Abstract
Seasonal changes in lipids and their fatty acid composition were measured in bark tissues of three wild pear species, Pyres betulaefolia, P. calleryana and P. serotina, to investigate their relation with cold hardiness and air temperature. From September to mid-December, cold hardiness of the three species developed gradually in response to the drop of air temperature. Simultaneously, the increase in the proportion of linolenic acid (C 18:3) in galactolipids was accompanied by the increase of linoleic acid (C 18:2) and decrease of oleic acid (C 18:1) in phospholipids. During this period, variations of fatty acid composition and cold hardiness were closely correlated with the change of air temperature. All of the three species obtained the strongest cold hardiness in mid-December, associated with higher levels of unsaturation in all individual lipids. From January to February, air temperature reached its lowest point, which seems likely to maintain the cold hardiness of trees, thereafter, it started to rise slowly, and gradually reduced the cold hardiness. The variation trends of C 18:3 in galactolipids and C 18:2 in the most dominant phospholipid were obviously reversed after January, which had a pronounced effect on the decrease of cold hardiness.
