Ecosystem implications of genetic variation in water-use of a dominant riparian tree

Genetic variation in dominant species can affect plant and ecosystem functions in natural systems through multiple pathways. Our study focuses on how genetic variation in a dominant riparian tree ( Populus fremontii, P. angustifolia and their natural F(1) and backcross hybrids) affects whole-tree water use, and its potential ecosystem implications. Three major patterns were found. First, in a 12-year-old common garden with trees of known genetic makeup, hybrids had elevated daily integrated leaf-specific transpiration ( E(tl); P=0.013) and average canopy conductance ( G(c); P=0.037), with both E(tl) and G(c) approximately 30% higher in hybrid cross types than parental types. Second, delta(13)C values of leaves from these same trees were significantly more negative in hybrids ( P=0.004), and backcross hybrids had significantly more negative values than all other F(1) hybrid and parental types ( P<0.001). Third, in the wild, a similar pattern was found in leaf delta(13)C values where both hybrid cross types had the lowest values ( P<0.001) and backcross hybrids had lower delta(13)C values than any other tree type ( P<0.001). Our findings have two important implications: (1). the existence of a consistent genetic difference in whole-tree physiology suggests that whole-tree gas and water exchange could be another pathway through which genes could affect ecosystems; and (2). such studies are important because they seek to quantify the genetic variation that exists in basic physiological processes-such knowledge could ultimately place ecosystem studies within a genetic framework.