{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T09:19:38Z","timestamp":1788254378685,"version":"build-2803163510"},"reference-count":36,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,8,28]],"date-time":"2026-08-28T00:00:00Z","timestamp":1787875200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Dongguan Science and Technology of Social Development Program","award":["20231800940372"],"award-info":[{"award-number":["20231800940372"]}]},{"name":"Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion","award":["MATEC2022KF011"],"award-info":[{"award-number":["MATEC2022KF011"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Toxics"],"abstract":"<jats:p>Citric acid (CA) and nitrogen (N) fertilizers have been widely applied to enhance phytoremediation of various contaminated soils, yet their combined effects and underlying mechanisms in cadmium (Cd)\u2013polycyclic aromatic hydrocarbon (PAH) co-contaminated systems remain poorly understood. Here, we investigated the combined effects of CA and ammonium nitrate on the phytoremediation of Cd\u2013phenanthrene (Phe) co-contaminated soil using marigold (Tagetes patula L.), with random forest, mantel tests, and structural equation modeling employed to explore hypothesized pathways and associations. The results demonstrated that combined CA and N application significantly promoted plant growth, Cd uptake, and Phe dissipation. Among the tested treatments, the low-dose combination (1 g CA + 0.1 g N pot\u22121) increased plant biomass by 88%, enhanced shoot Cd uptake by 121%, and achieved a Phe dissipation rate of 76.56%, representing the optimal remediation strategy. Mechanistically, the synergy between CA and N extends beyond simple growth promotion\u2014N drives biomass production and, independently, facilitates Cd mobilization through rhizosphere acidification, while CA enhances contaminant bioavailability and buffers N-induced salt stress, together maintaining rhizosphere ionic homeostasis for efficient Cd translocation and Phe dissipation. This study provides a mechanistic framework for designing combined amendment strategies to enhance phytoremediation of co-contaminated soils.<\/jats:p>","DOI":"10.3390\/toxics14090770","type":"journal-article","created":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T08:31:13Z","timestamp":1788251473000},"page":"770","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The Combined Effects of Citric Acid and Ammonium Nitrate on the Phytoremediation of Cd-Phenanthrene Co-Contaminated Soil Using Marigold"],"prefix":"10.3390","volume":"14","author":[{"given":"Xinzhuo","family":"Qian","sequence":"first","affiliation":[{"name":"College of Earth Sciences, Guilin University of Technology, Guilin 541004, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"methodology","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"given":"Ting","family":"Xu","sequence":"additional","affiliation":[{"name":"College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China"},{"name":"Guangxi Kangwanjia Farmland Soil Remediation Co., Nanning 530006, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"investigation","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"}]},{"given":"Xuemei","family":"Zhong","sequence":"additional","affiliation":[{"name":"College of Earth Sciences, Guilin University of Technology, Guilin 541004, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"writing-review-editing","vocabulary":"credit"}]},{"given":"Weijin","family":"Zheng","sequence":"additional","affiliation":[{"name":"Research Center for Eco-Environmental Engineering, Dongguan University of Technology, Dongguan 523808, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"}]},{"given":"Lizhu","family":"Yuan","sequence":"additional","affiliation":[{"name":"Research Center for Eco-Environmental Engineering, Dongguan University of Technology, Dongguan 523808, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"funding-acquisition","vocabulary":"credit"}]},{"given":"Bo","family":"Song","sequence":"additional","affiliation":[{"name":"College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"data-curation","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,28]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"133684","DOI":"10.1016\/j.jhazmat.2024.133684","article-title":"Rice husk and its derived biochar assist phytoremediation of heavy metals and PAHs co-contaminated soils but differently affect bacterial community","volume":"466","author":"Shang","year":"2024","journal-title":"J. Hazard. Mater."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"108","DOI":"10.1016\/j.jhazmat.2018.09.094","article-title":"Improving risk management by using the spatial interaction relationship of heavy metals and PAHs in urban soil","volume":"364","author":"Wu","year":"2019","journal-title":"J. Hazard. Mater."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"118556","DOI":"10.1016\/j.ecoenv.2025.118556","article-title":"Effects of exogenous organic acids on cadmium accumulation and cell wall components of Cosmos bipinnatus under cadmium stress","volume":"302","author":"Yu","year":"2025","journal-title":"Ecotoxicol. Environ. Saf."