This study focused on plants diversity and stability of aquatic communities in 19 restored lakeside wetlands of Chaohu Lake which is the fifth largest freshwater lake in China (Chen et al., 2023). The studied 19 restored lakeside wetlands located in the First Level Protected Area (FLPA) with a scope of 1 kilometer extended the shoreline of Chaohu Lake. The completed date of the 19 restored wetlands was listed in Supplementary Table S1 . This region experiences a subtropical monsoon climate, with an annual precipitation of 1,124.4 mm and a temperature of 16.7°C (Yang et al., 2024). Meanwhile, the studied 19 restored lakeside wetlands encompassed a variety of microhabitats such as plains, hills, marshes, and ponds ( Figure 1 ). The combination of diverse geological conditions and suitable climate in this area facilitated the colonization of abundant vascular plants. According to the lifeform and ecological types of vascular plants, lakeside wetlands vegetation was classified into five vegetation formations, including upland plants, wet grasslands, emergent plants, floating-leaved plants, and submerged plants (Jenkins et al., 2021; Yang et al., 2024).

To reveal plants coexisting strategies, a number of 19 sampling transects were conducted among 19 lakeside wetlands of Chaohu Lake in the spring (April 20th to May 12th) and autumn (September 23rd to October 12th) of 2023. Each sampling-transect of restored wetland traversed five vegetation formation with a length ranged from 0.5 to 2 kilometers that was positively correlated with the width of wetland. Meanwhile, a number of 8-15 herbaceous plant quadrats (1×1m) were set at each transect and a total of 427 samples were conducted in this study. Plant characteristics including abundance, height, coverage, phenology, above ground biomass of plants were recorded to analyze the spatial niche and interspecific competition among vascular plants (Yang et al., 2024). Additionally, 10 traits encompassing functional, morphological, and phenological parameters of plants were examined to elucidate the competitive strategies of plants (Wang et al., 2012). Specifically, the content of the 10 traits were listed in Supplementary Table S2 . The data of morphological, and phenological parameters of vascular plants were collected from field observation and Flora of China (Wu and Zhou, 2001).

The chi-square (χ² ) statistics were utilized to examine the interspecific associations of functional groups (Hurlbert, 1969). The χ² value was calculated according to the following formula (Gu et al., 2017; Jin et al., 2022).

Where a represents the number of quadrats where both species i and j occurred. b represents the number of quadrats where only species i occurred. c represents the number of quadrats where only species j occurred. d represents the number of quadrats where neither species i nor j occurred, and N represents the total number of quadrats. When χ² < 3.841, there is no interspecific association between species; when 3.84 ≤χ² ≤ 6.635, there is a moderate association between species; and when χ² > 6.635, there is significant association between species (Gu et al., 2017).

The Ochiai index (OI) was used to assess the degree of isolation between species. The OI index was calculated according to the following equation (Hu et al., 2022).

Where the value of a, b, and c in Equation 2 are the same as those in Equation 1. When OI value is 0, indicating that the species are completely independent. The closer the OI value is to 1 and χ²>0, the higher the probability of two species cooccur in the same habitat.

The Spearman rank correlation coefficient (r_ij) was used to assess the level of linear correlation between independent species (Gauthier, 2001). The calculation of r_ij was based on the following equations:

Where r ( i , j ) is the rank correlation analysis between species i and j. N is the total number of quadrats. X i k and X j k are the rank vector of i and j that were converted from the quantity of species i and j in kth quadrat. dk is the difference of the rank vector of species i and j. The value of r_(i,j) is ranged from -1 to 1. If r_(i,j) > 0, the species have a positive correlation, and if r_(i,j) < 0, species have a negative correlation.

The niche breadth (B) was utilized to analyze the niche of plants (Colwell and Futuyma, 1971; Jin et al., 2022).

The N_T is the total number of species i among five vegetations formations while N_j is the number of species i in each vegetation formation.

Morphological traits of vascular plants, such as relative average height (RH), relative coverage (RC), and relative abundance (RA), were used to assess plant competitiveness. The important value (IV), calculated as the average of relative abundance (RA), relative frequency (RF), and relative coverage (RC), was used to determine species significance in wetland ecosystems. Dominance (D) was employed to indicate plant prevalence among numerous species. These traits were calculated as the following equations (Gu et al., 2017; Jin et al., 2022).

