Submerged Macrophyte Species Research Articles

Variability response of aquatic macrophytes in inland lakes: A case study of Lake Nasser

Aquatic macrophytes are plants that live in water or wet soil, grow profusely in lakes and waterways, and provide several ecological benefits. Lake Nasser, an artificial reservoir, has been the most critical element in Egypt’s social and economic development. The temperature changes and the Ethiopian Renaissance Dam represent the most prominent challenge that poses the greatest threat to the Lake’s water. Intense disturbance in aquatic macrophytes, caused by the very large fluctuation in water level and temperature was observed. Currently, only three submerged macrophyte species (Myriophyllum spicatum, Potamogeton schweinfurthii and Najas marina) were detected at Lake Nasser. The composition and structure of the submerged macrophytes community had a pronounced impact on fish production and diversity in the Lake. As the Lake is located in the subtropical region, where warm water fosters plant growth, the dangers of some macrophytes may be high. Therefore, additional studies are needed to avoid the negative effects of climate change and the impact of the Renaissance Dam on Lake Nasser and to optimize the most benefit of its aquatic macrophytes.

Effect of water exchange rate on interspecies competition between submerged macrophytes: functional trait hierarchy drives competition

The “competition-trait similarity” and “competition-trait hierarchy” hypotheses can be used to predict competitive outcomes between terrestrial plant species in response to environmental variation. However, their validity in aquatic plants remains poorly understood, particularly in terms of variation in the water exchange rate (WER). We compared competitive outcomes and variation in functional traits in two pairs of submerged macrophytes (Vallisneria natans vs. Myriophyllum aquaticum and V. natans vs. Myriophyllum spicatum) at three levels of WER using the replacement series method. We found that the relative competitive ability of V. natans consistently decreased with increasing WER and decreasing the planting proportion of V. natans. Under these conditions, V. natans experienced reduced plant nutrient content and the inhibition of dissolved carbon dioxide absorption, which eventually shifted this species from a stronger to weaker competitor. With increasing WER and decreasing the planting proportion of V. natans, the below-:above-ground biomass ratio and root diameter increased, while the root length and specific root length decreased, for V. natans. In contrast, all of these traits exhibited the opposite patterns for the co-cultured Myriophyllum species. In addition, the branch number per plant mass increased in V. natans but exhibited no change in co-cultured Myriophyllum species under the same conditions. Our results indicate that WER affected the outcome of interspecies competition between submerged macrophyte species. Moreover, the relative competitive ability of each species within a pair was more strongly linked to species competition-trait hierarchy than to competition-trait similarity.

The interplay of nutrients, dissolved inorganic carbon and algae in determining macrophyte occurrences in rivers

Nitrogen and phosphorous concentrations are widely considered to drive macrophyte assemblages in rivers. However, Dissolved Inorganic Carbon (DIC) – available for plants as CO2 and HCO3− – is also of major relevance. Based on literature, we present a conceptual model on the interaction between algae, macrophytes, DIC, pH, light, N, P and the surface water and sedimental compartment. Analysing two separate datasets (i) on river physico-chemistry and chlorophyll-a, and (ii) on river physico-chemistry and macrophytes we quantify three connections within this concept: (1) the correlation of chlorophyll-a versus pH, (2) the correlation of TP versus chlorophyll-a and (3) the occurrence of HCO3-users and CO2-only-users among macrophytes along the DIC gradient. Chlorophyll-a correlated positively with pH (R-squared = 77%, p < .001) due to increased carbon dioxide uptake of phytoplankton. Surface water TP did not linearly correlate with chlorophyll-a concentrations. Obligate and optionally submerged macrophyte species that utilise HCO3− were separated from CO2-only-users by HCO3− concentrations, with an area under the curve (AUC) of 68% and 70% (both p < .001) between groups. Obligate and optionally submerged macrophyte assemblages only composed of HCO3-users and those exclusively composed of CO2-only-users showed an even stronger separation based on the HCO3− concentration, with both an AUC of 82% and 78% (both p < .001). Our results underline that DIC can greatly affect riverine macrophytes. However, absolute concentrations of HCO3− are less relevant, while the connection to pH is more important, reflecting CO2 concentrations. River monitoring and management should consider the interaction between nutrients DIC, surface water and sedimental compartment as important factors affecting macrophyte occurrence, rather than solely focussing on surface water nutrients.

