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Article

Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment

by
Yinhua Wang
1,
Xinyi Tian
1,
Chen Yang
1,
Changcheng Guo
2,
Yifan Li
3,
Xin Lyu
1,
Ningning Li
1 and
Hongyu Guo
1,*
1
Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Sciences, Tianjin Normal University, Tianjin 300387, China
2
Tianjin Key Laboratory of Water Resources and Environment, Tianjin Normal University, Tianjin 300387, China
3
College of Life Sciences, Nankai University, Tianjin 300071, China
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(9), 2031; https://doi.org/10.3390/agronomy15092031 (registering DOI)
Submission received: 27 July 2025 / Revised: 20 August 2025 / Accepted: 23 August 2025 / Published: 25 August 2025
(This article belongs to the Special Issue Trade-Offs in Crop Production: Yield and Quality, Resource Use Efficiency, and Environmental Sustainability)
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Abstract

Understanding plants’ productivity plasticity in response to environmental variations is crucial for evaluating their adaptive capacity and resilience in the face of rapid global changes. Phragmites australis, an important species in coastal wetlands, plays a vital role in ecosystem functions and wetland agriculture. Coastal areas are increasingly threatened by soil salinization due to rising sea levels and eutrophication driven by elevated nitrogen inputs. However, how P. australis adjusts its aboveground and belowground productivity under these environmental stresses remains poorly understood. We examined how P. australis alters its productivity in response to varying salinity and nitrogen enrichment levels through a mesocosm experiment. Our results showed that elevated salinity reduced both aboveground (by 2.7–13.7%) and belowground (by 15.3–24.7%) productivity, decreasing the belowground-to-aboveground biomass ratio of P. australis. In contrast, nitrogen enrichment promoted aboveground productivity (by 18.3–65.5%), but suppressed belowground biomass (by 11.7–29.7%), further reducing the biomass ratio. Nitrogen enrichment alleviated the negative impact of salinity on aboveground productivity, but exacerbated its effects on belowground biomass, further shifting resource allocation to aboveground growth. These findings underscore the adaptive plasticity of P. australis and suggest its potential role in supporting sustainable wetland agriculture, providing both ecological and economic benefits in the face of ongoing global environmental changes.

