刈割次数对紫花苜蓿镉吸收影响及生理响应

Effects of cutting frequency on cadmium uptake and physiological responses of Medicago sativa under cadmium stress

采用盆栽试验研究了4种镉(Cd)浓度(0,10,25,50mg/kg)下,刈割次数(1次,2次,3次)对紫花苜蓿生长和Cd累积量的影响及其生理响应。结果发现,多次刈割提高了紫花苜蓿地上部分的生长速率,促进了地上部分生物量的累积,3次刈割下地上部平均生长速率可达61.6mg/(株·d),但3次刈割显著抑制了根系的生长(P<0.05)。生长季内2次和3次刈割可以促进根系Cd吸收,增加地上部分Cd累积量,进而提高紫花苜蓿Cd富集量,单株最大镉积累量出现在25mg/kg Cd浓度的2次刈割处理中,达到75.98μg/株。同时,2次或3次刈割会降低紫花苜蓿相对电导率、MDA含量,增加脯氨酸含量,改善紫花苜蓿在Cd胁迫下的生理状况。综合分析表明,当土壤Cd浓度不高于25mg/kg时,紫花苜蓿生长季内2次刈割可以提高Cd污染土壤修复效率。

Alfalfa（Medicago sativa）is a promising plant species for phytoremediation in soils polluted by heavy metals.This species has been reported to have a high growth rate and great potential for cadmium（Cd）accumulation.Alfalfa plants must be cut several times to reduce soil Cd concentrations to acceptable levels.Therefore,the aim of this study was to evaluate the effects of one,two,and three cuttings on the growth,Cd content,and physiological characteristics of alfalfa plants grown in Cd-contaminated soil.Alfalfa plants were grown in soil containing no Cd（control）and Cd at three concentrations（10,25,50 mg/kg）and cut once,twice,or three times.A higher number of cutting events promoted the growth rate and biomass accumulation in the shoot.The highest average shoot growth rate was 61.6mg/（plant·d）in the three-cuttings treatment,but root growth was significantly lower in this treatment（P〈0.05）than in the other treatments and the control.Over the whole growth cycle,cutting twice or three times improved the Cd uptake rate in the root and Cd accumulation in the shoot,thus increasing Cd enrichment in alfalfa plants.The highest Cd accumulation was75.98μg/plant in the 25mg/kg Cd treatment with two cuttings.The relative electrical conductivity and malondialdehyde（MDA）contents were lower in the two-cuttings and three-cuttings treatments than in the single cutting treatment,but the proline contents were higher,which improved the tolerance of alfalfa to Cd toxicity under Cd stress.We concluded that in soil containing Cd at≤ 25mg/kg,two cuttings can significantly improve the repair efficiency of alfalfa plants growing in Cd-polluted soil.