Solid state fermentation of aquatic macrophytes for crude protein extraction

Aquatic macrophytes such as Elodea nuttalli, Vallisneria natans, Alterranthera philoxerides that are widely distributed in water environments of Lake Taihu basin were used as substrate of solid state fermentation to produce crude protein extraction. The effects of single-strain fermentation and mixed strains fermentation of aquatic macrophytes on the production of crude protein extraction and cellulase activity are analyzed, respectively. The experimental results showed that the crude protein content of products with mixed strains fermentation is higher than that with single-strain fermentation. The crude protein content of V. natans fermented by Aspergillus niger and Candida utilis is the highest among the aquatic macrophytes examined in this study. V. natans is used as the substrate to be fermented by C. utilis and A. niger; their ratio is 1:1 at 28 ± 1 °C for 72 h. The crude protein of fermented V. natans is as high as 49.54%, with 128.82% of its increase rate. The cellulose activity reaches a maximum of 4.21 μ/ml at 84 h of fementation of V. natans. Thus, the solid state fermentation of aquatic macrophytes to produce crude protein extraction is promising, which make aquatic macrophytes a potential resource and thus is beneficial to the long-term ecological restoration of eutrophic lakes.     

两种沉水植物对间隙水磷浓度的影响

为研究两种根系特征的沉水植物在生长过程中对间隙水中磷浓度的影响,选取根系较多的沉水植物苦草和根系相对较少的沉水植物黑藻作为实验材料,监测底泥中间隙水各形态磷含量及环境因子的变化,探讨不同根系特征沉水植物对间隙水中磷的影响。结果表明:黑藻和苦草实验组沉积物间隙水中各形态磷的浓度均呈不同程度的降低,黑藻和苦草对于稳定水质,减少底泥中磷向水中转移具有明显的效果;沉水植物不同,底泥间隙水中溶解性总磷(DTP)和溶解性活性磷(SRP)存在明显差异。实验结束时黑藻组和苦草组间隙水中DTP的浓度分别为0.24,0.01 mg/L,SRP的浓度分别为0.22 mg/L,0.004 mg/L。间隙水中磷的形态主要以DTP和SRP为主,溶解性有机磷(DOP)的含量相对较低。沉水植物对间隙水中磷的吸收是降低间隙水中磷含量的重要原因,苦草的吸收能力大于黑藻。沉水植物根系通过降低底泥p H值,提高氧化还原电位(Eh)的方式抑制了底泥中磷的释放。     

不同光照强度下物种组合对沉水植物苦草种间关系的影响

为了解种间关系对沉水植物群落结构的影响，在不同光照(20%自然光和50%自然光)和不同物种组合下，研究了长江中下游常见优势沉水植物苦草(Vallisneria natans)与黑藻(Hydrilla verticillata)和穗状狐尾藻(Myriophyllum spicatum)的相互作用。结果表明，在低光下，苦草与穗状狐尾藻混种时，苦草生物量、株高和叶数均没有明显变化，当穗状狐尾藻的比例较高时，苦草根长生长受到抑制，根叶比呈下降趋势；在高光下，穗状狐尾藻比例的增加会促进苦草单株生物量和叶生物量的增加，而对苦草株高、根长和叶数无显著影响；与黑藻混种相比，苦草与穗状狐尾藻混种时，苦草的株高、根长和叶数均无显著差异，而苦草的单株生物量和叶生物量均呈降低趋势。因此，物种组合和混种比例均会影响苦草与其他物种的相互作用关系，进而影响沉水植被的群落动态。     

Seed germination of three species of <Emphasis Type="Italic">Vallisneria</Emphasis> (Hydrocharitaceae), and the effects of freshwater microalgae