Selecting submerged macrophyte species for replanting in Mediterranean eutrophic wetlands

The criteria to select submerged plant species for restoration still need further evaluations for a better understanding of their suitability prior to undertaking large plantings which represent a large effort in terms of economical and human resources. In this study, previously to the restoration of a eutrophic area (Tancat de la Pipa) within the Albufera de València Natural Park, the growth of three submerged plants (Ceratophyllum demersum, Myriophyllum spicatum and Stuckenia pectinata), an amphibious species (Ranunculus sceleratus), and three charophytes species (Chara vulgaris, Tolypella glomerata and Nitella hyalina) has been evaluated under controlled laboratory conditions in order to rank their overall performance, based on their growth traits (total height reached, production of roots, etc.). The ranking was in the order of M. spicatum ~ S. pectinata > C. demersum and within the charophytes C. vulgaris > T. glomerata > N. hyalina. Moreover, considering the relationships of these species with other biotic factors (bird, fish and crayfish disturbance and herbivory) which can prevent the success of the revegetation, we propose starting the planting with M. spicatum, S. pectinata, R. sceleratus and C. vulgaris, which are available, are very easy to cultivate by vegetative reproduction from shoot tips and small specimens, have appropriate growth traits and certain degree of resistance to biotic factors. The other species (C. demersum, N. hyalina and T. glomerata) could be used subsequently once a suitable cover of submerged vegetation is settled in the area to enhance biodiversity, trying to reach the diversity which existed in the past in that area. Hence, the structural and functional complexity of the system under restoration might be achieved.

Functional traits of submerged macrophytes in eutrophic shallow lakes affect their ecological functions

Trait-based approaches have been widely used to explore the relationships between submerged macrophytes and their surrounding environments. However, the effects of functional traits on ecological functions of submerged macrophytes in eutrophic lakes are still not well understood. Here, 1745 individuals of eight dominant submerged macrophyte species in 19 Yangtze floodplain lakes were collected and classified as needle-leaf (Myriophyllum spicatum, Ceratophyllum demersum, Stuckenia pectinatus, Najas minor) or flat-leaf (Vallisneria natans, Hydrilla verticillata, Potamogeton wrightii, Potamogeton maackianus) types according to photosynthetic trait-based cluster analysis. The flat-leaf type submerged macrophytes possessed greater photosynthetic (e.g. higher Fv/Fm) and morphological traits (e.g. higher SLA), while the needle-leaf types held greater stoichiometric traits (e.g. higher plant N/P). Moreover, the RDA analysis indicated that water depth (distribution depth of submerged macrophytes) was the key factor influencing functional traits of flat-leaf types, while it was water quality (e.g. WTP and WChl a) for the needle-leaf types. Furthermore, the flat-leaf types showed better performance in improving underwater light conditions (e.g. SD, Kd, Zeu/WD and Red/Blue) and water quality (e.g. WChl a and TSM). Additionally, distribution depth (WD) of the flat-leaf types was shallower than the needle-leaf types in eutrophic shallow lakes along the middle-lower reaches of the Yangtze River. Our study highlights that functional traits of submerged macrophytes in eutrophic shallow lakes affect their ecological functions.

Spatio-temporal dynamic of submerged aquatic macrophytes in Lake Sapanca

Aquatic macrophytes are one of the key components of freshwater ecosystems and contribute to ecosystem functioning and environmental sustainability. They are assumed to be an ideal biomonitoring tool in long-term monitoring programs implemented by the EU Water Framework Directive due to their sensitivity to environmental factors. Therefore, this study focuses on the evaluation of the ecological status in Lake Sapanca using macrophyte composition and abundance in order to make future predictions on the health of aquatic ecosystems and to form effective management. Submerged macrophyte assemblages related to environmental parameters were investigated from February to November of 2017. A total of 12 submerged macrophyte species were recorded in the littoral zone of the lake. The main findings on the most dominant 7 species of this community indicated significant differences among stations and seasons. They also revealed that submerged macrophyte density was shaped in relation to environmental variables, particularly temperature and nutrients. Submerged macrophyte assemblages reached their highest species number and biomass value (5312 gm?2) in summer, while no species was recorded in winter. High biomass values of these species corresponded with lower macrophyte diversity. The macrophyte index results demonstrated that Lake Sapanca is at a critical level in terms of nutrient enrichment. More frequent observation of species such as Ceratophyllum demersum and Elodea canadensis, which indicated "massive" nutrient enrichment, revealed that the ecological status of the lake varies from meso- to eutrophic at the local level.

