[Altitudinal phenotypic plasticity of leaf characteristics of Polygonum viviparum]

We investigated leaf tissue structure, leaf epidermis characteristics and chloroplast ultrastructure of Polygonum viviparum at different altitudes (2300, 3200 and 3900 m) on the Qilian Mountain, using paraffin section, scanning electron microscopy and transmission electron microscopy methods. The results showed that plant leaves were typical bifacial. With increasing altitude, the number of leaf epidermal hair reduced but the diameter of hair increased, with more compact of the cuticular wax layer on leaf lower epidermis. Leaf thickness reached a maximum at 3200 m and was increased by 39.6% and 50.5%, respectively, compared with that from 2300 m and 3900 m. From 2300 m to 3200 m, the cell layers of palisade tissue increased from two to three, while intercellular space decreased. The cell layer of spongy tissue did not change, whereas intercellular space increased with increasing altitude. At 3900 m, the number of cell layer of palisade tissue reduced to two, epidermal cell volume and the intercellular space of palisade tissue increased while the intercellular space of spongy tissue decreased. The thickness of epidermal cell increased. There was no significant difference among three altitudes in the number of cell layers. The accumulation of surface appurtenances and the substomatal appendages, and stomata density of lower epidermis increased with altitude. Meanwhile, the position of stomata changed from arched epidermis to invagination. From 2300 m to 3200 m, the grana lamella increased from 6-9 to 8-12 and then reduced to 2-3 at 3900 m. The number of grana decreased, the lamellae became dense, the arrangement direction of grana was irregular at 3900 m. The chloroplasts swelling and the envelope partially degradation could be observed. The correlations among the anatomical characteristics of leaves indicated an apparent co-evolution between parts of anatomical indices in the leaves. In particular, indices such as spongy tissue thickness exhibited high plasticity across altitudes. Our results suggested that diffe-rences in anatomical structure and ultrastructure characteristics of P. viviparum along altitude were adaptation strategies for the complicated alpine heterogeneous habitats.