Responses Of Macrophytes Research Articles

Trait-specific groups of aquatic macrophytes respond differently to eutrophication of unshaded lowland streams

Understanding eutrophication effects on stream macrophytes is key to meaningful environmental management and governance. However, the response of macrophyte communities to eutrophication is complex and often the effect of eutrophication is obscured by other factors related to habitat variability including flow regime and light availability.In this study macrophyte community composition and abundance was quantified along a eutrophication gradient in 30 lowland streams. Slow flowing, medium sized streams with minimal shading were selected, to focus on examining water quality effects. The internal nutrient status of the plants and the bioavailable nutrient fraction of the sediment was measured and a national database of modelled stream descriptors was used to obtain information about land use and water quality variables. Statistical relationships between macrophyte community composition and clogginess and nutrient, underwater light, and carbon availability and flow disturbance were examined along the eutrophication gradient.Macrophytes with different growth strategies were related to different aspects of eutrophication and non-native taxa were found to dominate eutrophic streams.There was no relationship between nutrient concentrations and nutrient content of the macrophytes but sediment P was correlated with P concentrations in streams.Our results showed that 1) non-native species were common and clogginess was high in unshaded lowland streams with low water clarity and high nutrient and bicarbonate availability; 2) emergent species were associated with high nitrate availability and sediment phosphorus and low disturbance; 3) submerged species prevailed where water column total phosphorus and bicarbonate availability were high; and 4) nutrient concentrations that limit the development of clogginess are expected to be low where bicarbonate is high and flow or other physical disturbance is low. Our findings improve understanding of how stream macrophyte communities respond to changes in water quality related to eutrophication and anthropogenic changes in catchments and will contribute to informed management of macrophytes in streams.

Essential amino acid carbon isotope ratios as indicators of marine macrophyte response to environmental variation

Essential amino acid carbon isotope ratios as indicators of marine macrophyte response to environmental variation

Interspecific Differences in Carbon and Nitrogen Metabolism and Leaf Epiphytic Bacteria among Three Submerged Macrophytes in Response to Elevated Ammonia Nitrogen Concentrations.

Submerged macrophytes in eutrophic aquatic environments adapt to changes in ammonia nitrogen (NH4-N) levels by modifying their levels of free amino acids (FAAs) and soluble carbohydrates (SCs). As symbionts of submerged macrophytes, epiphytic bacteria have obvious host specificity. In the present study, the interspecific differences in the FAA and SC contents of Hydrilla verticillata (Linn. f.) Roylep, Vallisneria natans Hara and Chara braunii Gmelin and their leaf epiphytic bacterial communities were assessed in response to increased NH4-N concentrations. The results revealed that the response of the three submerged macrophytes to NH4-N stress involved the consumption of SCs and the production of FAAs. The NH4-N concentration had a greater impact on the variation in the FAA content, whereas the variation in the SC content was primarily influenced by the species. At the phylum level, the relative abundance of Nitrospirota on the leaves exhibited specific differences, with the order H. verticillata > V. natans > C. braunii. The dominant genera of epiphytic bacteria with denitrification effects on V. natans, H. verticillata and C. braunii leaves were Halomonas, Acinetobacter and Bacillus, respectively. When faced with NH4-N stress, the variation in epiphytic bacterial populations associated with ammonia oxidation and denitrification among submerged macrophytes could contribute to their divergent responses to heightened nitrogen levels.

Ciprofloxacin affects nutrient removal in manganese ore-based constructed wetlands: Adaptive responses of macrophytes and microbes

Ciprofloxacin (CIP) has received considerable attention in recent decades due to its high ecological risk. However, little is known about the potential response of macrophytes and microbes to varying levels of CIP exposure in constructed wetlands. Therefore, lab-scale manganese ore-based tidal flow constructed wetlands (MO-TFCWs) were operated to evaluate the responses of macrophytes and microbes to CIP over the long term. The results indicated that total nitrogen removal improved from 79.93% to 87.06% as CIP rose from 0 to 4 mg L−1. The chlorophyll content and antioxidant enzyme activities in macrophytes were enhanced under CIP exposure, but plant growth was not inhibited. Importantly, CIP exposure caused a marked evolution of the substrate microbial community, with increased microbial diversity, expanded niche breadth and enhanced cooperation among the top 50 genera, compared to the control (no CIP). Co-occurrence network also indicated that microorganisms may be more inclined to co-operate than compete. The abundance of the keystone bacterium (involved in nitrogen transformation) norank_f__A0839 increased from 0.746% to 3.405%. The null model revealed drift processes (83.33%) dominated the community assembly with no CIP and 4 mg L−1 CIP. Functional predictions indicated that microbial carbon metabolism, electron transfer and ATP metabolism activities were enhanced under prolonged CIP exposure, which may contribute to nitrogen removal. This study provides valuable insights that will help achieve stable nitrogen removal from wastewater containing antibiotic in MO-TFCWs.

