不同营养水平对外来物种凤眼莲生长特征及其竞争力的影响

入侵种凤眼莲(Eichhorniacrassipes)在中国的泛滥不仅与其强大的适应力和繁殖能力有关,还与水体的富营养化有很大的关系。作者通过盆栽实验比较了三个营养水平的模拟富营养条件下凤眼莲的生长特征和对当地种黄花水龙(Ludwigiapeploidesssp.stipulacea)和黑藻(Hydrillaverticillata)两个不同生长型的影响。结果表明:富营养条件增强了凤眼莲的生长繁殖能力,使其平均每母株克隆分株数、平均株高以及总生物量极大的增加。凤眼莲的生长优势导致了其竞争优势,对黄花水龙和黑藻都发生了明显的竞争效应。迅速繁殖的凤眼莲覆盖大量水面,通过排挤作用抑制了黄花水龙的生长(低营养水平除外);黑藻因光照缺乏,导致正常光合作用受阻,生物量急剧下降。凤眼莲对黑藻的竞争效应较黄花水龙更强。富营养化的水体为凤眼莲的成功入侵提供了优越条件,因此解决当前水体的富营养化状况能有效控制凤眼莲入侵,同时也有利于本地生物多样性的保护。     

3种沉水植物去除水体中氮磷能力研究

研究了3种沉水植物对不同质量浓度富营养化水体的净化能力,结果表明,轮叶黑藻、金鱼藻和狐尾藻对水体中的氮、磷都有很好的净化效果,对总氮去除能力从大到小依次为轮叶黑藻>金鱼藻>狐尾藻,对总磷去除能力从大到小依次为轮叶黑藻>狐尾藻>金鱼藻。实验表明,沉水植物是富营养化水体水生态系统重建的关键,在水体生态修复中,轮叶黑藻是一种很好的水体净化沉水植物。     

修复白洋淀镉污染水体的沉水植物筛选试验

为了筛选出适宜修复白洋淀镉(Cd)污染水体的沉水植物,该研究通过室内模拟试验,分析了四种沉水植物黑藻、狐尾藻、金鱼藻和菹草对Cd的耐受性及对底泥Cd的富集和迁移能力。结果表明:(1)通过毒性测试研究,Cd对黑藻、狐尾藻、金鱼藻及菹草的4 d-EC₅₀(半数抑制浓度)分别为0.51、0.81、0.03、0.12 mg·L^-1,狐尾藻对Cd的耐性最强,黑藻次之,金鱼藻对Cd的耐性最低; 四种沉水植物对Cd的最大富集量分别为27.89、15.28、22.54、32.74 g·kg^-1,菹草对Cd的富集能力最强,黑藻次之,狐尾藻对Cd的富集能力最低。(2)通过Cd污染底泥修复研究,黑藻、狐尾藻和菹草体内Cd富集量整体表现为根>叶片和茎(P<0.05); 地上部、根对Cd的富集能力分别表现为黑藻>菹草>狐尾藻,菹草>黑藻>狐尾藻; 三种沉水植物对Cd的迁移能力则表现为黑藻>狐尾藻>菹草。总之,黑藻对底泥中Cd富集和迁移能力均较强,且耐性较高,是最适合修复白洋淀Cd污染水体的沉水植物。     

不同基质中水鳖对共存的穗花狐尾藻和金鱼藻的影响

研究设置了营养水平不同的3种基质,在有或无浮水植物水鳖共存的情况下,混合种植营养吸收方式不同的两种沉水植物（仅从水中吸收营养的金鱼藻和从水和基质都能吸收营养的穗花狐尾藻）,探讨在不同的基质中浮水植物对沉水植物的影响。结果显示:实验中水鳖的存在均未对共存的两种沉水植物的生长产生抑制作用。当水鳖覆盖水面时,与无根的金鱼藻竞争光照和水体营养,促使其增加分枝数和茎长,并增加叶生物量的分配,最终导致水鳖的共存促进了金鱼藻的生物量积累。但与金鱼藻不同,有根的穗花狐尾藻可通过基质吸收营养,与共存的水鳖之间只存在光照竞争,使穗花狐尾藻仅以改变植株形态来适应浮水植物的表层覆盖,生物量积累并未发生显著变化。与沙处理相比,水鳖在营养水平较高的泥处理和泥沙混合处理中生长更旺盛,基质没有显著影响沉水植物的生物量和分株数。因此,在退化湿地生态系统中恢复水生植物时,为了提高群落的物种多样性,可以将沉水植物与少量的浮水植物组合配置,少量的浮水植物不会对沉水植物的生长带来负面影响。     

