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Article

Cu and Pb Co-Contamination Accelerates the Decomposition Rate of Litter from Invasive Aquatic Plant Eichhornia crassipes (Mart.) Solms and the Effect Increases with Its Invasion Degree

by
Yizhuo Du
1,
Yingsheng Liu
1,
Xiaoxuan Geng
1,
Yue Li
1,
Chuang Li
1,
Yulong Zhang
1,
Congyan Wang
1,2,3,* and
Daolin Du
4
1
School of Environment and Safety Engineering, Jiangsu University, Zhenjiang 212013, China
2
Key Laboratory of Ocean Space Resource Management Technology, Marine Academy of Zhejiang Province, Hangzhou 310012, China
3
Jiangsu Collaborative Innovation Center of Technology and Material of Water Treatment, Suzhou University of Science and Technology, Suzhou 215009, China
4
Jingjiang College, Jiangsu University, Zhenjiang 212013, China
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(7), 768; https://doi.org/10.3390/horticulturae11070768
Submission received: 4 June 2025 / Revised: 26 June 2025 / Accepted: 30 June 2025 / Published: 2 July 2025
(This article belongs to the Special Issue Nutrition Management and Weed Management Strategies in Horticultural Plants)
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Abstract

Invasive and native plants can coexist in the same ecosystem. Thus, the fallen leaves of invasive and native plants can be mixed, which can lead to co-decomposition. Invasive plants can create microenvironmental conditions conducive to their invasion process by influencing soil physicochemical properties, soil nutrient contents, and soil enzymatic activities through litter decomposition by released metabolites. Heavy metal contamination may affect the litter decomposition of invasive plants. This study was designed to elucidate the effects of the mono- and co-decomposition of the leaves of the invasive aquatic plant Eichhornia crassipes (Mart.) Solms (Common Water Hyacinth) and the native aquatic plant Nymphaea tetragona Georgi (Pygmy Water-Lily) on soil physicochemical properties, soil nutrient contents, and soil enzymatic activities under the mono- and co-contamination of Cu and Pb. This study was conducted over a six-month period using a polyethylene litter bag experiment. The type of heavy metals may be the most significant factor influencing the differences in the decomposition rate between E. crassipes and N. tetragona. The co-contamination of Cu and Pb increased the decomposition rate of the leaves of E. crassipes and the decomposition rate also increased as the invasion degree of E. crassipes increased relative to N. tetragona. The co-decomposition of the leaves of the two aquatic plants showed an antagonistic response under the mono-contamination of Pb and the control, but presented a synergistic response under the mono-contamination of Cu and the co-contamination of Cu and Pb, regardless of the invasion degree of E. crassipes. Soil enzymatic activities, especially the activities of polyphenol oxidase and cellulase, may be a significant factor influencing the litter decomposition of the two aquatic plants. Consequently, heavy metal contamination may affect the invasion process of E. crassipes with regard to the regulation of the released metabolites during the decomposition process, and this is specifically modulated by the type of heavy metals.

1. Introduction

Invasive plants can cause significant ecological effects, and in particular they can lead to the loss of biodiversity in native ecosystems [1,2,3,4]. Thus, the identification of the mechanisms that facilitate the successful invasion of invasive plants has become a pivotal area of scientific inquiry within the field of invasion ecology [2,5,6,7].
The current estimate of the number of species of invasive plants in China is 515 [8,9]. Presently, the estimated number of species of invasive aquatic plants in China is 152 [10]. A diverse array of invasive aquatic plants, including Eichhornia crassipes (Mart.) Solms (Common Water Hyacinth), has exerted a profound influence on aquatic ecosystems. In particular, as invasive aquatic plants disperse from their natural habitats and establish populations in occupied ecosystems, their invasive range may gradually expand, resulting in the formation of extensive monoculture communities, which ultimately leads to a significant decline in native species [11,12,13,14]. Thus, the structure and composition of native communities, as well as their diversity, may be influenced by these aquatic invaders, particularly as the degree of invasion increases over time. It is therefore crucial to identify the key mechanisms that facilitate the successful invasion of invasive aquatic plants, particularly when the invasion degree varies.
Invasive and native plants can coexist in the same ecosystem. Thus, the fallen leaves of invasive and native plants may decompose together [15,16,17,18]. In addition, invasive plants may produce more leaves, or the leaves of invasive plants may decompose faster and release more metabolites than those of native plants. This may provide more nutrients for the metabolic activity and diversity of soil decomposers, thereby facilitating the successful colonization of invasive plants [16,19,20,21]. Furthermore, invasive plants can create a microenvironmental condition conducive to their further invasion by influencing soil physicochemical properties, soil nutrient contents, and soil enzymatic activities through the decomposition process by released metabolites [22,23,24,25]. It is therefore important to elucidate the differences in the decomposition rate between invasive and native plants, as well as their effects on soil physicochemical properties, soil nutrient contents, and soil enzymatic activities, to elucidate the mechanisms underlying their successful invasion.
Environmental factors, such as the presence of heavy metals and the pollution they cause, may influence the invasion process of invasive plants. In particular, invasive plants may gain a more pronounced competitive advantage in growth under heavy metal contamination through their stronger growth performance, higher tolerance, and faster decomposition [26,27,28,29]. In addition, two (e.g., copper (Cu) and lead (Pb)) or more types of heavy metals may co-contaminate in the same area [16,30,31,32]. It is therefore important to estimate the differences in the decomposition rate between invasive and native plants, as well as their effects on soil physicochemical properties, soil nutrient contents, and soil enzymatic activities, especially in the case of co-contamination with two heavy metals (e.g., Cu and Pb). This will contribute to a more profound comprehension of the mechanisms that facilitate successful invasions, particularly in regard to the process of litter decomposition in the context of co-contamination with two heavy metals. However, advancements in this field remain insufficient.
This study was designed to elucidate the effects of the mono- and co-decomposition of the fallen leaves of the invasive aquatic plant E. crassipes and the native aquatic plant Nymphaea tetragona Georgi (Pygmy Water-Lily) on soil physicochemical properties, soil nutrient contents, and soil enzymatic activities under the mono- and co-contamination of Cu and Pb. The two aquatic plants exhibit comparable life forms and display analogous characteristics, including floating growth and clonal reproduction ability. The growth cycles of the two aquatic plants are also comparable, with the majority of growth occurring from March to October and the highest growth period occurring from May to September in China. An important factor in the widespread cultivation of the two aquatic plants in China is their use as horticultural plants. However, E. crassipes has been included in the list of invasive alien species in China due to its tendency to form extensive, single-dominant communities in the aquatic ecosystems of eastern China. The coexistence of the two aquatic plants is a common phenomenon in eastern China. In ecosystems in eastern Jiangsu, the two aquatic plants are contaminated by heavy metals, including the co-contamination of Cu and Pb [16,30,31,32].
This study sought to address the following questions: (1) Does the decomposition rate of the fallen leaves of E. crassipes exceed that of N. tetragona? (2) Does the decomposition rate of the leaves of E. crassipes increase in tandem with the invasion degree of E. crassipes? (3) Does the mono- and co-contamination of Cu and Pb exert a more pronounced deleterious impact on the decomposition rate of the leaves of N. tetragona than on that of E. crassipes?

