Plant Invasion Driven by Heavy Metals and Microplastics: From Mechanisms to Agroecological Management Implications

Abstract

Biological invasions and environmental pollution are the two primary threats facing contemporary agricultural ecosystems, and their interaction exacerbates agroecological risks and undermines agricultural sustainability. This study was conducted to systematically elucidate how heavy metals (HMs) and microplastics (MPs) alter the relative advantages of invasive plants in ecosystems, clarify the ecological processes involved, and propose recommendations for the protection of farmland ecosystems. The main conclusions are as follows: (1) Pollution acts as an environmental filter that negatively affects native species, including crops, while creating relative advantages for invasive plants with high tolerance and adaptive physiological mechanisms. (2) Pollution stress enables invasive plants to gain a competitive advantage over native plants through highly plastic resource allocation strategies, prioritization of growth, and more powerful allelopathic effects. (3) Pollution systematically amplifies the advantage of invasive plants by altering the strength of plant–soil feedback (PSF) and driving the restructuring of rhizosphere microbial communities. (4) Invasive plants can be used to produce biochar, which can then be applied in farmland ecosystems for the control of invasive plants and remediation of soil pollution. The framework constructed in this study indicates that heavy metal and microplastic pollution may enhance the invasion of alien plants, posing a serious threat to agroecosystem health and food security. However, using invasive plants as feedstock to produce biochar may offer a solution to the intertwined challenges of plant invasion and environmental pollution.

1. Introduction

Biological invasions and environmental pollution are two convergent major threats facing contemporary agricultural ecosystems that deeply impact both ecological security and agricultural production. These two crises are intensifying, primarily due to the environmental disturbance caused by increasing human activity in the context of the Anthropocene [1]. Environmental pollution, notably from heavy metals (HMs) and microplastics (MPs), has become widely accumulated in global farmland soils, emerging as a critical abiotic stress factor. Research indicates that approximately 14% to 17% of agricultural soils worldwide are contaminated with HMs, most of which are from agricultural application of sewage sludge produced by industrial activities, along with agricultural pesticides and fertilizers [2,3]. MPs are an emerging contaminant originating primarily from agricultural plastic sheeting and other industrial or domestic sources. They leach into the soil following the abrasion of these agricultural plastic films [4]. HMs and MPs can be absorbed by plants from the soil through the roots [5,6], while leaves may also absorb pollutants from atmospheric deposition via stomata or the cuticle, posing increasing risks from residue in farmlands [7,8,9,10]. These two types of pollutants can exert multilevel inhibitory effects on plant growth by interfering with physiological processes, metabolic balance, and molecular regulatory networks [11]. Concurrently, global economic integration and trade have accelerated the transboundary spread of species, diversifying invasion pathways and expanding their scale [12,13]. On a global scale, biological invasions have been recognized as one of the primary drivers of biodiversity loss and ecosystem degradation [14]. Research has shown that the global annual cost of invasive species is estimated at USD 420 billion, and continues to increase. Agricultural departments were the bearers of the greatest cost due to invasive species in at least 37% of the countries assessed [15,16].

Instead of isolating species, pollution produced by humans often creates “opportunity windows” for biological invasions [17]. More evidence suggests that, under the stress of HM and MP pollution, invasive plants frequently exhibit higher tolerance and adaptive capacity compared to native plants [18,19]. The mechanisms by which HMs and MPs drive plant invasions are complex and multifaceted. For instance, invasive plants can sustain growth under pollution stress by enhancing antioxidant defenses, regulating metal transport and vacuolar sequestration, and modifying biomass allocation strategies [20]. This suggests that HMs and MPs may not impose equal ecological pressure on invasive and native plants. They not only directly affect individual plants but also profoundly alter the plant–soil feedback (PSF) system by reshaping soil physicochemical properties and microbial community structure [21]. Moreover, MPs can act as vectors for HMs, modifying their bioavailability and thereby producing synergistic ecological effects [22].

