Reduction of benthic macroinvertebrates due to waterfowl foraging on submerged vegetation during autumn migration

If present in large numbers, as during migration, herbivorous waterfowlmay reduce the amount of submerged vegetation. Because the vegetation is a keyfactor in shallow eutrophic lakes, removal of the green biomass can be expectedto affect also other biota that depend on the vegetation. We conducted anexperiment to determine how the abundance of chironomids andPisidium sp. were affected by intense foraging ofwaterfowlon the submerged plant Potamogeton pectinatus. This wasdone in Lake Ringsjön in southern Sweden, during the autumn migration ofthe birds. Three treatments, replicated six times, were used: (i) closed cagesthat excluded all waterfowl, (ii) semi-open cages that excluded only largewaterfowl (geese and swans), and (iii) open plots where all waterfowl couldfreely enter. Waterfowl densities were monitored during the experiment. Theresults suggest that the foraging of large waterfowl (swans) had a clearlynegative effect on macroinvertebrate abundance and aboveground biomass ofP. pectinatus. At the end of the experiment, the densityofchironomids was about 46% lower in the open than in the closed cages. Ingeneral, the density of Pisidium sp. tended to be lower inthe open plots. Small waterfowl alone did not seem to affect either thevegetation or macroinvertebrates. We suggest that thePisidium sp. was influenced at an early stage of grazing,when waterfowl foraged on aboveground biomass, whereas chironomids wereaffectedat a later stage, when swans were digging for below-ground tubers.     

Propagule banks and regenerative strategies of aquatic plants

Abstract. The role of the propagule bank in aquatic plant maintenance was studied in two riverine wetlands. Four sites were selected, characterized respectively by flooding, drying up, both disturbances operating, and neither operating. Our hypothesis was that recolonization after drying up would mostly involve seeds and buds from the propagule bank, whereas recolonization after floods would mostly involve rhizomes. Dry sites were characterized by a high density of seeds, and a high similarity between seed species and established vegetation. Unspecialized fragments remaining in wet parts of the sediment probably also contribute to species maintenance. Species maintenance in sites subjected to flooding was highly dependent on deeply anchored rhizomes, as indicated by the strong floristic similarity between species that occur in the established vegetation and rhizomes in the bank. Regeneration of the community after scouring floods also involved seeds, some species being able to flower under water. When scouring flooding and drying up were superimposed, regenerative strategies exhibited in the bank did not simply result from the ‘addition’ of the two disturbance effects. When the disturbances did not occur too closely together in time, species were able to survive either by: (1) producing many propagules under aquatic conditions or (2) coping with the temporal variability by producing several types of propagules.     

黄河三角洲菹草生长模型及其对水质的影响

通过连续对菹草生长过程的观测 ,用指数方程拟合了菹草从 10月中旬至第 2年 5月底的整个生长过程 (p<0 .0 0 2 ) ,设K=2 .5 kg/ m2时 ,用 L ogistic方程拟合了从 3月到 5月底的生长过程 (p<0 .0 0 0 )。通过 7月底至 8月初、10月、翌年 3月和 5月份对一个菹草型水库和无或有不同规模水草的 5座水库水生生物的周年调查发现 :(1)菹草型水库 TP最高峰的月份比其它水库的推迟 ,其它水库 10月份 TP最高 ,而菹草型水库 3月份最高 ;(2 )菹草型水库浮游植物最高峰的月份比无水草水库的推迟 ,无水草水库出现在夏季 (7～ 8月份 ) ,草型水库的出现在秋季 (10月份 ) ;(3)菹草型水库 3月份浮游植物生物量明显高于其它水库的 ,其硅藻占据更高的优势度 ;(4 )菹草型水库和其它水库之间的总磷和浮游植物数量的年平均值无明显差别 ;(5 )不同水库藻类数量年平均值与 TP年平均值相关极显著 (p<0 .0 0 5 ) ,而 TP又与氯化物 (Cl)相关极显著 (p<0 .0 0 5 ) ;(6 )水草的存在使p H略有提高 ,并使其在不同时间的波动幅度减小     

蓖齿眼子菜对栅藻和微囊藻的他感作用及其参数

主要报道篦齿眼子菜 (俗称红线草 )的种植水抽滤液对栅藻、微囊藻生长的他感作用试验。应用修正的逻辑斯谛 (Logistic)方程和Lotka Volterra种群竞争模型来计算篦齿眼子菜对藻类的他感作用参数。纯培养试验结果表明 :种植水抽滤液对栅藻生物量和生长率都有一定的促进作用。当浓度大于等于 5 0 %时 ,对栅藻生长的影响则是有抑制效应 ,他感作用效应与种植水的浓度没有明显的相关性 ,他感作用参数平均为 - 0 0 2 6。所有浓度设对照。微囊藻的生长都有明显的抑制作用 ,他感作用参数平均为 - 0 2 37。共培养试验结果表明 :篦齿眼子菜种植水抽滤液对纯培养试验结果有放大效应。所有的种植水抽滤液浓度对栅藻生长都起促进作用 ,对栅藻的生物量效应、生长率存在明显的对数正相关 ,但与他感作用参数的相关不明显 ,共培养的他感作用参数平均为 0 0 2 0 ;对微囊藻生长抑制作用更加明显 ,共培养的他感作用参数平均为 - 0 4 2 0。不管是纯培养还是共培养中 ,种植水抽滤液对栅藻的他感作用系数值都很低 ;而种植水抽滤液浓度对微囊藻的生物量效应、生长率或他感作用的参数都存在明显的线性负相关 ,并且他感作用系数值约高一个数量级     

