| Salinity tolerance threshold of plants including forest trees is obtained based on the reduction in wood yield (total biomass) under saline conditions compared to non- saline conditions. In order to determine salinity tolerance threshold and yield decreases percentage per unit increase of soil salinity in selected Populus euphratica Oliv provenances, a split plot experiment based on randomized complete block design (RCBD). with two factors provenances in 13 types (1- Mofid hybrid (P. euphratica x P. alba), 2- Dezfoul, 3-Zabol, 4-Gotvand, 5-Lorestan, 6-Hamidiyeh, 7- Yazd 1, 8- Yazd 2, 9-Gharekhlar, 10-Kerman, 11-Garmsar, 12- Manjil, 13-Esfaahn) and soil salinity in five levels (2.8, 5.96, 9.47, 13.2 and 16.47 dSm-1). The study was performed with 3 replications during 2022-2024 at Hosein Abad Station of the National Salinity Research Center. At the end of experiment, salinity tolerance threshold and yield reduction slope were calculated based on increased dry weight (biomass) in during applying salinity treatments in the years 2023 and 2024. The results showed, the lowest salinity tolerance threshold was observed in Kerman (2.81 dS/m), Hamidiyeh (3.76 dS/m) provenances and Mofid hybrid (2.89 dS/m). On the contrary, the highest salinity tolerance threshold was observed in Garmsar (6.57 ds/m) and Dezful (6.05 ds/m) provenances, respectively. The highest yield reduction slope was observed in Mofid hybrid (8.19%), Manjil (7.42%), Garmsar (7.15%) and Kerman (6.89%) and Hamidiyeh (6.80%) provenances, respectively. In contrast, the lowest yield reduction slope was observed in Gotvand (4.53%), Esfahan (4.57%), Gharekhlar (4.88%), ZAbol (5.16%) and Dezful (5.30%) provenances, respectively. Overall, the results showed that reduced the yield by 50% in Gotvand, Gharekhlar, Dezful, ZAbol, Esfahan and Yazd 1 provenances, were observed in salinity intensity 15.55 dS/m, 15.51 dS/m, 15.32 dS/m, 15.27 dS/m, 14.99 dS/m and 14.05 dS/m, respectively. levels of salinity that reduced the yield by 50% in Gotvand, Gharekhlar, Dezful, ZAbol, Esfahan and Yazd 1 provenances, were about 80% to 60% greater than salinity that reduced the yield by 50% in Mofid hybrid, Kerman and Hamidiyeh provenances. Therefore, according to the results obtained, the provenances of Gotvand, Gharkhlar, Dezful, Zabol, Isfahan, and Yazd 1 were identified as the most tolerant provenances to salinity and Mofid hybrid and provenances of Kerman and Hamidiyeh were identified as the most sensitive provenances to salinity. Finally, it should be noted that the reported data were related to two-year tree growth and were based on changes in their total biomass under field conditions. |