2. Materials and Methods

2.1. Study Design

Plant communities of E. crassipes and N. tetragona were randomly selected on 28 October 2023 in Zhenjiang, Jiangsu, China (32.207~32.208° N, 119.516~119.517° E). The selected plant communities were primarily comprised of herbaceous aquatic plants, with no woody aquatic plants. Intact mature leaves of adult individuals of two aquatic plants were randomly picked from the selected communities. Leaves of each plant were collected in at least three plant communities with a minimum distance of 50 m between each collection site. Subsequently, leaves of each plant were then thoroughly mixed. The distance between selected communities of E. crassipes and N. tetragona was ≥100 m. The collected leaves of both aquatic plants were then subjected to a moderate washing process and subsequently dried naturally at room temperature in a greenhouse (32.206° N, 119.512° E) in Zhenjiang under natural light until their dry weights stabilized. The pond sediments from the same site were also collected and thoroughly mixed.
A six-month experimental study was conducted from 6 November 2023 to 6 May 2024 using polyethylene litter bags to simulate the litter decomposition of the two aquatic plants. Each polyethylene litter bag (length: 12 cm; width: 8 cm; mesh size: 425 μm) was designated as one of the five treatments: (1) no leaves (control) (imitating the absence of the two aquatic plants), (2) 6 g of N. tetragona leaves (imitating the condition without E. crassipes invasion), (3) 4 g of N. tetragona leaves and 2 g of E. crassipes leaves (imitating the condition with light invasion of E. crassipes), (4) 2 g of N. tetragona leaves and 4 g of E. crassipes leaves (imitating the condition with heavy invasion of E. crassipes), and (5) 6 g of E. crassipes leaves (imitating the condition with full invasion of E. crassipes). The polyethylene litter bags were then buried in the collected pond sediments, with ~2 kg pond sediments per polyethylene plastic planting pot, at a depth of ~2 cm in the polyethylene plastic planting pots (top diameter: 30 cm; height: 24 cm; manufacturer: Yutianzhougang Plastic Product Factory, Tangshan, China) with one polyethylene litter bag per polyethylene plastic planting pot. The pond sediments were not sterilized to ensure the natural presence of decomposers.
The polyethylene litter bags in the polyethylene plastic planting pots were treated with the mono- and co-contamination of Cu and Pb. The mono- and co-contamination of Cu and Pb were simulated by CuSO4·5H2O (reagent grade: AR; purity: ≥ 99.0%; manufacturer: Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) and (CH3COO)2Pb·3H2O (reagent grade: BC; purity: ≥99.0%; manufacturer: Sangon Biotech Co., Ltd., Shanghai, China). There were three conditions of heavy metals as follows: (I) Cu solution (imitating the condition with the mono-contamination of Cu (Cu)); (II) Pb solution (imitating the condition with the mono-contamination of Pb (Pb)); and (III) the equivalently mixed Cu and Pb solutions (imitating the condition with the co-contamination of Cu and Pb (combined Cu and Pb)). The final concentration of all three conditions of heavy metals was set at 35 mg/L (imitating the condition with the mono- and co-contamination of Cu and Pb). Distilled water was used as a control (0 mg/L, imitating the condition with the control). The concentration of the three types of heavy metals present in this study are equal to the natural contamination values of the two heavy metals in Zhenjiang, eastern China (30–36 mg·L−1) [30,31,32,33,34]. Three replicates were conducted per treatment. The polyethylene plastic planting pots were placed in a greenhouse (32.206° N, 119.512° E) in Zhenjiang with natural light for a period of six months.
According to the experimental period of previous studies [35,36,37,38], the decomposition processes in this study lasted for approximately 180 d. All polyethylene litter bags were collected after ~180 d of experimental treatment. The decomposed leaves of the two aquatic plants in the polyethylene litter bags were moderately washed and then dried naturally at a temperature of ~25 °C until the dry weight no longer changed to survey the variables involved in the process of litter decomposition. In addition, soil samples were collected from a depth of ~1 cm in the vicinity of the polyethylene litter bags and then sieved through a 2 mm sieve to analyze the soil physicochemical properties, soil nutrient contents, and soil enzymatic activities.

2.2. Determination of the Decomposition Variables

The decomposition coefficient (k) was used to define the decomposition rate of the leaves of the two aquatic plants as follows [39]:
X t =   X o ∗ e − k t
where Xo and Xt are the dry weight of the leaves of the two aquatic plants at the beginning and end of the decomposition at time t, respectively.
The stress intensity index (SII) of different treatments on the k of the leaves of the two aquatic plants was calculated as SII = 1 − (ks/kck), where ks and kck indicate the mean of the k of the leaves of the two aquatic plants with the mono- and co-contamination of Cu and Pb and without the mono- and co-contamination of Cu and Pb, respectively [40,41,42]. The value of SII ranges from 0 to 1, where a value close to 1 specifies a stronger stress, while a value close to 0 specifies a weaker stress.
The expected k of the mixed leaves of the two aquatic plants was defined as follows [21,43,44]:
E x p e c t e d   k = k x + k y 2
where kx and ky are the observed actual k of the leaves of the two aquatic plants, respectively.
The mixed-effect intensity of the co-decomposition (MEIC) of the leaves of the two aquatic plants was computed as follows [21,43,44]:
M E I C = k k e − 1
where k and ke are the observed actual k and the expected k, respectively, of the mixed leaves of the two aquatic plants with co-decomposition. The value of the MEIC specifies a synergistic effect when it is >0 and specifies an antagonistic effect when it is <0.