高寒典型草原主要物种的株高和盖度预测种群和群落地上生物量

为快速、准确、无破坏地测定草原地上生物量,在祁连山高寒典型草原植物生长旺季,观测了冬季和春秋季放牧地60个样方内各物种的株高、盖度等生长指标。以冬季牧地紫花针茅（Stipa purpurea）、醉马草（Achnatherum inebrians）、赖草（Leymus secalinus）、扁穗冰草（Agropyron cristatum）、二裂委陵菜（Potentilla bifurca）、银灰旋花（Convolvulus ammannii）6个主要物种的株高、盖度、株高和盖度的乘积为自变量,分别预测同物种、其他物种和群落地上生物量。用春秋季牧场的数据验证模型的精确性和稳定性。结果表明：主要物种的生长指标可预测其自身、其他物种和群落地上生物量。对自身种群,株高和盖度乘积的复合因子预测效果最好;4种禾草对其他物种、二裂委陵菜对菊科植物种群,株高、盖度单因子预测效果优于复合因子;6个主要物种单独或2-6个种结合均可预测群落地上生物量,但是以6个物种株高和盖度的乘积同时预测时决定系数最大,可解释群落地上生物量89.5%的变异,为高寒典型草原群落地上生物量最优预测模型。     

广西澄江喀斯特湿地沉水植物碳、氮、磷化学计量特征

沉水植物是水生生态系统中重要的初级生产者。当前有关沉水植物生态化学计量特征的研究主要集中在非喀斯特区,而在喀斯特区的相关研究较为缺乏。因此,以广西澄江喀斯特典型湿地中的7种沉水植物为研究对象,分析沉水植物地上部分及底泥的碳（C）、氮（N）、磷（P）化学计量特征。结果显示,（1）7种沉水植物地上部分总碳、总氮和总磷平均含量最大值均出现在小茨藻（Najas minor）分别为（325.4±5.01） g/kg、（33.07±1.59） g/kg和（3.79±0.16） g/kg;C ： N、C ： P、N ： P平均值分别为10.14±0.18、96.23±3.56和9.47±0.32,C ： N最大值（11.89±0.54）出现在苦草（Vallisneria natans）,C ： P和N ： P最大值（113.27±18.14和11.13±1.63）均出现在穗花狐尾藻（Myriophyllum spicatum）。（2）底泥有机碳、总氮、总磷、碱解氮和速效磷含量平均值分别为（15.05±0.56） g/kg、（2.06±0.08） g/kg、（0.58±0.01） g/kg、（162.53±9.16） mg/kg和（21.73±0.86） mg/kg,有机碳、总氮、总磷、碱解氮和速效磷的平均含量最大值均出现在小茨藻（N.minor）分别为（18.54±1.04） g/kg、（2.55±0.25） g/kg、（0.66±0.03） g/kg、（214.82±32.05） mg/kg和（26.37±3.31） mg/kg;底泥的C ： N、C ： P和N ： P平均值分别是7.33±0.14、25.7±0.72和3.53±0.09,C ： N、C ： P和N ： P最大值分别出现在金鱼藻（Ceratophyllum demersum）（7.45±0.32）、小茨藻（N. minor）（28.29±1.29）和黑藻（Hydrilla verticillata）（3.89±0.25）。（3）沉水植物的地上部分总碳与底泥的有机碳和总氮均呈显著负相关性;沉水植物的地上部分总氮与底泥有机碳、碱解氮、C ： P均呈显著正相关性;沉水植物地上部分C ： N、C ： P均与底泥有机碳、总氮、总磷、碱解氮、C ： P、N ： P呈显著负相关,表明不同喀斯特湿地沉水植物和底泥之间的养分耦联性不同。本研究为喀斯特湿地生态系统生态化学计量学研究提供理论依据。     