Mercury Removal from Mining Wastewater by Phytoaccumulation in Autochthonous Aquatic Plant Species

Mining wastewater (MWW) can contain mercury in high concentrations. In this study, four autochthonous aquatic plant species (Eichhornia Crassipes—EC, Marsilea Quadrifolia—MQ, Ludwigia Helminthorrhiza—LH, and Lemna Minor—LM) were identified and tested for phytoaccumulation of total mercury (THg). To better study the accumulation phenomenon and macrophyte responses, this work has been divided into three phases, and pilot-scale reactors have been used to simulate real conditions. The results highlighted that, in case of 15 µgTHg,fed, the bioconcentration factor (BCF) was significantly higher in EC (19.04) and LH (18.41) with respect to MQ and LM (almost six times and two times higher, respectively). EC granted the best results in terms of THg accumulation (50.90%) and lower evapotranspiration of THg phenomenon with respect to LH. A significant decrease of the BCF (from 23.45 to 21.98) and an increase of the TF (from 0.23 up to 0.73) after 42 d highlighted that a breaking-time in terms of THg accumulation was reached due to the deterioration of the roots. In terms of the kinetics of THg removal by bioaccumulation, an HLT of 69.31 d was found, which is more than the breaking-time of the EC system, proving that a periodic replacement of exhausted macrophytes is required to obtain a higher percentage of THg removal.

The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H2O2) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H2O2 can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H2O2 concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H2O2 was maintained up to about 200 μmol m−2 s−1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H2O2 concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H2O2 concentration, following a unique negative relationship with H2O2 concentration. If H2O2 exceeded 45 μmol/gFW, the homeostasis collapsed, and H2O2 and Chl-a significantly declined afterward. The above findings indicate that H2O2 has a negative effect on the physiological condition of the plant. The increase in H2O2 concentration was prevented by antioxidant activities, which elevated with increasing H2O2 concentration.

The temperature increase due to climate warming can affect the photosynthetic responses of aquatic macrophytes from tropical lotic ecosystems

The temperature increase due to climate warming can affect the photosynthetic responses of aquatic macrophytes from tropical lotic ecosystems

Increasing depth reduces macrophyte coverage but increasing transparency promotes composition turnover through environmental thresholds

Context Environmental filters modify the coverage and frequency patterns of macrophyte communities. Aims We characterised the thresholds in depth and transparency at which the macrophyte distribution shifted in an Atlantic Forested wetland. Methods Macrophyte communities were characterised in 150 plots divided into 6 transects. Key results Threshold indicator taxa analysis (TITAN) indicated that free-floating life forms respond negatively to depth and transparency increase. Rooted-floating species responded negatively to an increase in depth and transparency; by contrast, submerged species responded positively to increased transparency. Conclusion TITAN also highlighted that the entire macrophyte community responded negatively to increased depth but exhibited a synchronous turnover among species responding positively and negatively to transparency. Implications Our results demonstrated that macrophyte responses to increasing depth and transparency are non-linear and depend on species life forms.

Linking trait network to growth performance of submerged macrophytes in response to ammonium pulse