2.3. Determination of Soil Physicochemical Properties, Soil Nutrient Contents, and Soil Enzymatic Activities

A Digital Portable Multi-Parameter Soil Detector was used to determine pH, moisture content, electrical conductivity, and the levels of nitrogen, phosphorus, and potassium in soil in situ (model: TZS-pHWY-7G; manufacturer: TOP Instrument Co., Ltd., Hangzhou, China).
Several soil enzymatic activities involved in decomposition processes were investigated, including the activities of polyphenol oxidase, catalase, FDA hydrolase, cellulase, β-xylosidase, β-glucosidase, and sucrase. The determination methods for the analyzed soil enzymatic activities in this study are described in Table S1.

2.4. Statistical Analysis

Deviations from the normality and homogeneity of variances were assessed by using Shapiro–Wilk’s test and Bartlett’s test, respectively. Differences in the values of the k of the leaves of the two aquatic plants, soil physicochemical properties, soil nutrient contents, and soil enzymatic activities among different treatments were evaluated by using a multiple comparison with Tukey’s test. The effects of the invasion degree of E. crassipes and the type of heavy metals on the k of the leaves of the two aquatic plants, soil physicochemical properties, soil nutrient contents, and soil enzymatic activities were assessed by two-way ANOVA. The partial Eta-squared (η2) values were measured to determine the effect size of each factor for use in the two-way ANOVA. Path analysis was employed to evaluate the influences of soil physicochemical properties, soil nutrient contents, soil enzymatic activities, the invasion degree of E. crassipes, and the type of heavy metals on the k of the leaves of the two aquatic plants based on the values of the path coefficient (i.e., the standardized regression coefficient). Statistically significant differences were set at a threshold of p ≤ 0.05. Statistical analyses were conducted by using SPSS Statistics 26.0 (IBM, Inc., Armonk, NY, USA).

3. Results

3.1. Differences in the Decomposition Variables

The value of the k of the leaves of E. crassipes with all invasion degrees was significantly lower than that of N. tetragona without the mono- and co-contamination of Cu and Pb (p < 0.05; Figure 1). When treated with the mono-contamination of Cu, the value of the k of the leaves of E. crassipes with light invasion was significantly higher than that of E. crassipes with full invasion (p < 0.05; Figure 1). When treated with the mono-contamination of Pb, the value of the k of the leaves of E. crassipes with light and heavy invasion was significantly lower than that of N. tetragona (p < 0.05; Figure 1). When treated with the co-contamination of Cu and Pb, the value of the k of the leaves of E. crassipes with heavy and full invasion was significantly higher than that of N. tetragona and E. crassipes with light invasion (p < 0.05; Figure 1).
The value of the k of the leaves of N. tetragona was significantly higher in the control than when treated with the mono-contamination of Cu and the co-contamination of Cu and Pb (p < 0.05; Figure 1). The value of the k of the leaves of E. crassipes with light invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the mono-contamination of Pb (p < 0.05; Figure 1). The value of the k of the leaves of E. crassipes with heavy and full invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the control, the mono-contamination of Cu, and the mono-contamination of Pb (p < 0.05; Figure 1).
The results of two-way ANOVA analysis revealed that both the type of heavy metal treatment and the interactions of the invasion degree of E. crassipes significantly affected the value of the k of the leaves of the two aquatic plants (p < 0.0001; Table S2). In contrast, the invasion degree of E. crassipes did not significantly affect the value of the k of the leaves of the two aquatic plants (p > 0.05; Table S2).
The value of the SII of the co-contamination of Cu and Pb on the k of the leaves of N. tetragona was >0, but the value of the SII of the co-contamination of Cu and Pb on the k of the leaves of E. crassipes was <0 (Figure S1). In addition, the value of the SII of the co-contamination of Cu and Pb on the k of the leaves of both aquatic plants decreased with an increase in the invasion degree of E. crassipes (Figure S1).
The value of the observed k was similar to that of the expected k for the co-decomposition of the leaves of the two aquatic plants under all treatments (p > 0.05; Figure 2a). The value of the MEIC of the co-decomposition of N. tetragona and E. crassipes with light and heavy invasion treated with the mono-contamination of Cu and the co-contamination of Cu and Pb was >0, but the value of the MEIC of the co-decomposition of N. tetragona and E. crassipes with light and heavy invasion treated with the control and the mono-contamination of Pb was <0 (Figure 2b). There were no significant differences in the value of the MEIC of the co-decomposition of the leaves of the two aquatic plants across different treatments (p > 0.05; Figure 2b).