The height of individuals of the ith species is represented by H_i. C_i signifies the total coverage of the ith species, while A_i represents the total number of individuals of the ith species. S indicates the total number of species in the quadrat, and F_i denotes the total number of quadrats in which the ith species appears.

The variation of relative height (ΔRH) and relative coverage (ΔRC) were used to evaluate the growth rate of plants. The calculation of ΔRH and ΔRC was based on the following equations:

Where R H t 2 is the relative height of plants at time t₂. R H t 1 is the relative height of plants at time t₁. Analogously, R C t 2 is the relative coverage of plants at time t₂ while R C t 1 is the relative coverage of plants at time t₁.

All the data were calculated with Excel and analyzed via Origin 2024 pro.

A total of 220 vascular plants from 64 families and 168 genera were identified in 19 restored wetlands around Chaohu Lakeside ( Figure 2 ). The proportion of local species in the regional species pool varied among different plant taxa. Among them, the species from Poaceae, Asteraceae, Cyperaceae, Polygonaceae, and Fabaceae contributed to15%, 10.91%, 5.91%, 5.45%, and 4.55% of the total species, respectively. Poaceae, particularly annual and biennial weeds, were more dominant than forbs in wetlands, that embraced 33% of richness and 38.76% of abundance (Sutherland, 2004). Poaceae, Cyperaceae, and Polygonaceae were major contributors to the weed list in this region, characterized by fast growth rate, high adaptability, and rapid reproduction (Baker, 1974).

Annual species primarily propagated through seeds, while most perennial species spread through asexual reproduction. The total mass of annual species’ seeds was twice as much as that of perennial plants in the soil of emergent communities (Drahota and Reichart, 2015). Aquatic vegetation restoration provided high-energy food sources (seeds, tubers, and submerged aquatic plants) tend to enhance waterfowl diversity of wetlands (Lishawa et al., 2020; Zhou et al., 2020). Species like Beckmannia syzigachne (B. syzigachne) and Echinochloa caudata (E. caudata), prevalent in abandoned farmland, were often used as pioneer species for wetland restoration (Yan et al., 2023). However, perennial species such as S. canadensis, P. australis, and T. angustifolia are not edible by birds, and their proliferation can reduce bird diversity in restored wetlands. This condition can be revised by controlling invasive plants (Lishawa et al., 2020).

The predominant species of upland vegetation formation was mainly originated from the Asteraceae and Fabaceae families, such as Solidago canadensis (S. canadensis), Erigeron canadensis (E. canadensis), Sonchus oleraceus (S. oleraceus), Glycine soja (G. soja) and Vicia sativa L (V. sativa). S. canadensis was initially introduced as an ornamental plant, but escaped and became pervasive in wetlands (Wang et al., 2021). The shading tolerance capacity of S. canadensis enabled it adapted to various environmental variables (Wu et al., 2020). On the other hand, G. soja, a native species under state protection (category II), is known for its climbing and strangling behavior towards other species. While Cyperaceae and Polygonaceae were mainly obligate or facultative wetland species like Bolboschoenus planiculmis, Cyperus difformis, Persicaria lapathifolia, and Persicaria orientalis which mainly distributed in wet grassland and emergent vegetation formations.

According to the plant source, the proportion of native species, artificially planted species, alien species, and alien invasive species accounted for 63.64%, 21.82%, 3.18%, and 11.36%, respectively. The top five native species with higher important value were Phragmites australis (P. australis), Paspalum distichum (P. distichum), Cynodon dactylon (C. dactylon), Potamogeton crispus (P. crispus), and T. angustifolia, with IV of 0.054, 0.043, 0.042, 0.030, and 0.026 respectively. Among many invasive plants, A. philoxeroides, S. canadensis, and E. canadensis tended to be more pervasive and predominant in lakeside wetlands with IV values of 0.064, 0.029, and 0.026, respectively. A. philoxeroides, as an invasive species, can spread quickly through vegetative propagation and adapt well to diverse habitats under different light regimes conditions (Pan et al., 2006). S. canadensis exhibits high drought stress tolerance, low nutrient stress tolerance, high fecundity, and diffusion ability, making it the most threatened invasive species in wetlands (Wang et al., 2023). Another invasive species Erigeron canadensis (E. canadensis) with high growth rate that can secrete allelochemicals to inhibit the growth of neighboring plants (Yan et al., 2020).