Extreme precipitation events caused by climate change leads to large variation of nitrogen input to aquatic ecosystems. Our previous study demonstrated the significant effect of different ammonium pulse patterns (differing in magnitude and frequency) on submersed macrophyte growth based on six plant morphological traits. However, how connectivity among plant traits responds to nitrogen pulse changes, which in turn affects plant performance, has not yet been fully elucidated. The response of three common submersed macrophytes (Myriophyllum spicatum, Vallisneria natans and Potamogeton maackianus) to three ammonium pulse patterns was tested using plant trait network (PTN) analysis based on 18 measured physiological and morphological traits. We found that ammonium pulses enhanced trait connectivity in PTN, which may enable plants to assimilate ammonium and/or mitigate ammonium toxicity. Large input pulses with low frequency had stronger effects on PTNs compared to low input pulses with high frequency. Due to the cumulative and time-lagged effect of the plant response to the ammonium pulse, there was a profound and prolonged effect on plant performance after the release of the pulse. The highly connected traits in PTN were those related to biomass allocation (e.g., plant biomass, stem ratio, leaf ratio and ramet number) rather than physiological traits, while phenotype-related traits (e.g., plant height, root length and AB ratio) and energy storage-related traits (e.g., stem starch) were least connected. V. natans showed clear functional divergence among traits, making it more flexible to cope with unfavorable habitats (i.e., high input pulses with low frequencies). M. spicatum with high RGR revealed strong correlations among traits and thus supported nitrogen accumulation from favourable environments (i.e., low input pulses with high frequencies). Our study highlights the responses of PTN for submerged macrophytes to ammonium pulses depends on their intrinsic metabolic rates, the magnitude, frequency and duration of the pulses, and our results contribute to the understanding of the impact of resource pulses on the population dynamics of submersed macrophytes within the context of global climate change.

Extraction of macrophyte community spatial variation allows to adapt the macrophyte biological index for rivers to the conditions of the middle Dnipro river

The aquatic macrophytes are widely used to indicate the trophic status of water bodies. For Ukrainian water bodies, which represent a wide ecological diversity, the indicator scales of the trophicity regime have not been developed. The purpose of the research is to develop an approach to adapt the Macrophyte Biological Index for Rivers (MBIR) for the conditions of the middle course of the Dnipro River. The difficulty in solving the problem is that the effect of eutrophication occurs against the variability of a complex of environmental factors and processes of natural and anthropogenic origin. The extraction of the eutrophication gradient is a prerequisite for assessing the response of plants to this factor and for constructing adequate indicator scales. The influence of natural factors on aquatic macrophyte communities is assumed to be spatially structured due to the long-term coevolution of the environment and biota. The pure plant response to the effects of eutrophication was assessed after extracting the spatial component of plant community variation. The pure response of aquatic macrophytes to the eutrophication factor provided an opportunity to construct an adequate scale for indicating the trophic status of water bodies, which correlates strongly with the scores of the MBIR. The studies were carried out within the Dnipro-Orilskiy Nature Reserve in the waters of the Dnipro reservoir, which was created on the Dnipro River. The aquatic macrophyte surveys were conducted at 76 locations. Studies were conducted in 50–100 m long plots along the shoreline. The remote sensing data from the Sentinel-2 satellite was used to estimate the indexes of the eutrophication, turbidity, and transparency of the water. The distance-based Moran's eigenvector maps were produced from the geographic coordinates of the sampling points to be used as the spatial variables. Three versions of the Canonical Correspondence Analysis (CCA) were performed: 1) the CCA with the environmental factors and spatial variables as constrained predictors; 2) the CCA with the spatial variables as constrained predictors; 3) the CCA with the environmental factors as constrained predictors and the spatial variables as conditional predictors. The species scores on the corresponding ordinate axes were considered to estimate the species optimum. The variations of the species scores on the corresponding ordinate axes were considered to estimate the species tolerance. Species scores were converted into the CSd indicator values, and tolerance was converted into the Ed coefficients of ecological amplitude. The indicator values and environmental amplitude coefficients obtained for the ordination accounting for spatial effects had no statistically significant correlation coefficients with other indicator scales. The CSd indicator values that were obtained for community ordination accounting for pure environmental effects were statistically significantly correlated with the MBIR and other of the indicator scales. The coefficient of environmental amplitude Ed was negatively correlated with the E. The MBIR revealed that the level of eutrophication in 102 locations (67.1%) was estimated as Bad, in 37 locations (24.3%) it was estimated as Poor, and in 13 locations (8.6%) it was estimated as Moderate. The extraction of the spatial component of macrophyte community variation resulted in the evaluation of indicator scales that correlated statistically significantly with the original MBIR scale.

Photosynthetic Responses of Freshwater Macrophytes to the Daily Light Cycle in Songkhla Lagoon.

Macrophytes play an important role in the freshwater ecosystem. However, human activities and climate change are currently affecting aquatic lakes and species in various ways. The heterogeneity of macrophyte ecophysiology might lead to different responses to changing environments. To understand the photosynthetic responses of freshwater macrophytes to changes in light, six freshwater macrophyte species from Songkhla Lagoon were investigated. The results showed that there was a diurnal response of photosynthetic activities in all species. The Fv/Fm and ∆F/Fm' of all species decreased at midday (9 a.m.-3 p.m.) then recovered at 6 p.m. close to the 6 a.m. level. As well as alpha, the positive relation between alpha and light showed the adaptation of plants. The saturating irradiance (Ik) revealed that plants from different light regimes showed different responses to light and temperature changes. To maintain a positive carbon balance and cope with light and temperature conditions, macrophytes had strategies such as modifying light harvesting capacity and light use. This study provides a better understanding of the vulnerability of each species to environmental changes and photosynthetic responses that enable species from different light regime to adapt to changing light environments.

