Temporal and spatial differentiation characteristics of soil arsenic during the remediation process of Pteris vittata L. and Citrus reticulata Blanco intercropping.

The intercropping of hyperaccumulators and fruit trees has great application prospects owing to its environmental and economic benefits. However, the variation tendency and spatial distribution characteristics of pollutants in soil are unclear. A 19-month pot positioning experiment was conducted to clarify the spatio-temporal characteristics of arsenic (As) during Pteris vittata L.-Citrus reticulata Blanco intercropping process. The results showed that: (1) In the early stage, the solubilization of soil As by P. vittata was dominant. At 3 months, the water-soluble As in P. vittata rhizosphere soil increased by 19.4-55.4% compared with the initial state. In the later stage, the As extraction from soil by P. vittata was dominant. At 19 months, the water-soluble As in P. vittata rhizosphere soil decreased by 24.6-71.2% compared with the initial state. The water-soluble As in C. reticulata rhizosphere soil in intercropping, under the role of P. vittata, reached 1.75-2.35 times that of monoculture at 7 months, and was not significantly different from that of monoculture at 19 months. (2) The spatial distribution characteristics of soil As, affected by As-hyperaccumulation of P. vittata, showed that the As variability of intercropping and P. vittata monoculture was greater than that of C. reticulata monoculture. The area of P. vittata remediating soil was approximately 15 cm horizontally around its planting point and at least 25 cm vertically. (3) P. vittata-C. reticulata intercropping did not affect the phytoremediation efficiency and effectively reduced the risk of As pollution for C. reticulata. The As concentration in C. reticulata leaves of open intercropping decreased by 39.0-64.2% (early-maturity) and 25.6-59.1% (late-maturity) compared with that of monoculture, similar to that in clean soil. This study analyzed the As migration characteristics during P. vittata-C. reticulata intercropping through time and space and provides important theoretical support for the remediation and safe use of As-contaminated farmland.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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