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Yuan, L., Qian, X., Zheng, W., Chen, X., Lv, B., Zhong, X., and Wong, J.W.C. (2026). Mineral elements-mediated responses govern cadmium accumulation in plants under C14 alkane stress. Front. Microbiol., 17.","DOI":"10.3389\/fmicb.2026.1830534"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"117140","DOI":"10.1016\/j.jece.2025.117140","article-title":"Effects of wheat straw biochar with different proportions on phytoremediation efficiency and microbial communities of PAH-contaminated soils","volume":"13","author":"Ma","year":"2025","journal-title":"J. Environ. Chem. Eng."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"133169","DOI":"10.1016\/j.cej.2021.133169","article-title":"Remediation of emerging contaminated sites due to uncontrolled e-waste recycling","volume":"430","author":"Lin","year":"2022","journal-title":"Chem. Eng. J."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"506","DOI":"10.1016\/j.jhazmat.2007.07.014","article-title":"Accumulation of polycyclic aromatic hydrocarbons and heavy metals in lettuce grown in the soils contaminated with long-term wastewater irrigation","volume":"152","author":"Khan","year":"2008","journal-title":"J. Hazard. Mater."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"145973","DOI":"10.1016\/j.jclepro.2025.145973","article-title":"A novel slow-release citric acid for enhancing the phytoremediation of uranium-contaminated soil by Indian mustard (Brassica juncea L.) and ryegrass (Lolium perenne L.)","volume":"519","author":"Yang","year":"2025","journal-title":"J. Clean. Prod."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"10283","DOI":"10.1038\/s41467-025-65191-3","article-title":"Identification of a PFAS hyperaccumulator and elucidation of its translocation mechanism for sustainable phytoremediation","volume":"16","author":"Guo","year":"2025","journal-title":"Nat. Commun."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"138750","DOI":"10.1016\/j.jhazmat.2025.138750","article-title":"Individual and combined inoculation of plant growth-promoting endophytic bacteria enhance Ricinus communis L. to remediate Cu\/Cd polluted soil","volume":"494","author":"Li","year":"2025","journal-title":"J. Hazard. Mater."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"136479","DOI":"10.1016\/j.jhazmat.2024.136479","article-title":"Synergistic promotion mechanism and structure-function relationship of nonmetallic atoms doped carbon nanodots driving Tagetes patula L. to remediate cadmium-contaminated soils","volume":"480","author":"Xing","year":"2024","journal-title":"J. Hazard. Mater."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"117551","DOI":"10.1016\/j.ecoenv.2024.117551","article-title":"Exogenous organic acids promoted phytoremediation by Hydrangea macrophylla in cadmium-contaminated soil","volume":"290","author":"Song","year":"2025","journal-title":"Ecotoxicol. Environ. Saf."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"123164","DOI":"10.1016\/j.indcrop.2026.123164","article-title":"Regulation mechanisms of the combined addition of nitrogen fertilizer and nitrification inhibitor on phytoremediation efficiency and greenhouse gas emissions in heavy metal contaminated soil: A field study","volume":"244","author":"Zhang","year":"2026","journal-title":"Ind. Crops Prod."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"100957","DOI":"10.1016\/j.eti.2020.100957","article-title":"The impact of low molecular weight organic acids from plants with C3 and C4 photosystems on the rhizoremediation of polycyclic aromatic hydrocarbons contaminated soil","volume":"19","author":"Sivaram","year":"2020","journal-title":"Environ. Technol. Innov."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"383","DOI":"10.1080\/15226514.2019.1663488","article-title":"Phytoextraction of cadmium-contaminated soils: Comparison of plant species and low molecular weight organic acids","volume":"22","author":"Yu","year":"2020","journal-title":"Int. J. Phytoremediat."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"129034","DOI":"10.1016\/j.jhazmat.2022.129034","article-title":"Nitrogen addition enhanced the polycyclic aromatic hydrocarbons dissipation through increasing the abundance of related degrading genes in the soils","volume":"435","author":"Wang","year":"2022","journal-title":"J. Hazard. Mater."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"150610","DOI":"10.1016\/j.scitotenv.2021.150610","article-title":"Nitrogen addition facilitates phytoremediation of PAH-Cd cocontaminated dumpsite soil by altering alfalfa growth and rhizosphere communities","volume":"806","author":"Li","year":"2022","journal-title":"Sci. Total Environ."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/BF00015405","article-title":"Effects of inorganic nitrogen application on the dynamics of the soil solution composition in the root zone of maize","volume":"180","author":"Yanai","year":"1996","journal-title":"Plant Soil"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"100212","DOI":"10.1016\/j.crbiot.2024.100212","article-title":"Efficient phytoremediation of Cd-contaminated soils by Tagetes patula L.: Greenhouse experiment, field study and meta-analysis","volume":"7","author":"Yuan","year":"2024","journal-title":"Curr. Res. Biotechnol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"100202","DOI":"10.1016\/j.crbiot.2024.100202","article-title":"Coupling electrokinetic remediation with ryegrass for the synergistic remediation of Cd and C14 alkane co-contaminated soil","volume":"7","author":"Yuan","year":"2024","journal-title":"Curr. Res. Biotechnol."