Comparative transcriptomic and metabolomic analyses provide insights into the responses to NaCl and Cd stress in Tamarix hispida

Salinity and heavy metal pollution seriously affect plant growth. Tamarix hispida (T. hispida) has the potential to remediate soil saline-alkali and heavy metal pollution. In this study, the response mechanisms of T. hispida under NaCl, CdCl2 (Cd) and combined CdCl2 and NaCl (Cd-NaCl) stresses were explored. Overall, the antioxidant system showed changes under the three stresses. The addition of NaCl inhibited the absorption of Cd2+. However, there were obvious differences in the transcripts and metabolites identified among the three stress responses. Interestingly, the number of DEGs was greatest under NaCl stress (929), but the number of differentially expressed metabolites (DEMs) was lowest (48), with 143 and 187 DEMs identified under Cd and Cd-NaCl stress, respectively. It is worth noting that both DEGs and DEMs were enriched in the linoleic acid metabolism pathway under Cd stress. In particular, the content of lipids changed significantly under Cd and Cd-NaCl stress, suggesting that maintaining normal lipid synthesis and metabolism may be an important way to improve the Cd tolerance of T. hispida. Flavonoids may also play an important role in the response to NaCl and Cd stress. These results provide a theoretical basis for cultivating plants with improved salt and cadmium repair abilities.