New insights into the growth response of the macrophyte Vallisneria natans exposed to phosphite

Renewed interest in phosphite, an analog of phosphate, has increased due to its widespread distribution and increasing abundance in many waterbodies. However, up until recently very little is known about their ecological effects on aquatic organisms. Herein we studied the effects of phosphite via root and foliar exposure on the growth responses of the dominant pioneer macrophyte V. natans. Overall, both exposures of phosphite to V. natans resulted in significant reductions in the leaf length, root length, relative growth rate (RGR) and photosynthetic pigments, suggesting phosphite had an inhibitory effect on the plant growth. Our results further confirmed phosphite could induce the oxidative stresses in the V. natans cells, as indicated by the significantly increased intracellular enzyme activities i.e. superoxide dismutase activity (SOD) and malondialdehyde (MDA). Microscopic evidence also showed phosphite penetrated the cell membrane and destroyed membrane integrity under high phosphite stress. Besides, V. natans leaves exhibited intuitive deterioration symptoms, which seemed to be more sensitive to phosphite toxicity than roots. It is concluded that the increased abundance of phosphite in waterbodies cannot be utilized as a bioavailable P source but impose adverse physiological and metabolic limitations to plant growth, which should be receive more attention in the ecological risk assessment. Our result is necessary to build a comprehensive understanding of phosphite biogeochemical behaviors in aquatic ecosystems.

Response of Macrophytes to Periodical Changes in the Water Level in Lake Bol’shoe Miassovo, Southern Urals, Russia

Response of Macrophytes to Periodical Changes in the Water Level in Lake Bol’shoe Miassovo, Southern Urals, Russia

In-situ anatomical and elemental response of aquatic macrophytes against nutrient enrichment in freshwater tropical lakes

Nutrient enrichment in lakes due to municipal wastewater discharge and agricultural run-off leads to excessive growth of algae and aquatic macrophytes leading to their altered trophic states. This paper presents the effect of wastewater-induced nutrient enrichment on the anatomical changes and elemental profiling in three common aquatic macrophytes of freshwater lakes in India’s Central Gangetic Plain. It is observed that with increase in trophic state, biomineral depositions are seen in the leaf anatomy of aquatic macrophytes. Elemental variations in free-floating (Eichhornia crassipes), submerged (Hydrilla verticillata) and emergent (Typha latifolia) macrophytes collected from three different lakes with different catchment characteristics and trophic state using EDS (Energy-Dispersive X-Ray Spectroscopy) spectra show that with increasing trophic state, elemental constituent in the aquatic macrophytes also increases. The rhizome of Eichhornia crassipes showed the formation of calcium oxalate crystals in SEM (Scanning Electron Microscope) images and EDS analysis. Among macrophytes, floating and submerged macrophytes show a greater number of elemental constituents as compared to the emergent macrophytes. The findings of this study show that the anatomical and elemental responses of macrophytes are dependent both on the water quality and trophic state of the lakes. In-situ responses of macrophytes are based on their tolerance level against the pollution load and environmental changes. This study has important implications for understanding the response mechanism of macrophytes with changing water quality and increasing trophic state, which may help in proper management of freshwater ecosystem.

Differential Responses of Eelgrass and Macroalgae in Pacific Northwest Estuaries Following an Unprecedented NE Pacific Ocean Marine Heatwave