},{"key":"ref_21","unstructured":"(2018). Soil Environmental Quality\u2014Risk Control Standard for Soil Contamination of Agricultural Land (Standard No. GB 15618-2018)."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"138826","DOI":"10.1016\/j.jhazmat.2025.138826","article-title":"Comprehensive multi-omics integration to unravel poplar molecular responses to a phenanthrene contamination gradient","volume":"495","author":"Gallois","year":"2025","journal-title":"J. Hazard. Mater."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"109382","DOI":"10.1016\/j.ecoenv.2019.109382","article-title":"Soil phenanthrene phytoremediation capacity in bacteria-assisted Spartina densiflora","volume":"182","author":"Cox","year":"2019","journal-title":"Ecotoxicol. Environ. Saf."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"111290","DOI":"10.1016\/j.envres.2021.111290","article-title":"Influence of electrical fields enhanced phytoremediation of multi-metal contaminated soil on soil parameters and plants uptake in different soil sections","volume":"198","author":"Yuan","year":"2021","journal-title":"Environ. Res."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"124564","DOI":"10.1016\/j.envres.2026.124564","article-title":"Cadmium-containing straw return obstructs carbon storage and aggravates nitrogen deficiency in paddy soils","volume":"302","author":"Huang","year":"2026","journal-title":"Environ. Res."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"2531","DOI":"10.1080\/10643389.2013.829764","article-title":"Enhanced phytoremediation: A review of low molecular weight organic acids and surfactants used as amendments","volume":"44","author":"Agnello","year":"2014","journal-title":"Crit. Rev. Environ. Sci. Technol."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"4038","DOI":"10.1093\/jxb\/erab019","article-title":"Organic acids: Versatile stress-response roles in plants","volume":"72","author":"Panchal","year":"2021","journal-title":"J. Exp. Bot."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"20484","DOI":"10.1021\/acs.est.5c04872","article-title":"Tissue-Specific Metabolic Reprogramming, Not Anthocyanins, Drives Chromium Tolerance in Brassica rapa","volume":"59","author":"Fang","year":"2025","journal-title":"Environ. Sci. Technol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"121343","DOI":"10.1016\/j.indcrop.2025.121343","article-title":"Engineered sulfur and iron nanoparticles enhance cotton tolerance to lead stress via distinct molecular and physiological strategies","volume":"233","author":"Zhang","year":"2025","journal-title":"Ind. Crops Prod."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"119815","DOI":"10.1016\/j.indcrop.2024.119815","article-title":"Phytoremediation of lead polluted mine soil by synergistic effect of chelating agents and nitrogen in hemp","volume":"222","author":"Deng","year":"2024","journal-title":"Ind. Crops Prod."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"127159","DOI":"10.1016\/j.jhazmat.2021.127159","article-title":"Melatonin alleviates aluminum-induced growth inhibition by modulating carbon and nitrogen metabolism, and reestablishing redox homeostasis in Zea mays L.","volume":"423","author":"Ren","year":"2022","journal-title":"J. Hazard. Mater."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"124102","DOI":"10.1016\/j.envpol.2024.124102","article-title":"Effects of nitrogen regulation on heavy metal phytoextraction efficiency (Leucaena leucocephala): Application of a nitrogen fertilizer and a fungal agent","volume":"355","author":"Liu","year":"2024","journal-title":"Environ. Pollut."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"135186","DOI":"10.1016\/j.scitotenv.2019.135186","article-title":"Regulatory mechanisms of nitrogen (N) on cadmium (Cd) uptake and accumulation in plants: A review","volume":"708","author":"Yang","year":"2020","journal-title":"Sci. Total Environ."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1016\/S0378-3774(98)00116-4","article-title":"Model for assessing impact of salinity on soil water availability and crop yield","volume":"41","author":"Lamsal","year":"1999","journal-title":"Agric. Water Manag."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"2677","DOI":"10.1093\/jxb\/erp119","article-title":"Root-to-shoot Cd translocation via the xylem is the major process determining shoot and grain cadmium accumulation in rice","volume":"60","author":"Uraguchi","year":"2009","journal-title":"J. Exp. Bot."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"923","DOI":"10.1007\/s41748-024-00386-0","article-title":"Enhancing the Phytoextraction of Cd, Cu, Pb, and Zn by Portulaca oleracea in a Heavily Contaminated Soil Using Low Molecular Weight Organic Substances: Is Phytoremediation Viable?","volume":"8","author":"Thalassinos","year":"2024","journal-title":"Earth Syst. Environ."}],"container-title":["Toxics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2305-6304\/14\/9\/770\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,1]],"date-time":"2026-09-01T08:57:23Z","timestamp":1788253043000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2305-6304\/14\/9\/770"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,8,28]]},"references-count":36,"journal-issue":{"issue":"9","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["toxics14090770"],"URL":"https:\/\/doi.org\/10.3390\/toxics14090770","relation":{},"ISSN":["2305-6304"],"issn-type":[{"value":"2305-6304","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,8,28]]}}}