Two experiments were conducted to investigate seed germination under natural temperature and light regimes and to evaluate the influence of freshwater microalgae on seed germination of threeVallisneria species. Seeds exposed to natural seasonal temperature and light changes for 24 months germinated only in spring, perhaps indicating an annual dormancy/non-dormancy cycle. The ecological background of the natural habitat seems to play predominant roles in seed germinability. Mean cumulative seed germination percentages of Vallisneria natans, V. denseserrulata, andV.spinulosa of the first year were 35.2, 19.2, and 11.2%, respectively, and of the second year were 80, 72, and 32.4%, respectively. Germination rates differed significantly among the three Vallisneria species exposed to natural seasonal temperature and light changes in the first year, but differed only between Vallisneria spinulosa and the other two species in the second year. The differences of germination may influence the geographical distribution and thus be related to different survival strategies of the species. Seed germination rates in culture solution inoculated with algae were significantly higher than in solution with no algae. A strong correlation occurred between total biomass of freshwater microalgae and seed germination of the three studied species. Apparently, the extracellular products of freshwater microalgae may play an important role in seed germination. These results support the hypothesis that Vallisneria colonization may be mediated by algae facilitation.     

Plant growth-promoting rhizobacteria isolation from rhizosphere of submerged macrophytes and their growth-promoting effect on Vallisneria natans under high sediment organic matter load

Sediment organic matter is a key stressor for submerged macrophyte growth, which negatively impacts the ecological restoration of lakes. Plant growth-promoting rhizobacteria (PGPR) were screened from the rhizosphere of submerged macrophytes and used due to their promoting effect on Vallisneria natans under a high sediment organic matter load. Root exudates were used as the sole carbon source to obtain the root affinity strains. Eight isolates were selected from the 61 isolated strains, based on the P solubilization, IAA production, cytokinins production and ACC deaminase activity. The analysis of the 16S rDNA indicated that one strain was Staphylococcus sp., while the other seven bacterial strains were Bacillus sp. They were all listed in low-risk groups for safety use in agricultural practices. The plant height significantly increased after inoculation with PGPR strains, with the highest rate of increase reaching 96%. This study provides an innovative technique for recovering submerged macrophytes under sediment organic matter stress.     

Hoary cress (Cardaria draba (L.) Desv.) seed germination ecology,longevity and seedling emergence

The effects of gibberellic acid (GA₃), potassium nitrate (KNO₃), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA₃ in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5‐cm depth.     

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.     

Effect of environmental factors on seed germination and emergence of Lepidium vesicarium

Lepidium vesicarium is a weed species with a wide distribution in the rangelands and dry‐land farming in East Azarbaijan, Iran. The experiments were undertaken to assay the effects of light, temperature, pH, osmotic potential, NaCl concentration and burial depth on seed germination and emergence of L. vesicarium. Germination was maintained at high levels (> 80%) over a wide day/night temperature range (10/5 to 30/20°C), but a severe reduction in the germination rate of L. vesicarium was found below 20/10°C. Germination of L. vesicarium was influenced by different light/dark regimes, as the germination rate was highest at 16 h light for the all treatments (0, 8, 12, 16 and 24 h light). Germination was 92–95% over a wide range of pH (2‐10). Germination was >50% at a water potential of ?0.7 MPa and salinity of 21 dS/m, indicating that drought and salt conditions have a minimal impact on seed germination. With increasing burial depth from 0 to 2 cm, the number of days required for 50% emergence increased and no germination was observed at burial depths deeper than 3 cm. This suggests that L. vesicarium would become troublesome in the rangelands and for growers in reduced‐tillage cropping systems. The ability to emerge from shallow depths, coupled with tolerance of a wide pH range, drought and salinity at germination, should be taken into account when managing this weed species.     

