Diversity and Plasticity of Hydraulic Traits Across a Relative Moisture Supply Gradient: Results From Multiple Common Gardens

ABSTRACT Maintaining cellular hydration is essential for plant metabolic activity and carbon gain. Plants typically maintain hydration through efficiency of water transport networks, the ability to avoid network disruption, and retention of water via accumulation of osmotica. Given their global domain and their enduring presence across geological eras, plants have evolved with large variations in moisture supply across geographic and temporal space, notably via trait adaptation and plasticity. We quantified plastic and genetically fixed variation in 6 key hydraulic traits across 10 Eucalyptus species in 4 common gardens spanning a climatic relative‐moisture gradient in Victoria, Australia. These traits generally shift plastically within species across gardens while maintaining interspecific trends across species within gardens. Species grown at or originating from drier sites tend to have lower hydraulic conductivity, narrower xylem conduits, greater conduit density, greater bulk xylem density, greater fibre wall fraction, and more negative turgor loss point, consistent with expectations based on maximizing whole‐plant growth. Genetically fixed variation was usually greater than plastic variation, but some traits were more plastic in species native to moister areas. Variation in xylem anatomy largely explained variation in hydraulic conductivity and xylem density, notwithstanding idiosyncratic site and species effects.