Light intensity effects on the growth and biomass production of submerged macrophytes in different water strata

This study investigated the effects of light intensity on growth and biomass production of three submerged macrophyte species including Hydrilla verticillata, Vallisneria natans, and Ceratophyllum demersum in different water strata. For this purpose, water was classified into six strata designed: 5 cm, 30 cm, 60 cm, 90 cm, 120 cm, and 150 cm in the field under natural conditions. Results revealed that very high and very low heat intensity affected the growth of submerged macrophyte species differently. The growth of macrophytes was inhibited because of the high light intensity at 5 cm water strata. However, at 150-cm water strata, the macrophytes were died due to low light penetration. Among macrophyte species, the biomass production of Hydrilla verticillata and Ceratophyllum demersum was highest in the water strata at 90 cm, while Vallisneria natans were died in water strata of 120 cm due insufficient illumination. Furthermore, Hydrilla verticillata and Ceratophyllum demersum showed resilience and grown normally in later stages. The highest height of Vallisneria natans (35.3 cm), including Hydrilla verticillata (45.8 cm) and Ceratophyllum demersum (28.2 cm), was observed in water strata at 30, 60, and 60 cm. This study revealed that high and low light intensity affects the chlorophyll contents of macrophytes that results an impact on their growth and biomass production.

To what degree do spatial and limnological predictors explain the occurrence of a submerged macrophyte species in lotic and semi-lotic/lentic environments of a dammed river?

Insufficient knowledge about ecology of weed macrophytes from a large-scale perspective narrows the necessary decision-making for biodiversity conservation. The present study aimed to assess the occurrence frequency of Egeria densa in lotic and lentic/semi-lotic environments from a Brazilian dammed river, as well as to quantify the attributed explanation (pure or combined) by limnological and spatial variables on species occurrence frequency. Between 2006 and 2010, we repeatedly visited sample points classified as lotic (45) or lentic/semi-lotic environments (23) to collect data on species occurrence and limnological variables. We also generated spatial variables derived from latitude and longitude of sample points. E. densa showed a recurrent occurrence in the sample points classified as lentic/semi-lotic. Both spatial variables (16) and limnological variables (total phosphorus, nitrate, nitrite, transparency and turbidity) significantly contributed to explaining the species occurrence frequency. Forty-nine percent of the occurrence frequency variation was accounted purely by spatial variables. However, less than five percent of occurrence frequency variation was accounted purely by limnological variables. The several dams placed along the river determined the lentic/semi-lotic environments formation and regulated the dispersion processes of individuals of E. densa, consequently causing a recurrent occurrence of this species in particular environmental classes.

Effects of Diversity, Coverage and Biomass of Submerged Macrophytes on Nutrient Concentrations, Water Clarity and Phytoplankton Biomass in Two Restored Shallow Lakes

Transplantation of submerged macrophytes to restore shallow lakes has been used as an effective measure to maintain a clear water state. Water quality is highly correlated with submerged macrophytes community, however, the relationships between water quality and the diversity, coverage and biomass of submerged macrophytes are, so far, not yet well studied. We analyzed the correlations of nutrient concentrations, water clarity and phytoplankton biomass with the metrics of submerged macrophytes community in two Chinese restored shallow subtropical lakes, Lake Wuli (Wuli-E, 5 ha) and Lake Qinhu (Qin-E, 8 ha). A similar biomass of submerged macrophytes was transplanted into each lake, while both the species richness and coverage of macrophytes in Qin-E were lower than Wuli-E. After a 1–2-year restoration, the diversity almost had no change, but the biomass density and coverage decreased in Wuli-E. As for Qin-E, the coverage of submerged macrophytes increased but biomass density and diversity decreased. The dominance of canopy-forming submerged macrophyte species Myriophyllum spicatum was observed in Qin-E and less meadow-forming biomass and species was observed than that in Wuli-E. Moreover, it was also observed that Wuli-E had a better water quality than that of Qin-E after transplantation. Path analysis results showed that macrophyte coverage and the diversity related to meadow-forming species (e.g., Vallisneria spinulosa) had strong effects on enhancing clarity and reducing nutrient concentrations. But the high biomass density accompanied by the canopy-forming species like M. spicatum was unfavorable for controlling nutrients. Our results provide important insight into the different roles that macrophyte diversity, biomass and coverage play in improving water clarity and controlling nutrient concentrations. This new knowledge will be instrumental in implementing more effective lake restoration, especially using macrophyte transplantation as a restoration tool in warm shallow lakes.

