angiosperm vessel traits critically affect water transport, influencing plant metabolism and performance.
• The vessel "packing rule" (trade-off between diameter and number) is established, but its link to hydraulic function variation is unclear.

Purpose of the Study:

• To investigate how xylem traits and leaf mass covary with the packing rule in stems across and within angiosperm species.
• To define the limits of hydraulic efficiency and safety strategies in angiosperms.

Main Methods:

• Analysis of literature data (3992 species intraspecific, 54 species interspecific) and new data from 80 tree species branches.
• Examination of vessel diameter, lumen area, vessel density, lumen fraction, non-vessel lumen fraction, specific stem conductivity, and wood density.
• Statistical analysis of scaling relationships and correlations between traits.

Main Results:

• Mean vessel lumen area scaled with a -1.0 power of vessel density.
• Lumen fraction correlated positively with vessel density in stems and branches.
• Wood density showed a weak negative correlation with mean vessel lumen area.
• Vessel area scaled positively with leaf mass.
• Specific stem conductivity correlated with mean vessel lumen area and wood density.

Conclusions:

• The study validates and extends the packing rule's implications for hydraulic function.
• Key limits on hydraulic efficiency and safety strategies within and across angiosperm species were identified.