1. Introduction

Understanding plants’ productivity plasticity in response to environmental variations is essential for assessing their adaptive capacity and resilience in the face of rapid global change [1]. Phragmites australis (common reed) is an important species in coastal wetlands worldwide [2,3], playing a vital role in maintaining ecosystem functions, such as water purification [4], habitat provision [5], and erosion control [6]. Its dense root systems help stabilize soils and prevent coastal erosion [7], while its ability to absorb excess nutrients and contaminants makes it an important plant for water quality management [8]. Additionally, P. australis contributes significantly to the sequestration of carbon in coastal environments, performing a crucial blue carbon function by trapping carbon in its biomass and in the sediments beneath wetlands [9]. This process helps mitigate climate change by reducing atmospheric carbon dioxide levels [10]. In the context of ecological agriculture, P. australis can be used to help restore degraded wetlands [11], improve soil structure [12], and increase soil organic matter [13]. As a crop in wetland agriculture, P. australis holds substantial economic value due to its utility in fiber production [14], paper-making [15], and construction materials [16]. It is also a valuable feedstock for livestock, offering a sustainable alternative to other forage crops [17]. Furthermore, its high biomass production has great potential for bioenergy and bio-based products, including biofuels [18], making it a valuable resource in integrated farming systems. Its use as a renewable resource in bioenergy systems can help reduce reliance on fossil fuels [19], promoting a circular economy. The combination of its ecological contributions and economic value makes P. australis essential for wetland agriculture and sustainable land use practices in coastal areas.
Coastal areas are facing increasing threats from sea level rise caused by climate change [20], resulting in notable alterations in soil conditions and increased salinity levels [21]. Between 1901 and 2018, global sea levels rose by approximately 0.2 m [21], with projections suggesting this rate will accelerate over the coming century [22]. Rising sea levels contribute to greater tidal ranges, causing more frequent flooding of coastal regions [23], which in turn, leads to saltwater intrusion into estuarine and freshwater wetlands [24]. Moreover, the combined effects of rising sea levels, intensified storm surges, reduced freshwater flow due to shifting rainfall patterns, and extreme tidal events are expected to exacerbate the penetration of saltwater into previously unaffected inland zones [25]. This saltwater intrusion is particularly harmful to low-salinity wetlands, where freshwater and saltwater ecosystems exist in a delicate balance [26]. The consequent soil salinization accelerates soil structure degradation, reduces agricultural productivity and biodiversity, and increases the vulnerability of these ecosystems to additional climate-related stresses [27,28]. This complex interplay between rising sea levels and saltwater intrusion poses a critical challenge to sustaining coastal ecosystems and the wetland agriculture that depends on them.
On the other hand, with the intensification of human activities, a significant amount of nitrogen is being released into natural ecosystems [29]. Currently, nitrogen emissions from human activities exceed 60% of the natural nitrogen fixation capacity of ecosystems [30]. The primary sources of nitrogen include agricultural fertilization, industrial emissions, and transportation pollution [31]. This excess nitrogen input has profound environmental impacts, particularly on aquatic systems [32]. In coastal regions, elevated nitrogen levels often cause eutrophication [33], leading to algal blooms and subsequent hypoxic zones, where oxygen depletion severely impacts biodiversity and disrupts ecosystem services [34]. In addition, increased nitrogen alters the biogeochemical cycles of coastal soils, influencing the growth of plants in coastal areas [35]. Coastal wetlands, which play a critical role in carbon sequestration and serve as vital habitats, may be significantly affected [36]. The overabundance of nitrogen can shift plant community composition, reducing species diversity and ecosystem stability [37]. Over time, this disruption may accelerate coastal degradation, impair ecosystem health, and affect the survival of communities dependent on these ecosystems. The growing nitrogen input thus represents a major challenge to the sustainability of coastal ecosystems [38].
Soil salinization resulting from rising sea levels and eutrophication driven by increasing nitrogen inputs may interact to significantly affect plant productivity in coastal regions [39,40]. However, how P. australis adjusts its aboveground and belowground productivity in response to the combined effects of salinization and nitrogen enrichment remains poorly understood. This study investigated how P. australis alters its aboveground and belowground productivity under varying salinity and nitrogen enrichment conditions. We hypothesized that elevated salinity would negatively impact the overall productivity of P. australis, while nitrogen enrichment would enhance its aboveground productivity and alter the belowground-to-aboveground biomass ratio. Additionally, we hypothesized that nitrogen enrichment may interact with salinity to further influence the productivity of P. australis.
By exploring the productivity plasticity of P. australis in response to these dynamic environmental changes, this research contributes to a more comprehensive understanding of its resilience amidst rapid global change. Given that the ecological contributions and economic value of P. australis are closely linked to its biomass productivity, understanding its productivity plasticity in response to environmental variations is crucial for evaluating its potential as a keystone species in wetland ecological agriculture, where its adaptability could enhance the sustainability and restoration of coastal wetland ecosystems. Furthermore, the findings of this study may inform the development of management strategies for the restoration and conservation of coastal ecosystems, thereby supporting the preservation of the ecological and agricultural benefits provided by P. australis in the context of ongoing global environmental shifts.

