Purpose

This research aims to improve the efficiency of phytoremediation of Cd in soil using sunflowers and optimizing the model of Cd uptake by plants.

Methods

Five low molecular weight organic acids (LMWOAs), oxalic acid (OA), acetic acid (AA), tartaric acid (TA), malic acid (MA), and citric acid (CA) at 2, 4, and 6 mmol/kg, were applied to sunflowers at 20, 30, and 40 days after seed emergence. The pH, electric conductivity (EC), total nitrogen (TN), total phosphorus (TP), catalase activity, amylase activity, invertase activity, and Cd content in rhizosphere soil and Cd in plant tissues were analyzed.

Results

Plant biomass was greater at the application rates of 2 and 4 mmol/kg. For each acid treatment, the Cd content in roots and leaves increased, while that of the stem and bud decreased. The total Cd accumulation increased due to the increase in plant biomass, especially root tissues; LMWOAs applied at 20 or 30 days after seedling emergence achieved higher Cd accumulations by expanding the Cd absorption capacity of rhizosphere soil. Application time had a more significant influence on plant biomass, Cd content, and accumulation in plant tissues than the variation of LMWOAs. Soil invertase activity and pH are the main factors causing the change in Cd form. An improved Freundlich model, using soil EC and pH, had higher accuracy than a model using pH alone.

Conclusions

LMWOAs can increase Cd accumulation in plants, and a lower application rate (2 mmol/kg) and earlier application date (20 days after seedling emergence) are beneficial for improving the phytoremediation efficiency of sunflower. The increase of root biomass expanded the contact area between plants and soil, which was one of the reasons for the increase of Cd accumulation. EC could be used as a supplementary index to improve the Freundlich model when using pH.

中文翻译：

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利用改进的 Freundlich 模型研究碱性土壤中低分子量有机酸增强向日葵中 Cd 的积累

目的

本研究旨在提高向日葵植物修复土壤中镉的效率，优化植物对镉的吸收模型。

方法

五种低分子量有机酸 (LMWOA)、草酸 (OA)、乙酸 (AA)、酒石酸 (TA)、苹果酸 (MA) 和柠檬酸 (CA)，浓度为 2、4 和 6 mmol/kg ，分别在种子出苗后 20、30 和 40 天施用于向日葵。对pH值、电导率(EC)、总氮(TN)、总磷(TP)、过氧化氢酶活性、淀粉酶活性、转化酶活性、根际土壤Cd和植物组织Cd含量进行了分析。

结果

在 2 和 4 mmol/kg 的施用率下，植物生物量更大。每次酸处理，根和叶中Cd含量增加，而茎和芽中Cd含量下降。由于植物生物量的增加，特别是根组织的增加，Cd 的总积累量增加；在出苗后 20 或 30 天施用 LMWOA 通过扩大根际土壤的 Cd 吸收能力实现了更高的 Cd 积累。施用时间对植物生物量、Cd 含量和植物组织中积累的影响比 LMWOA 的变化更显着。土壤转化酶活性和 pH 值是导致 Cd 形态变化的主要因素。使用土壤 EC 和 pH 值的改进 Freundlich 模型比单独使用 pH 值的模型具有更高的准确度。

结论

LMWOA可以增加植物体内Cd的积累，较低的施用量（2 mmol/kg）和较早的施用日期（出苗后20天）有利于提高向日葵的植物修复效率。根系生物量的增加扩大了植物与土壤的接触面积，是Cd积累增加的原因之一。EC 可作为补充指标，在使用 pH 时改进 Freundlich 模型。