Although the research in this area is growing, our current understanding remains fragmented. Findings often vary depending on the study organism, pollution type, and experimental scale employed. Moreover, most previous studies and reviews have only focused on single pollution factors or lack a systematic “environment–plant–microbe” theoretical framework, leaving a gap regarding invasive plant responses to pollution stress and their cascading ecological and agricultural consequences. A literature search of the Web of Science using the keywords “heavy metals”, “microplastics”, “farmland”, and “invasive plants” yielded 403 articles. After excluding articles irrelevant to the topic (ecology/botany/invasive plants), those with duplicate or entirely identical content, low-quality articles (such as insufficient replicates), a total of 134 articles remained for inclusion in this review. This narrative review aims to describe the positive correlation between HMs and MPs and the establishment and spread of invasive plants, and to provide a conceptual framework for developing management and restoration strategies for biological invasions in polluted ecosystems, including agroecosystems.

2. HMs and MPs Establish an Environmental Filter to Shape Pollution-Tolerant Plant Communities

2.1. The Pollution Filter Exerts Asymmetric Filtering on Invasive Plants and Native Plants

Environmental factors function as an environmental filter by differentially selecting for plants based on their physiological tolerance and functional traits [23]. HMs such as Cd, Cr, and Pb exert systemic impacts on plant physiological homeostasis by interfering with photosynthesis, inhibiting root development, disrupting cell membrane integrity, and inducing the excessive accumulation of reactive oxygen species (ROS) [24,25,26]. MPs exert their ecological effects on the agroecosystem through both physical and chemical pressures. They alter soil structure, increasing porosity and disrupting water retention capacity, inducing drought-like stress in plants [27]. They can also block seed surfaces or root hair pores, restricting water and nutrient uptake and consequently inhibiting seedling emergence and establishment [28]. At the physiological level, MPs induce ROS accumulation, disrupt ion homeostasis, and reduce photosynthetic efficiency, exacerbating plant growth pressure [29].

Under the selective pressure exerted by HMs and MPs, invasives and natives are often affected asymmetrically. Some invasive weeds, such as Pennisetum purpureum, Paspalum dilatatum, Galinsoga quadriradiata, Erigeron canadensis, and Erigeron annuus, are characterized by high tolerance, enabling them to exhibit better growth characteristics in the presence of HMs and MPs, such as increased biomass and survival probabilities [30,31]. Invasive plants have more advantages than native ones due to species specificity. The invasive species Phytolacca americana exhibits a high capacity for Cd bioconcentration and adaptability to Cd pollution in contaminated soils, which is attributed to its high translocation factor [32]. Some invasive weeds possess more effective metal detoxification and vacuolar sequestration mechanisms under HM contamination, decreasing the damage from HMs [20]. However, native plants frequently adopt an avoidance strategy by reducing growth under pollution stress, which might lead to a disadvantage in resource competition [20]. Similarly, studies indicate that MPs exert significant inhibitory effects on the antioxidant activity and biomass accumulation of native plants, whereas their impact on invasive plants is relatively limited [33]. Furthermore, MP particles can block seed pores, negatively affecting the seed germination rate of native plants, while the seed germination of invasive plants was not affected [34].

Admittedly, some native plants are defined as hyperaccumulators and can detoxify HMs, such as Phytolacca acinose [35]. However, studies often ignore the importance of concentration in plants. For instance, the invasive plant Phytolacca americana exhibits more growth advantages than Phytolacca acinose under high Cd pollution stress, which means that native plants may be more sensitive to pollutants than invasive species [36]. It cannot be ruled out that the invasion advantage will decrease when the pollution concentration is extremely high. One study showed that, when the copper concentration reached 2430 mg/kg, both the invasive plant Reynoutria japonica and the native plant Urtica dioica exhibited 100% mortality, indicating that all plants are severely inhibited under extremely high concentrations [37]. The competitive ability of invasive species was reduced under Zn and Cu treatments, but the ultimate outcome of successful invasion remained unchanged, suggesting that the invasion advantage may be weakened at high concentrations [38]. Additionally, the tolerance of different plants to different HMs varies significantly, exhibiting a high degree of species specificity [39,40]. What makes it more complex is the involvement of factors such as the phenotypic plasticity of invasive plants and PSF, making it currently impossible to determine the threshold at which each HM promotes invasion. Moreover, the studies retrieved so far lack investigations on different MP concentrations, and instead mostly simulate highly polluted environments from these two pollutants.