How many submerged macrophyte species are needed to improve water clarity and quality in Yangtze floodplain lakes?

Successful re-establishment and maintenance of submerged macrophytes is a pivotal problem for the restoration of shallow eutrophic lakes, since submerged macrophytes can facilitate a shift of lake ecosystems from a turbid water state to a clear water state through their structuring roles. However, little is known about the optimal number of macrophyte species (species richness) needed for the recovery of shallow eutrophic lakes. Here, we investigated 19 shallow eutrophic lakes along the mid-lower reaches of the Yangtze River to reveal the underlying interrelations among water clarity, water quality and species richness. Our results showed positive correlations of water nutrients (TN and TP) with Kd and Red/Blue light ratio, suggesting that bad water quality can significantly lower water clarity. The results of path analysis indicated that the underwater light climate directly affects morphological and physiological traits and species richness of submerged macrophytes. Changes in functional traits also affected significantly the species richness of submerged macrophytes. Moreover, the presence of submerged macrophytes not only had positive effects on the underwater light climate (water clarity), but also on water quality. Most importantly, the assemblage of three or more submerged macrophyte species can significantly improve water clarity in these sampled eutrophic lakes, but not water quality. Additionally, the basic species assemblage of Myriophyllum spicatum and Vallisneria natans can be used for restoration of submerged macrophytes in shallow eutrophic Yangtze floodplain lakes. It is concluded that species richness and species assemblage are critical for recovery of submerged macrophytes in shallow eutrophic lakes.

Correction: Xu, C., et al. Effects of Artificial LED Light on the Growth of Three Submerged Macrophyte Species during the Low-Growth Winter Season: Implications for Macrophyte Restoration in Small Eutrophic Lakes. Water 2019, 11, 1512

The authors wish to make the following corrections to this paper [...]

Correlation study of Submerged Macrophytes Growth and Environmental Factors in Lake Qionghai Wetland

The characteristics of submerged macrophytes communities, water environment factors and substrate environmental factors of Lake Qionghai wetland were investigated in April 2018 by laying out 21 sample points. A total of 8 submerged macrophytes species were recorded in the 21 sample points. Myriophyllum spicatum, Vallisneria natans, Ceratophyllum demersum, and Potamogeton malaianus were the main submerged macrophytes species in Lake Qionghai wetland. The depth of submerged macrophytes was less than 2m, and submerged plants were found in most areas of lakeside zone. Submerged macrophytes had a strong adaptability to substrate, it could grow in artificial stacked group rocks, natural lakeside stone sand, natural alluvial river sand, loess and silt, etc, but the substrate with high nutrition was more favorable to the growth of submerged macrophytes than the substrate with low nutrition. Water nutrients, bottom nutrients and water depth are the decisive factors affecting the growth of submerged macrophytes, while transparency, chemical oxygen demand, light, temperature, water flow and pH are the decisive factors affecting the survival of submerged macrophytes.