Sediment type and the clonal size greatly affect the asexual reproduction,productivity, and nutrient absorption of Vallisneria natans

Most aquatic vegetation restorations involve the transplantation of submerged macrophytes. Sediment type and the clonal size are of great significance as they determine the fate of submerged macrophytes. In order to ensure successful restoration, a simulation experiment was conducted using aquarium mesocosms to investigate the response of stolon propagation capacity, the morphological features and productivity of Vallisneria natans for four types of sediment (lake mud [L], lake mud + sand [L + S, 50:50, v/v mixture], sand [S], clay [C]), and three types of clonal sizes. Results showed that sediment types significantly affected V. natans biomass accumulation, stolon propagation ability, ramet morphological characteristics, and productivity, where the asexual reproduction ability and productivity ranked as L > L + S > S > C in four sediment types. Total biomass, maximum net production, number of ramets, root diameter, number of stolons, and stolon propagation rate were all highest in L. In L and L + S, the plant chlorophyll content was higher than in S and C. The root diameter and the ratio of aboveground/underground biomass in S were the smallest among the four sediments. Moreover, when more V. natans seedlings were linked, more ramets and biomass were produced. The stolon propagation rate was ranked as the stolon with single seedling greater than the stolon with two‐linked seedlings greater than the stolon with three‐linked seedlings in L and L + S. The concentration of total nitrogen, total phosphorus, and NO₃^?‐N in water was remarkably reduced in four aquariums. Findings provide a scientific basis for restoring submerged macrophytes in different sediment settings.     

Comparison of the extent of genetic variation of Vallisneria natans and its sympatric congener V. spinulosa in lakes of the middle-lower reaches of the Yangtze River

Vallisneria natans and Vallisneria spinulosa are two morphologically very similar and sympatrically dominant submerged macrophytes in lakes of the middle-lower reaches of the Yangtze River. Genetic variation was compared based on a total of 196 individuals from six V. natans populations and 201 individuals from seven V. spinulosa populations. Using eight ISSR primers, a total of 139 and 129 DNA fragments were generated with 121 being polymorphic in V. natans and 99 in V. spinulosa. The two species maintained higher genetic variation both at the species and population levels in comparison with other aquatic macrophytes. A higher level of genetic diversity among populations was found in V. natans than in V. spinulosa: the percentage of polymorphic loci (PPL) in V. natans was 52-62% vs. 38-47% in V. spinulosa; gene diversity (H) was 0.21 in V. natans vs. 0.17 in V. spinulosa.Both an analysis of molecular variance (AMOVA) and F-estimation (F_ST) showed that most of the total genetic variation resided within populations of both species (AMOVA: 85% and 80%; F_ST: 0.132 and 0.202), indicating low genetic differentiation between populations. Principal coordinates analysis (PCA) indicated evident gene flow between populations of both species. The outcrossing reproductive mode and pervasive gene flow might have played important roles in maintaining high genetic diversity and in shaping low population differentiation of the two Vallisneria species, while the extent of clonal growth might account for the different levels of population divergence between them.     

Can allelopathically active submerged macrophytes stabilise clear-water states in shallow lakes?

Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is supposed to be one of the mechanisms that contribute to the stabilisation of clear-water states in shallow lakes. The relevance of this process at ecosystem level, however, is debated because in situ evidence is difficult to achieve. Our literature review indicates that allelopathically active species such as Myriophyllum, Ceratophyllum, Elodea and Najas or certain charophytes are among the most frequent submerged macrophytes in temperate shallow lakes. The most common experimental approach for allelopathic interference between macrophytes and phytoplankton has been the use of plant extracts or purified plant compounds. Final evidence, however, requires combination with more realistic in situ experiments. Such investigations have successfully been performed with selected species. In situ allelopathic activity is also influenced by the fact that phytoplankton species exhibit differential sensitivity against allelochemicals both between and within major taxonomic groups such as diatoms, cyanobacteria and chlorophytes. In general, epiphytic species apparently are less sensitive towards allelochemicals than phytoplankton despite living closely attached to the plants and being of key importance for macrophyte growth due to their shading. Light and nutrient availability potentially influence the sensitivity of target algae and cyanobacteria. Whether or not additional stressors such as nutrient limitation enhance or dampen allelopathic interactions still has to be clarified. We strongly propose allelopathy as an important mechanism in the interaction between submerged macrophytes and phytoplankton in shallow lakes based on the frequent occurrence of active species and the knowledge of potential target species. The role of allelopathy interfering with epiphyton development is less well understood. Including further levels of complexity, such as nutrient interference, grazing and climate, will extend this ecosystem-based view of in situ allelopathy.     

