Abstract: Leaf anatomical structure of Populus euphratica naturally distributed in Shaya County, Xinjiang at five different developmental stages was examined using conventional paraffin section method. We measured leaf thickness, upper and lower cuticle thickness, upper and lower epidermis thickness, spongy tissue thickness, palisade tissue thickness, and the ratio of palisade tissue to spongy tissue. Combining the methods of coefficient of variation and principal component analysis, four important indicators related to salt tolerance, namely leaf thickness, spongy tissue, palisade tissue, and midvein vascular bundle area, were identified. The salt tolerance of Populus euphratica at different developmental stages was evaluated and ranked using the fuzzy mathematical membership function. The results showed that: (1) The epidermal tissue of leaves became more developed with the developmental stages, while leaf thickness, palisade tissue, and spongy tissue showed a decreasing and then increasing trend. They were lowest at the mature stage, near-mature stage, respectively, and highest in the over-mature stage. The ratio of palisade to spongy was greater than 2.58 in each developmental stage, indicating good adaptability of Populus euphratica to saline stress across various developmental stages. (2) The salt tolerance of Populus euphratica at five different developmental stages was ranked from strong to weak as follows: over-mature > mature > seedling > near-mature > young. Leaf anatomical structure indicators can effectively reflect the salt tolerance characteristics of Populus euphratica and serve as an evaluation index for salt tolerance. Over-mature and mature stages exhibited stronger salt tolerance.

Key words: Populus euphratica, developmental stage, leaf blade, anatomical structure, salt tolerance