摘要:为探明间作作物根系分泌低分子量有机酸对土壤重金属生物有效性的影响，采用矿区周边农田土壤进行室内盆栽试验，研究了云南本土超累积植物续断菊（Sonchus asper L.Hill）和玉米（Zea mays L.）间作下，植物生长、根系低分子量有机酸分泌量、根际土壤Pb提取形态以及植物Pb积累特点。结果表明：与单作相比，间作续断菊地上部和根部生物量、根长、根内径和根系体积均显著增加（P < 0.05）；间作玉米根部生物量、根长、根内径和根系体积显著增加（P < 0.05）。柠檬酸、草酸是续断菊和玉米根系分泌的主要低分子量有机酸，间作导致续断菊根系低分子量有机酸的分泌量增加，玉米根系低分子量有机酸的分泌量降低。续断菊根际土壤生物有效态Pb含量增加85.2%（P < 0.05），而玉米根际土壤生物有效态Pb含量降低26.1%（P < 0.05）。续断菊体内Pb含量显著增加18.0%~43.2%（P < 0.05），富集系数提高26.0%，而转运系数降低42.0%；玉米地上部Pb含量显著降低24.3%（P < 0.05），转运系数降低43.1%。续断菊根系分泌的柠檬酸和草酸数量，均与土壤生物有效态Pb含量呈显著正相关，且土壤有效态Pb含量分别与续断菊地上部和根部的Pb含量呈显著正相关。表明间作增加了续断菊对Pb的吸收积累量，与间作体系植物根系分泌的低分子有机酸介导下的土壤有效态Pb含量增加密切相关。
关键词:Pb污染/
低分子量有机酸/
续断菊/
玉米/
间作
Abstract:There is a close relationship between low-molecular-weight organic acids (LMWOAs) secreted by plant roots and plant accumulation of heavy metals when intercropping accumulators and crops in heavy metal-contaminated soils. However, the specific mechanism behind this remains unclear. Sonchus asper L. Hill is a native hyper accumulator that can be found in Yunnan. Plant growth, amounts of LMWOAs secreted by plant roots, rhizosphere soil extractable lead (Pb) contents, and plant Pb accumulation characteristics were studied under S. asper-Zea mays L. intercropping in soil that was collected from a farmland surrounding a mining area, in order to investigate the effects of the LMWOAs produced by intercropping roots on heavy metal bioavailability in soils. The results showed that the aboveground and root biomass, root length, root inner diameter, and root volume of S. asper were significantly increased (P < 0.05), and that the root biomass, root length, root diameter, and root volume of Z. mays were significantly increased (P < 0.05) under the intercropping systems compared to under the monoculture systems. The major LMWOAs secreted by the roots of both S. asper and Z. mays were citric acid and oxalic acid. Intercropping resulted in an increase and decrease in the LMWOA contents secreted by S. asper and Z. mays roots, respectively. The bio-available Pb content in the rhizosphere soil of S. asper increased by 85.2% (P < 0.05), and that of Z. mays decreased by 26.1% (P < 0.05) under intercropping. The Pb content, enrichment factor, and transfer coefficient increased by 18.0%-43.2%, increased by 26.0%, and reduced by 42.0% in S. asper under intercropping, respectively. Compared to the monoculture system, the shoot Pb content and Pb transfer coefficient decreased by 24.3% and 43.1% (P < 0.05) in Z. mays under the intercropping system, respectively. The amounts of citric acid and oxalic acid secreted by S. asper roots were significantly positively correlated with the soil bio-available Pb content, and the bio-available Pb content in soil was significantly positively correlated with S. asper shoot and root Pb contents. The results indicate that intercropping increases the uptake and accumulation of Pb in S. asper. These are both closely correlated with increases in soil bio-available Pb, which is mediated by plant roots that secrete LMWOAs.
Key words:Pb pollution/
Low-molecular-weight organic acid/
Sonchus asper L. Hill/
Zea mays L./
Intercropping
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