Variation of six local poplar clones in growth and eco-physiological traits in two types of arid valleys

Six clones of native poplars were used in a field trial to investigate variations in survival, growth, and adaptation to arid-warm and arid-hot valleys. In the arid-hot valley, clone Y1-2 exhibited the highest survival rate and growth condition, surpassing other clones, while clones B7-4 and P3-6 demonstrated superior survival and growth performance in the arid-warm valley. Clone B7-4 displayed the highest soluble sugar content in leaves across both habitats. SOD and APX activities, along with MDA content in leaves, were higher in the arid-hot valley for all clones compared to the arid-warm valley. Long-term water use efficiency, as indicated by δ13C in leaves, was significantly higher for all clones in the arid-hot valley, particularly for H1-6, T3-2, and P3-6. Increases in upper epidermis thickness were observed in clones E1, B7-4, and P3-6, while Y1-2 exhibited a higher palisade parenchyma thickness (PT) in the arid-hot valley compared to the arid-warm valley. Vein densities were higher in leaves of clones E-1, B7-4, Y1-2, and P3-6 in both valleys compared to other clones, with B7-4 showing a significant increase in mean vein width in the arid-hot valley. In conclusion, the superior growth performance of clone B7-4 in the arid-warm valley may be attributed to its stronger osmotic adjustment and higher capacity to maintain water transportation through venation. The exceptional performance of clone Y1-2 in the arid-hot valley may be associated with its compact arrangement of PT, as well as its stronger capacity for hydraulic transport and antioxidant resistance in leaves.