沉水植物菹草的人工种子技术

为满足水生态系统重建及水体景观对沉水植物种苗的需求,本文建立了菹草（Potamogeton crispus L.）人工种子的制作方法,并分析了菹草人工种子的萌发条件。结果表明,以海藻酸钠为包埋剂,在包埋剂中添加IBA 1.0 mg/L + 6-BA 0.5 mg/L,制备的菹草人工种子在灭菌自来水中萌发率可达80％,且转株率达20％。在15－25℃之间,温度对菹草人工种子萌发和转株的影响不显著;氮磷水平对菹草人工种子萌发和转株的影响不显著;光强对菹草人工种子的萌发和转株有显著影响,较高的光强有较高的萌发率和转株率,光强为40μmol/ m2. s时,菹草人工种子萌发率、转株率可达67.8％、35.6％;底质对菹草人工种子的萌发和转株有显著影响,菹草人工种子在黄沙壤上的萌发率、转株率分别为60%和42.2%,黄沙壤比淤泥和砂石更适合菹草人工种子萌发和转株;菹草人工种子在野外湖水的试验中萌发率、转株率分别达到28%、15%。     

Degraded Softwater Lakes: Possibilities for Restoration

In the Netherlands, the characteristic flora of shallow softwater lakes has declined rapidly as a consequence of eutrophication, alkalization and acidification. The sediment of most lakes has become nutrient rich and anaerobic. We expected that, if a vital seed bank was still present, restoration of the original water quality and sediment conditions would lead to the return of softwater macrophytes. The restoration of 15 degraded, shallow, softwater lakes in the Netherlands was monitored from 1983 to 1998. In eutrophied as well as in acidified lakes, removal of accumulated organic matter from the sediment and shores was followed by rapid recolonization of softwater macrophytes present in the seedbank. After isolation from alkaline water and subsequent mud removal, this recovery was also observed in alkalized lakes. Further development of softwater vegetation correlated strongly with the water quality. When renewed eutrophication was successfully prevented, softwater macrophytes could expand. However, in acidified lakes, Juncus bulbosus and Sphagnum species became dominant after restoration. Liming of an acidified lake was followed by re‐acidification within 3 years. Recolonization by softwater macrophytes was inhibited by high turbidity of the water column and spreading of large helophytes on the shore. As an alternative, controlled inlet of alkaline, nutrient‐poor groundwater was studied in a few lakes. The pH of those lakes increased, the carbon and nitrogen availability decreased and softwater macrophytes returned. Successful restoration has contributed considerably to maintaining biodiversity in softwater lakes in the Netherlands.     

Germination and emergence of Astrodaucus orientalis (L.) Drude populations influenced by environmental factors and seed burial depth

Astrodaucus orientalis is a weed species in cropping systems and rangelands in Iran. The effects of temperature, light, NaCl concentration, water potential, seed burial depth and crop residue cover were assessed on seed germination and seedling emergence of two populations of A. orientalis from Ardabil (Meshginshahr population) and East Azarbayjan (Tabriz population) provinces of Iran. The A. orientalis populations indicated different responses to environmental factors and burial depth. In the Tabriz population the greatest germination (88.5%) was observed in 20/12°C day/night temperature but in the Meshginshahr population (83.2%) it was obtained in 24/16°C day/night temperature. Over a broad range of light period (10–24 hr light) germination was 74–83%, but it decreased (less than 37%) under 24 hr dark in both A. orientalis populations. With respect to water potential, the C₅₀ parameters were −0.62 and − 0.49 MPa for Tabriz and Meshginshahr populations, respectively. The D₅₀ parameters (the burial depth that caused 50% decrease in emergence) for Tabriz and Meshginshahr populations were 2.42 and 3.13 cm, respectively. Generally, the results showed that emergence of both populations of A. orientalis was delayed as depth of burial increased up to 4 cm and in cropping systems a shallow tillage that locates the seeds to >4 cm of depth in soil could be used in order to suppress seedling emergence. Our findings also could be useful in integrated management of A. orientalis in winter annual crops and rangelands.     

