Preliminary study on the salt tolerance of arroyo willow ( Salix lasiolepis), a native California willow

Human activities including river control and agricultural practices have increased salinity levels in many Southwestern watersheds. Increased salinity can limit the success of trees used to remediate degraded riparian areas. This study investigates the salinity tolerance of a native California willow, Salix lasiolepis (Arroyo willow). Asexually propagated cuttings and saplings were grown in soilless medium under greenhouse conditions. Salt content of the medium was altered using dilute NaCl (concentrations ranging from 9 to 200 mM NaCl). Mean new growth for each population decreased with increasing NaCl concentration. However, significant variation in response to salinity was noted across several variables, including ecotype, stage of development, season of sample collection and protocol (pretreatment vs. acclimation). This preliminary study suggests that specific populations of Arroyo willow may be better suited for revegetation of salt-contaminated riparian sites. It also suggests that salt tolerance of Salix lasiolepis may be enhanced with gradual, cumulative NaCl doses.