Seasonal Changes in the Chemical Composition and Anaerobic Digestibility of Harvested Submerged Macrophytes

Anaerobic digestion is an effective method for treating excessive submerged macrophytes, which are causing severe environmental issues worldwide. The biomethane potential (BMP) of submerged macrophytes varies depending on the seasonal changes in the lignin content of each species and the species composition of harvested submerged macrophytes. In this study, the seasonality of the chemical composition and BMP of three dominant submerged macrophytes species, i.e., Egeria densa, Elodea nuttallii, and Potamogeton maackianus, were elucidated. The theoretical monthly methane yield (TMMY) and theoretical annual methane yield (TAMY) of the submerged macrophytes harvested from Lake Biwa were then estimated. The methane yields of E. densa and E. nuttallii were 212–252 and 189–284 mL g-VS−1, respectively, while that of P. maackianus was lower, at 140–165 mL g-VS−1. Although chemical composition parameters, such as the lignin content, significantly changed between different seasons (p < 0.05), they range from only 7.8–14.6%. Therefore, the seasonal variations in the methane yield of the harvested submerged macrophytes depend on the species composition. The calculated TMMY of submerged macrophytes harvested from Lake Biwa was lower from autumn to spring (171–186 mL g-VS−1) than that in summer (213–231 mL g-VS−1) due to the predominance of P. maackianus. The estimated TAMYs for several years revealed that a constant volume of methane gas could be obtained annually from the harvested submerged macrophyte.

First Report on the Occurrence of Invasive Macrophyte Elodea canadensis Michx. in Sapanca Lake

Objective: Elodea canadensis Michx. is a common invasive aquatic macrophyte that has successfully spread along European, Asian and Australian inland waters. The aim of this study is to evaluate the presence and distribution of an alien and invasive species, E. canadensis, in Sapanca Lake (Turkey) for the first time. Materials and Methods: Sampling for macrophytes and main environmental parameters was carried out seasonally between the years 2016 and 2017 along the coasts of Sapanca Lake. Macrophytes samples were taken from bounded areas. Morphological observations were made on both unfixed-living and dried materials, and morphological details were observed under a light microscope. Results: Elodea canadensis Michx. was reported for the first time in Sapanca Lake during the spring period of 2016 with water temperatures of 20.9 ±0.9°C. A total of six submerged macrophytes species were recorded together with E. canadensis. Conclusion: The first record of this species in Sapanca Lake is important for contributing to the changing biodiversity dynamics of the lake and also contributes to the assessment of the possible ecological and economic risks of the region in terms of lake management.

Effects of Artificial LED Light on the Growth of Three Submerged Macrophyte Species during the Low-Growth Winter Season: Implications for Macrophyte Restoration in Small Eutrophic Lakes

Eutrophication of lakes is becoming a global environmental problem, leading to, among other things, rapid reproduction of phytoplankton, increased turbidity, loss of submerged macrophytes, and the recovery of these plants following nutrient loading reduction is often delayed. Artificial light supplement could potentially be a useful method to help speeding up recovery. In this study, three common species of submerged macrophytes, Vallisneria natans, Myriophyllum spicatum and Ceratophyllum demersum, were exposed to three LED light treatments (blue, red and white) and shaded (control) for 100 days (from 10 November 2016 to 18 January 2017) in 12 tanks holding 800 L of water. All the three LED light treatments promoted growth of the three macrophyte species in terms of shoot number, length and dry mass. The three light treatments differed in their effects on the growth of the plants; generally, the red light had the strongest promoting effects, followed by blue and white. The differences in light effects may be caused by the different photosynthetic photon flux density (PPFD) of the lights, as indicated by an observed relationship of PPFD with the growth variables. The three species also responded differently to the light treatments, V. natans and C. demersum showing higher growth than M. spicatum. Our findings demonstrate that artificial light supplement in the low-growth winter season can promote growth and recovery of submerged macrophytes and hence potentially enhance their competitiveness against phytoplankton in the following spring. More studies, however, are needed to elucidate if LED light treatment is a potential restoration method in small lakes, when the growth of submerged macrophytes are delayed following a sufficiently large external nutrient loading reduction for a shift to a clear macrophyte state to have a potential to occur. Our results may also be of relevance when elucidating the role of artificial light from cities on the ecosystem functioning of lakes in urban areas.