2.2. Competitive Advantages of Invasive Plants Under the Filter

Resource availability significantly influences biomass accumulation and trait multifunctionality in both woody and herbaceous plants [41,42]. However, different plants exhibit varying resource use efficiencies. Globally common crops such as rice, wheat, maize, and soybean often show low resource use efficiency in farmland, typically leading to a high-input but low-return trend in agroecosystems [43]. Studies have shown that invasive plants generally possess higher resource use efficiency than natives [44]. For example, Shi et al. found that the invasive plant Solanum rostratum prefers to adopt the C-strategy in competition, taking resources from native plants, rapidly expanding its population size, and gaining invasive advantages [45]. Environmental fluctuations such as resource pulses are more conducive to the invasion of alien plants such as Conyza canadensis, potentially due to the stronger adaptability of invasive plants to resource variability [46]. Under HM or MP stress, invasive plants tend to allocate more resources towards rapidly increasing plant height and crown width to enhance their spatial preemption capacity [1,47,48]. This is consistent with the predictions of the Evolution of Increased Competitive Ability (EICA) hypothesis [49]. Furthermore, HMs and MPs might significantly influence the resources available in the soil by affecting nutrient flux, cycling, and related gene expression [50,51,52]. This might facilitate the selection of plants with high resource use efficiency, which can pass the environmental filters.

Studies have demonstrated that Amaranthus retroflexus in Cd-contaminated environments, and four invasive weeds (Paspalum dilatatum, Sphagneticola trilobata, Pennisetum purpureum, and Alternanthera philoxeroides) in MP-contaminated environments, exhibit stronger resource acquisition capabilities compared to native plants [40,47]. Their advantages are due to the trait and strategy plasticity of invasive species. At the morphological level, invasive plants exhibit greater plasticity in above-ground and below-ground biomass allocation under pollution stress [53]. For instance, invasives may expand the proportion of root allocated and thickness [54,55] in response to resource patches in soils contaminated with HMs or MPs. The invasive plant counteracts the negative effects of PE-MPs by achieving a higher root-to-shoot ratio and root mass fraction than native plants [56]. Under high-concentration HM pollution, invasive weeds like Alternanthera philoxeroides may reduce biomass allocation to roots to minimize pollutant uptake and alleviate toxicity, while its native congener Alternanthera sessilis lacks this function [57]. Additionally, as the diversity of MPs increases, invasive plants suffer greater negative impacts than native plants, possibly due to their root biomass allocation [54]. The result indicates that the root- and biomass-allocated plasticity of invasives was species- and condition-specific, rather than showing a constant trend. For instance, in the invasive plant Alternanthera philoxeroides, the leaf biomass ratio increased but stolon mass ratio decreased under Cd stress [58]. This specificity of biomass allocation is even manifested at different geographic scales within the same species, as exemplified by Phytolacca americana [59]. Alternatively, when facing copper stress, Alternanthera philoxeroides exhibited two forms of root plasticity, silence and escape; above the threshold of 500 mg/kg, its root length decreased, yet root biomass increased and the belowground root system expanded [60]. Invasive plants may also show plasticity in their leaves and photosynthate. The leaves of invasive grasses might have significantly greater areas, crown width, chlorophyll contents, and photosystem II efficiency, thereby enhancing light capture and utilization [30,38]. Similarly, the invasive plant Ageratina adenophora can maintain basic N allocation by adjusting photosynthetic pigment ratios and energy allocation rather than pursuing maximum photosynthetic rates, providing a continuous energy source for individual growth [61]. This again shows that the plasticity of invasives is specific, which might indicate that Ageratina adenophora is also stronger and more flexible than native species.

The Novel Weapons Hypothesis (NWH) proposes that native species are sensitive to the allelochemicals of alien plants, conferring a stronger competitive advantage to invasive populations in the introduced range than in their native range [62]. Notably, HMs and MPs might modify patterns of plant–plant interactions, particularly through allelopathy as a competitive defense tool. Research indicates that HM or MP stress may enhance the synthesis and release of allelochemicals in some invasive plants such as Phytolacca americana, Alternanthera philoxeroides and Lactuca sativa as a response to pest and disease pressure, while simultaneously inhibiting the physiological activities of neighboring plants [63,64,65]. Research has shown that Cu and Pb can significantly intensify the independent allelopathy of Solidago canadensis and the co-allelopathy of two invasive Asteraceae species but weaken the independent allelopathy of Conyza canadensis [39]. Importantly, these secondary metabolites may persist in the soil and function for extended periods due to the strong adsorption capacity of MPs or the chelation of HM ions, creating more opportunities for invasive species to establish a growth advantage [66,67]. However, under Cd stress, the enhanced insect resistance of Alternanthera philoxeroides is mainly attributed to Cd accumulation and mechanical defense, rather than changes in leaf-specialized metabolites (including allelochemicals) [68]. This implies that allelochemicals remain unchanged, but the defense strategy differs, which indicates that the allelochemical plasticity of invasive plants was also specificity.