3.2. Differences in Soil Physicochemical Properties, Soil Nutrient Contents, and Soil Enzymatic Activities

Soil pH under E. crassipes with full invasion treated with the mono-contamination of Pb was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3a). Soil pH under the control was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3a). Soil pH under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3a).
Soil moisture under the control was significantly greater than that under N. tetragona and E. crassipes with full invasion treated with the control (p < 0.05; Figure 3b). Soil moisture under E. crassipes with heavy invasion treated with the mono-contamination of Cu was significantly lower than that under the mono-contamination of Cu as well as N. tetragona and E. crassipes with light and full invasion treated with the mono-contamination of Cu (p < 0.05; Figure 3b). When treated with the mono-contamination of Pb, soil moisture under E. crassipes with full invasion was significantly greater than that under N. tetragona and E. crassipes with light and heavy invasion (p < 0.05; Figure 3b). Soil moisture under E. crassipes with heavy invasion was significantly higher when treated with the control and the co-contamination of Cu and Pb than when treated with the mono-contamination of Cu (p < 0.05; Figure 3b). Soil moisture under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the control and the co-contamination of Cu and Pb (p < 0.05; Figure 3b). Soil moisture under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Cu than when treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3b).
Soil electrical conductivity under the mono-contamination of Cu was significantly lower than that under N. tetragona and E. crassipes with all invasion degrees treated with the mono-contamination of Cu (p < 0.05; Figure 3c). Soil electrical conductivity under the mono-contamination of Cu was significantly lower than under the control and the co-contamination of Cu and Pb (p < 0.05; Figure 3c). Soil electrical conductivity under E. crassipes with light invasion was significantly higher when treated with the mono-contamination of Cu than when treated with the control (p < 0.05; Figure 3c).
When treated with the mono-contamination of Cu, soil nitrogen content under E. crassipes with full invasion was significantly greater than that under E. crassipes with light invasion (p < 0.05; Figure 3d). Soil nitrogen content under the control was significantly lower than that under the mono-contamination of Cu and the co-contamination of Cu and Pb (p < 0.05; Figure 3d). Soil nitrogen content under E. crassipes with light invasion was significantly higher when treated with the mono-contamination of Cu and the co-contamination of Cu and Pb than when treated with the control and the mono-contamination of Pb (p < 0.05; Figure 3d). Soil nitrogen content under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the control (p < 0.05; Figure 3d).
Soil phosphorus content under E. crassipes with full invasion treated with the mono-contamination of Pb was significantly greater than under the mono-contamination of Pb, and greater than that of N. tetragona and E. crassipes with light and heavy invasion treated with the mono-contamination of Pb (p < 0.05; Figure 3e). Soil phosphorus content under the co-contamination of Cu and Pb was significantly greater than that under N. tetragona and E. crassipes with light invasion treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3e). Soil phosphorus content under the co-contamination of Cu and Pb was significantly greater than that under the control (p < 0.05; Figure 3e). Soil phosphorus content under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the control and the mono-contamination of Cu (p < 0.05; Figure 3e).
Soil potassium content under N. tetragona treated with the mono-contamination of Cu was significantly greater than that under E. crassipes with full invasion treated with the mono-contamination of Cu (p < 0.05; Figure 3f). When treated with the mono-contamination of Pb, soil potassium content under E. crassipes with full invasion was significantly greater than that under N. tetragona and E. crassipes with light and heavy invasion (p < 0.05; Figure 3f). Soil potassium content under the mono-contamination of Cu and the co-contamination of Cu and Pb was significantly greater than that under the control (p < 0.05; Figure 3f). Soil potassium content under N. tetragona was significantly higher when treated with the mono-contamination of Cu than when treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3f). Soil potassium content under E. crassipes with light invasion was significantly higher when treated with the mono-contamination of Cu than when treated with the control and the mono-contamination of Pb (p < 0.05; Figure 3f). Soil potassium content under E. crassipes with heavy invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the control and the mono-contamination of Cu (p < 0.05; Figure 3f).
Soil polyphenol oxidase activity under the mono-contamination of Cu was significantly greater than that under N. tetragona and E. crassipes with heavy and full invasion treated with the mono-contamination of Cu (p < 0.05; Figure 3g). When treated with the mono-contamination of Pb, soil polyphenol oxidase activity under E. crassipes with full invasion was significantly greater than that under N. tetragona and E. crassipes with light and heavy invasion (p < 0.05; Figure 3g). Soil polyphenol oxidase activity under E. crassipes with light and heavy invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the mono-contamination of Cu and the mono-contamination of Pb (p < 0.05; Figure 3g). Soil polyphenol oxidase activity under E. crassipes with full invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the control, the mono-contamination of Cu, and the mono-contamination of Pb (p < 0.05; Figure 3g). Soil polyphenol oxidase activity under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Pb than when treated with the mono-contamination of Cu (p < 0.05; Figure 3g).
Soil catalase activity under N. tetragona treated with the mono-contamination of Cu was significantly greater than that under the mono-contamination of Cu and E. crassipes with light and full invasion treated with the mono-contamination of Cu (p < 0.05; Figure 3h). Soil catalase activity under the mono-contamination of Pb was significantly greater than that under N. tetragona and E. crassipes with light and full invasion treated with the mono-contamination of Pb (p < 0.05; Figure 3h). When treated with the mono-contamination of Pb, soil catalase activity under E. crassipes with heavy invasion was significantly greater than that under E. crassipes with full invasion (p < 0.05; Figure 3h). Soil catalase activity under the co-contamination of Cu and Pb was significantly greater than that under the control and the mono-contamination of Cu (p < 0.05; Figure 3h). Soil catalase activity under the mono-contamination of Pb was significantly greater than that under the mono-contamination of Cu (p < 0.05; Figure 3h). Soil catalase activity under E. crassipes with light invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the mono-contamination of Cu (p < 0.05; Figure 3h). Soil catalase activity under E. crassipes with heavy invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the control, the mono-contamination of Cu, and the mono-contamination of Pb (p < 0.05; Figure 3h). Soil catalase activity under E. crassipes with full invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the mono-contamination of Cu and the mono-contamination of Pb (p < 0.05; Figure 3h). Soil catalase activity under E. crassipes with full invasion was significantly higher when treated with the control than when treated with the mono-contamination of Pb (p < 0.05; Figure 3h).