High-resolution imaging of rhizosphere oxygen (O2) dynamics in Potamogeton crispus: effects of light, temperature and O2 content in overlying water

Radial oxygen loss (ROL) for macrophytes is intimately involved in their survival and growth, thus detailed characterizations of ROL and its implication for geochemical processes are of particular interest. We experimentally investigated ROL patterns from the submerged macrophyte species Potamogeton crispus and determined how light, temperature and O2 content in overlying water regulate O2 micro-distributions in the rhizosphere. Planar optodes were firstly used for non-destructive imaging of the O2 micro-distributions around single roots of P. crispus planted in rhizotrons containing sediment. The dynamic changes in below-ground O2 concentrations and oxygenation expansion at different light intensities (0–216 μmol photons m−2), temperatures (14 and 25 °C) and O2 content in overlying waters (0–256 μmoL−1) were quantified. P. crispus-mediated ROL is predominantly localized to the root apices with an average rate of 168.1 ± 21.4 nmol m−2 s−1 under nearly natural conditions (light, saturated overlying water at 14 °C), maintaining a visible oxygenated rhizosphere zone with a radius of 1.33 ± 0.21 mm. ROL is closely correlated with light intensity, suggesting photosynthetic O2 evolution. In darkness, the rhizosphere O2 availability is significantly reduced and strongly affected by the O2 content in overlying water, which passively diffuses into the plant leaves. Elevated temperatures lead to diminished ROL as a result of increased O2 demand of the surrounding sediment. A high O2 microheterogeneity around P. crispus root apices is firstly demonstrated, and we provide direct empirical evidences that ROL are regulated dynamically by the shifting light, temperature and O2 content in overlying water.

Macrophyte identity shapes water column and sediment bacterial community

By assembling mesocosms and utilizing high-throughput sequencing, we aim to characterize the shifts of the bacterial community in freshwaters driven by two contrasting submerged macrophyte species, Ceratophyllum demersum L. and Vallisneria spiralis L. Although the microbe in both the water column and sediment were largely modulated by the macrophyte, the effect varied considerably depending on bacterial locations and macrophyte species. Actinobacteria was the most abundant taxa in the water column of all the three treatments, but its abundances were significantly higher in the two planted treatments. Moreover, Alphaproteobacteria showed high abundance only in the unplanted control. For bacterial taxa in the sediment, C. demersum significantly increased the relative abundance of Anaerolineae but reduced the relative abundance of Betaproteobacteria and Gammaproteobacteria, while V. spiralis increased the relative abundance of Deltaproteobacteria and Gammaproteobacteria. Additionally, in the C. demersum treatment, the water column bacterial community increased more dramatically in richness, alpha diversity, and the relative abundance of the dominant taxa than those in the V. spiralis treatment. Taken together, the findings from this study reveal that the two species of submerged macrophyte modified the bacterial community in waters, despite the obvious interspecific performance differences.

Effects of water depth on growth of submerged macrophytes &lt;i&gt;Vallisneria natans&lt;/i&gt; and &lt;i&gt;Myriophyllum spicatum&lt;/i&gt;

水深是影响浅水湖泊沉水植物生长的主要因素之一.莲座型苦草（Vallisneria natans）和冠层型穗花狐尾藻（Myriophyllum spicatum）是我国长江中下游浅水湖泊中常见的沉水植物种类，二者在形态特征上具有较大的差异.在自然水体中，水深变化对这两种植物的生长以及竞争格局的影响还有待研究.本文设计了3个水深梯度（水深0.5、1.5、2.5 m），探讨混栽条件下苦草和穗花狐尾藻生长和竞争格局对水深变化的响应.结果显示在实验系统内，中水深（1.5 m）处理组对两种植物的生长均最有利，表现为两种植物的相对生长率和生物量均最高.低水深（0.5 m）处理组苦草的生物量和相对生长率均显著低于高水深（2.5 m）处理组；穗花狐尾藻则相反，高水深对其生长的抑制作用更大.2种沉水植物在高水深胁迫时均表现出地上部分（叶长或茎长）增加，地下部分（根长）减少的形态响应特征.此外，随着水深由高到低，苦草与穗花狐尾藻生物量之比逐渐减小，表明苦草在两种植物中的竞争优势逐渐降低.研究表明湖泊水深变化不仅能够影响沉水植物的丰度，同时还可能会影响沉水植物的群落结构，而在我国浅水湖泊的生态修复实践中，在通过水位调控恢复沉水植物时，调控范围应考虑目标植物（如苦草）的光合特征.;Water depth is one of the primary factors that affected submerged macrophyte growth. The rosette plant (Vallisneria natans) and canopy plant (Myriophyllum spicatum) are two common submerged macrophyte species in lakes of the middle and lower reaches of Yangtze River, China. The two species differ greatly in morphological characteristics. How the fluctuation of water depth could affect their growth and their competitive patterns remains to be studied. In this study, three water depth levels (0.5 m, 1.5 m and 2.5 m) were established to explore the responses of growth and competitive patterns of the two plant species to water depth under the condition of mixed planting. Our results showed that both macrophyte species favored in moderate water depth (1.5 m) environment, with highest values of plant biomass and relative growth rate (RGR) in this water depth. The biomass and RGR of V. natans in low water depth treatment (0.5 m) were significantly lower than that in high water depth treatment (2.5 m). However, the opposite pattern was observed in M. spicatum, high water depth treatment has a greater repression effect on its growth. The two species showed the similar responses in morphology, with the indictors of the aboveground part (leaf length or shoot length) increased and that of the underground parts (root length) decreased under the stress of high water depth. Moreover, the biomass ratios of V. natans to M. spicatum are gradually reduced with the water depth, indicated that the competitive advantage of V. natans were increased with water depth. Our study indicates that water depth fluctuations in lakes may affect not only the abundance of submerged macrophytes, but also their community structure. In restoration of shallow lakes, our study suggests that the photosynthetic characteristics of the key species (such as V. natans) should be fully considered when adjusting water levels to rebuild submerged macrophytes.