To determine interspecific relationship among vascular plants, a total of 30 predominant species and 435 pair of relation were analyzed in the spring and autumn, respectively ( Figure 3 ). In spring, alien invasive plants such as A. philoxeroides, G. carolinianum, E. canadensis, and S. canadensis exhibited higher dominance. A. philoxeroides, as semiaquatic species showed a positive correlation with hydrophyte and macrophyte like Rumex japonicus (R. japonicus), Leersia japonica, and T. angustifolia with OI exceed 0.35. Conversely, A. philoxeroides exhibited a negative correlation with xerophytes and mesophytes like G. carolinianum, E. canadensis, and S. oleraceu, with OI value of 0.31, 0.07, and 0.03, respectively. On the other hand, G. carolinianum, E. canadensis, and S. canadensis are xerophilous or mesic plants mainly found in upland vegetation formation. Furthermore, the G. carolinianum and E. canadensis showed positively correlated with most xerophilous or mesic species in spring but negative correlations in autumn. Specifically, S. canadensis exhibited a positive correlation with vine and herbaceous plants with larger size while it obtained a negative correlation with herbaceous plants with smaller size.

The dominant native species identified in this study were P. australis, Vicia sativa, and T. angustifolia. Among them, P. australis showed a positive interspecific correlation with T. angustifolia, with an OI of 0.34 and χ² of 13.64, indicating a significant overlap in their ecological niche. Both P. australis and T. angustifolia, known as obligate wetland species, are widely utilized in wetland restoration projects. The positive correlation observed in invasive plants suggested their superior competitive ability over native species. Furthermore, the intensity of interspecific competition between invasive and native plants was more intense than that among different invasive species. Interestingly, xerophilous or mesic species such as Humulus scandens (H. scandens), Nelumbo nucifera Gaertn (N. nucifera) and Hydrilla verticillate (H. verticillate) showed no correlation with macrophytes, for that most macrophyte were monocultured. Additionally, the presence of hydrophytic habitats have effectively restricted the spread of xerophilous and mesic invaders (Dou et al., 2022).

The strategies employed by plants to alleviate competition involves niche partitioning in both space and time ( Figure 4 ). The distribution of vascular plants within various vegetation formations such as upland plants, wet grassland plants, emergent plants, floating-leaved plants, and submerged plants was 51.36%, 31.36%, 8.64%, 4.55%, and 4.09%, respectively (Yang et al., 2024). As shown in Figure 4C , the average niche breadth upland plants, wet grassland plants, emergent plants, floating-leaved plants, and submerged plants were 1.28 ± 0.36, 1.53 ± 0.52, 1.67 ± 0.60, 1.48 ± 0.52, and 1.58 ± 0.49, respectively. This result supported the hypothesis that the niche of functional groups in wetlands was predominantly influenced by hydrological conditions (Deane et al., 2017). Meanwhile, species of wet grassland and emergent vegetation formations usually obtained higher tolerance to hydrological changes. Specifically, species like A. philoxeroides, N. nucifera, and Rumex japonicus exhibited wider niche breadth exceeding 2.85 compared with S. canadensis of 1.34. Due to the coexistence of these adaptive species that contributed to the ecotone’s higher biodiversity (Yang et al., 2024).

