水生植物对富营养水体水质净化作用研究

利用富营养浅水湖泊武汉东湖中所建立的大型实验围隔系统,对沉水植物的水质净化作用作了现场实验研究。重建后的沉水植物可以显著改善水质,水体透明度显著提高,水色降低。在研究期间,水生植物围隔CODcr和BOD5一般分别为20和5mg/L左右;对照围隔和大湖水体则分别约为40和10mg/L。水生植物围隔水体中检出的有机污染种类也较对照围和大湖水体柢。实验结果表明恢复以沉水植物为主的水生植被是改善营养湖泊水质和重建生态系统的有效措施。     

沉水植物光合作用的特点与研究进展

沉水植物属于高等植物,由陆生被子植物演化而来,它们在形态、光合生态生理方面对水下生活环境发生了一系列适应性变化。沉水植物的光合作用受水体中光、温度、pH和无机碳等影响,本文对此进行了综述。水中低CO2扩散率以及细胞外较厚的扩散层阻碍了沉水植物净碳的吸收,因此,沉水植物光合作用速率受到无机碳供应的限制。为获得无机碳,沉水植物在形态结构和生理生化上表现一定的特性,包括薄的叶片层并含有叶绿体以及对HCO3-利用的能力,拟C4型和CAM型光合代谢途径的选择。这些是沉水植物碳浓缩机制的具体体现。     

沉水植物光合作用测定的电化学方法

光合作用速率测定是植物光合作用研究的重要基础,沉水植物由于所处生境的特殊性,难以应用在陆生植物光合作用研究中发展起来的速率测定方法.在对水体中二氧化碳的基本特征进行详细描述的基础上,介绍了在沉水植物光合作用研究中广泛应用的电化学方法--pH-stat法和pH-drift法的原理,并给出了应用实例.这两种测定水生植物光合作用的电化学方法所依据的溶液无机碳浓度的变化可以利用Gran滴定法方便地计算出来.     

3种种植方式下沉水植物恢复效果研究

恢复沉水植物是受污染水体生态修复与重建的有效措施之一,人工快速大面积恢复沉水植物的方法是关键。选取杭州西湖西进区域茅家埠和浴鹄湾近岸水域,分别采用扦插法、沉栽法和播种法对沉水植物菹草、苦草和黑藻进行种植。研究表明：运用沉栽法种植的菹草存活率比用播种法种植的存活率高71.1%;运用扦插法种植的苦草比沉栽法和播种法的存活率分别高84.3%和87.8%;运用扦插法种植的黑藻比用播种法种植的存活率高69%;3种种植方式下最终的单株植物生物量间无显著差异。     

沉水植物苦草化学成分研究

通过使用乙酸乙酯溶剂对沉水植物苦草（Vallisneria natans）全草进行超声连续提取,采用硅胶柱色谱法和光谱分析法分离和鉴定化学成分。从苦草中分离到6个化合物：6,10,14-三甲基-2-十五酮（1）、棕榈酸（2）、4,22-二烯-3β-豆甾酮（3）、5α,豆甾烷-3,6-二酮（4）、硬脂酸（5）、棕榈酸乙酯（6）。化合物1—6为首次从该植物中发现。     

Diurnal Ion Fluctuations in the Mesophyll Tissue of the Crassulacean Acid Metabolism Plant Mesembryanthemum crystallinum

Both laboratory- and field-grown Mesembryanthemum crystallinum plants exhibited large scale diurnal ion fluctuations. In mesophyll tissue, potassium and sodium levels varied in conjunction with acid levels while chloride levels varied in opposition. Thus, dark CO₂ fixation in this Crassulacean acid metabolism species seems analogous to the common plant process of malate synthesis to balance cation surplus. Sodium levels in the epidermis appeared to fluctuate in opposition to those in the mesophyll. It is proposed that inorganic cations cycle between mesophyll and epidermal tissue to balance malate accumulation and to produce stomatal opening in the dark.     