2. Materials and Methods

2.1. Plant Material

P. australis is the dominant plant species in the Tianjin coastal wetland, China, covering an area of over 3000 hectares. Its biomass is utilized as forage, raw material for paper production, and as construction material. The climate of the Tianjin coastal wetland is characterized as a warm temperate semi-humid continental monsoon climate, with an annual average temperature of approximately 12 °C and an annual precipitation of about 528.24 mm.
In early March 2024, a total of 60 healthy spring buds of P. australis with their attached rhizomes (at a depth of approximately 30 cm) were collected from a freshwater wetland located at 38°39′ N, 117°34′ E, in the coastal region of Tianjin, China. This wetland is adjacent to an estuarine river and experiences periodic tidal flooding. Due to rising sea levels and saltwater intrusion, the salinity of this wetland is projected to increase, reaching approximately 10 PSU (Practical Salinity Unit) by the middle of the 21st century [41]. Additionally, nitrogen input is expected to rise by 10–20 gN·m−2·a−1 by the middle of the 21st century [42].
The rhizomes of P. australis were approximately 3 cm in length and 0.5 cm in diameter. To ensure random selection, the collected spring buds were randomized from various locations before the experiment.

2.2. Mesocosm Experiment

A mesocosm experiment was conducted in a glasshouse at Tianjin Normal University, which was open to the ambient environment, ensuring that sunlight and temperature (25 ± 5 °C) closely resembled outdoor conditions throughout the study. The glass roof of the structure prevented natural rainfall from entering. P. australis ramets were grown in PVC pots with a diameter of 20 cm, a height of 50 cm, and sealed bottoms.
We collected soil from the same wetland where the P. australis spring buds were sampled, and thoroughly mixed the soil. The soil type of this wetland is marsh soil. The final mixture, which was non-saline (0 PSU), had a pH of 7.0, an organic matter content of 4.6%, a total nitrogen content of 66.1 mg·kg−1, and an available phosphorus content of 28.5 mg·kg−1, was then added to each pot to a depth of 35 cm.
In mid-March 2024, we planted P. australis spring buds with their rhizomes, positioning them about 2 cm below the soil surface in separate pots, one bud per pot. A total of 60 pots were prepared and watered with fresh water to promote the growth of P. australis buds. By the end of April 2024, we selected 30 pots containing healthy, similarly sized P. australis individuals to minimize variation in initial growth before the experiment began.
The 30 pots were randomly distributed across all combinations of salinity (0 PSU and 10 PSU) and nitrogen enrichment levels (N0: 0 gN·m−2·a−1, N1: 10 gN·m−2·a−1, N2: 20 gN·m−2·a−1), with five replicates for each combination. The pots, corresponding to specific salinity and tidal treatment combinations, were then placed into six treatment tanks. In each tank, the water level was kept 5 cm below the soil surface to simulate conditions found at higher elevations in the local coastal wetland. To facilitate water flow, four sets of holes (six per set, each 0.8 cm in diameter) were drilled along the sides of each pot, between the rim and base, and covered with mesh to prevent soil loss. To minimize shading from neighboring plants, the pots were spaced approximately 0.5 m apart.
Beginning on 6 May 2024, we initiated the salinity and nitrogen enrichment treatments for the pots. Over a 10-day period, commercial marine aquarium salt (Luhua brand, Tianjin Changlu Hangu Saltern Co., Ltd., Tianjin, China) was progressively added to the tanks for the 10 PSU (~0.17 M NaCl L−1) treatments, with salinity levels increased incrementally until the target soil porewater salinity was attained. For the nitrogen enrichment treatments, NH4NO3 granules (which gradually dissolve in soil porewater) were evenly applied to the soil surface weekly, in accordance with the specified nitrogen enrichment levels (0 g NH4NO3/pot/week for the N0 treatment; 0.017 g NH4NO3/pot/week for the N1 treatment; 0.034 g NH4NO3/pot/week for the N2 treatment). Daily monitoring was conducted to maintain the soil porewater salinity and nitrogen enrichment levels. Additionally, the experimental pots in each treatment tank were rotated regularly to reduce potential biases from temperature, light, and other environmental variables.
In October 2024 (the end of the growing season), we recorded plant height (measured as the highest point of the leaves after vertical stretching), basal stem diameter, and number of leaves, and subsequently harvested both aboveground and belowground biomass. During the harvesting of belowground biomass, nearly all roots and rhizomes were fresh and viable. The belowground biomass was then carefully rinsed with freshwater using a sieve (mesh size 0.25 mm) to remove soil attached to the roots and rhizomes. All biomass samples were dried at 60 °C until a constant weight was achieved, after which they were weighed.

