Effects of different concentrations of NaCl on salt tolerance of roots in poplar ‘107’ (Populus×euramericana ‘Neva’) and transgenic poplar ‘18-1’ and ‘18-4’ with NTHK1 (Nicotiana tabacum histidine kinase-1) were investigated. The results showed that dry weight and length of roots in ‘18-1’ and ‘18-4’ were significantly higher than that of ‘107’. Under the stress of 400 mmol·L-1 NaCl for 60 min, the K+ leakage amount of ‘107’ were 49.34% and 19.68% higher than those of ‘18-1’ and ‘18-4’ respectively. And the...