The 2013-2016 northeast Pacific Ocean marine heatwave (MHW) had myriad impacts on marine communities, but little is known about how this event affected coastal estuaries. We examined the extent to which elevated temperatures associated with the offshore MHW were observed in four estuaries (Willapa Bay, Washington and Netarts Bay, Yaquina Bay, and Coos Bay, Oregon) and the responses of macrophytes at marine dominated sites within these estuaries. Records of eelgrass (Zostera marina), ulvoid macroalgae (Ulva and Enteromorpha spp.), and environmental characteristics, including water temperature, were analyzed over three periods: before (2006-2010), during (2015-2016), and after (2017-2019) the MHW. During the MHW, all four estuaries experienced “estuarine heatwaves” (anomalous warm water events) at monitoring stations and there was an associated decline in macroalgae biomass. In northern estuaries (Willapa and Netarts bays) where water temperatures are normally higher and estuaries are shallower, aboveground eelgrass biomass declined and did not recover for at least three years after the MHW. In southern estuaries (Yaquina and Coos bays), where water temperatures are normally colder and estuaries are deeper, the MHW was associated with a neutral, or temporarily positive, change in aboveground eelgrass biomass. Our analysis supports the hypothesis that upwelling intensity and estuarine depth determined the severity of MHW impacts on macrophytes at marine dominated sites, and that the colder and deeper estuaries in the south may serve as refuges for eelgrass but not macroalgae. We suggest that estuary-specific responses were predictable given the drivers of macrophyte abundance at marine dominated sites, and that baseline ocean upwelling and estuarine temperature can be used to anticipate macrophyte responses at marine dominated sites to MHWs in the future.

Ecotoxicological responses and removal of submerged macrophyte Hydrilla verticillate to multiple perfluoroalkyl acid (PFAA) pollutants in aquatic environments

The ubiquitous existence of perfluoroalkyl acids (PFAAs) in aquatic environments might pose toxic potential to ecosystems. To assess the ecotoxicological responses and removal of submerged macrophyte to multiple PFAA pollutants in aquatic environments, a typical submerged macrophyte, Hydrilla verticillate, was exposed to solutions with 12 typical PFAAs in the present study. The results showed that PFAAs at concentrations higher than 10 μg/L had significantly passive effects on biomass, relative growth rates, chlorophyll contents, and chlorophyll autofluorescence. PFAAs could induce the accumulation of hydrogen peroxide and lipid peroxidation in H. verticillate. Significant upregulation of CAT was observed in treatments with more than 10 μg/L PFAAs (p < 0.05). The results also showed that 13.53–20.01% and 19.73–37.72% of PFAAs could be removed in treatments without plants and with H. verticillate, respectively. The removal rates of PFAAs were significantly correlated with perfluoroalkyl chain length in treatments with H. verticillate. The removal of PFAAs was suggested to be related to the uptake of plant tissues and biosorption of microbiota. Furthermore, the dominant microbiota and biomarkers were identified in water and biofilm. Betaproteobacteriales was the most dominant microbiota at the order level. The presence of PFAAs could significantly increase the relative abundance of Micrococcales, Verrucomicrobiales, Rhizobiales, Sphingomonadales, Roseomonas, Cyanobium_PCC_6307, and Synechococcales. Our results provide scientific basis for evaluating the ecotoxicological responses and removal of submerged macrophytes in response to multiple PFAA pollutants at environmentally relevant levels, thereby providing insights into PFAA management and removal.

Anthropogenic Stressors in Upland Rivers: Aquatic Macrophyte Responses. A Case Study from Bulgaria.

Upland rivers across Europe still exhibit undisturbed conditions and represent a treasure that we cannot afford to lose. We hypothesize that the combination of pristine and modified conditions could demonstrate biological responses along the stressor gradients. Thus, the response of aquatic macrophyte communities to anthropogenic stressors along upland rivers in Bulgaria was studied. Six stressors were selected out of 36 parameters grouped into hydromorphological, chemical variables and combined drivers (catchment land use). The stressors strongly affected species richness on the basis of biological type (bryophytes vs. vascular plants) and ecomorphological type (hydrophytes vs. helophytes). Hydrological alteration expressed by the change of the river’s base flow and altered riparian habitats has led to a suppression of bryophytes and a dominance of riverbank plant communities. Seventy-five percent of mountain sites were lacking bryophytes, and the vegetation at semi-mountainous sites was dominated by vascular plants. It can be concluded that hydropeaking, organic and inorganic pollution, and discontinuous urban structures caused important modifications in the aquatic macrophyte assemblages. Macrophyte abundance and the biological and ecomorphological type of aquatic macrophytes reflect multi-stressor effects in upland rivers.

