Multiple human-mediated introductions shape the disjunct distribution of an invasive weed Amaranthus palmeri in China

doi:10.1016/j.jia.2026.01.011

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Multiple human-mediated introductions shape the disjunct distribution of an invasive weed Amaranthus palmeri in China

Jingjing Cao¹^*, Yongpan Qian¹^*, Jianying Guo¹,Hongwei Wang², Jianguo Fu³, Yibo Zhang¹, Wanxue Liu¹,Fanghao Wan¹, Rui Wang¹^#

¹ State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China

² College of Plant Protection, Henan Agricultural University, Zhengzhou 450002, China

³ Animal, Plant and Food Inspection Center, Nanjing Customs, Nanjing 210019, China

Highlights

1.Trade-mediated propagules serve as direct genetic proxies, overcoming the limitation of unsampled native sources in invasion pathway reconstruction.

2.Multiple human-mediated introductions, not secondary spread from the initial introduction, dominate the genetically diverse and disjunct distribution of Amaranthus palmeri in China.

3.Soybean import volume predicts local genetic richness, highlighting the role of trade-driven propagule pressure in shaping invasion hotspots.

Abstract
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摘要

生物入侵对全球农业、粮食安全及自然生态系统构成严峻威胁，而国际贸易日益频繁，其网络也持续拓展，正持续加剧这一风险。以经由国际农产品贸易入侵的恶性杂草长芒苋（Amaranthus palmeri）为例，其在中国形成的广域不连续分布格局，其成因指向入侵生物学的一个核心问题：此类分布究竟源于初始入侵点的桥头堡式二次扩散，还是由人类活动介导的多次独立传入所致？为阐明其异质性分布格局的形成机制，本研究整合遗传学与稳定同位素地理溯源技术，系统检验了上述两种假说。创新性地将国际贸易中截获的繁殖体（混杂于进口大豆中的种子）作为源种群的动态遗传代表样本，并结合碳、氮稳定同位素指纹进行来源验证，克服了在广阔来源地直接采样的难题。通过对中国24个地理隔离种群（784株）及从美国、阿根廷和巴西进口大豆中收集的410粒种子进行叶绿体DNA测序分析，发现中国实地采集种群的核苷酸多样性（π = (0.78 ± 0.18) × 10^-3）和单倍型多样性（Hd = 0.47 ± 0.04）均显著高于首次发现的北京南苑种群及来自美国来源区域的繁殖体集合，且拥有更为丰富的单倍型（31个）。种群遗传结构分析显示，南苑种群与中国多数实地种群存在显著遗传分化（F_ST > 0.20），其遗传影响仅限于本地，未能构成全国性入侵的桥头堡来源。中性检验与多峰型错配分布表明，这些中国种群未经历近期扩张或选择，其遗传特征更接近来源地稳定的大种群。尤为重要的是，港口地区的单倍型丰富度与当地历史大豆进口量呈显著正相关（r = 0.59，P < 0.05），而种群间遗传距离与环境因子无显著关联。综上，长芒苋在中国的间断分布并非由初始入侵点的二次扩散导致，而是主要由与国际大豆贸易相关的、反复发生的、跨洲际的多次独立人类介导引入所驱动。本研究构建了一套基于贸易介导入侵植物繁殖体的入侵路径重建新框架，不仅阐明了特定入侵案例的机制，也为全球化贸易时代实施源头管控、制定精准生物安全策略提供了关键科学依据与研究方法。

Abstract

A central challenge in invasion biology is to determine whether disjunct distributions of invasive species stem from secondary spread from an initial introduction bridgehead or from recurrent, human-mediated introductions. The devastating alien weed Amaranthus palmeri, with its large-scale disjunct distribution across China, provides an ideal system to address this question. We tested the competing hypotheses of bridgehead-mediated expansion (originating from the initial introduction in Beijing, 1985) versus multiple independent introductions. By integrating genetic analyses with stable isotope geolocation, we treated propagules from imported soybean shipments as direct, traceable links to potential source populations. Newly field-collected populations in China harbored significantly higher nucleotide diversity (π=(0.78 ± 0.18) × 10^-3) and haplotype diversity (Hd = 0.47 ± 0.04) than both the initial introduced population and the pooled propagules from the primary source, the United States (US). Significant genetic differentiation (F_ST > 0.20) was observed both among newly field-established populations and between them and the initial introduction. Non-significant neutrality tests, coupled with multimodal mismatch distributions (Raggedness index = 0.0946, P > 0.05), indicated that these populations did not undergo a recent demographic expansion or selection. Genetic diversity and structure correlated with regional soybean import volume (r = 0.59, P < 0.05) but not with environmental distance (Mantel r = 0.24, P > 0.05). Our findings demonstrate that recurrent transcontinental introductions, mediated by global grain trade, are the dominant force shaping the genetic pattern and invasion process. This study provides a framework for reconstructing invasion pathways and highlights the need for proactive, source-targeted biosecurity strategies to manage invasions in the Anthropocene.

Keywords: Amaranthus palmeri transboundary dispersal multiple introductions bridgehead effect invasion pathways grain trade agricultural biosecurity

Online: 13 January 2026

Fund:

This research was supported by grants from National Key R&D Program of China (2022YFC2601000, 2022YFC2601100) and the National Nature Science Foundation of China (32272569, 32402403, 31471827).

About author: Jingjing Cao, E-mail: caojingjing319@163.com; Yongpan Qian, E-mail: 15666501468@163.com; #Correspondence Rui Wang, E-mail: wangrui@caas.cn * These authors contributed equally to this work

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Jingjing Cao, Yongpan Qian, Jianying Guo, Hongwei Wang, Jianguo Fu, Yibo Zhang, Wanxue Liu, Fanghao Wan, Rui Wang. 2026. Multiple human-mediated introductions shape the disjunct distribution of an invasive weed Amaranthus palmeri in China. Journal of Integrative Agriculture, Doi:10.1016/j.jia.2026.01.011

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