Germination responses ofRubus palmatus var.coptophyllus andRubus parvifolius seeds with different burial durations to a variable light and temperature regime

To clarify the adaptive significance of seed dormancy, the effects of burial duration were examined for two deciduousRubus species:Rubus palmatus var.coptophyllus andRubus parvifolius, which are found mainly in relatively stable, shaded sites and disturbed sites, respectively. In early summer, newly ripened seeds were buried under litter on the soil surface in a pine forest, and germination tests were carried out for the seeds retrieved from the soil litter after 0 (not buried), 1, 2, 3, 5 and 8 or 9 months of burial. In general, the germination percentages increased and light requirements for germination decreased with increased burial duration. The percentage of seeds germinated with alternating temperatures in darkness also increased with increasing burial duration for both species. After 8 or 9 months of burial (corresponding to the next germination season in the field), the percentage of non-dormant seeds (including germination under alternating temperatures in the dark) was about 80% and 40% forR. palmatus var.coptophyllus andR. parvifolius, respectively. These seed dormancy traits of the twoRubus species may explain the differences in germination strategy in their habitats:R. palmatus var.coptophyllus seems to have adapted to the seasonal occurrence of favorable growing conditions after the dormancy breakage, whileR. parvifolius seems to have adapted to favorable conditions created by temporally unpredictable disturbances.     

Consumer-driven nutrient release to the water by a small omnivorous fish enhanced ramet production but reduced the growth rate of the submerged macrophyte Vallisneria denseserrulata (Makino) Makino

Small fish are highly associated with submerged macrophytes but may potentially hamper their growth due to nutrient excretion that stimulate growth of phytoplankton and periphyton growth. We conducted a mesocosm experiment to elucidate the effects of the small omnivore Chinese bitterling Acheilognathus macropterus on the growth of phytoplankton, periphyton and the submerged macrophyte Vallisneria denseserrulata. The treatments were fishless as well as low (LF) and high (HF) fish density. We found that the concentrations of nutrients and the phytoplankton biomass increased substantially in both fish treatments, leading to a significantly higher light attenuation compared with the control. Moreover, bitterling substantially enhanced the biomass of periphyton on plant leaves. Consequently, the relative growth rate (RGR) of V. denseserrulata was significantly suppressed in HF, while RGR in the LF treatment did not differ significantly from the controls. However, the bitterling also stimulated the ramet production of V. denseserrulata, significantly. Our results indicate that Chinese bitterling reduce the RGR of V. denseserrulata under high fish density condition. Therefore, the density of Chinese bitterling should be kept low in order to reduce the negative effects of the fish on the RGR of submerged macrophytes (e.g. V. denseserrulata), when restoring lakes by plant transplantation.

     

Seed bank persistence of clonal weeds in contrasting habitats: implications for control

The ability of weeds to form a seed bank is important for their population dynamics and management because it provides a refuge enabling reinvasion after established target plants have died. However, knowledge of the differential seed behaviour of individual species over multiple years and varying environmental conditions is surprisingly rare but necessary for effective control of diverse weed populations. We established a seed burial experiment in alpine habitats differing in management regime (i.e., forest, hay meadow and pasture) to determine whether seeds of the unpalatable perennial weeds, Veratrum album (white hellebore) and Gentiana lutea (yellow gentian) were able to delay germination and remain viable over 3 years. Our study shows that both species formed a short-term persistent seed bank; in the third-year, the soil seed banks of both species were nearly depleted, having declined to <5% of their original size. Both species had strikingly different germination strategies: G. lutea seeds mainly germinated in their first-year, whilst the majority of V. album seeds germinated in their second-year. The fraction of dormant G. lutea seeds increased with seed age, indicating that seeds remained viable after forgoing germination in the previous year. Habitat-specific differences in seed germination increased with seed age, with germination fractions being lowest in moist hay meadows. This suggests that the negative effects of anoxic conditions became more pronounced as seeds aged in hay meadows. Conversely, seed dormancy was equal among habitats. The absence of a long-term persistent seed bank has important implications for the management of both nuisance and endangered-plant populations. In the case of V. album and G. lutea, re-colonization of habitats from the seed bank is unlikely after established plants have been removed.     

