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Harvesting is a direct and simple artificial method to regulate submerged macrophyte communities. However, there is still a gap in whether the succession of different seasonal submerged macrophytes can be achieved by harvesting. The morphological, physiological index, competition intensity of Hydrilla verticillata ( H. verticillata ) and underwater light under different harvesting intensities of Potamogeton crispus ( P. crispus ) was studied by a controlled experiment. Under moderate harvesting intensity (harvest 30% and 45% of plant height) of P. crispus , H. verticillata was the least inhibited, resulting in accumulating more Chl a and higher plant height. The underwater light created by moderate-intensity harvesting was favorable for H. verticillata to compete with P. crispus . Thus, moderate-intensity harvesting of P. crispus can promote the growth of H. verticillata . In practice, moderate harvesting intensity of P. crispus can be used to create conditions for the growth of summer species to achieve seasonal succession of submerged macrophytes and maintain the clear-water state of the lake.

In recent years, iron oxide nanoparticles (Fe O NP) have emerged as a promising eco-friendly approach to mitigate various abiotic stresses. However, the role of surface-coated Fe O NP with bio-derived organic compounds, particularly fulvic acid, in mitigating saline-alkali stress in Chinese kale plants has not yet been explored. In this study, we investigated for the first time the effects of green-synthesized Fe O NP, both uncoated (UFe) and fulvic acid-coated (FFA), on mitigating saline-alkali stress in Chinese kale, with a specific focus on modulating physiological responses and biochemical parameters. Both UFe and FFA alleviated growth inhibition caused by saline-alkali stress; however, FFA consistently outperformed UFe across all measured parameters. UFe and FFA treatments restored shoot and root biomass, improved relative water content, and stabilized the membrane integrity by reducing electrolyte leakage and lipid peroxidation. Photosynthetic capacity was strongly enhanced, as reflected by higher net photosynthetic rate, stomatal conductance, Rubisco activity, chlorophyll index, and PSII efficiency. Oxidative stress was alleviated through significant reductions in H O and MDA, supported by activation of SOD, CAT, and APX enzymes and strong recovery of the ascorbate-glutathione cycle, particularly under FFA treatment. At the transcriptional level, both treatments upregulated genes associated with antioxidant defense (SOD, CAT, APX, GR, DHAR), osmolyte biosynthesis (P5CS1), stress tolerance (LEA), photosynthesis (RBCS, LHCB1), and secondary metabolism (PAL, CYP79F1); however, this response was more pronounced in FFA-treated plants. These transcriptional changes were consistent with enhanced accumulation of osmolytes, including soluble sugars, free amino acids, and proline. Untargeted LC-MS/MS metabolomics identified 46 differentially regulated metabolites spanning sugars, amino acids, organic acids, glucosinolates, and phenolics. Multivariate analyses (PLS-DA and VIP scores) further highlighted proline, glucobrassicin, sinigrin, tryptophan, citric acid, and caffeoylquinic derivatives as key discriminators, enriched in both treatments but more substantially in stress + FFA, reflecting enhanced osmoprotection, redox stability, and secondary metabolism. Fulvic acid functionalization substantially enhanced the stress-mitigation potential of Fe O NP, with FFA conferring significant improvements in growth, photosynthesis, antioxidant defense, gene regulation, and metabolic reprogramming, suggesting its potential as a nano-biofertilizer for saline-alkali soils.

Heterophyllous aquatic plants produce aerial (i.e., floating and terrestrial) and submerged leaves—the latter lack stomata—while homophyllous plants contain only submerged leaves, and cannot survive on land. To identify whether differences in morphogenetic potential and/or physiological stress responses are responsible for variation in phenotypic plasticity between two plants types, responses to abscisic acid (ABA) and salinity stress were compared between the closely related, but ecologically diverse pondweeds, Potamogeton wrightii (heterophyllous) and P. perfoliatus (homophyllous). The ABA-treated (1 or 10 μM) P. wrightii plants exhibited heterophylly and produced leaves with stomata. The obligate submerged P. perfoliatus plants were able to produce stomata on their leaves, but there were no changes to leaf shape, and stomatal production occurred only at a high ABA concentration (10 μM). Under salinity stress conditions, only P. wrightii leaves formed stomata. Additionally, the expression of stress-responsive NCED genes, which encode a key enzyme in ABA biosynthesis, was consistently up-regulated in P. wrightii , but only temporarily in P. perfoliatus . The observed species-specific gene expression patterns may be responsible for the induction or suppression of stomatal production during exposure to salinity stress. These results suggest that the two Potamogeton species have an innate morphogenetic ability to form stomata, but the actual production of stomata depends on ABA-mediated stress responses specific to each species and habitat.