深圳市建成区入侵植物对草本植物种类及功能多样性的影响

入侵植物对城市生态系统形成潜在威胁,有待引起足够的关注。为探究城市入侵植物对草本植物种类及功能多样性的影响,以深圳市建成区入侵植物鬼针草（Bidens pilosa）和南美蟛蜞菊（Sphagneticola trilobata）为例,分析了不同绿地类型中不同程度的单独入侵和共同入侵对草本植物群落物种多样性和功能多样性的影响规律。结果显示：①Margalef物种丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数和Pielou均匀度指数均与入侵植物盖度呈显著负相关（P<0.05,0.5865 < R² < 0.9356）。②功能丰富度指数（FRic）、功能均匀度指数（FEve）和Rao二次熵指数（FD_Q）与入侵植物盖度有一定的相关关系（0.0000 < R² < 0.2211）。③群落的特征加权平均株高（CWM_H）与入侵植物盖度有一定的正相关关系（0.0716 < R² < 0.2262）。④与未入侵的样方相比,鬼针草轻度入侵显著提高了物种多样性（P<0.05）,鬼针草和南美蟛蜞菊单独重度入侵均显著降低物种多样性（P<0.05）,二者各种程度的分别单独入侵及共同入侵都显著提高了群落加权平均株高（CWM_H）（P<0.05）。⑤对不同的绿地类型分开计算发现,鬼针草单独入侵和二者共同入侵都显著提高了各种绿地类型的物种多样性（P<0.05）,南美蟛蜞菊单独入侵只对部分绿地类型的群落物种多样性影响显著。⑥鬼针草和南美蟛蜞菊之间的生态效应可能为拮抗作用。研究结果为进一步揭示植物入侵对城市草本植物群落的影响规律提供参考,为有效防治城市外来植物入侵提供一定的依据。     

意大利苍耳与乌拉尔甘草种间竞争能力比较

意大利苍耳已经开始入侵乌拉尔甘草农田,然而对其入侵后果目前知之甚少。通过研究意大利苍耳与乌拉尔甘草的种间竞争关系,以期为意大利苍耳对乌拉尔甘草农田生态系统的入侵能力及入侵后果的评估提供试验依据。模拟了甘草农田的土壤水肥条件,采用取代试验法,设置意大利苍耳与乌拉尔甘草的单种种植和混种种植2种种植模式,待意大利苍耳生育期结束后进行收获,分别比较了该两种植物的个体生长及生物量积累在单种种植与混种种植两种处理间的差异,并比较单种和混种模式下乌拉尔甘草的地下器官中甘草酸含量的差别,通过计算相对产量、相对竞争强度和竞争攻击系数来比较该两种植物种间竞争能力的相对强弱。结果表明：与单种模式相比,混种模式下意大利苍耳个体生长的形态学性状和有性繁殖能力均有显著增加,其株高、冠幅和种子数量较单种处理分别增加了13%、27%和56%。而乌拉尔甘草的个体生长及克隆繁殖能力均显著降低,其根瘤的形成也受到显著的抑制,混种处理的乌拉尔甘草的株高、冠幅、根总长度、根总表面积、根平均直径以及根瘤数量比单种处理分别下降了35%、45%、55%、63%、19%和76%。单种处理下每株甘草根状茎的平均条数为3条,而与意大利苍耳混种后,其根状茎的发育被完全抑制。与单种处理相比,混种处理中的意大利苍耳生物量积累均显著的增加了,其中根、茎、叶、果实及总生物量与单种模式相比分别增加了84%、73%、84%、73%和77%,而混种模式却极显著降低了乌拉尔甘草生物量和地下器官甘草酸含量的积累,使其根、茎、叶、总生物量以及甘草酸含量与单种模式相比分别下降了72%、80%、65%、71%和63%。混种模式中的意大利苍耳相对产量（RY_a）大于1,而乌拉尔甘草相对产量（RY_b）小于1,表明意大利苍耳受到邻株同种其他个体的种内竞争压力大于来自邻株乌拉尔甘草的种间竞争压力,而乌拉尔甘草受到邻株同种其他个体的种内竞争压力则小于来自邻株意大利苍耳的种间竞争压力。混种模式中的意大利苍耳相对竞争强度（RCI_a）小于0,其竞争攻击系数（A_q）大于0,而乌拉尔甘草的相对竞争强度（RCI_b）则在0-1之间,其竞争攻击系数（A_b）小于0,表明在该两种植物的混生群落中,乌拉尔甘草的竞争能力弱于意大利苍耳。总体来看,在二者混生的群落中,意大利苍耳在竞争中占据明显的优势地位,对乌拉尔甘草的产量和品质均造成强烈的负面影响。     