洪湖5种优势沉水植物光合荧光特性比较研究

利用水下饱和脉冲荧光仪(DIVING-PAM),原位观测洪湖5种优势沉水植物——苦草[Vallisneria natans(Lour.)Hara]、黑藻[Hydrilla verticillata(L.f.)Royle]、狐尾藻(Myriophyllum verticillatum L.)、菹草(Potamogeton crispus L.)和马来眼子菜(Potamogeton wrightii Morong)的量子产量及快速光曲线。结果显示:5种沉水植物苦草、黑藻、狐尾藻、菹草和马来眼子菜最大量子产量(Fv/Fm)分别为0.603、0.723、0.751、0.778和0.646。各物种的开放PSⅡ反应中心原初光能捕获效率(Fv′/Fm′)的大小依次为菹草狐尾藻黑藻马来眼子菜苦草,且除黑藻与狐尾藻间差异不显著外,其他物种间差异均显著;各物种光能利用能力(α)的大小依次为菹草黑藻狐尾藻马来眼子菜苦草,且除黑藻与狐尾藻间差异不显著外,其他物种间差异均显著;各物种无光抑制的最大潜在相对电子传递速率(rETRm)的大小依次为菹草狐尾藻黑藻马来眼子菜苦草,且各物种间差异显著;半饱和光强(Ek)的大小依次为狐尾藻菹草黑藻苦草马来眼子菜,且除狐尾藻与菹草间差异不显著外,其他物种间差异均显著。研究表明:洪湖5种优势沉水植物中,菹草和狐尾藻较耐强光,光合速率较高,而苦草则有较强的耐弱光能力。     

Gas Exchange Characteristics of the Submerged Aquatic Crassulacean Acid Metabolism Plant, Isoetes howellii

The submerged aquatic plant Isoetes howellii Engelmann possesses Crassulacean acid metabolism (CAM) comparable to that known from terrestrial CAM plants. Infrared gas analysis of submerged leaves showed Isoetes was capable of net CO₂ uptake in both light and dark. CO₂ uptake rates were a function of CO₂ levels in the medium. At 2,500 microliters CO₂ per liter (gas phase, equivalent to 1.79 milligrams per liter aqueous phase), Isoetes leaves showed continuous uptake in both the light and dark. At this CO₂ level, photosynthetic rates were light saturated at about 10% full sunlight and were about 3-fold greater than dark CO₂ uptake rates. In the dark, CO₂ uptake rates were also a function of length of time in the night period. Measurements of dark CO₂ uptake showed that, at both 2,500 and 500 microliters CO₂ per liter, rates declined during the night period. At the higher CO₂ level, dark CO₂ uptake rates at 0600 h were 75% less than at 1800 h. At 500 microliters CO₂ per liter, net CO₂ uptake in the dark at 1800 h was replaced by net CO₂ evolution in the dark at 0600 h. At both CO₂ levels, the overnight decline in net CO₂ uptake was marked by periodic bursts of accelerated CO₂ uptake. CO₂ uptake in the light was similar at 1% and 21% O₂, and this held for leaves intact as well as leaves split longitudinally. Estimating the contribution of light versus dark CO₂ uptake to the total carbon gain is complicated by the diurnal flux in CO₂ availability under field conditions.     

Selected Nucleic Acid Precursors in Studies of Aquatic Microbial Ecology

The use of radiolabeled nucleosides and nucleic acid bases to estimate the rates of RNA and DNA synthesis in naturally occurring microbial assemblages requires numerous assumptions, several of which are evaluated herein. Comparative time series analyses of the uptake and incorporation, labeling specificity, and extent of catabolism of [2-³H]adenine, [methyl-³H]thymidine, and [5-³H]uridine were performed with pure bacterial and algal cultures, as well as with environmental samples. [³H]thymidine yielded the most variable results, especially with regard to the extent of nonspecific macromolecular labeling. The pathways of [³H]thymidine and [³H]adenine metabolism were further evaluated by isotope dilution methods and by comparing incorporation patterns of thymidine labeled at different sites of the molecule. The advantages, uncertainties, and limitations of the use of radiolabeled nucleic acid precursors in studies of aquatic microbial ecology are discussed and a prospectus for future studies presented.     

