| Abiotic stresses such as drought and salinity are important limiting factors in plant growth and development,and the selection of resistant forest tree species is of great importance for the greening of difficult terrain.Poplar（Populus L.）species are fast-growing and reproduce rapidly,and the American black poplar（P.deltoides）and its hybrids（P.×canadensis）of the black poplar school（Sect.Aigeiros）are important tree species for afforestation and industrial timber forestry.In this study,ten black poplar clones were tested in pots to study their growth and physiological and biochemical indicators under different levels of drought stress and Na Cl stress,and on this basis,the drought and salt tolerance of each asexual line was comprehensively evaluated using principal component analysis,in order to select the best clones with high resistance to stress.The main findings of the study are as follows.（1）Under continuous drought stress,the differences in seedling ramet height increment,basal diameter increment and biomass increment among the 10 clones were significant,among which the seedling ramet height increment,ground diameter increment and biomass increment of asexual line 1733 were the largest,indicating that this asexual line has strong drought resistance.（2）Under continuous drought stress,the chlorophyll content of the clones showed a general trend of increasing and then decreasing,with a small increase in mild drought and a decrease in moderate and severe drought;the chlorophyll content of clones I-107 and 1627 was the highest in severe drought.（3）The cell membrane permeability of the seedling leaves of the 10 clones tended to increase with the duration of drought,with obvious changes among different treatments.The highest;superoxide dismutase（SOD）and peroxidase（POD）activities increased and then decreased,with the greatest activity under moderate drought.Compared with normal water supply,the clones 1627 and 1733 showed the greatest increase in SOD activity,and the clones 1733 and 1641 showed the greatest increase in POD activity;the accumulation of osmoregulatory substances gradually increased with increasing drought,and under severe drought The accumulation of osmoregulatory substances gradually increased with the increase of drought,and under severe drought,the free proline（Pro）content and the greatest increase were both in the clones 1627 and 1733,which were significantly different from the control2025.（4）Under salt stress,seedling ramet height increment,basal diameter increment and biomass of all clones decreased with increasing salt treatment concentration,indicating that salt stress had an inhibitory effect on the growth of clones.（5）The chlorophyll content of all 10 black poplar clones decreased with increasing salt stress.The chlorophyll content of clones 2025 and 1725 was higher under high salt stress.（6）The cell membrane permeability and MDA content of the seedling leaves of the 10 clones showed an increasing trend with increasing salt concentration,and the smaller increase in cell membrane permeability at 0.6% salt concentration was found in 1725 and I-107;SOD and POD activities first increased and then decreased,and the SOD and POD activities of clones 1733 and 1725 were always at a higher level;the free proline content of each asexual line tested gradually increased with increasing salt concentration.The free proline content of all the clones increased gradually with the increase of salt concentration.（7）The drought resistance of the ten clones was evaluated by principal component analysis,and the clones were 1733,1627,I-107,1641,1640,1725,1723,2025,1716 and1722 in descending order of strength.The clones 1733 and 1627 were more drought tolerant than the control I-107 and 2025,and the clones 1733 and 1725 were more salt tolerant than the control I-107 and 2025,in descending order of salt tolerance. |