Determining suitable submerged macrophyte biomass in terms of dissolved oxygen concentration and biodiversity in the South Basin of Lake Biwa, Japan

After a regime shift in eutrophic lakes from a turbid water state with phytoplankton blooms to a clear water state, troublesome issues caused by excessive growths of aquatic plants occurred. This study investigated the relationships between submerged macrophyte biomass, and associated fauna and flora, and environmental factors at 52 stations in the South Basin of Lake Biwa. Polynomial regression analysis gave 5 significant regression equations (P 6000 g m−2 or PVI was > 60%, DO concentrations became too low for the survival of fish and invertebrates (< 4.3 mg l−1). In addition, the cubic regressions of periphyton and epifauna taxa richness showed inflection points were at 3000 g m−2 of submerged macrophyte biomass. Epifaunal biomass, submerged macrophyte species richness, periphyton and epifaunal taxa richness showed inflection points at 30% PVI. Previous studies suggested that regime shifts occur at particular thresholds, and community structure and biodiversity change significantly. Therefore, we assumed regression inflection points were threshold indicators. We recommend an appropriate submerged macrophyte biomass of 3000–6000 g m−2 or a PVI of 30–60% to maintain the ecosystem in a clear water state with fewer troublesome issues — starting at these levels macrophyte growth should be controlled in Lake Biwa.

Antioxidant systems of aquatic macrophytes in three life forms: a case study in Lake Erhai, China

Antioxidant systems are vital in life activities of macrophytes. Species with different life forms need to cope with distinct environments by modifying physiological characters, especially antioxidant systems. In order to find differences among life forms and consequence of lake eutrophication, we studied three antioxidant enzymes activity (superoxide dismutase SOD, ascorbate oxidase APX and catalase CAT) and total soluble phenolics (TP) content in leaves of 26 macrophyte species in September 2013 in Lake Erhai, China. We found that antioxidation varied accordingly with life forms. The activities of SOD and APX in emergent macrophytes (EM) and floating-leaved macrophytes (FM) were much lower than those of submerged macrophytes (SM). On the contrary, TP content was much higher in EM and FM species. There was a negative correlation between TP and antioxidant enzyme activities (CAT and APX). The results suggested that EM and FM species rely on phenolics might to adapt to adverse environments (higher herbivores predation pressure and UV radiation intensity), while SM species more rely on antioxidant enzymes possibly due to lower demand for antioxidation and/or lack of light and inorganic C availability for phenolics synthesis. We also found FM species represent highest fitness in term of antioxidant system, which would lead to overgrowth of FM species and littoral zone bogginess during lake eutrophication. Finally, it is necessary to carry out the verification experiment under the control condition in the later stage, especially for the dominant ones in eutrophic lakes, to understand the exact adaptive mechanisms of them.