Invasive Crayfish Threaten the Development of Submerged Macrophytes in Lake Restoration

Submerged macrophytes enhance water transparency and aquatic biodiversity in shallow water ecosystems. Therefore, the return of submerged macrophytes is the target of many lake restoration projects. However, at present, north-western European aquatic ecosystems are increasingly invaded by omnivorous exotic crayfish. We hypothesize that invasive crayfish pose a novel constraint on the regeneration of submerged macrophytes in restored lakes and may jeopardize restoration efforts. We experimentally investigated whether the invasive crayfish (Procambarus clarkii Girard) affects submerged macrophyte development in a Dutch peat lake where these crayfish are expanding rapidly. Seemingly favourable abiotic conditions for macrophyte growth existed in two 0.5 ha lake enclosures, which provided shelter and reduced turbidity, and in one lake enclosure iron was added to reduce internal nutrient loading, but macrophytes did not emerge. We transplanted three submerged macrophyte species in a full factorial exclosure experiment, where we separated the effect of crayfish from large vertebrates using different mesh sizes combined with a caging treatment stocked with crayfish only. The three transplanted macrophytes grew rapidly when protected from grazing in both lake enclosures, demonstrating that abiotic conditions for growth were suitable. Crayfish strongly reduced biomass and survival of all three macrophyte species while waterfowl and fish had no additive effects. Gut contents showed that crayfish were mostly carnivorous, but also consumed macrophytes. We show that P. clarkii strongly inhibit macrophyte development once favourable abiotic conditions for macrophyte growth are restored. Therefore, expansion of invasive crayfish poses a novel threat to the restoration of shallow water bodies in north-western Europe. Prevention of introduction and spread of crayfish is urgent, as management of invasive crayfish populations is very difficult.     

Diurnal Fluctuations in Ethylene Formation in Chenopodium rubrum

Ethylene formation was studied in 5- to 6-d-old Chenopodium rubrum seedlings under the following light regimes: continuous light (CL), continuous darkness (CD), and alternating light/darkness (12 h of each). No significant regular oscillations in ethylene formation were found in either the CL or CD groups. In the light/dark regime, pronounced diurnal fluctuations in ethylene formation were observed. Activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase was transiently increased on transfer from light to dark and vice versa. In CL, ACC oxidase activity did not change significantly, whereas in CD, it decreased continuously after the initial increase. The in vivo levels of ACC and N-malonyl-ACC (MACC) were constant for the first few hours of darkness, then decreased dramatically, but increased again in the light. In constant darkness, the level of ACC displayed endogenous rhythm, with minimum values at h 12 and 44, and a maximum value at h 32 to 36. The level of MACC in both shoots and roots decreased in the CD group until h 12, and then remained constant until h 30 before decreasing continuously. We conclude that the photoperiodic regime affects both ACC and MACC levels, as well as the conversion of ACC to ethylene. Correlation of the described changes in ethylene formation to photoperiodic flower induction is discussed.     

Aquatic Macrophytes Alter Metabolism and Nutrient Cycling in Lowland Streams

Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management.     