When treated with the mono-contamination of Pb, soil FDA hydrolase activity under E. crassipes with full invasion was significantly greater than that with just N. tetragona (p < 0.05; Figure 3i). Soil FDA hydrolase activity under E. crassipes with heavy invasion treated with the co-contamination of Cu and Pb was significantly greater than that under the co-contamination of Cu and Pb (p < 0.05; Figure 3i). Soil FDA hydrolase activity with just N. tetragona was significantly higher when treated with the mono-contamination of Cu and the co-contamination of Cu and Pb than when treated with the mono-contamination of Pb (p < 0.05; Figure 3i). Soil FDA hydrolase activity under E. crassipes with heavy invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the control and the mono-contamination of Pb (p < 0.05; Figure 3i). Soil FDA hydrolase activity under E. crassipes with full invasion was significantly higher when treated with the co-contamination of Cu and Pb than when treated with the mono-contamination of Pb (p < 0.05; Figure 3i).
Soil cellulase activity under E. crassipes with heavy invasion treated with the control was significantly greater than that under the control, and N. tetragona and E. crassipes with light and full invasion treated with the control (p < 0.05; Figure 3j). Soil cellulase activity under the control was significantly greater than that under E. crassipes with full invasion treated with the control (p < 0.05; Figure 3j). When treated with the mono-contamination of Cu, soil cellulase activity under E. crassipes with light invasion was significantly greater than that under E. crassipes with heavy and full invasion (p < 0.05; Figure 3j). When treated with the mono-contamination of Cu, soil cellulase activity with just N. tetragona was significantly greater than that under E. crassipes with heavy invasion (p < 0.05; Figure 3j). Soil cellulase activity under N. tetragona and E. crassipes with light invasion treated with the mono-contamination of Pb was significantly greater than that treated with the mono-contamination of Pb and E. crassipes with invasion treated with the mono-contamination of Pb (p < 0.05; Figure 3j). Soil cellulase activity under E. crassipes with light and full invasion treated with the mono-contamination of Pb was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3j). Soil cellulase activity under E. crassipes with heavy invasion treated with the co-contamination of Cu and Pb was significantly greater than that under the co-contamination of Cu and Pb and E. crassipes with light invasion treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3j). Soil cellulase activity under N. tetragona and E. crassipes with full invasion treated with the co-contamination of Cu and Pb was significantly greater than that under the co-contamination of Cu and Pb (p < 0.05; Figure 3j). Soil cellulase activity under the control was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3j). Soil cellulase activity with just N. tetragona and under light invasion with E. crassipes was significantly higher when treated with the mono-contamination of Pb and the co-contamination of Cu and Pb than when treated with the control and the mono-contamination of Cu (p < 0.05; Figure 3j). Soil cellulase activity under E. crassipes with heavy invasion decreased in the following order: the co-contamination of Cu and Pb > the control > the mono-contamination of Pb > the mono-contamination of Cu (p < 0.05; Figure 3j). Soil cellulase activity under E. crassipes with full invasion decreased in the following order: the co-contamination of Cu and Pb > the mono-contamination of Pb > the control ~ the mono-contamination of Cu (p < 0.05; Figure 3j).
When treated with the mono-contamination of Pb, soil β-xylosidase activity under E. crassipes with full invasion was significantly greater than that with just N. tetragona (p < 0.05; Figure 3k). Soil β-xylosidase activity under E. crassipes with full invasion was significantly higher when treated with the control and the co-contamination of Cu and Pb than when treated with the mono-contamination of Pb (p < 0.05; Figure 3k).
Soil β-glucosidase activity under E. crassipes with heavy invasion treated with the control was significantly greater than that under the control, and N. tetragona and E. crassipes with light and full invasion treated with the control (p < 0.05; Figure 3l). Soil β-glucosidase activity under the control was significantly lower than that under N. tetragona and E. crassipes with all invasion degrees treated with the control (p < 0.05; Figure 3l). Soil β-glucosidase activity under the mono-contamination of Cu was significantly greater than that under N. tetragona and E. crassipes with light and heavy invasion treated with the mono-contamination of Cu (p < 0.05; Figure 3l). Soil β-glucosidase activity under the mono-contamination of Pb and E. crassipes with light invasion was significantly lower than that under N. tetragona and E. crassipes with heavy and full invasion treated with the mono-contamination of Pb (p < 0.05; Figure 3l). Soil β-glucosidase activity under N. tetragona treated with the mono-contamination of Pb was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3l). Soil β-glucosidase activity under the co-contamination of Cu and Pb was significantly lower than that under N. tetragona and E. crassipes with all invasion degrees treated with the co-contamination of Cu and Pb (p < 0.05; Figure 3l). When treated with the co-contamination of Cu and Pb, soil β-glucosidase activity under E. crassipes with light and full invasion was significantly greater than that under E. crassipes with heavy invasion (p < 0.05; Figure 3l). Soil β-glucosidase activity under the mono-contamination of Cu and the mono-contamination of Pb was significantly greater than that under the control and the co-contamination of Cu and Pb (p < 0.05; Figure 3l). Soil β-glucosidase activity under N. tetragona and E. crassipes with light and full invasion decreased in the following order: the co-contamination of Cu and Pb > the mono-contamination of Pb > the control ~ the mono-contamination of Cu (p < 0.05; Figure 3l). Soil β-glucosidase activity under E. crassipes with heavy invasion decreased in the following order: the co-contamination of Cu and Pb > the mono-contamination of Pb > the control > the mono-contamination of Cu (p < 0.05; Figure 3l).
Soil sucrase activity under E. crassipes with heavy invasion treated with the mono-contamination of Cu was significantly greater than that under the mono-contamination of Cu (p < 0.05; Figure 3m). Soil sucrase activity under E. crassipes with heavy invasion treated with the mono-contamination of Pb was significantly greater than that under the mono-contamination of Pb (p < 0.05; Figure 3m). Soil sucrase activity under E. crassipes with full invasion was significantly higher when treated with the mono-contamination of Cu than when treated with the control and the mono-contamination of Pb (p < 0.05; Figure 3m).
Based on the results of two-way ANOVA analysis, the invasion degree of E. crassipes significantly affected the activities of catalase, cellulase, and β-glucosidase in soil (p < 0.05; Table S2); the type of heavy metals significantly affected the pH, electrical conductivity, potassium content, and the activities of polyphenol, catalase, FDA hydrolase, cellulase, β-xylosidase, β-glucosidase, and sucrase in soil (p < 0.05; Table S2); the interactions of the invasion degree of E. crassipes and the type of heavy metals significantly affected the nitrogen content and the activities of cellulase and β-glucosidase in soil (p < 0.05; Table S2).

