Heavy metal pollution of soil, especially by lead (Pb) and cadmium (Cd), is a serious problem worldwide. The application of safe chelating agents, combined with the growing of tolerant trees, constitutes an approach for phytoremediation of heavy-metal-contaminated soil. This study aimed to determine whether the two safe chelators, tetrasodium glutamate diacetate (GLDA) and citric acid (CA), could improve the phytoremediation capacity of black locust (Robinia pseudoacacia L.) in a Pb-Cd-contaminated soil and to find the key factors affecting biomass accumulation of stressed black locust. In Pb- and Cd-stressed black locust plants, medium and high concentration GLDA treatment inhibited growth, chlorophyll synthesis, and maximum photochemical efficiency (Fv/Fm), promoted the absorption of Pb and Cd ions, and resulted in shrinkage of chloroplasts and starch grains, compared to those in Pb- and Cd-stressed plants not treated with GLDA. The effects of CA on plant growth, ion absorption, chlorophyll content, chlorophyll fluorescence, and organelle size were significantly weaker than those of GLDA. The effect of both agents on Cd absorption was greater than that on Pb absorption in all treatments. The levels of chlorophyll a and plant tissue Cd, and rates of starch metabolism, were identified as key factors affecting plant biomass accumulation in GLDA and CA treatments. In the future, GLDA can be combined with functional bacteria and/or growth promoters to promote the growth of Pb- and Cd-stressed plants, and further improve soil restoration efficiency following pollution by heavy metals. Application of CA combined with the growing of black locust plants has great potential for restoring Cd-polluted soil. These findings also provide insights into the practical use of GLDA and CA in phytoremediation by R. pseudoacacia and the tolerant mechanisms of R. pseudoacacia to Pb-Cd-contaminated soil.

中文翻译：

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外源螯合剂影响铅镉胁迫下刺槐幼苗的生长、生理特性和细胞超微结构。

土壤重金属污染，特别是铅（Pb）和镉（Cd）污染，是世界范围内的一个严重问题。安全螯合剂的应用，结合耐受性树木的种植，构成了重金属污染土壤的植物修复方法。本研究旨在确定两种安全的螯合剂谷氨酸二乙酸四钠 (GLDA) 和柠檬酸 (CA) 是否可以提高 Pb-Cd 污染土壤中刺槐 (Robinia pseudoacacia L.) 的植物修复能力，并寻找影响胁迫刺槐生物量积累的关键因素 在Pb和Cd胁迫的刺槐植物中，中和高浓度GLDA处理抑制生长、叶绿素合成和最大光化学效率（Fv/Fm），促进Pb和Cd离子的吸收，导致叶绿体和淀粉收缩与未经 GLDA 处理的 Pb 和 Cd 胁迫植物中的谷物相比。CA对植物生长、离子吸收、叶绿素含量、叶绿素荧光和细胞器大小的影响明显弱于GLDA。在所有处理中，两种药剂对 Cd 吸收的影响均大于对 Pb 吸收的影响。叶绿素a和植物组织Cd的水平以及淀粉代谢率被确定为影响GLDA和CA处理中植物生物量积累的关键因素。未来，GLDA可以与功能菌和/或生长促进剂结合，促进Pb和Cd胁迫植物的生长，进一步提高重金属污染后的土壤修复效率。CA的施用结合刺槐植物的种植对于镉污染土壤的修复具有巨大的潜力。这些发现还为 GLDA 和 CA 在刺槐植物修复中的实际应用以及刺槐对 Pb-Cd 污染土壤的耐受机制提供了见解。