Reproductive allocation is a key process in the plant life cycle and aquatic plants exhibit great diversity in their reproductive systems. In the present study, we conduct a field investigation of three aquatic macrophytes: Stuckenia pectinata, Myriophyllum spicatum, and Potamogeton perfoliatus. Our results showed that widespread species, including S. pectinata and M. spicatum had greater plasticity in their allocation patterns in the form of increased sexual and asexual reproduction, and greater potential to set seeds and increase fitness in more eutrophic environments. P. perfoliatus also exhibited a capacity to adopt varied sexual reproductive strategies such as setting more offspring for the future, although only in clear conditions with low nutrient levels. Our results establish strategies and mechanisms of some species for tolerating and surviving in varied eutrophic lake conditions.

• Background and Aims Molecular-based studies of thermotolerance have rarely been performed on wild plants, although this trait is critical for summer survival. Here, we focused on thermotolerance and expression of heat shock transcription factor A2 (HSFA2) and its putative target gene (chloroplast-localized small heat shock protein, CP-sHSP) in two allied aquatic species of the genus Potamogeton (pondweeds) that differ in survival on land. • Methods The degree of thermotolerance was examined using a chlorophyll bioassay to assess heat injury in plants cultivated under non-and heat-acclimation conditions. Potamogeton HSFA2 and CP-sHSP genes were identified and their heat-induction was quantified by real-time PCR. • Key Results The inhibition of chlorophyll accumulation after heat stress showed that Potamogeton malaianus had a higher basal thermotolerance and developed acquired thermotolerance, whereas Potamogeton perfoliatus was heat sensitive and unable to acquire thermotolerance. We found two duplicated HSFA2 and CP-sHSP genes in each species. These genes were induced by heat shock in P. malaianus, while one HSFA2a gene was not induced in P. perfoliatus. In non-heat-acclimated plants, transcript levels of HSFA2 and CP-sHSP were transiently elevated after heat shock. In heat-acclimated plants, transcripts were continuously induced during sublethal heat shock in P. malaianus, but not in P. perfoliatus. Instead, the minimum threshold temperature for heat induction of the CP-sHSP genes was elevated in P. perfoliatus. • Conclusions Our comparative study of thermotolerance showed that heat acclimation leads to species-specific changes in heat response. The development of acquired thermotolerance is beneficial for survival at extreme temperatures. However, the loss of acquired thermotolerance and plasticity in the minimum threshold temperature of heat response may be favourable for plants growing in moderate habitats with limited daily and seasonal temperature fluctuations.

Investigations were carried to unravel mechanism(s) for higher tolerance of floating over submerged leaves of long leaf pondweed (Potamogeton nodosus Poir) against photoinhibition. Chloroplasts from floating leaves showed ~5- and ~6.4-fold higher Photosystem (PS) I (reduced dichlorophenol-indophenol → methyl viologen → O₂) and PS II (H₂O → parabenzoquine) activities over those from submerged leaves. The saturating rate (V ₘₐₓ) of PS II activity of chloroplasts from floating and submerged leaves reached at ~600 and ~230 µmol photons m⁻² s⁻¹, respectively. Photosynthetic electron transport rate in floating leaves was over 5-fold higher than in submerged leaves. Further, floating leaves, as compared to submerged leaves, showed higher F ᵥ/F ₘ (variable to maximum chlorophyll fluorescence, a reflection of PS II efficiency), as well as a higher potential to withstand photoinhibitory damage by high light (1,200 µmol photons m⁻² s⁻¹). Cells of floating leaves had not only higher mitochondria to chloroplast ratio, but also showed many mitochondria in close vicinity of chloroplasts. Electron transport (NADH → O₂; succinate → O₂) in isolated mitochondria of floating leaves was sensitive to both cyanide (CN⁻) and salicylhydroxamic acid (SHAM), whereas those in submerged leaves were sensitive to CN⁻, but virtually insensitive to SHAM, revealing the presence of alternative oxidase in mitochondria of floating, but not of submerged, leaves. Further, the potential of floating leaves to withstand photoinhibitory damage was significantly reduced in the presence of CN⁻ and SHAM, individually and in combination. Our experimental results establish that floating leaves possess better photosynthetic efficiency and capacity to withstand photoinhibition compared to submerged leaves; and mitochondria play a pivotal role in protecting photosynthetic machinery of floating leaves against photoinhibition, most likely by oxidation of NAD(P)H and reduction of O₂.

BACKGROUND AND AIMS: The plastic alterations of clonal architecture are likely to have functional consequences, as they affect the spatial distribution of ramets over patchy environments. However, little is known about the effect of mechanical stresses on the clonal growth. The aim of the present study was to investigate the clonal plasticity induced by mechanical stress consisting of continuous water current encountered by aquatic plants. More particularly, the aim was to test the capacity of the plants to escape this stress through clonal plastic responses. METHODS: The transplantation of ramets of the same clone in two contrasting flow velocity conditions was carried out for two species (Potamogeton coloratus and Mentha aquatica) which have contrasting clonal growth forms. Relative allocation to clonal growth, to creeping stems in the clonal biomass, number and total length of creeping stems, spacer length and main creeping stem direction were measured. KEY RESULTS: For P. coloratus, plants exposed to water current displayed increased total length of creeping stems, increased relative allocation to creeping stems within the clonal dry mass and increased spacer length. For M. aquatica, plants exposed to current displayed increased number and total length of creeping stems. Exposure to current induced for both species a significant increase of the proportion of creeping stems in the downstream direction to the detriment of creeping stems perpendicular to flow. CONCLUSIONS: This study demonstrates that mechanical stress from current flow induced plastic variation in clonal traits for both species. The responses of P. coloratus could lead to an escape strategy, with low benefits with respect to sheltering and anchorage. The responses of M. aquatica that may result in a denser canopy and enhancement of anchorage efficiency could lead to a resistance strategy.

