Cd胁迫下长白落叶松幼苗根系有机酸的分泌研究

Organic Acid Secretion from Larix Olgensis Roots under Cd Stress

用A1层暗棕壤栽植长白落叶松幼苗(1 a生和2 a生),1个月后用CdCl2溶液对土壤进行Cd胁迫处理,使土壤Cd2+浓度分别达1、2、4、8 mg kg-1,在胁迫处理后第3 d、10 d和30 d,分别采集上述两种幼苗的根际土壤样品,研究不同Cd胁迫程度(水平)和胁迫时间处理后,长白落叶松幼苗根系分泌的有机酸种类和数量,以期为系统研究有机酸在森林生态系统中的作用提供理论依据。结果表明,Cd胁迫促进1 a生苗根系分泌有机酸种类和数量增加,增加量因胁迫时间和胁迫程度而异;增加有机酸种类数量的胁迫时长顺序为30 d>3 d>10 d,即在一定胁迫程度范围内,苗木受胁迫时间较短、胁迫较重时新检出有机酸的种类较多。同样,在一定胁迫程度和胁迫时长内,苗木根系分泌有机酸总量随胁迫程度提高而增加,达到最大值后胁迫程度继续提高则分泌有机酸的总量降低。在其它条件一定时,随胁迫时间延长,根系有机酸分泌总量降低。在不同的胁迫时间,有机酸分泌量大多以3 d增幅最大;对于不同种类有机酸,苹果酸分泌量增幅最大,其次为柠檬酸或草酸。对于2 a生苗,大多数Cd胁迫处理也增加其根系分泌的有机酸种类数量,且在一定胁迫程度内有机酸分泌总量随胁迫程度增加而增加。

Larix olgensis seedlings of 1 a and 2 a were planted in A1 horizon of dark brown forest soils for 1 month,and the Cd2+content in the soils was adjusted with Cd Cl2 solution to 1, 2, 4 and 8 mg kg-1, respectively. At 3, 10, and30 days of CdCl2 applications, soil samples from the rhizosphere were collected, and the types and contents of organic acids secreted from roots of 1 a and 2 a seedlings under different Cd levels and treatment times were analyzed in order to provide a theoretical basis for systematically studying the significance of organic acids in forest ecosystems. The results showed that Cd stress increased both the types and contents of organic acids secreted from roots of 1 a,seedlings and the degree of increase varied with treatment time and stress level. Under a certain stress, the more types of organic acids were newly detected from the seedling roots treated at a heavier stress level for a shorter time. In a certain degree of Cd stress, the total contents of organic acids secreted from roots increased and then decreased with stress levels. The total contents of organic acids decreased with the treatment time. The organic acid reached a maximum at 3 d and the increase amplitude followed the order of malic acid > citric acid or oxalic acid > succinic acid. Cd stress also increased the kinds and contents of organic acids secreted from 2 a seedling roots, and total contents of organic acids were increased with the stress levels.