Changes in Aquatic Macrophytes after Liming Thrush Lake, Minnesota

Thrush Lake, Minnesota, was treated with limestone in 1988 to evaluate the efficacy of protective base addition against the loss of sport fisheries in a sensitive, mildly acidic lake. Prior to treatment, the lake was stressed (pH 6.46, ANC 64 μeq/L) but not severely degraded by acidic deposition and had a macrophyte community typical of lakes in northeastern Minnesota with low acid-neutralizing capacity (ANC). This paper describes the changes observed in aquatic plant communities during the 5 years after treatment, as pH and ANC slowly returned to pretreatment levels. Sphagnum platyphyllum, intolerant of non-acid conditions, was completely eliminated from the lake. The charo-phyte, Nitella, that originally shared dominance in the deep littoral zone with S. platyphyllum, decreased in importance during the first 2 years after treatment. Two vascular plants, Potamogeton pusillus and Najas flexilis, were first found in the lake the year after treatment and were abundant for 2 years after liming, probably in response to a combination of more neutral pH and reduced cover of Nitella. As the ANC and pH slowly returned to pretreatment conditions, Nitella again increased in coverage and depth range, with a concomitant decrease in P. pusillus and N. flexilis. The moss, S. platyphyllum, had not reinvaded the lake by 1993, 2 years after its dramatic decline.     

Salt Tolerance in Aquatic Macrophytes: Ionic Relation and Interaction

Effects of seawater salinity (SWS) and pure NaCl on the intracellular contents of Na⁺, K⁺, Mg²⁺, Ca²⁺, chlorophylls (Chl) and carotenoids (Car) were studied in three submerged aquatic macrophytes, Hydrilla verticillata, Najas indica and Najas gramenia, which differed in their tolerance to salinity. NaCl resulted in significant increase in Chl/Car ratio in the salt-sensitive H. verticillata and moderately salt-tolerant N. indica, but not in the salt-tolerant N. gramenia. SWS treatment did not result in any significant change in the ratio. The intracellular content of Na⁺ increased significantly in all the test plants upon exposure to both NaCl and SWS. The content of K⁺ decreased significantly in these plants upon salinity treatment, except in N. gramenia. The contents of Ca²⁺ and Mg²⁺ decreased significantly upon NaCl treatment and remained unchanged or increased upon SWS treatment. No relationship between salt tolerance and K⁺/Na⁺ ratio was observed. The maintenance of a minimal level of K⁺ was observed to be the most probable requirement of salt tolerance in aquatic macrophytes.     

Submerged Macrophytes Mitigate Direct and Indirect Insecticide Effects in Freshwater Communities

Understanding how ecological interactions mitigate the impacts of perturbations such as pesticides in biological communities is an important basic and applied question for ecologists. In aquatic ecosystems, new evidence from microcosm experiments suggests that submerged macrophytes can buffer cladocerans from pulse exposures to the widely used insecticide malathion, and that mitigation increases with macrophyte density. However, whether these results scale up to more complex aquatic communities where ecological interactions such as competition can alter toxicity is unknown. Further, macrophyte abilities to mitigate different insecticide exposure scenarios (i.e. single versus repeated pulses) have never been tested. To address these gaps, we performed a factorial mesocosm experiment examining the influence of four macrophyte treatments (0, 10, 50, or 100 Elodea Canadensis shoots planted per mesocosm) crossed with three malathion exposure scenarios (no insecticide, single pulse, repeated pulses) on aquatic communities containing zooplankton, phytoplankton, periphyton, two snail species, and larval amphibians. In the absence of macrophytes, single malathion pulses caused short-term declines in cladoceran abundance followed by their rapid recovery, which precluded any indirect effects (i.e. trophic cascades). However, repeated malathion pulses caused cladoceran extinctions, resulting in persistent phytoplankton blooms and reduced abundance of one snail species. In contrast, with macrophytes present, even at low density, malathion had no effect on any taxa. We also discovered novel effects of macrophytes on the benthic food web. In the two highest macrophyte treatments, we observed trends of reduced periphyton biomass, decreased abundance of one snail species, and decreased amphibian time to and mass at metamorphosis. To our knowledge, this is the first evidence of negative submerged macrophyte effects on amphibians, a taxa of global conservation concern. Our findings suggest that facilitating macrophytes could be an important strategy for buffering freshwater communities from insecticides, though consideration of their impacts on animal species is necessary.     