The role of positive interactions in structuring plant and animal communities is increasingly recognized, but the generality of current theoretical models has remained practically unexplored in animal communities. The stress gradient hypothesis predicts a linear increase in the intensity of facilitation as environmental conditions become increasingly stressful, whereas other theoretical models predict a maximum at intermediate environmental stress. We tested how competition and facilitation between herbivores change over a manipulated gradient of nutrient availability. We studied the effect of grazing by pond snails (Lymnaea stagnalis L.) as bulk grazers on aquatic caterpillars (Acentria ephemerella Denis and Schiffermüller) as small specialist grazers along an experimental gradient of environmental nutrient concentration. Higher nutrient levels increased overall total plant biomass but induced a shift toward dominance of filamentous algae at the expense of macrophytes. Facilitation of caterpillars by snail presence peaked at intermediate nutrient levels. Both caterpillar biomass and caterpillar grazing on macrophytes were highest at intermediate nutrient levels. Snails facilitated caterpillars possibly by removing filamentous algae and increasing access to the macrophyte resource, whereas they did not affect macrophyte biomass or C : nutrient ratios, a measure of food quality. We conclude that competition and facilitation in herbivore communities change along nutrient availability gradients that affect plant biomass and community composition. Understanding how interspecific interactions may change in strength and direction along environmental gradients is important to predict how the diversity and structure of communities may respond to the introduction or removal of herbivore species in ecosystems.

We tested whether Tundra Swans use information on the spatial distribution of cryptic food items (belowground Sago pondweed tubers) to shape their movement paths. In a continuous environment, swans create their own food patches by digging craters, which they exploit in several feeding bouts. Series of short (<1 m) intra-patch movements alternate with longer inter-patch movements (>1 m). Tuber biomass densities showed a positive spatial auto-correlation at a short distance (<3 m), but not at a larger distance (3-8 m). Based on the spatial pattern of the food distribution (which is assumed to be pre-harvest information for the swan) and the energy costs and benefits for different food densities at various distances, we calculated the optimal length of an inter-patch movement. A swan that moves to the patch with the highest gain rate was predicted to move to the adjacent patch (at 1 m) if the food density in the current patch had been high (>25 g/m⁲) and to a more distant patch (at 7-8 m) if the food density in the current patch had been low (<25 g/m⁲). This prediction was tested by measuring the response of swans to manipulated tuber densities. In accordance with our predictions, swans moved a long distance (>3 m) from a low-density patch and a short distance (<3 m) from a high-density patch. The quantitative agreement between prediction and observation was greater for swans feeding in pairs than for solitary swans. The result of this movement strategy is that swans visit high-density patches at a higher frequency than on offer and, consequently, achieve a 38% higher long-term gain rate. Swans also take advantage of spatial variance in food abundance by regulating the time in patches, staying longer and consuming more food from rich than from poor patches. We can conclude that the shape of the foraging path is a reflection of the spatial pattern in the distribution of tuber densities and can be understood from an optimal foraging perspective.

Compared to terrestrial environments, grazing intensity on belowground plant parts may be particularly strong in aquatic environments, which may have great effects on plant-community structure. We observed that the submerged macrophyte, Potamogeton pectinatus, which mainly reproduces with tubers, often grows at intermediate water depth and that P. perfoliatus, which mainly reproduces with rhizomes and turions, grows in either shallow or deep water. One mechanism behind this distributional pattern may be that swans prefer to feed on P. pectinatus tubers at intermediate water depths. We hypothesised that when swans feed on tubers in the sediment, P. perfoliatus rhizomes and turions may be damaged by the uprooting, whereas the small round tubers of P. pectinatus that escaped herbivory may be more tolerant to this bioturbation. In spring 2000, we transplanted P. perfoliatus rhizomes into a P. pectinatus stand and followed growth in plots protected and unprotected, respectively, from bird foraging. Although swan foraging reduced tuber biomass in unprotected plots, leading to lower P. pectinatus density in spring 2001, this species grew well both in protected and unprotected plots later that summer. In contrast, swan grazing had a dramatic negative effect on P. perfoliatus that persisted throughout the summer of 2001, with close to no plants in the unprotected plots and high densities in the protected plots. Our results demonstrate that herbivorous waterbirds may play a crucial role in the distribution and prevalence of specific plant species. Furthermore, since their grazing benefitted their preferred food source, the interaction between swans and P. pectinatus may be classified as ecologically mutualistic.