Root metaxylem and root architecture phenotypes interact to regulate
water use under drought stress
Abstract: At the genus and species level, variation in root anatomy and
architecture may interact to affect strategies of drought avoidance. To
investigate this idea, root anatomy and architecture of the
drought-sensitive common bean (Phaseolus vulgaris) and drought-adapted
tepary bean (Phaseolus acutifolius) were analyzed in relation to water
use under terminal drought. Intraspecific variation for metaxylem
anatomy and axial conductance was found in the roots of both species.
Genotypes with high-conductance root metaxylem phenotypes acquired and
transpired more water per unit leaf area, shoot mass, and root mass than
genotypes with low-conductance metaxylem phenotypes. Interspecific
variation in root architecture and root depth was observed where P.
acutifolius has a deeper distribution of root length than P. vulgaris.
In the deeper-rooted P. acutifolius, genotypes with high root
conductance were better able to exploit deep soil water than genotypes
with low root axial conductance. Contrastingly, in the shallower-rooted
P. vulgaris, genotypes with low root axial conductance had improved
water status through conservation of soil moisture for sustained water
capture later in the season. These results indicate that metaxylem
morphology interacts with root system depth to determine a strategy of
drought avoidance and illustrate synergism among architectural and
anatomical phenotypes for root function.