Loss of Submerged Macrophytes in Shallow Lakes in North‐Eastern Germany

During the 1950s, the submerged vegetation of shallow lakes in north‐eastern Germany was dominated by nutrient tolerant species, with Ceratophyllum demersum and Myriophyllum sp. being most common. Almost one third of 300 investigated lakes had already lost their submerged macrophytes at that time. Very shallow lakes showed either high or low macrophyte abundance. Increasing depth resulted in medium macrophyte abundances, which may contribute to the stabilisation of local or temporary clearwater states. Forty years later, the percentage of lakes without macrophytes had dramatically increased. Between 55 and 85% of the investigated lakes showed a low abundance. The decline was most pronounced in very shallow lakes. The majority of the investigated lakes showed summer TP concentrations below 100 μg L^–1, but no colonisation by submerged macrophytes, which indicates a resilience against re‐colonisation.     

Sediment and Water Nutrient Characteristics in Patches of Submerged Macrophytes in Running Waters

(1) The relative importance of sediments and water as nutrient sources for submerged macrophytes in running waters is poorly understood. Here we present water and sediment nutrient characteristics within macrophyte patches in Bavarian rivers. (2) No significant differences between early (June/July) and late summer (August/September) sediment nutrient characteristics could be detected within macrophyte patches. Therefore, a single sediment sample per macrophyte patch was considered to be sufficient for characterising nutrient concentrations during the main growing season in running waters. (3) Sediment TP (total phosphorus) is not a useful parameter for predicting trophic status in running waters. Sediment porewater SRP (soluble reactive phosphorus) concentration is not correlated to water body SRP or TP concentration; nor is it correlated with sediment TP content. Potamogeton coloratus, a oligotrophic species, is associated with low overlying and porewater SRP concentrations but high sediment TP content. Eutrophic species, such as Potamogeton pectinatus, are associated with low sediment TP. (4) It is hypothesized that Chara hispida primarily takes up sediment ammonia for nitrogen nutrition. (5) Nutrient characteristics of the water body and the sediment of eight macrophyte species in Bavarian rivers are described.     

A Simple Model of Phosphorus Retention Evoked by Submerged Macrophytes in Lowland Rivers

This study was designed to quantify and model the effects of macrophytes on phosphorus retention in a lowland river. The seasonal course of phosphorus retention was calculated from the measured difference in TP between beginning and end of a 30-km river course and the estimated lateral P input. The coverage of submersed macrophytes was mapped and coincided with the difference between theoretical water level (without vegetation) and the observed one. Therefore, the increase in water level was used as measure of the macrophytes’ abundance. In years with rare vegetation (1991–1994), P was retained in winter and remobilized in summer. In years with dense stands of macrophytes (1995–2002), net P retention was highest in summer and amounted up to 20% of TP load, and was negative during winter. The annual P budget was close to zero in both periods. The found sinusoidal annual pattern of total phosphorus retention was used to create a retention model for vegetated lowland rivers.     

Seasonal and Interspecific Nutrient Mitigation Comparisons of Three Emergent Aquatic Macrophytes

The purpose of this study was to measure both summer and winter nutrient mitigation efficiencies of three aquatic plants found in agricultural drainage ditches in the lower Mississippi River Basin. Mesocosms (1.25 × 0.6 × 0.8 m) were filled with sediment and planted with monocultures of one of three obligate wetland plant species, Typha latifolia, Thalia dealbata, and Sagittaria latifolia, or left nonvegetated to serve as controls. Mesocosms were amended with nitrate, ammonium, and phosphate over a 4-h hydraulic retention time, followed by an 8-h flushing with nonamended water to assess residual nutrient leaching in both summer and winter exposures. Significant interactions between vegetation type and season were noted for both nitrate and total inorganic phosphorus concentrations and loads. Future research will focus on altering hydraulic retention time for improved efficiency, as well as the specific contribution of microbial activity to nutrient mitigation.