2.3. Data Analysis

To assess the impacts of salinity, nitrogen enrichment level, and their interactions on the productivity metrics of P. australis, we conducted ANOVAs followed by Tukey HSD post hoc tests for multiple comparisons, with a significance threshold of 0.05. Data were Ln-transformed to satisfy the assumptions of normality of residuals and homogeneity of variances required for ANOVA. Statistical analyses were performed using SPSS 21 (IBM Corp., Chicago, IL, USA).
We also evaluated the impact of salinity on the productivity metrics of P. australis at different nitrogen enrichment levels. The effect size was determined using the formula Ln [(mean value of a productivity metric under 10 PSU condition)/(mean value of the productivity metric under 0 PSU condition)]. A positive effect size suggests a stimulatory influence of salinity, while a negative effect size implies an inhibitory impact of salinity.

3. Results

3.1. Effects of Salinity and Nitrogen Enrichment Level on Height of P. australis

Figure 1a shows that salinity reduced the height of P. australis across all nitrogen enrichment levels (Table 1). In contrast, nitrogen enrichment positively influenced the height of P. australis, regardless of salinity conditions (Figure 1a, Table 1). The negative effect of salinity on the height of P. australis decreased with increasing nitrogen enrichment, leading to a significant interaction between salinity and nitrogen enrichment levels (Figure 1b, Table 1).

3.2. Effects of Salinity and Nitrogen Enrichment Level on Basal Stem Diameter of P. australis

Figure 2a demonstrates that the basal stem diameter of P. australis decreased with increasing salinity across all nitrogen enrichment levels (Table 1). In contrast, the basal stem diameter of P. australis consistently increased with higher nitrogen enrichment levels, regardless of salinity conditions (Figure 2a, Table 1). As nitrogen enrichment levels rose, the negative impact of salinity on the basal stem diameter of P. australis decreased, resulting in a significant interaction between salinity and nitrogen enrichment levels (Figure 2b, Table 1).

3.3. Effects of Salinity and Nitrogen Enrichment Level on Number of Leaves of P. australis

Figure 3a illustrates that salinity decreased the number of leaves of P. australis across all nitrogen enrichment levels (Table 1). In contrast, the number of leaves of P. australis increased with higher nitrogen enrichment levels, irrespective of salinity conditions (Figure 3a, Table 1). As nitrogen enrichment levels rose, the negative effects of salinity on the number of leaves decreased, resulting in a significant interaction between salinity and nitrogen enrichment levels (Figure 3b, Table 1).

3.4. Effects of Salinity and Nitrogen Enrichment Level on Aboveground Biomass of P. australis

Figure 4a illustrates that the aboveground biomass of P. australis decreased with increasing salinity across all nitrogen enrichment levels (Table 1). In contrast, the aboveground biomass of P. australis increased with higher nitrogen enrichment levels, regardless of salinity conditions (Figure 4a, Table 1). The negative impact of salinity on the aboveground biomass of P. australis decreased as nitrogen enrichment levels rose, leading to a significant interaction between salinity and nitrogen enrichment levels (Figure 4b, Table 1).

3.5. Effects of Salinity and Nitrogen Enrichment Level on Belowground Biomass of P. australis

Figure 5a demonstrates that elevated salinity reduced the belowground biomass of P. australis across all nitrogen enrichment levels (Table 1). Additionally, the belowground biomass of P. australis decreased as nitrogen enrichment levels increased (Figure 5a, Table 1). The negative effect of salinity on the belowground biomass of P. australis became more pronounced with higher nitrogen enrichment levels, resulting in a significant interaction between salinity and nitrogen enrichment levels (Figure 5b, Table 1).