不同营养条件对金鱼藻净化作用及其生理生态的影响

以沉水植物金鱼藻（Ceratophyllum demersum）为研究对象,研究了较高营养条件（N:1030 mg/L,P:13 mg/L）对金鱼藻去除氮、磷能力的影响,金鱼藻的含磷量、生物量与净光合作用速率对营养负荷的响应。结果表明,金鱼藻-沉积物处理系统可有效去除氮、磷（去除率80%以上）,但去除效率随水中营养盐浓度的升高而下降。试验结束时各试验组金鱼藻总磷含量达7.0113.09 mg/g （平均9.03 mg/g）,显著高于对照组（2.853.17 mg/g,平均3.05 mg/g）,表明金鱼藻可以吸收水体中的磷。营养盐对金鱼藻生长有明显抑制,其抑制作用随营养盐浓度增高而加剧,除对照组外,各试验组金鱼藻均有叶片脱落,试验结束时金鱼藻生物量降至初始生物量的48.3%63.3%。在较高营养水体中,金鱼藻的净光合作用速率由试验开始时-0.0370.058 mg/（gh）显著上升至试验结束时0.180.44 mg/（gh）,而对照组变化不大,这表明在试验后期,随着水体营养盐浓度降低,金鱼藻开始进行恢复性生长,说明水体营养盐浓度对金鱼藻的净光合作用速率和生长速率有明显影响。金鱼藻尚不适宜作为滇池草海生态修复的先锋物种。       

水盾草在中国的分布特点和入侵途径

水盾草(Cabomba caroliniana)是原产南、北美洲的水生植物,近年来在野外调查中发现它在中国已经成为归化植物。通过华东、华南和华中地区的实地考察,调查点共300多个,覆盖我国东南沿海及华中10省（市、区）80多个县（市）。结果发现有水盾草分布的点67个。目前水盾草在中国分布于浙江北部的杭嘉湖平原和宁绍平原、江苏南部的太湖流域及上海西部的淀山湖附近的河网地带。从地理纬度上看,自29°33′7″N（建德梅城）至31°35′2″N（常熟昆承湖）;主要的水域类型为一些水流缓慢、水位稳定的小河道和中小型湖泊。在水盾草所处的沉水植物群落中,共调查到大型沉水植物8科18属21种,常见种为苦草(Vallisneria natans)、金鱼藻(Ceratophyllum demersum)、黑藻(Hydrilla verticillata)、菹草(Potamogeton crispus),这些也是浙北、苏南地区水域主要的水生植物。根据水盾草与各个种的种间相遇百分率来看,金鱼藻最高,为51.33%,其次为苦草、黑藻和菹草,分别为45.05%、36.56%、35.64%。可见相对其他水生植物群落而言,由这些种所组成的水生植物群落更易为水盾草所侵入。从各个分布点水盾草所处状态来看,有些点的水盾草已成为群落的优势种,有的刚刚定居,还有的则仍处于零星漂浮状态,这也表明水盾草在我国仍在进一步扩散之中。根据水盾草种子无成熟的胚及植株对脱水的敏感性,推测中国的水盾草最初可能是作为水族馆观赏水草引进而逸生的。从原产地水盾草分布纬度范围、适生环境、气候条件,结合其在我国的分布特点分析,水盾草在我国尚有很大的扩散空间,为了避免类似凤眼莲(Eichhornia crassipes)那样的事件在中国重演,必须引起有关部门及科技人员对水盾草的重视。     

Effects of Eichhornia crassipes and Ceratophyllum demersum on Soil and Water Environments and Nutrient Removal in Wetland Microcosms

Wetland plants are important components that influence the biogeochemistry of wetland ecosystems. Therefore, remediation performance in wetlands can differ depending on the growth forms of plants. In this study, the effects of Eichhornia crassipes (floating plant) and Ceratophyllum demersum (submerged plant) on the wetland soil and water environments were investigated using a microcosm study with simulated hydrology of retention-type wetlands between rainfall events. The C. demersum microcosm (SP) showed the fastest recovery with a diel fluctuation pattern of dissolved oxygen, pH, and oxidation-reduction potential (ORP) from the impacts of nutrient inflow. Moreover, SP exhibited the lowest decrease in sediment ORP, the highest dehydrogenase activity, and more organic forms of nitrogen and phosphorus. E. crassipes microcosms exhibited the lowest water temperature, and efficiently controlled algae. In the presence of plants, the total nitrogen and phosphorus concentrations in water rapidly decreased, and the composition of organic and inorganic nutrient forms was altered along with a decrease in concentration. The results indicate that wetland plants help retain nutrients in the system, but the effects varied based on the wetland plant growth forms.     