Morphological responses of the submerged macrophyte Vallisneria natans along an underwater light gradient: A mesocosm experiment reveals the importance of the Secchi depth to water depth ratio

Bottom light availability (BLA), represented by the ratio of the Secchi disk depth to water depth (SD/WD), plays a fundamental role in the growth and reproduction of submerged macrophytes. However, studies thus far have mainly explored the interactions between macrophyte responses and BLA through field investigations; this means that knowledge of such responses to various underwater light conditions in mesocosm experiments is rudimentary at best. We hypothesized that the growth and clonal reproduction of submerged macrophytes decrease with decreasing BLA and collapse beyond a critical threshold. Here we performed a 42-day outdoor mesocosm experiment with a species of perennial submerged macrophyte, Vallisneria natans, along a decreasing SD/WD gradient. Over this gradient, the primary morphological traits (plant height, root length, plant biomass), relative growth rate, and shoot increment rate of V. natans exhibited a significant trend of initial increase followed by a decrease. The photoinhibition occurred at high and low-light stress, indicating that an intermediate SD/WD (0.55–0.65) provides optimal growth conditions. The number of ramets, ramet biomass, ramet/total biomass ratio, and root/shoot ratio all decreased with decreasing SD/WD ratio, suggesting that V. natans allocates more resources for clonal reproduction and population stability rather than increased shoot biomass at higher BLA conditions. The results of principal component analysis and threshold detection indicated that the growth traits of V. natans had a higher SD/WD tipping point value (0.55 vs. 0.50) than the reproductive capacity and stability, indicating that only values of SD/WD ≥ 0.55 ensured the growth and the vegetative reproduction of V. natans. Additionally, an inverted U-shaped relationship between growth traits and a linear relationship between reproduction and stability reflect the resource allocation strategies and resilience of V. natans to decreasing underwater light conditions.

Flow regime and nutrient input control invasive alien aquatic plant distribution and species composition in small closed estuaries

Nutrient pollution is facilitating the encroachment of invasive aquatic plants in various water bodies globally. This study investigated seasonal aquatic macrophyte responses in two temporarily closed estuaries with different nutrient inputs. Consistent effluent discharge from the upstream wastewater treatment works (WWTW) facilitated the establishment of numerous freshwater invasive alien aquatic plants (IAAPs) in the uThongathi Estuary. IAAPs (Myriophyllum aquaticum, Pistia stratiotes and Pontederia crassipes) were only displaced from the estuary after high flow events (>5 m3 s−1). In the less polluted uMdlotane Estuary nutrient pulses (>1 mg/L DIN) associated with high rainfall changed the aquatic macrophyte composition. The nutrient tolerant non-rooted Ceratophyllum demersum outcompeted the rooted submerged macrophyte Stuckenia pectinata. Species composition changed in response to flow and nutrient inputs, with the exception of emergent macrophytes, such as the grass Echinochloa pyramidalis, that remained consistent in cover and distribution in the uMdlotane Estuary. This study demonstrated that aquatic macrophytes are more responsive to nutrient inputs in unimpacted estuaries compared to consistently nutrient-rich systems where flow is an important driver of IAAPs community dynamics. Many temporarily closed estuaries are subjected to nutrient pollution from WWTWs and restoration efforts such as diversion of discharges to constructed wetlands needs urgent implementation.

Rapid adaptive responses of rosette-type macrophyte Vallisneria natans juveniles to varying water depths: The role of leaf trait plasticity.

Rosette‐type submerged macrophytes are widely distributed across a range of water depths in shallow lakes and play a key role in maintaining ecosystem structures and functions. However, little is known about the rapid adaptive responses of such macrophytes to variations in water depth, especially at the juvenile stage. Here, we conducted a short‐term in situ mesocosm experiment, in which the juveniles of Vallisneria natans were exposed to a water depth gradient ranging from 20 to 360 cm. Twenty‐two leaf‐related traits were examined after 4 weeks of growth in a shallow lake. Most (18) traits of V. natans generally showed high plasticity in relation to water depth. Specifically, juveniles allocated more biomass to leaves and had higher specific leaf area, leaf length‐to‐width ratio, chlorophyll content, and carotenoids content in deep waters, displaying trait syndrome associated with high resource acquisition. In contrast, V. natans juveniles in shallow waters had higher leaf dry matter content, leaf soluble carbohydrate content, carotenoids per unit chlorophyll, and peroxidase activity, pertaining to resource conservation. Notably, underwater light intensity was found to be the key factor explaining the trait plasticity along the water depth gradient, and 1.30 mol photons m−2 d−1 (at 270 cm) could be the optimal irradiance level based on the total biomass of V. natans juveniles. The present study highlights the significance of leaf trait plasticity for rosette‐type macrophytes in response to variations in water depth and sheds new light on the differences between trade‐offs in deep‐ and shallow‐water areas.