3.6. Effects of Salinity and Nitrogen Enrichment Level on Ratio of Belowground to Aboveground Biomass of P. australis

Figure 6a reveals that the ratio of belowground to aboveground biomass of P. australis decreased as salinity increased across all nitrogen enrichment levels (Table 1). Additionally, this ratio declined with increasing nitrogen enrichment levels (Figure 6a, Table 1). The negative impact of salinity on the ratio of belowground to aboveground biomass became more pronounced as nitrogen enrichment levels increased, leading to a significant interaction between salinity and nitrogen enrichment levels (Figure 6b, Table 1).

3.7. Effects of Salinity and Nitrogen Enrichment Level on Total Biomass of P. australis

Figure 7a demonstrates that elevated salinity reduced the total biomass of P. australis across all nitrogen enrichment levels (Table 1). In contrast, the total biomass of P. australis increased with higher nitrogen enrichment levels, regardless of salinity conditions (Figure 7a, Table 1). The negative impact of salinity on the total biomass of P. australis tended to decrease as nitrogen enrichment levels rose (Figure 7b, Table 1). Despite the influence of both salinity and nitrogen enrichment on the growth of P. australis, the plant still maintained relatively high overall productivity (Figure 7a).

4. Discussion

4.1. Aboveground Growth of P. australis Under Different Salinity and Nitrogen Enrichment Conditions

Our results demonstrated that increased salinity reduced the height, basal stem diameter, leaf number, and aboveground biomass of P. australis (Figure 1, Figure 2, Figure 3 and Figure 4, Table 1), indicating that salt stress is a key factor limiting its aboveground productivity. One of the mechanisms by which salinity affected the aboveground growth of P. australis is osmotic stress [43]. As salinity increases, the osmotic potential of the soil solution decreases, making water absorption more difficult for plants [44]. This water deficit can cause a reduction in turgor pressure, impairing cell expansion and elongation, which ultimately restricts overall plant growth [45]. Moreover, the accumulation of sodium ions can lead to ion toxicity, disrupting essential cellular processes and damaging the plant’s ability to function normally, further hindering plant growth [46]. Additionally, salinity-induced oxidative stress may also contribute to the reduction in plant growth. High salt concentrations promote the accumulation of reactive oxygen species (ROS), which can damage cell membranes, proteins, and DNA [47]. While plants possess antioxidant defense systems to counteract ROS damage, under high salinity conditions, the production of ROS may exceed the plant’s capacity to neutralize them, leading to cellular damage and a decline in growth performance [48]. This oxidative stress might exacerbate the negative effects of salinity on P. australis, contributing to the observed decrease in aboveground productivity.
On the other hand, nitrogen enrichment positively influenced the aboveground growth of P. australis, with enhanced height, basal stem diameter, leaf number, and aboveground biomass observed across the salinity treatments (Figure 1, Figure 2, Figure 3 and Figure 4, Table 1). Nitrogen is an essential nutrient for plants, involved in the synthesis of proteins, enzymes, and chlorophyll, all of which are crucial for cell division, photosynthesis, and overall growth [49]. Nitrogen enrichment may enhance the plant’s ability to carry out these essential functions, thus promoting growth even in the face of environmental stresses, such as high salinity [50]. This suggests that nitrogen enrichment could serve as a potential strategy for improving the aboveground growth and productivity of P. australis under challenging environmental conditions, such as soil salinization.
The interaction between salinity and nitrogen enrichment observed in this study (Figure 1, Figure 2, Figure 3 and Figure 4, Table 1) suggests that nitrogen supplementation may alleviate the negative impacts of salinity on the aboveground growth of P. australis. One possible mechanism behind this interaction was that nitrogen may facilitate the synthesis of compatible solutes, such as proline and sugars, which help maintain osmotic balance and cellular hydration under saline conditions [51]. Moreover, nitrogen could enhance the plant’s ability to regulate oxidative stress, supporting its growth even under stressful environmental conditions, such as high salinity [52]. Additionally, nitrogen may help the plant regulate ion homeostasis by promoting processes that exclude or sequester sodium ions, thereby preventing ion toxicity and supporting continued growth under high salinity conditions [53].

