Abstract: Taking two cotton cultivars with different fiber strength (KC-1, aver age fiber strength 35 cN·tex-1; and AC-33B, average fiber strength 32 cN ·tex-1) as test materials, a field experiment with two planting dates (25 April and 25 May) was conducted in Nanjing of Jiangsu (lower reaches of Yangtze River Valley) and Xuzhou of Jiangsu (Yellow River Valley) to study the dynamic changes of plant sucra se, sucrose synthase, sucrose phosphate synthase, and β-1,3-glucanase activit ies during the development of cotton fiber at different air temperatures and the ir relationships with fiber length and strength. In the development period of fi ber elongation, sucrase and β-1,3-glucanase activities were higher; while du ring the period of fiber thickening, sucrose synthase and sucrose phosphate synt hase activities increased rapidly and were high, but sucrase and β-1,3-glucan ase activities had a rapid decrease. The higher sucrase activity in fiber elonga tion development period favored the fiber length development, while the rapid in crease of sucrose synthase and sucrose phosphate synthase and the rapid decrease of sucrase and β-1,3-glucanase activity favored the development of fiber str ength. For cotton variety KC-1, the sucrase and β-1,3-glucanase activities i n its early development period and the sucrose synthase and sucrose phosphate sy nthase activities in its middle and later development periods were all higher th an those of AC-33B. In this study, 233 ℃ was the optimal temperature for hig h strength fiber formation, and 233 ℃〖KG-*2〗-〖KG-*7〗255 ℃ was the opti mal temperature for long length fiber formation.

Key words: Betula platyphylla, radial growth, altitude, rapid warming.