3.3. Correlations Patterns Between the k of the Leaves of the Two Aquatic Plants, Soil Physicochemical Properties, Soil Nutrient Contents, and Soil Enzymatic Activities

According to the results of correlation analysis, the value of the activities of polyphenol oxidase, FDA hydrolase, and cellulase in soil were significantly positively correlated with the value of the k of the leaves of the two aquatic plants (p < 0.05; Table S3).

3.4. The Influences of Soil Physicochemical Properties, Soil Nutrient Contents, Soil Enzymatic Activities, the Invasion Degree of E. crassipes, and the Type of Heavy Metals on the k of the Leaves of the Two Aquatic Plants

According to the results of path analysis, the influences of the activities of polyphenol oxidase and cellulase in soil on the k of the leaves of the two aquatic plants was clearly higher than that of soil variables based on the value of the path coefficient (Figure 4).
The influences of the type of heavy metals were obviously higher than those of the invasion degree of E. crassipes on the k of the leaves of the two aquatic plants, soil physicochemical properties, soil nutrient contents, and soil enzymatic activities (Figure 4).

4. Discussion

The decomposition rate of the leaves of invasive plants is typically higher than that of native plants, which accelerates the nutrient cycling in soil and facilitates further invasion [16,20,45,46]. Also, the leaves of E. crassipes exhibited a faster decomposition rate than those of N. tetragona under the co-contamination of Cu and Pb. In addition, the co-contamination of Cu and Pb exerted a more pronounced inhibitory effect on the decomposition rate of the leaves of N. tetragona, whereas it elicited a stimulatory effect on the decomposition rate of the leaves of E. crassipes. Notably, the magnitude of this promoting effect increased in tandem with the invasion degree of E. crassipes. Hence, the co-contamination of Cu and Pb can possibly increase the decomposition rate of the leaves of E. crassipes. Furthermore, this promoting effect was observed to increase with the invasion degree of E. crassipes compared to just N. tetragona. Thus, the co-contamination of Cu and Pb can facilitate the process of nutrient cycling in soil by quickly decomposing and releasing more nutrients from the leaves of E. crassipes compared to that of N. tetragona, thus potentially accelerating the invasion process of E. crassipes. However, the leaves of E. crassipes exhibited a slower decomposition rate than those of N. tetragona under the mono-contamination of Pb and the control. Hence, speculatively, the mono-contamination of Pb and the control may impede the invasion process of E. crassipes by inhibiting the decomposition rate and suppressing nutrient cycling in soil. The decomposition rate of the leaves of E. crassipes was comparable to that of N. tetragona under the mono-contamination of Cu. Hence, the mono-contamination of Cu did not affect the invasion process of E. crassipes with regard to the process of litter decomposition. It can be posited that the type of heavy metals may prove to be the most significant factor influencing the differences in the decomposition rate between E. crassipes and N. tetragona. The results of path analysis also supported this hypothesis. This finding may be attributed to a difference in the leaching proportion of soluble components (i.e., those that are more readily decomposed) in the leaves of the two aquatic plants under different types of heavy metals. Specifically, the co-contamination of Cu and Pb may facilitate the leaching of soluble components in the leaves of E. crassipes to a greater extent than in N. tetragona, and the opposite is true for the mono-contamination of Pb and the control. Thus, heavy metal contamination may possibly affect the invasion process of E. crassipes in terms of regulation of the decomposition process, and is specifically modulated by the type of heavy metals. Specifically, the co-contamination of Cu and Pb may facilitate the invasion process of E. crassipes with respect to the process of litter decomposition. Hence, the co-contamination with multiple heavy metals should be avoided as much as possible, particularly in aquatic ecosystems, to prevent the generation of the Matthew effect in their ecological effects, especially with regard to the interaction with the invasion process of these aquatic invasive plants.
The mixed-effect intensity of the co-decomposition of the leaves of the two aquatic plants was found to be less than zero under the mono-contamination of Pb and the control. Hence, the co-decomposition of the leaves of the two aquatic plants may result in an antagonistic response under the mono-contamination of Pb and the control, regardless of the invasion degree of E. crassipes. Thus, the co-decomposition of the leaves of the two aquatic plants may result in an antagonistic interruption of the decomposition process under the mono-contamination of Pb and the control compared to their mono-decomposition. This phenomenon may be attributed to the reciprocated interference facilitated by the secondary components existing in the mixed leaves of the two aquatic plants under the mono-contamination of Pb and the control [15,47,48,49]. Thus, the leaves of N. tetragona can probably impede the invasion process of E. crassipes by hindering the nutrient cycling in soil under the mono-contamination of Pb and the control. This phenomenon may be caused by the antagonistic responses of the co-decomposition of the leaves of the two aquatic plants, regardless of the invasion degree of E. crassipes. However, the mixed-effect intensity of the co-decomposition of the leaves of the two aquatic plants was found to be greater than zero under the mono-contamination of Cu and the co-contamination of Cu and Pb. Hence, the co-decomposition of the leaves of the two aquatic plants can result in a synergistic response under the mono-contamination of Cu and the co-contamination of Cu and Pb, regardless of the invasion degree of E. crassipes. Thus, the co-decomposition of the leaves of the two aquatic plants may synergistically accelerate their decomposition process under the mono-contamination of Cu and the co-contamination of Cu and Pb compared to their mono-decomposition. This phenomenon may be attributed to the reciprocal acceleration recruited by the secondary components that exists in the mixed leaves of the two aquatic plants under the co-contamination of Cu and Pb [21,50,51]. The synergistic response of the co-decomposition of the leaves of the two aquatic plants under the mono-contamination of Cu and the co-contamination of Cu and Pb may also be attributed to the fact that polyphenol oxidase is a copper-containing enzyme that participates in the litter decomposition of plants [52,53]. Nevertheless, the results of the correlation analysis and path analysis indicate that soil polyphenol oxidase activity is a key factor influencing the decomposition process of the two aquatic plants.
The results of the correlation analysis indicated a significant positive correlation between the activities of polyphenol oxidase, FDA hydrolase, and cellulase in soil and the decomposition rate of the leaves of the two aquatic plants. In addition, the influences of the activities of polyphenol oxidase and cellulase in soil on the decomposition rate of the leaves of the two aquatic plants were more pronounced than those of other soil variables, as evidenced by the results of the path analysis. Thus, soil enzymatic activities, particularly the activities of polyphenol oxidase and cellulase in soil, may be a significant factor influencing the decomposition process of the two aquatic plants. This phenomenon may be attributed to the pivotal roles these two enzymes play in the decomposition of cellulose and polyphenol, the primary constituents of plant litter.
Nevertheless, the experimental design of the present study has some limits. For example, the study did not analyze the initial chemical composition of the leaves (e.g., C:N ratio, lignin, and cellulose content) for either species. Thus, the experimental design needs to be further improved, especially with the addition of the analysis of the initial chemical composition of the leaves for both species, to obtain more comprehensive and reasonable results on the effects of the three heavy metal conditions on the mono- and co-decomposition of the leaves of invasive E. crassipes and native N. tetragona.