2.3. Invasive Plants Expand Their Advantage by Reshaping the Rhizosphere Microenvironment

Rhizosphere microorganisms and nutrients profoundly affect plant growth, defense, and competition through PSF [69,70]. However, the effects of soil microorganisms on different plants are unequal. The feedback relationship between plants and microbiomes in the soil can facilitate invasive species while inhibiting natives, an idea known as the Enhanced Mutualism Hypothesis (EMH) [71,72,73,74]. A global meta-analysis showed that HMs significantly alter soil SOC, soil enzyme activities, microbial diversity, microbial respiration, and microbial biomass carbon, which may disturb soil environmental and microbial activity [75,76]. The structure of the soil microbiome and environment is also disturbed by MPs, which can reduce bacterial biodiversity, change soil pore structure, and reduce water retention capacity. They can even establish a special microecosystem known as the “Plastisphere” [77,78,79]. Furthermore, invasive plants can disrupt the native plant rhizosphere microbial mutualistic network, causing natives to fall into a competitive disadvantage [80]. Some evidence indicates that invasive plants may have more advantages than natives under polluted conditions. For instance, the invasive plant Phytolacca americana can cope with Mn pollution by modulating the composition of its root volatile organic compounds (VOCs) and recruiting pollution-tolerant microbes such as Bacillus [81]. By comparing the PSF indices (home/away) under different Cd concentrations, it was found that the PSF of the invasive species Phytolacca americana remained consistently near 0, whereas in native species it increased with rising Cd concentration, and its minimum value remained above 0. This indicates that Cd pollution significantly amplifies the relative difference in PSF indices between these two species, demonstrating at the PSF level that the presence of Cd may increase invasion advantage [36]. Erigeron canadensis also becomes more resistant to Cd and Pb by altering the rhizosphere microbial community and recruiting key taxa with metal resistance and plant growth-promoting abilities, including Lysobacter, Corynebacterium, Humicola, and Colletotrichum [82]. Additionally, under PVC-MP and PLA-MP stress, invasive plants selectively enriched Arthrobacter, Sphingomonas, Microvirga, and Azospirillum in their rhizosphere, which can enhance the tolerance of invasive plants to MP stress [31]. These studies suggest that PSF is a key indicator that increases the advantages of invasive plants under pollution stress.

In addition, soil properties can influence pollutants. For example, a field study showed that soil pH was positively correlated with Cd and As concentrations, affecting metal bioavailability, plant uptake, and PSF processes [79,83]. Soil organic matter and nutrient elements such as N, P, and K increased with the invasion of Prosopis juliflora, while HMs contents in the soil decreased, which may be related to legume specificity and root adsorption [36]. Furthermore, soil texture also profoundly influences the spatial distribution of HMs, mainly due to the adsorptive capacity of clay [84]. Research indicates that changes in soil salinity caused by reclamation increase the accumulation of Cr, Cu, Pb, and Zn in Spartina alterniflora and Phragmites australis [85]. Moreover, a higher proportion of clay leads to greater retention of MPs in sediments [86]. Therefore, soil properties such as pH, nutrients, organic matter, clay proportion, and salinity all affect the spatial distribution and bioavailability of heavy metals in soil, thereby complicating the filtering of invasive and native plants by pollutant-shaped environmental filters.

