中文摘要：

设置麦棉改良3：1式套作试验，在棉花苗期取小麦根区土壤，采用1／2Hoagland—Aron营养液振荡提取法收集小麦根区化感物质。在1／2Hoagland—Aron营养液中分别添加相当于0．36，1．44mg·L^-1的上述化感提取物质（CL1、CL2），以含0．4％无水乙醇同等浓度的1／2Hoagland—Aron营养液为对照（CK）。在砂培条件下研究了麦棉套作系统中小麦根区化感物质对棉苗生长的影响。结果表明：CL1对棉苗的生长影响较小，CL2对棉苗的生长有显著的抑制作用，表现在棉苗物质积累降低，根系内源保护酶活性显著下降，MDA含量上升，电解质渗出率升高。砂培小麦后，以小麦近根系石英砂移栽棉花，小麦残留的根系分泌物导致棉苗鲜重下降，叶片的生长受到抑制，棉苗叶面积降低。因此，小麦根系分泌物产生的化感作用影响了棉苗的生长，从而导致了麦套棉弱苗晚发。

英文摘要：

Effect of allelopathic substance from wheat（Yumai 34） root zones in wheat-cotton interplanting system on the growth of cotton（Nucotn 33B） seedling was studied by conducting sand culture experiments. Allelopathic substance was extracted from 4 kg soil from wheat root zones by mixed impregnant, which was composed of Methanol, Acton and Ethyl acetiate by 1 ： 1 ： 1, and 50 g soil was extracted by 100ml mixed impregnant. Then the mixed impregnant was evaporated to dryness in a flash evaporator at less than 50℃ under a vacuum, the residue dissolved in Ethanol to 11 mL. Cotton seedling was cultured by 1/2 Hoagland-Aron nutrition solution contained 0.36 mg · L^-1 and 1.44 mg · L^-1 extracted in a green-house （13h light, white fluorescent lamp, 26℃ and 11h dark, Compared humidity 60%. ）, using 1/2 Hoagland-Aron nutrition solution which contained 0.4% Ethanol as control. Results showed that content of K in stem declined, CAT and SOD activity of cotton root was inhibited significantly, MDA content and comparative conductance of cotton seedling＇s root raised, and inhibit effect enhanced with concentration of abstracted substance raised. When the wheat seedling cultured in sand with 1/2 Hoagland-Aron nutrition solution （pH=6.5） grew to three-leaf stage, sand adhered to wheat root zone was collected and the cotton seedling were transplanted into. Data showed that the growth of cotton seedling was inhabited by residue of wheat root exudates, leaf area of cotton decreased and comparative conductance of cotton seedling＇s root was raised also. The weak growth of cotton seedlings in wheat-cotton interplanting system was possibly caused by allelopathy from wheat root exudates.