铅胁迫下小花南芥与玉米间作对根系分泌物有机酸的影响

Effects of Arabisalpina L. var. parviflora Franch and Zea mays L. intercropping system on root-exudated organic acids under lead stress

为了揭示Pb胁迫对间作和单作的超累积植物和作物根系分泌低分子有机酸的影响,研究设置400 mg·L^-1 Pb胁迫,采用水培曝气法试验,以玉米和小花南芥单作为对照处理,研究Pb胁迫下玉米和小花南芥间作对植物根系形态、根系分泌有机酸及Pb吸收的影响。结果表明：与单作相比,间作小花南芥情况下,玉米根系分泌物检测到乳酸;玉米分根条数、根表面积和根密度与单作相比分别增加60%、15%和42%,地下部和地上部干重生物量分别增加108%和75%,玉米地下部Pb含量下降44%;与单作相比,间作玉米条件下,小花南芥根系分泌物检测到乙酸和乳酸,小花南芥根系分泌物量与单作相比增加103%-1 700%,小花南芥地下部和地上部Pb累积量分别比单作增加49%和75%,转运系数增加22%。相关分析结果表明,单作小花南芥只有地上部Pb累积量与草酸显著相关,而间作小花南芥地下部和地上部Pb累积量与草酸、柠檬酸和苹果酸显著相关。研究表明超富集植物小花南芥与玉米间作体系,根系分泌的有机酸改变了Pb在小花南芥和玉米体内的累积特征,促进超累积植物小花南芥累积Pb,减少农作物玉米植株体内Pb含量。Pb胁迫下超累积植物小花南芥与玉米间作是一种可行的修复模式。

Cultivated soils contamination by heavy metals have become increasingly contentious to decision makers, farmers, consumers and health professionals around the globe. Phytoremediation is a key strategy for decontaminating cultivated soils polluted by heavy metals. Hyperaccumulator plants are limited by their soil occupation rather than agricultural production in China. Intercropping system of hyperaccumulator plants and crops have been recommended for both of remediation and production in the same time. The accumulation of heavy metal in plants is due to root growth and root exudates. However, plant root morphology and exudates vary, which is a key issue in intercropping systems. In order to investigate the effects of lead（Pb） stress on the exudates of organic acids by hyperaccumulator plant and crop roots in intercropping and monocropping systems, a hydroponic aeration experiment was conducted in a greenhouse. A crop（maize） or hyperaccumulator（Arabisalpina L. var. parviflora Franch） monocropping and intercropping systems were set up as the control and treatment plots, respectively. The effects of 400 mg×L^-1 Pb stress on root morphology, organic acids（oxalic acid, tartaric acid, citric acid, malic acid, lactic acid and acetic acid） exudation and lead accumulation in the intercropping and monocropping systems were determined. The results showed that compared with monocropped maize, lactic acid was obtained from intercropped maize root exudates. The numbers of split root, root surface area and root density of intercropped maize increased by 60%, 15% and 42%, respectively. Root and shoot biomass under intercropped maize increased by 108% and 75%, respectively, whereas root Pb content of intercropped maize decreased by 44%. Compared with monocropped A. alpina, acetic acid and lactic acid determined from root exudates of intercropped A. alpine, showing 103%-1 700% increase in root exudates amount. Also Pb accumulation in underground and aboveground plant parts of intercropped A. alpina increased respectively by 49% and 75% with 22% increase in transfer coefficient of Pb. Furthermore, for monocropped A. alpine, Pb content in shoots was only significantly positively correlated with oxalic acid content; but for intercropped A. alpine, it was significantly positive correlated with contents of oxalic acid, oxalic acid and malic acid both in shoot and root of A. alpine. The results suggested that root exudation of organic acids was critical in changing Pb accumulation characteristics in maize and A. alpina intercropping system. The number and components of organic acids in root exudates changed under intercropping system, which affected Pb content and accumulation characteristics of A. alpine and maize. Pb content increased in A. alpine and decreased in maize. In short, hyperaccumulator A. alpine and maize were recommended for remediation of cultivated soil contaminated with Pb.