2.4. Combined Pollution Stress Shapes a Stronger Filter, but the Direction of Invasion Is Uncertain

Whether in the natural environment or farmland, HMs and MPs do not act on their own but often co-act as combined pollutants, causing more severe ecological and agricultural crises [87]. In facility agriculture, the coexistence of HMs and MPs is far from a simple additive state, and involves complex physical, chemical, and biological interactions, significantly affecting each other’s migration and transformation pathways as well as overall ecotoxicity [88]. Due to their large specific surface area and diverse surface functional groups, MPs can absorb HMs such as Cd, Pb, and Zn, modifying their mobility and bioavailability in soil and water [89,90]. This complexity renders combined pollution a central challenge in understanding and predicting farmland invasion dynamics, as well as in assessing ecological risks. Javed indicated that Cd weakens the competitiveness of native species, creating favorable conditions for invasive plants, which has been verified under conditions of single pollutants (MPs or Cd) as well as combined MP-Cd pollution [91]. However, some studies have shown different results. Feng found that the presence of MPs suppresses the contribution of Cd to invasion success [92]. Due to the scarcity of literature that simultaneously contains the keywords “heavy metals”, “microplastics”, and “invasive plants”, it is currently not possible for us to determine whether the combined pollution of HMs and MPs has a positive or negative effect on the invasive success of alien plants. Notably, the combined pollution of HMs and MPs does increase toxicity to plants, demonstrating that the environmental filtering effect remains under stress [93]. MPs cause the actual exposure levels of plants and microorganisms to HMs to deviate from predictions based on single-pollutant conditions [94]. Consequently, traditional prediction methods based on pollution intensity or species traits struggle to accurately capture invasion potential under combined pollution scenarios [95,96].

2.5. A Conceptual Model of Environmental Filters for the Facilitation of Invasion by HMs and MPs: Taking Agroecosystems as an Example

Farmland was chosen as an example primarily because agroecosystems are more prone to biological invasions than other ecosystems [97,98]. Agroecosystems have suffered from intense human disturbance for a long time, which is a key reason why it is prone to invasion [99,100]. Moreover, crops in farmland are often monotonous, with low levels of biodiversity, which also makes alien plants more likely to thrive and spread rampantly in agricultural fields, according to the Biotic Resistance Hypothesis (BRH) [101]. Additionally, agricultural fertilization results in significantly higher soil nitrogen and phosphorus levels than in natural habitats, enabling many invasive plants to rapidly exploit these enriched resources and thereby suppress native plants in competition [102,103].

Synthesizing the preceding sections, we construct a conceptual mechanistic framework illustrating how pollution drives biological invasions in agroecosystems (Figure 1). This framework emphasizes that, within farmland environments, HM and MP contamination systematically facilitates the colonization and expansion of invasive weeds through a series of mutually reinforcing ecological processes, ultimately threatening agricultural production. Firstly, HM and MP pollution acts as an environmental filter, screening the farmland biotic community. High-intensity pollution stress eliminates crops and native plants with weak tolerance, while creating survival opportunities for invasive weeds equipped with pollutant tolerance and adaptive mechanisms, altering the initial composition of field vegetation. Secondly, pollution stress reshapes the rules of interspecific competition within farmlands. Leveraging their highly plastic resource allocation strategies, growth-prioritizing tactics, and potentially enhanced allelopathic effects, invasive weeds can gain an advantage under HMs and MPs, progressively encroaching upon the living space of crops. More importantly, pollution further amplifies this invasive advantage through PSF mechanisms. Pollution-induced changes in the soil environment drive the restructuring of rhizosphere microbial communities. Invasive weeds are often capable of domesticating or attracting pollution-tolerant microorganisms that help alleviate stress and facilitate nutrient acquisition, establishing positive feedback. These processes form self-reinforcing positive feedback over temporal scales. This feedback progressively diminishes the resistance and resilience of farmland ecosystems to subsequent disturbances, rendering contaminated farmlands not only more susceptible to invasion but also, once occupied by invasive weeds, increasingly difficult to restore to a crop-dominated healthy state. Such farmland may become trapped in a long-term vicious cycle, severely undermining land productivity for agriculture and the capacity to deliver ecological services.