Seed dormancy release and germination characteristics of <i>Corispermum lehmannianum</i> Bunge,an endemic species in the Gurbantunggut desert of China

Seed dormancy release and germination of Corispermum lehmannianum Bunge were tested using various treatments: temperature, cold stratification, gibberelins (GA3), dry storage and sand burial. Results showed that temperature and light did not affect the germination of fresh seeds, cold stratification and GA3 could improve seed germination, whereas dry storage and sand burial did not. The germination percentage was highest at 35/20 °C after the cold stratification and GA3 treatments. Corispermum lehmannianum seeds were classified as non-deep, Type-2, physiological dormancy (PD), whose seed dormancy could be released by cold stratification and GA3.     

THE NINETY-YEAR PERIOD FOR DR. BEAL'S SEED VIABILITY EXPERIMENT

In 1879 Dr. W. J. Beal selected seeds of 23 different species of locally common plants, mixed 50 seeds of each species with moist sand in unstoppered one-pint bottles, and buried the bottles in a sandy knoll to be unearthed and the viability of the seeds tested periodically. The year 1970 marked the ninetieth year the seed had been buried, and the thirteenth bottle was recovered to test for seed viability. Of the three species which had germinated in the 1960 test (curly dock, Rumex crispus; evening primrose, Oenothera biennis; and moth mullein, Verbascum blattaria), only V. blattaria had viable seed with 20% germination. No other species germinated. All ten seedlings of V. blattaria were grown to maturity, and seeds were then harvested to study the possible deviations from normality and the requirements for seed germination. All seedlings emerging from the first progeny seed appeared normal. The most prominent requirement for germination was light, and this is a possible explanation of why the seeds had remained viable but dormant for so long a period. One-third of the freshly harvested seed germinated in darkness and, furthermore, redrying of dark-moistened seed in the absence of light induced additional germination. Germination of dark-moistened seed was not completely restored when the still moist seeds were subsequently exposed to light. However, when dark-moistened seeds were dried and then remoistened in the light, germination was about 95 %. About 5 % of the seed did not germinate under the conditions used. We find that 5 % of the population of V. blattaria seeds are dormant for unknown reasons, that 30 % will germinate if supplied only with moisture, and that 65 % are inhibited and require light and moisture simultaneously for germination. Supplying this 65 % of the population with moisture in darkness results in the development of a second type of inhibition which is no longer light reversible. It appears that the simultaneous requirement for light and moisture is an important factor in permitting V. blattaria seeds to remain dormant during prolonged burial.     

An alternative mechanism for shade adaptation: implication of allometric responses of three submersed macrophytes to water depth

Allometric scaling models describing size-dependent biological relationships are important for understanding the adaptive responses of plants to environmental variation. In this study, allometric analysis was used to investigate the biomass allocation and morphology of three submerged macrophytes (Potamogeton maackianus, Potamogeton malaianus and Vallisneria natans) in response to water depth (1.0 and 2.5?m) in an in situ experiment. The three macrophytes exhibited different allometric strategies associated with distinct adjustments in morphology and biomass allocation in response to varying water depths. In deeper water, after accounting for the effects of plant size, P. maackianus and P. malaianus tended to enhance light harvesting by allocating more biomass to the stem, increasing shoot height and specific leaf area. V. natans tended to allocate more biomass to the leaf than to the basal stem (rosette), showing a higher leaf mass ratio and shoot height in deeper water. The three species decreased biomass allocation to roots as water depth increased. The main effect of water depth treatments was reduced light availability, which induced plastic shoot or leaf elongation. This shows that macrophytes have evolved responses to light limitation similar to those of terrestrial plants.