4.2. Belowground Biomass of P. australis Under Different Salinity and Nitrogen Enrichment Conditions

Our results indicated that the belowground biomass of P. australis decreased with increased salinity (Figure 5, Table 1). This decline might be attributed to the osmotic stress on roots and rhizomes caused by elevated salinity, which reduced the plant’s ability to absorb water and nutrients from the soil [54]. Moreover, under saline conditions, the roots and rhizomes of P. australis may also experience ion toxicity [55] and metabolic disturbances [56]. As a result, the plant’s ability to develop and sustain belowground biomass could be compromised. In addition, salinity-induced oxidative stress could further damage root and rhizome cells, impairing their growth and function [57], which would ultimately reduce belowground productivity of P. australis.
Interestingly, we observed a significant decrease in belowground biomass of P. australis with increasing nitrogen enrichment levels (Figure 5, Table 1). Although nitrogen is an essential nutrient for plant growth, high nitrogen level could lead to an imbalance in nutrient uptake [58]. Moreover, high nitrogen availability may increase the production of reactive oxygen species (ROS) in roots and rhizomes [59], which could cause oxidative damage and further inhibit root and rhizome growth [60]. Additionally, high nitrogen levels may alter root architecture, reducing the plant’s ability to establish a robust root system and further limiting belowground biomass [61].
We found that the negative effect of salinity on belowground biomass intensified with increasing nitrogen levels, suggesting a significant interaction between salinity and nitrogen enrichment (Figure 5, Table 1). One possible explanation for this interaction might be that nitrogen enrichment exacerbates the salt stress on belowground biomass of P. australis by increasing the plant’s metabolic activity. As nitrogen enrichment promotes overall plant growth, it may lead to higher nutrient and water demands [62], which would in turn intensify the plant’s vulnerability to salinity stress. In saline environments, increased nitrogen uptake could stimulate root metabolic activity, thereby promoting the uptake of other ions, including sodium. The accumulation of sodium ions in the roots may lead to ion toxicity, further impairing root growth [55]. Furthermore, the interaction between nitrogen and salinity could also involve changes in the plant’s antioxidant defense systems. Under high nitrogen levels and salinity conditions, the production of reactive oxygen species (ROS) in roots and rhizomes may surpass the plant’s capacity to neutralize them, leading to oxidative stress and impaired root and rhizome development [57].

4.3. Ratio of Belowground to Aboveground Biomass of P. australis Under Different Salinity and Nitrogen Enrichment Conditions