3. Invasive Plant Management and Potential Application Value

3.1. Control Strategies for Alien Invasive Plants

Given the significant threat that invasive plants pose to ecosystems, including farmland, research related to the prevention and control of alien plant invasions has gradually increased. The use of chemical methods, such as clopyralid, can effectively suppress the invasive grass Hieracium caespitosum and successfully restore the competitive ability of native grasses, increasing their cover by 7–65% [104]. However, chemical control may pose risks to the environment, impair soil nitrogen fixation, and exacerbate the hazards of microplastics, posing a serious threat to food security [105,106]. A study has shown that the application of selective herbicides may lead to the emergence of other invasive species and require long-term spraying management [107]. The use of biological methods may reduce environmental pollution; for example, the Sclerotium rolfsii SC64 strain effectively controls Solidago canadensis and significantly restores biodiversity during the process [108]. Alternatively, natural enemies of invasive plants can be utilized. In Australia, researchers have explored the use of D. quadrijuga, a natural enemy of H. amplexicaule in its native range, as a biocontrol agent because it has shown effective local suppression of the plant’s populations [109]. However, if not properly managed, biological control can cause even more severe ecological crises. Due to the lack of corresponding resistance in native species, specialist pathogens from the native range may preferentially infect native species, or may spread from invasive plants to natives and crops, leading to disease outbreaks with serious ecological and economic consequences [110]. Even the introduction of insects can result in enemy spillover effects, severely endangering ecological security [111]. Mechanical or physical methods, such as regular mowing, can suppress invasive plants like Erigeron annuus and Solidago canadensis [112,113]. The manual uprooting of Datura stramonium by farmers can also reduce the harm caused by invasive plants in farmlands [114]. Such approaches are environmentally friendly but have low efficiency and may require more monitoring and management measures for agricultural invasive species, for example, by using machine learning combined with human footprint data to predict high-risk areas [115]. Promoting sustainable agricultural activities and reducing suitable habitats for invasive plants and effectively prevents weed infestation in farmlands through intercropping [115,116].

Furthermore, controlling cultivation methods and farm size is also crucial. Large-scale farms practicing monoculture are more susceptible to specific invasive plants [117,118], and on some farms, the use of the same herbicide across multiple crop cycles makes the emergence of “superweeds” more likely [119]. Mechanized farming facilitates the spread of invasive plants. For example, Galzania can be rapidly spread across vast areas by heavy machinery [120].

3.2. Invasive Plants as Valuable Resources: Potential Benefits for Crops and the Remediation of HMs and MPs Pollution

The contributions of invasive plants to agriculture are not entirely negative. Endophytes isolated from certain invasive plants, such as Phragmites australis, can promote rice growth [121]. Composting using Ageratina adenophora as a raw material can promote barley growth [122]. Additionally, some research has indicated that invasive species can be used to remediate environmental pollution. For instance, Bidens pilosa and Lantana camara have been demonstrated to absorb and accumulate heavy metals such as Cu, Zn, and Cd from contaminated soils [123,124]. However, this method may pose serious ecological uncontrollability. The invasives may escape from treatment sites and further encroach upon the living space of native plants (including crops) in surrounding farmlands, exacerbating the simplification of farmland community structure and biodiversity loss [125,126]. Conversely, biochar produced from invasive plants may provide enhanced risk manageability and be more eco-friendly, effectively reducing pollution. The addition of biochar derived from Alternanthera philoxeroides can reduce HMs, particularly Cd, in livestock sludge [127]. Biochar produced from Mikania micrantha and Parthenium hysterophorus can effectively alleviate Cd toxicity in cereal crops such as wheat [128,129]. Furthermore, a biochar composite material primarily made from Ageratina adenophora can remove over 65% of Cd from farmlands [130]. Moreover, the Cd ion removal efficiency of such invasive plant-derived biochar even increases with the diversity of the invasive plants used [131]. Biochar prepared from the invasive plant Solidago canadensis L. and applied to agricultural soil contaminated with PE-MPs and PLA-MPs can increase microbial biomass, inorganic nitrogen, and enzyme activities [132].

3.3. Invasive Plants in Farmlands May Foster a Sustainable Positive Cycle of Agroecosystems Centered on Income Generation: A Conceptual Model

Given the strong soil remediation capacity and crop detoxification and yield-enhancing effects, as well as the promising application prospects and economic benefits of biochar derived from invasive plants [133], we propose a positive feedback loop framework centered on income generation, with farmers, farmland and biotechnology companies as key actors, and invasive plants and biochar as the pathways (Figure 2). This framework aims to transform invasive plants from waste into a resource. Farmers actively harvest invasive plants to reduce ecological risks to farmland, creating conditions for subsequent yield-enhancing experiments. They then sell the harvested invasive plants to biotechnology companies, generating direct income as a first revenue stream. The companies produce activated biochar from the invasive plants and sell it back to farmers, while also providing guidance on its application. In this process, companies earn profits and farmers obtain remediation materials. Finally, farmers apply the biochar to remediate contaminated farmlands, which ensures food security, suppresses the reinvasion of exotic plants, increases crop yields, and generates a second income stream from yield gains, while also reducing future harvesting costs.