Another factor that influences species fluctuations is the annual climate variability. A previous study by Zheng et al. (2024) highlighted the significant impact of temporal shifts and functional traits on grassland productivity. In contrast, Usinowicz et al. (2017) found that the benefits of asynchronous coexistence were more pronounced in tropical and subtropical forests compared to temperate forests. Figure 4D illustrates the explicit partition of plants’ temporal niche. The result indicated that 160 species were observed in spring and 148 species in autumn. The distribution of species along the X-axis indicates that 33.6% of investigated species occurred in spring, 26.8% in autumn, and 39.5% in both seasons. Wang et al. (2012) noted that 25.45% of species matured from late spring to summer, with 8.18% achieving the highest biomass in early spring and 4.09% maintaining consistent biomass throughout the year. Additionally, 62.27% of plants matured in early autumn ( Figure 4A ). The partition of plants reproductive phenology can effectively enrich the seed bank of wetland as well as facilitate the survive rate of plants.

According to the reproductive capacity of plants, annual species generally embraced shorter germination times compared to perennial species (Shipley and Parent, 1991). In lakeside wetlands, the species pool consisted of 97 annual plants (44.09%) and 123 perennial herbs (55.91%). Spring-dominant species were typically annual herbs with smaller size and biomass, such as Azolla pinnata, Spirodela polyrhiza, and Galium spurium. Annual herbs tend to spread quickly due to shorter generation times or higher fecundity, giving them a selective advantage over biennials and perennials (Sutherland, 2004). On the other hand, perennial hygrophytes like Phragmites, Typhaceae and Cyperaceae embrace well-developed rhizomes or corms that provide flooding tolerance (Wang et al., 2022). In the initial stages of wetland restoration, annuals typically dominate the species composition, but there is a gradual shift towards perennials in long-term succession (Jenkins et al., 2021).

Species predominant in autumn were mainly from the Poaceae family, such as Echinochloa colona, E. caudata, and Setaria viridis, with seeds maturing in autumn. These species were often accompanied by planted species like N. nucifera, Nymphaea tetragona, and T. angustifolia. Notably, G. carolinianum matured in spring and completed its life cycle in summer. While most species withered in autumn, Panicum bisulcatum bloomed and outperformed others in terms of height and coverage. Species coexisting in spring and autumn were characterized by perennial macrophytes with greater competitiveness in terms of height and biomass. Additionally, species with wider temporal niche tended to possess higher niche breadth as well ( Figure 4D ).

Ultimately, the interspecific competition among plants is a competition for resources. The competitiveness of plants is usually size asymmetric that the larger plants typically receiving a greater share of light resources which may suppress neighboring plants’ fitness (Aschehoug et al., 2016). In this study, relative height (RH) and relative coverage (RC) were introduced into the Lotka-Volterra model to assess the competitiveness and strategies for plant coexistence in a large community (Silvertown, 2004; Tilman, 1990). Because majority (62.27%) of plants in this region reached maturity in the autumn, leading to the use of autumnal traits to determine stability conditions, while variations of traits between spring and autumn were used to assess the strategies of plants (Chesson, 2000).

The coverage and height tradeoff are the most common strategies for plant coexistence in the presence of interspecific competition. If Δ R H Δ R C > 1 , the species is determined by the height tradeoff strategy. If Δ R H Δ R C < 1 , the species is determined by the coverage tradeoff strategy. When Δ R H Δ R C ≈ 1 , the species is determined by both coverage and height tradeoff strategies. When the Δ R H Δ R C is negative, the equation is substituted by R H R C . Plants applied height tradeoff strategy are these species like E. canadensis, Miscanthus lutarioriparius, E. caudata, and N. nucifera, while the coverage tradeoff strategy is observed in G. carolinianum, A. philoxeroides, Trapa natans, and P. crispus ( Figure 5 ).

Our results indicated that plants in different vegetation formations may adopt disparate strategies. In upland vegetation formation, S. canadensis was predominant by height and coverage while E. canadensis and G. carolinianum were driven by height and coverage strategies, respectively. Additionally, plants in different habitat may also adopt different strategies. For example, P. australis adopted coverage strategy in hygrophilous habitat while it employed height strategy in aquatic habitat. According to the Lotka-Volterra model, species with trading strategies tend to coexist, while non-trading strategy species are more likely to be excluded by competitive species (De Mazancourt and Schwartz, 2010). The weaker competitors increase their fitness via traits trade off while stronger competitors are suppressed by their conspecific neighbors (Stoll and Prati, 2001). The increase in dominance of a species in one resource comes at the expense of competitiveness in another resource.