We observed a significant decline in the ratio of belowground to aboveground biomass of P. australis with increasing salinity (Figure 6, Table 1). As previously mentioned, elevated salinity may induce osmotic stress [54], ion toxicity [55], metabolic disruptions [56], and oxidative stress [57], which could negatively affect plant growth, particularly the roots and rhizomes in the soil. This might lead to a reduction in belowground biomass relative to the aboveground biomass.
We also found that the ratio of belowground to aboveground biomass of P. australis decreased with higher nitrogen enrichment levels (Figure 6, Table 1). As mentioned earlier, elevated nitrogen levels may cause an imbalance in nutrient uptake [58], increase reactive oxygen species (ROS) production [59,60], and alter root architecture [61]. These factors could directly affect the roots in the soil, leading to a reduced belowground-to-aboveground biomass ratio.
The significant interaction between salinity and nitrogen enrichment levels indicated that the negative impact of salinity on the ratio of belowground to aboveground biomass was intensified as nitrogen levels increased (Figure 6, Table 1). As discussed earlier, elevated nitrogen uptake could stimulate root metabolic activity, increasing the plant’s demand for nutrients and water [62]. Under saline stress, this heightened demand for nutrients and water may exacerbate ion toxicity to roots and rhizomes. The combined stress from both high nitrogen and salinity could further impair root and rhizome growth in the soil. Additionally, the increased production of reactive oxygen species (ROS) under both nitrogen enrichment and salinity stress might cause oxidative damage to roots and rhizomes [57,60], further hindering their growth and reducing the belowground biomass relative to the aboveground biomass.
Although elevated salinity negatively impacted the overall growth of P. australis, and nitrogen enrichment reduced its belowground biomass, our findings suggest that P. australis exhibits remarkable productivity plasticity in response to variations in salinity and nitrogen levels. This productivity plasticity is primarily reflected in the reduced ratio of belowground to aboveground biomass, with a greater allocation of resources to aboveground growth, as salinity and nitrogen levels increased. Such a shift in resource allocation enables more efficient use of available resources, helping P. australis maintain relatively high overall productivity (Figure 7a), despite the environmental changes, such as salinization and eutrophication [63,64], in coastal areas. Future studies need to explore changes in osmolytes, antioxidant activity, and ion concentrations in P. australis under varying salinity and nitrogen enrichment conditions to further examine the underlying metabolic mechanisms driving the productivity plasticity of P. australis.

5. Conclusions

Our results showed that P. australis productivity was significantly influenced by variations in salinity and nitrogen enrichment levels. Elevated salinity resulted in reduced aboveground and belowground productivity, accompanied by a decrease in the ratio of belowground to aboveground biomass. In contrast, nitrogen enrichment promoted aboveground productivity but suppressed belowground productivity, leading to a further decline in the belowground-to-aboveground biomass ratio. Additionally, our study revealed significant interactions between salinity and nitrogen enrichment for most productivity metrics of P. australis. Specifically, nitrogen enrichment appeared to mitigate the negative impacts of salinity on aboveground productivity, but conversely, it exacerbated the adverse effects of salinity on belowground productivity and further shifted resource allocation to aboveground growth. These findings underscore the adaptive plasticity of P. australis in aboveground and belowground productivity in response to environmental changes, enabling it to maintain relatively high overall productivity. This suggests that P. australis could play a crucial role in supporting sustainable wetland agriculture by providing both ecological and economic benefits in the face of ongoing global environmental changes. Our results also indicate that in coastal wetlands affected by salinization due to saltwater intrusion, appropriate nitrogen enrichment may partially alleviate the negative impact of salinization on the productivity of P. australis.

Author Contributions

Conceptualization, Y.W. and H.G.; funding acquisition, Y.W. and H.G.; methodology, Y.W. and H.G.; investigation, C.G., X.T., C.Y., X.L., Y.L. and N.L.; formal analysis, Y.W., C.G., X.T., C.Y., X.L., Y.L., N.L. and H.G.; writing—original draft preparation, Y.W., C.G., X.T., C.Y., X.L., Y.L., N.L. and H.G.; writing—review and editing, Y.W., C.G., X.T., C.Y., X.L., Y.L., N.L. and H.G. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the National Natural Science Foundation of China (31300357, 32001179) and the Natural Science Foundation of Tianjin City (20JCZDJC00220).