Decomposition dynamics of aquatic macrophytes in the lower Atchafalaya, a large floodplain river

Decomposition of aquatic macrophytes can considerably influence carbon cycling and energy flow in shallow freshwater aquatic ecosystems. The Atchafalaya River Basin (ARB) is a large floodplain river in southern Louisiana that experiences a seasonal floodpulse and is spatially composed of a mosaic of turbid riverine and stagnant backwater areas. During two seasons, winter and fall of 1995, we examined decomposition of four common aquatic macrophytes in the ARB: water hyacinth (Eichhornia crassipes), arrowhead (Sagittaria platyphylla), coontail (Ceratophyllum demersum) and hydrilla (Hydrilla verticillata). To determine decay rates, we used litter bags of two mesh sizes (5 mm and 0.25 mm) and analyzed data with a single exponential decay model. Analysis of decay rates established several trends for aquatic macrophyte decomposition in the ARB. First, macrophytes decayed faster in fall than winter due to the effect of increased temperature. Second, macroinvertebrates were the primary decomposers of macrophytes in riverine sites and microbes were the primary decomposers in backwater areas. These trends may have been related to decomposer-habitat interactions, with well-oxygenated riverine sites more hospitable to invertebrates and backwater areas more favorable to microbes because of high organic inputs and reduced flow. Decay rates for macrophytes, ranked from slowest to fastest, were E. crassipes<S. platyphylla<C. demersum<H. verticillata. Slower decomposition of E. crassipes was probably a result of microbial inhibition by the waxy-cutin outer layer and low nutritional value. The accelerated decomposition of C. demersum and H. verticillata was most likely a function of the large surface area of the highly dissected leaves. Macroinvertebrate numbers were twice as high in riverine sites compared to backwater sites. In the winter, amphipods Gammarus spp. and Hyallela azteca composed a large percentage of the total density on detritus. In the fall, Caenis sp. was prevalent in the backwater habitat and dipterans were abundant in the riverine site. We investigated the microbial component involved in the decomposition of E. crassipes and S. platyphylla and found that the highest microbial respiration rates occurred early in the winter at the backwater site. Bacterial density in the winter on E. crassipes and S. platyphylla averaged 1.4×10⁶ cm^-2 after two days and decreased to 2.0×10⁵ cm^-2 after 28 d. Our results emphasized the importance of the microbial community in the decomposition of macrophytes in the ARB, especially in backwater habitats and in the early stages of decay.     

Host Range of Mycoleptodiscus terrestris, a Microbial Herbicide Candidate for Eurasian Watermilfoil, Myriophyllum spicatum

A native strain of the fungal plant pathogen Mycoleptodiscus terrestris is capable of causing under experimental conditions necrotic shoot lesions and a generalized decline and disintegration of Eurasian watermilfoil (Myriophyllum spicatum), an exotic submerged aquatic weed in North America. The potential of this fungus to cause disease on nontarget plants was evaluated on 33 species and cultivars in 11 families. The nontarget selection, intended as a Tier I group, was biased toward probable suscepts consisting of submerged, floating, and emergent aquatic species and terrestrial crop plants. The plants were exposed to the fungal mycelium formulated in alginate beads. Pathogenicity rather than phytotoxicity was the primary mode of attack by the fungus. Of the 16 nontarget aquatic species tested, the fungus was pathogenic to Hydrilla verticillata (hydrilla), Myriophyllum aquaticum (parrotfeather), and Ceratophyllum demersum (coontail), but only in hydrilla did it cause plant mortality comparable to that in Eurasian watermilfoil. The remaining 13 submerged, floating, and emergent aquatic species were unaffected. Of the 17 terrestrial species screened, none was significantly affected by the fungus in germination studies, but postemergent disease symptoms developed on seedlings of 10 species. Four of the 10, Medicago sativa (alfalfa), Lotus corniculatus (birdsfoot trefoil), Trifolium hybridum (alyce clover), and T. repens (white clover), developed disease affecting 26-50% of their tissues. Thus, this host range testing scheme, based on the concept of screening plants under the maximum hazard potential, helped to identify susceptible species. Nonetheless, it exaggerated the nontarget risk due to the small number of host species tested. Screening a taxonomically diverse and larger selection of plants as well as testing under conditions of less severe exposure to the fungal inoculum are necessary to obtain a more realistic view of the host range than presently indicated.     