ent-Labdane diterpenes from the aquatic plant Potamogeton pectinatus

Four new ent-labdane diterpenes were isolated from the freshwater aquatic plant Potamogeton pectinatus, together with two known furano-ent-labdanes. The new compounds were assigned the structures methyl-15,16-epoxy-12(R)-acetoxy- 8(17), 13(16),14-ent-labdatrien-19-oate,15,16-epoxy-12(R)-acetoxy-8(17), 13(16),14-ent-labdatrien-19-oic acid, 8(17),13-ent-labdadien-15 --> 16-lactone-19-oic acid and 16-hydroxy-8(17),13-ent-labdadien-15,16-olid-19-oic acid by spectroscopic means. Some of these labdanes showed a strong algicidal activity against Raphidocelis subcapitata.     

Genetic variation within and between populations of Potamogeton pusillus agg.

Patterns of isozyme variation were examined in 17 populations of P. pusillus and P. berchtoldii, together with one population of P. trichoides taken for comparison. Both P. pusillus and P. berchtoldii displayed low levels of variation within populations associated with high levels of interpopulation differentiation. This pattern of partitioning of genetic variation within and between populations is attributed to the founder effect, frequent vegetative propagation by turions, dominant self-fertilization and limited seedling recruitment. The mechanism of pollen transfer was investigated in cultivation. Effective pollination takes place in air above the water surface (autogamy, geitonogamy, anemogamy), on the water surface (epihydrogamy) or below water surface (hydroautogamy). The species are self-compatible. The low level of infra-population variation together with rare occurrence of heterozygotes suggest that selfing is the most frequent mode of pollination, although the protogynous flowers may occasionally permit some cross-pollination. Unique enzyme markers were found for P. pusillus and P. berchtoldii, and also for the single population of P. trichoides. All multienzyme phenotypes were species-specific. Isozyme data support the separate position of P. pusillus and P. berchtoldii. UPGMA dendogram based on enzyme data of 133 plant samples revealed three distinct main enzymatic entities perfectly corresponding to the three morphologically defined species.     

ENDOPHYTIC ALGAE OF CHONDRUS CRISPUS (RHODOHYTA). II. ACROCHAETE HETEROCLADA SP. NOV., A. OPERCULATA SP. NOV., AND PHAEOPHILA DENDROIDES (CHLOROPHYTA)1

The occurrence of three endophytic green algae within Chondrus crispus Stackh. is reported. Two of them are new to science and are described as Acrochaete heteroclada Correa and Nielsen sp. nov. and A. operculata Correa and Nielsen sp. nov. The algae were studied in unialgal culture and in association with the host following infection of C. crispus under laboratory conditions. The experimental infection showed A. heteroclada to be initially epiphytic, with endophytic filaments growing into the cortex of the host during late infection. A. operculata is entirely endophytic when associated with the host. Phaeophila dendroides (Crouan frat.) Batters behaves as an epiphyte at 15 and 24°C but penetrates the host tissues at 20°C. For all three species, a close physical association with the host is established only when zoospores settle and germinate on the surface of C. crispus.     

Secondary production and seasonal development of epiphytic Enallagma civile Hagen, 1861 (Odonata: Coenagrionidae) in a newly constructed urban wetland floodway ecosystem

Secondary production and seasonal development of the damselfly Enallagma civile Hagen, 1861 Hagen, H. (1861), Synopsis of the Neuroptera of North America, Washington, DC: Smithsonian Institution Miscellaneous Collection.[Crossref] , [Google Scholar] were determined as part of an epiphytic macroinvertebrate study in the Dallas Floodway Extension Trinity River Project Lower Chain of Wetlands, Dallas, TX, USA. These wetlands were constructed to mitigate flooding of the Trinity River, but also provided quality wildlife habitat and removal of wastewater effluent contaminants. Variations in life history were observed between two macrophytes and three different wetlands of varying age, effluent source, and vegetation establishment. Mean annual production of E. civile was 1393 mg/m²/year, standing stock biomass was 1376 mg/m²/year, cohort production/biomass (P/B) ratio was 4.30/year, and annual P/B was 10.18/year. These values are in the upper range of known Odonata production values from a lentic system. Enallagma civile biomass growth rates were observed to be higher from populations on the better established macrophyte (Potamogeton nodosus Poiret, 1816) and in the longest established wetland.     

Ontogenetic variation in response to temperature change in the control of seed dormancy of Rumex obtusifolius L. and Rumex crispus L.

Abstract After the onset of imbibition, the dormant seeds of Rumex obtusifolius and R. crispus are stimulated to germinate by a change from an initial low temperature to a warmer temperature for a relatively brief period: the warmer that temperature the shorter is the optimum period spent at it, and this optimum value is unaffected by the initial temperature. The optimum period is more critical in R. crispus than in R. obtusifolius (about 1 h and 2.5 to 4 h, respectively, for a warmer temperature of 35°C in the dark); in the light the length of the period at the warmer temperature is less critical in both species. The sensitivity of the seeds to the change to the warmer temperature increases with time from the start of imbibition at a rate which is positively related to the initial temperature. In R. obtusifolius maximum sensitivity was typically reached after 3 to 5 d when the initial temperature was 20°C and then remained constant, or declined only slightly, over the period investigated (10 d). At the same initial temperature, however, R. crispus showed a cyclical pattern of sensitivity with peaks occurring at 3–4 d intervals from the start of imbibition.