Data Availability Statement

All data supporting the findings of this study were included within the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Height of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the height of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 1. Height of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the height of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 2. Basal stem diameter of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the basal stem diameter of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 2. Basal stem diameter of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the basal stem diameter of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 3. Number of leaves of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the number of leaves of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 3. Number of leaves of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the number of leaves of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 4. Aboveground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the aboveground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 4. Aboveground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the aboveground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 5. Belowground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the belowground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 5. Belowground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the belowground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 6. Ratio of belowground to aboveground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the ratio of belowground to aboveground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 6. Ratio of belowground to aboveground biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the ratio of belowground to aboveground biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Figure 7. Total biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the total biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
Figure 7. Total biomass of P. australis under different salinity and nitrogen enrichment level treatments (a), and effect size of salinity on the total biomass of P. australis under different nitrogen enrichment levels (b). In Panel (a), data are presented as means + SE (n = 5). Shared letters indicate means that are not significantly different from each other (Tukey’s HSD tests, significance level of 0.05).
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Table 1. Summary of ANOVAs examining the effects of salinity, nitrogen enrichment level, and the interaction between them on height, basal stem diameter, number of leaves, aboveground biomass, belowground biomass, ratio of belowground to aboveground biomass, and total biomass of P. australis (all Ln-transformed).
Table 1. Summary of ANOVAs examining the effects of salinity, nitrogen enrichment level, and the interaction between them on height, basal stem diameter, number of leaves, aboveground biomass, belowground biomass, ratio of belowground to aboveground biomass, and total biomass of P. australis (all Ln-transformed).
Source of VariancedfFp
Height of P. australis
        Salinity1, 2468.842<0.001 ***
        Nitrogen enrichment level2, 2487.094<0.001 ***
        Salinity × Nitrogen enrichment level2, 246.0730.007 **
Basal stem diameter of P. australis
        Salinity1, 2448.276<0.001 ***
        Nitrogen enrichment level2, 2473.835<0.001 ***
        Salinity × Nitrogen enrichment level2, 2411.707<0.001 ***
Number of leaves of P. australis
        Salinity1, 2433.266<0.001 ***
        Nitrogen enrichment level2, 2433.510<0.001 ***
        Salinity × Nitrogen enrichment level2, 243.8820.035 *
Aboveground biomass of P. australis
        Salinity1, 2424.685<0.001 ***
        Nitrogen enrichment level2, 24188.146<0.001 ***
        Salinity × Nitrogen enrichment level2, 243.6290.042 *
Belowground biomass of P. australis
        Salinity1, 24150.181<0.001 ***
        Nitrogen enrichment level2, 2490.532<0.001 ***
        Salinity × Nitrogen enrichment level2, 243.9230.034 *
Ratio of belowground to aboveground biomass
        Salinity1, 2458.096<0.001 ***
        Nitrogen enrichment level2, 24686.846<0.001 ***
        Salinity × Nitrogen enrichment level2, 2419.290<0.001 ***
Total biomass of P. australis
        Salinity1, 2473.858<0.001 ***
        Nitrogen enrichment level2, 2427.634<0.001 ***
        Salinity × Nitrogen enrichment level2, 240.7870.467
Note: *, 0.01 < p < 0.05; **, p < 0.01; ***, p < 0.001.
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Wang, Y.; Tian, X.; Yang, C.; Guo, C.; Li, Y.; Lyu, X.; Li, N.; Guo, H. Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment. Agronomy 2025, 15, 2031. https://doi.org/10.3390/agronomy15092031

AMA Style

Wang Y, Tian X, Yang C, Guo C, Li Y, Lyu X, Li N, Guo H. Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment. Agronomy. 2025; 15(9):2031. https://doi.org/10.3390/agronomy15092031

Chicago/Turabian Style

Wang, Yinhua, Xinyi Tian, Chen Yang, Changcheng Guo, Yifan Li, Xin Lyu, Ningning Li, and Hongyu Guo. 2025. "Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment" Agronomy 15, no. 9: 2031. https://doi.org/10.3390/agronomy15092031

APA Style

Wang, Y., Tian, X., Yang, C., Guo, C., Li, Y., Lyu, X., Li, N., & Guo, H. (2025). Adaptive Plasticity of Phragmites australis in Aboveground and Belowground Productivity Under Salinization and Nitrogen Enrichment. Agronomy, 15(9), 2031. https://doi.org/10.3390/agronomy15092031

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