5. Conclusions

This study aimed to illuminate the effects of three types of heavy metals on the mono- and co-decomposition of the fallen leaves of invasive E. crassipes and native N. tetragona. The main findings are as follows: (1) The leaves of E. crassipes exhibited a faster decomposition rate than those of N. tetragona under the co-contamination of Cu and Pb. Hence, E. crassipes can further advance its invasion process via its faster decomposition rate. (2) The co-contamination of Cu and Pb increased the decomposition rate of the leaves of E. crassipes and the promoting effect increased with the invasion degree of E. crassipes compared to N. tetragona. Thus, co-contamination with Cu and Pb may play a role in accelerating the growth of invasive species over native plants. (3) The activities of soil enzymes, particularly those of polyphenol oxidase and cellulase, may be the pivotal factor influencing the decomposition process of the two aquatic plants. These findings highlight the intricate relationship between heavy metal contamination and invasion dynamics, suggesting that the environment should not be further polluted. Future research should further investigate soil enzyme responses to heavy metals as a potential avenue for managing invasive aquatic plants.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11070768/s1, Table S1: The determination methods for the analyzed soil enzymatic activities in this study; Table S2: Two-way ANOVA on the effects of the invasion degree of Eichhornia crassipes (Mart.) Solms and the type of heavy metals on the decomposition coefficient (k) of the leaves of Nymphaea tetragona Georgi and Eichhornia crassipes (Mart.) Solms: soil physicochemical properties, soil nutrient contents, and soil enzymatic activities; Table S3: Correlations (r) between the decomposition coefficient (k) of the leaves of Nymphaea tetragona Georgi and Eichhornia crassipes (Mart.) Solms: soil physicochemical properties, soil nutrient contents, and soil enzymatic activities; Figure S1: The stress intensity index of different treatments on the decomposition coefficients of the leaves of Nymphaea tetragona Georgi and Eichhornia crassipes (Mart.) Solms.