Vegetative Propagule Pressure and Water Depth Affect Biomass and Evenness of Submerged Macrophyte Communities

Vegetative propagule pressure may affect the establishment and structure of aquatic plant communities that are commonly dominated by plants capable of clonal growth. We experimentally constructed aquatic communities consisting of four submerged macrophytes (Hydrilla verticillata, Ceratophyllum demersum, Elodea nuttallii and Myriophyllum spicatum) with three levels of vegetative propagule pressure (4, 8 and 16 shoot fragments for communities in each pot) and two levels of water depth (30 cm and 70 cm). Increasing vegetative propagule pressure and decreasing water level significantly increased the growth of the submerged macrophyte communities, suggesting that propagule pressure and water depth should be considered when utilizing vegetative propagules to re-establish submerged macrophyte communities in degraded aquatic ecosystems. However, increasing vegetative propagule pressure and decreasing water level significantly decreased evenness of the submerged macrophyte communities because they markedly increased the dominance of H. verticillata and E. nuttallii, but had little impact on that of C. demersum and M. spicatum. Thus, effects of vegetative propagule pressure and water depth are species-specific and increasing vegetative propagule pressure under lower water level can facilitate the establishment success of submerged macrophyte communities.     

Biosorption and growth inhibition of wetland plants in water contaminated with a mixture of arsenic and heavy metals

The potential of wetland plants as an onsite biosorbent and a biomonitor for combined pollution of arsenic and four heavy metals from non‐point sources was investigated in this study. Ceratophyllum demersum, Hydrilla verticillata, Hydrocharis dubia, and Salvinia natans were exposed to a water containing mixture of As, Cr, Cu, Pb, and Zn. Growth inhibition and biosorption potential of the wetland plants in artificially contaminated conditions were studied. These contaminants significantly reduced the growth of the plants. The tested wetland plants accumulated appreciable amounts of the contaminants in the following order: Pb>Cr>Cu>Zn>As. H. verticillata showed distinct visual change and a high biosorption factor (BSF) rank for As and heavy metals among the plants used in the study. As an unspecific collector of contaminants, it might be useful as a biomonitor and biosorbent in the As and heavy metal‐contaminated aquatic system.     

Growth of Hydrilla verticillata (L.f.) Royle under controlled conditions

Aquatic macrophytes are important resources for the maintenance of trophic chains and in biogeochemical processes, but they can also be deleterious for several uses if present in excess. Hydrilla verticillata was found in the Paraná River (Brazil) after 2005, which requires monitoring owing to the invasive potential of this species. In this study, we measured the growth of H. verticillata under controlled conditions and compared the growth dynamics for the two development strategies (branch and tuber). We show that this species has great potential to develop in tropical (Brazilian) aquatic ecosystems. The parameters from the modelling of the growth kinetics indicated a doubling time of 19.8 days for H. verticillata growing from stems; however, the growth from tubers were much faster, with doubling times ranging from 2.5 to 11 days. The delay for the tubers to sprout caused a decrease in the number of branches of H. verticillata stems. From the growth parameters obtained from the experiments under controlled conditions, we concluded that the high temperature and light availability in most South American reservoirs (including the Porto Primavera Reservoir where it was first recorded) are suitable for H. verticillata to compete and probably displace other native aquatic macrophytes, such as Egeria najas, Egeria densa, and Cerathophyllum demersum. This is a matter of concern because these and other submersed species are commonly found in several natural and man-made South-American aquatic ecosystems, where they are key for biodiversity maintenance.     

Community collocation of four submerged macrophytes on two kinds of sediments in Lake Taihu, China

To explore a method for rapid restoration and artificial regulation of submerged macrophytes in large-scale restoration of eutrophic lakes, the succession and the biodiversity changes of four communities composed of four native, common submerged macrophytes, Hydrilla verticillata, Potamogeton malaianus, Vallisneria spiralis and Najas marina, on two kinds of sediments were investigated. Under low light intensity (reduced by 99%), the plant biomass changed with seasonal changes, plant competition, and environmental stress. The competitive capability for light differed in the four species due to different shoot height and tiller number. After 405 days of transplantation, H. verticillata became dominant in all communities. The biomass of H. verticillata, with strong ability to endure low water light environment, accounted for more than 90% of the total community biomass, and P. malaianus had only weak growth, while V. spiralis and N. marina almost disappeared. Based on livability and biomass of submerged macrophytes on two sediment types, brown clay sediment appeared to be more favorable for the settlement of the plants, while fertile sludge sediment was suitable for vegetative growth. In conclusion, the improvement of habitats and the selection of appropriate plant species are of the greatest importance for ecological restoration of the aquatic ecosystem.     