4. Research Gaps and Future Directions

The conceptual framework of pollution-driven plant invasions constructed in this review provides a systematic perspective for understanding how HM and MP contamination facilitates the alien plants invasion in ecosystems, especially agroecosystems. In addition, we propose a tripartite win-win agricultural management framework centered on invasive plant-derived biochar to reduce farmland pollution while generating income. However, the research area still has several gaps that need to be addressed through future interdisciplinary research.

4.1. The Synergistic or Antagonistic Effects of Combined Pollution Remain Unclear

Although studies have shown that HMs and MPs often co-occur in the environment, the synergistic or antagonistic mechanisms through which they affect invasive plants are still lacking systematic investigation. Existing evidence is even contradictory, indicating that we are currently unable to predict invasion risks under combined pollution. Future research should develop predictive models for invasion risk under combined pollution based on controlled experiments, integrating multiple factors such as the type, concentration, aging degree of HMs and MPs, and soil properties. Machine learning or process-based models for invasion risk prediction should be developed to support early warning in agroecosystems.

4.2. The Threshold Effect Between Pollution Concentration and Invasion Success Has Not Been Quantified

Most current studies employ simulations with high pollution concentrations, and there is a lack of investigation into the variation in invasion advantage across different pollution gradients. Some studies suggest that extremely high concentrations may suppress all plants, indicating the existence of a “promotion–inhibition” threshold, yet the specific threshold under each pollution type remains undetermined. Future efforts should conduct multi-factor, multi-scale, long-term field empirical research, establish cross-regional long-term monitoring networks, and combine controlled experiments with field surveys to explore the spatiotemporal dynamics of pollution-driven invasions.

4.3. Lack of Long-Term Field Observational Data to Validate Successional Trajectories and Management Consequences

Most current conclusions are derived from short-term controlled experiments, which struggle to reflect the long-term dynamics of pollution–invasion interactions under the influence of agricultural cropping cycles, climatic fluctuations, and management practice interventions. Establishing long-term positioning observation studies is crucial for assessing whether pollution-induced invasive advantages will continuously expand, reach equilibrium, or potentially be counteracted by well-adapted pollution-tolerant crop varieties or rotation systems. Such research constitutes an indispensable scientific foundation for predicting the long-term ecological and economic impacts of invasions and for optimizing adaptive farmland management strategies.

4.4. Species Specificity and Geographic Variation Are Underestimated

Different invasive plants exhibit highly species-specific responses to HMs and MPs, and even significant differences exist among different geographic populations of the same species. This specificity poses a challenge to constructing general models. Future research should deeply analyze the molecular mechanisms underlying “plant–microorganism–soil” interactions, using multi-omics techniques such as metagenomics, metabolomics, and transcriptomics to reveal how invasive plants regulate rhizosphere microbial communities under pollution stress, thereby enhancing their adaptability and competitiveness.

4.5. The Synergy Between Pollution-Driven Invasion Management and Resource Utilization Remains to Be Explored

Although invasive plant-derived biochar has shown potential in pollution remediation, its long-term effectiveness, economic feasibility, and ecological safety in real farmland environments have not been systematically evaluated. Future studies should formulate agricultural management strategies under coupled pollution–invasion scenarios, proposing graded management schemes adapted to different pollution levels and invasion pressures, such as buffer strip design, crop rotation adjustments, and timing of biochar application.

5. Conclusions

This study proposes a conceptual model of pollution-driven biological invasion and a tripartite win-win farmland management model centered on biochar. The main conclusions are as follows:

(1)

HMs and MPs, as pollution stressors, shape an environmental filter. Invasive plants, owing to their high tolerance, high competitiveness (primarily driven by their plasticity, high resource use efficiency, and allelochemicals), and rhizosphere-specific enrichment of detoxifying microorganisms, pass through this filter more easily than native plants, thereby leading to invasion success. This theoretical framework is also applicable to agroecosystems.

(2)

In agriculture, invasive plants can be turned from waste into treasure. Through the active harvesting of invasive plants by farmers and their sale to biotechnology companies, and the subsequent production of invasive plant-derived biochar by these companies for sale back to farmers, it is possible to remediate contaminated farmland, control invasions, and increase crop yield and farmers’ incomes.

Future research should focus on the effects of combined pollution stress on invasive plants; the development of predictive models for invasion under pollution stress; long-term dynamic tracking of plant–soil feedback (PSF) changes in invasive plants under pollution stress; and the formulation of more rational agricultural management policies for graded pollution management and invasion control.