Author Contributions

Conceptualization, Y.D., Y.L. (Yingsheng Liu), X.G., Y.L. (Yue Li), C.L. and C.W.; methodology, C.W.; formal analysis, Y.D., Y.L. (Yingsheng Liu), X.G., Y.L. (Yue Li), C.L. and Y.Z.; investigation, Y.D., Y.L. (Yingsheng Liu), X.G., Y.L. (Yue Li), C.L.; resources, Y.Z.; data curation, Y.D. and Y.L. (Yingsheng Liu); writing—original draft preparation, C.W.; writing—review and editing, Y.D., Y.L. (Yingsheng Liu), X.G., Y.L. (Yue Li), C.L., Y.Z., C.W. and D.D.; supervision, C.W.; project administration, C.W. and D.D.; funding acquisition, C.W. and D.D. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the following sources: Open Science Research Fund of Key Laboratory of Ocean Space Resource Management Technology, Marine Academy of Zhejiang Province, China (KF-2024-112); National Natural Science Foundation of China (32071521); Special Research Project of School of Emergency Management, Jiangsu University (KY-C-01); Jiangsu Collaborative Innovation Center of Technology and Material of Water Treatment (no grant number); and the Research Project on the Application of Invasive Plants in Ecological Restoration of Heavy Metals in Coastal Soil in Jiangsu (20250444).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The decomposition coefficients of the leaves of N. tetragona and E. crassipes. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences at 0.05 probability (p ≤ 0.05). Abbreviations: CK, the control; CKNT, N. tetragona treated with the control; CKNTECL, light invasion of E. crassipes treated with the control; CKNTECH, heavy invasion of E. crassipes treated with the control; CKEC, full invasion of E. crassipes treated with the control; CuNT, N. tetragona treated with the mono-contamination of Cu; CuNTECL, light invasion of E. crassipes treated with the mono-contamination of Cu; CuNTECH, heavy invasion of E. crassipes treated with the mono-contamination of Cu; CuEC, full invasion of E. crassipes treated with the mono-contamination of Cu; PbNT, N. tetragona treated with the mono-contamination of Pb; PbNTECL, light invasion of E. crassipes treated with the mono-contamination of Pb; PbNTECH, heavy invasion of E. crassipes treated with the mono-contamination of Pb; PbEC, full invasion of E. crassipes treated with the mono-contamination of Pb; CuPbNT, N. tetragona treated with the co-contamination of Cu and Pb; CuPbNTECL, light invasion of E. crassipes treated with the co-contamination of Cu and Pb; CuPbNTECH, heavy invasion of E. crassipes treated with the co-contamination of Cu and Pb; CuPbEC, full invasion of E. crassipes treated with the co-contamination of Cu and Pb.
Figure 1. The decomposition coefficients of the leaves of N. tetragona and E. crassipes. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences at 0.05 probability (p ≤ 0.05). Abbreviations: CK, the control; CKNT, N. tetragona treated with the control; CKNTECL, light invasion of E. crassipes treated with the control; CKNTECH, heavy invasion of E. crassipes treated with the control; CKEC, full invasion of E. crassipes treated with the control; CuNT, N. tetragona treated with the mono-contamination of Cu; CuNTECL, light invasion of E. crassipes treated with the mono-contamination of Cu; CuNTECH, heavy invasion of E. crassipes treated with the mono-contamination of Cu; CuEC, full invasion of E. crassipes treated with the mono-contamination of Cu; PbNT, N. tetragona treated with the mono-contamination of Pb; PbNTECL, light invasion of E. crassipes treated with the mono-contamination of Pb; PbNTECH, heavy invasion of E. crassipes treated with the mono-contamination of Pb; PbEC, full invasion of E. crassipes treated with the mono-contamination of Pb; CuPbNT, N. tetragona treated with the co-contamination of Cu and Pb; CuPbNTECL, light invasion of E. crassipes treated with the co-contamination of Cu and Pb; CuPbNTECH, heavy invasion of E. crassipes treated with the co-contamination of Cu and Pb; CuPbEC, full invasion of E. crassipes treated with the co-contamination of Cu and Pb.
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Figure 2. The observed (blue bars) and expected (orange bars) decomposition coefficients of the mixed litter (a), and the mixed-effect intensity of the co-decomposition (b) of the leaves of N. tetragona and E. crassipes. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences at 0.05 probability (p ≤ 0.05). “ns” indicate no statistically significant differences at 0.05 probability (p > 0.05). Abbreviations have the same meanings as presented in Figure 1.
Figure 2. The observed (blue bars) and expected (orange bars) decomposition coefficients of the mixed litter (a), and the mixed-effect intensity of the co-decomposition (b) of the leaves of N. tetragona and E. crassipes. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences at 0.05 probability (p ≤ 0.05). “ns” indicate no statistically significant differences at 0.05 probability (p > 0.05). Abbreviations have the same meanings as presented in Figure 1.
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Horticulturae 11 00768 g003aHorticulturae 11 00768 g003bHorticulturae 11 00768 g003cHorticulturae 11 00768 g003d
Figure 3. Soil physicochemical properties, soil nutrient contents, and soil enzymatic activities. (a) Soil pH; (b) soil moisture; (c) soil electrical conductivity; (d) soil nitrogen content; (e) soil phosphorus content; (f) soil potassium content; (g) soil polyphenol oxidase activity; (h) soil catalase activity; (i) soil FDA hydrolase activity; (j) soil cellulase activity; (k) soil β-xylosidase activity; (l) soil β-glucosidase activity; (m) soil sucrase activity. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences (p ≤ 0.05). Abbreviations have the same meanings as presented in Figure 1.
Figure 3. Soil physicochemical properties, soil nutrient contents, and soil enzymatic activities. (a) Soil pH; (b) soil moisture; (c) soil electrical conductivity; (d) soil nitrogen content; (e) soil phosphorus content; (f) soil potassium content; (g) soil polyphenol oxidase activity; (h) soil catalase activity; (i) soil FDA hydrolase activity; (j) soil cellulase activity; (k) soil β-xylosidase activity; (l) soil β-glucosidase activity; (m) soil sucrase activity. Data (means ± SEs; n = 3) with different letters indicate statistically significant differences (p ≤ 0.05). Abbreviations have the same meanings as presented in Figure 1.
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Figure 4. Schematic diagram of the influences of soil physicochemical properties, soil nutrient contents, soil enzymatic activities, the invasion degree of E. crassipes, and the type of heavy metals on the k of the leaves of the two aquatic plants. The light blue numbers represent the influences of the invasion degree of E. crassipes on the measured variances. The dark blue numbers represent the influences of the type of heavy metals on the surveyed variances. The fuchsia numbers represent the influences of soil physicochemical properties, soil nutrient contents, and soil enzymatic activities on the decomposition coefficients of the leaves of the two aquatic plants. Positive values indicate positive influences, while negative values indicate negative influences. The stronger the influence, the greater the deviation from 0 and vice versa.
Figure 4. Schematic diagram of the influences of soil physicochemical properties, soil nutrient contents, soil enzymatic activities, the invasion degree of E. crassipes, and the type of heavy metals on the k of the leaves of the two aquatic plants. The light blue numbers represent the influences of the invasion degree of E. crassipes on the measured variances. The dark blue numbers represent the influences of the type of heavy metals on the surveyed variances. The fuchsia numbers represent the influences of soil physicochemical properties, soil nutrient contents, and soil enzymatic activities on the decomposition coefficients of the leaves of the two aquatic plants. Positive values indicate positive influences, while negative values indicate negative influences. The stronger the influence, the greater the deviation from 0 and vice versa.
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MDPI and ACS Style

Du, Y.; Liu, Y.; Geng, X.; Li, Y.; Li, C.; Zhang, Y.; Wang, C.; Du, D. Cu and Pb Co-Contamination Accelerates the Decomposition Rate of Litter from Invasive Aquatic Plant Eichhornia crassipes (Mart.) Solms and the Effect Increases with Its Invasion Degree. Horticulturae 2025, 11, 768. https://doi.org/10.3390/horticulturae11070768

AMA Style

Du Y, Liu Y, Geng X, Li Y, Li C, Zhang Y, Wang C, Du D. Cu and Pb Co-Contamination Accelerates the Decomposition Rate of Litter from Invasive Aquatic Plant Eichhornia crassipes (Mart.) Solms and the Effect Increases with Its Invasion Degree. Horticulturae. 2025; 11(7):768. https://doi.org/10.3390/horticulturae11070768

Chicago/Turabian Style

Du, Yizhuo, Yingsheng Liu, Xiaoxuan Geng, Yue Li, Chuang Li, Yulong Zhang, Congyan Wang, and Daolin Du. 2025. "Cu and Pb Co-Contamination Accelerates the Decomposition Rate of Litter from Invasive Aquatic Plant Eichhornia crassipes (Mart.) Solms and the Effect Increases with Its Invasion Degree" Horticulturae 11, no. 7: 768. https://doi.org/10.3390/horticulturae11070768

APA Style

Du, Y., Liu, Y., Geng, X., Li, Y., Li, C., Zhang, Y., Wang, C., & Du, D. (2025). Cu and Pb Co-Contamination Accelerates the Decomposition Rate of Litter from Invasive Aquatic Plant Eichhornia crassipes (Mart.) Solms and the Effect Increases with Its Invasion Degree. Horticulturae, 11(7), 768. https://doi.org/10.3390/horticulturae11070768

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