Concentrations of Trace Metals in Dominant Aquatic Plants of the Lake Provala (Vojvodina, Yugoslavia)

The trace metal (Fe, Mn, Zn, Cu, Ni, Pb, Cd, Sr, and Cr) contents in the most common submerged and floating aquatic plants Ceratophyllum demersum L., Myriophyllum spicatum L., and Nymphoides flava Hill. of Provala Lake were evaluated. Considerable higher contents of iron, manganese, zinc, nickel, lead and strontium were found in submerged species than in the floating ones. The presence of cadmium and lead in plant tissues points to a certain degree of lake water pollution.     

Adaptation of submerged macrophytes to both water depth and flood intensity as revealed by their mechanical resistance

Little is known about the mechanical resistance response of submerged macrophytes to floods. An experiment was conducted to investigate the plant growth, root anchorage strength, and stem tensile properties of five submerged macrophytes under three initial water levels (1.0, 2.5, and 4.0 m) with four water level fluctuation speeds (0, 5, 15, and 25 cm d⁻¹). Our results demonstrate that the biomass, relative growth rate, root anchorage strength, and stem tensile properties of the five species decreased with increasing initial water level, suggesting that deep water can inhibit plant growth and decrease their mechanical resistance. Floods weakened the stem tensile properties and strengthened the root performances of Myriophyllum spicatum, Hydrilla verticillata, and Potamogeton malaianus in shallow water. However, floods induced opposite mechanical resistance responses from plants in deep water, indicating a possible trade-off between stem breakage and uprooting under flooding conditions. M. spicatum, Ceratophyllum demersum, and P. malaianus were more tolerant of deep water and flood intensity than Potamogeton maackianus and H. verticillata, as indicated by their larger biomass, plant heights, stem tensile properties, and root anchorage strength. This is the first article that mechanically explains the competitive capability and survival potential of submerged macrophytes to water depth and flood intensity.     

Separate and interactive effects of competition and herbivory on the growth, expansion, and tuber formation of Hydrilla verticillata

This study examined the interaction and main-effect impacts of herbivory by the leaf-mining fly Hydrellia pakistanae and plant competition from Vallisneria americana on the growth, expansion and tuber formation of Hydrilla verticillata in a 2 × 2 factorial design experiment. The study was conducted in 14,000-L tanks, over two growing seasons. Each tank represented a single experimental unit and contained 32 1-L pots. At the beginning of the experiment half of these were planted with H. verticillata while the other half were either left empty or planted with V. americana (the competitor). H. pakistanae fly larvae (the herbivore) were added to tanks as appropriate. No significant interactions were identified between herbivory and competition on any parameter of H. verticillata growth analyzed (i.e., total tank biomass accumulation, total number of rooting stems, total tuber number, total tuber mass, and tuber size), indicating that the factors were operating independently and neither antagonism nor synergism was occurring. Both competition and herbivory impacted the growth of H. verticillata. H. verticillata plants grown in the presence of V. americana developed less total biomass, had fewer total basal stems, had fewer tubers and less tuber mass per tank, and produced significantly smaller tubers relative to control plants. Herbivory also suppressed H. verticillata biomass accumulation and tended to suppress the number and total mass of tubers produced in each tank. Both factors showed 30–40% reduction of total H. verticillata biomass, although the mechanism of impact was different. Competition suppressed expansion of H. verticillata into adjoining pots but had little impact on its growth in pots where it was originally planted. Herbivory resulted in a general suppression of growth of H. verticillata in all pots. Although herbivory significantly impacted H. verticillata biomass, it did not result in competitive release for V. americana under the current experimental conditions. We conclude that management activities that promote competition or herbivory will impact the growth and expansion of H. verticillata. Furthermore, since these factors operated independently, the combined use of both factors should be beneficial for suppression of H. verticillata dominance.