Contrasts in xylem hydraulics and water use underlie the sorting of different sand-fixing shrub species to early and late stages of dune stabilization

Abstract

Dominating sand-fixing shrubs play crucial roles in the stabilization and rehabilitation of sand dunes. Different sandfixingshrub species often separate along the temporal-spatial environmental gradient during the sand dune stabilization process; however, the physiological mechanisms underlying such a separation remain poorly understood, which limits our ability to identify the causes of land desertification and the cruxes of rehabilitation. We investigatedxylem hydraulics and water use characteristics of four important shrub species used for sand dune fixation projects in northern China that show distinct preferences to different stages of dune stabilization, i.e. two species succeed inactive dunes and the other two in fixed dunes. The major aim was to examine the roles of xylem hydraulics, water useand the coordination of these two aspects in determining the habitat preferences of sand-fixing shrubs along theprocess of dune stabilization in water-limited environments. The two active-dune species consistently exhibited higherstem hydraulic conductivity but lower resistance to drought-induced xylem embolism than the two fixed-dune species,which reflects contrasting requirements to shrub hydraulic functionality in sand dunes of the two successional stages that differ substantially in soil water regimes. In coordination with contrasts in hydraulics, they also diverged clearly inwater use strategies with the fixed-dune shrubs showing more conservative water use. Our results highlight the criticalroles that hydraulics and water utilization play in determining the adaptation of dominating sand-fixing shrub species to their respective environments shaped by the plant-soil interactions during sand dune vegetation development.