闽江河口湿地植物枯落物立枯和倒伏分解主要元素动态

采用分解袋法,对闽江河口湿地2种挺水植物——芦苇(Phragmites australis)和互花米草(Spartina alterniflora)花和叶枯落物的立枯和倒伏分解过程及C、N、P元素动态进行研究。结果表明:(1)立枯分解是2种湿地盐沼植物重要的分解阶段,干物质损失率在13.26%—31.89%之间。多项式模型能较好描述2种植物花和叶的枯落物分解残留率动态。(2)立枯分解阶段,芦苇花和叶的C含量主要为波动下降,互花米草较为稳定;倒伏阶段后期,2种植物都以升高为主。立枯分解阶段2种植物枯落物N含量略有下降,而倒伏阶段逐渐上升。分解过程中枯落物P含量的波动较大。(3)2种植物花和叶C、N的NAI值在分解过程中<100%。芦苇的花和叶中P的NAI值在立枯和倒伏分解阶段都经历了明显下降和升高的过程,而互花米草在立枯阶段变化不大,倒伏阶段下降较为明显。(4)与芦苇相比,互花米草的花和叶枯落物C库较高,N库较低,P库差异不大。     

Single-species versus mixed-species community: which one is better for shore stabilization. A case study of Chongming Island, China

There are five vegetation communities for shore stabilization on the southern coast of Chongming Island: a reed (Phragmites australis) community, a 4-yr-old Salix babylonica-Phragmites australis community (4Sb), an 8-yr-old S. babylonica-P. australis community (8Sb), a 4-yr-old Taxodium ascendens-Phragmites australis community (4Ta), and an 8-yr-old T. ascendens-P. australis community (8Ta). One major question is which is better for shore stabilization: the reed community (a single-species community) or 4Sb, 8Sb, 4Ta and 8Ta (mixed-species communities)? The soil stability index (K) and root length density (RLD) were selected as indicators for evaluating soil stability in response to water erosion. There are two main types of shore facing downward erosion and erosion scarp retreat along the southern coast of Chongming Island, and the erosion period may occur from March to August (scenario 1) or October to December (scenario 2). The assumed erosion period is scenario 1, and 4Sb is the most suitable plant community for preventing erosion scarp failure and mitigating shoreline retreat because it has the greatest K and RLD in the 20-50-cm deep soil layer among all of the vegetation communities within all intertidal zones. Additionally, 4Sb and 8Ta provide the best protection for reducing downward beach face erosion compared to the other vegetation types in the lower intertidal zone (LIT). At the middle intertidal zone (MIT) and higher intertidal zone (HIT), the reed community is optimal for protecting the shore face because it has the greatest K and RLD at 0-20-cm soil among the five vegetation communities in March-April and July-August within the MIT and HIT. Under scenario 2, 4Sb is still the most suitable type for reinforcing the scarp and preventing shoreline retreat. With respect to shore face downward erosion, 8Ta might provide the best protection for beach surfaces within the intertidal zones because it had the greatest K and RLD at 0-20-cm depth among the five vegetation types in November-December within the LIT, MIT and HIT.     

Floating-leaved and emergent vegetation as habitat for fishes in a eutrophic temperate lake without submerged vegetation

Although submerged vegetation is considered to be the most suitable refuge against predators and form of foraging habitat for small fishes, submerged plants are often scarce or lacking in turbid eutrophic lakes. To evaluate emergent (Zizania latifolia) and floating-leaved (Nelumbo nucifera) vegetation as refuge areas against predators and as foraging habitats for small fishes, we investigated the fauna, abundance, and size distribution of the fish community as well as the abundance of possible prey for small fishes in beds of each vegetation type in a eutrophic shallow lake: Lake Teganuma in Japan. The leaves and stems of N. nucifera occupied an area 4.2 times larger than that of Z. latifolia. The high coverage of the water surface with plants most likely induced the hypoxia found in the N. nucifera bed. The diversity of small fishes was greater in the Z. latifolia bed with piscivorous fish than in the N. nucifera bed without piscivorous fish. The diversity of fish species in the vegetation was enhanced when there was an increased diversity of possible food sources rather than an absence of predators. Some aquatic insects of the same species had a much lower δ¹³C signature at hypoxic locations than at less hypoxic locations in the N. nucifera bed. Such site differences within a bed were not observed in the organisms caught in the Z. latifolia bed. The insects in hypoxic zones with a δ¹³C signature lower than ?30 ‰ were more depleted in ¹³C than the surface sediment or attached algae, suggesting that the larvae in the hypoxic zones incorporated the organic materials generated by methane-oxidizing bacteria. We can therefore conclude that floating-leaved vegetation, especially a N. nucifera bed, is not suitable as a replacement for submerged vegetation because of its potential to induce hypoxia, which can decrease the diversity of the fish fauna.     

几种水生植物腐解过程的比较研究

研究水生植物腐烂分解过程及其养分动态对认识水生态系统物质循环过程具有重要意义。通过室内植物分解模拟试验,对6种水生植物的腐解过程及腐解残余物成分的变化进行了比较研究。结果表明,在64 d的腐解过程中,浮叶植物的分解速率最快,沉水植物其次,挺水植物最慢;同种植物的分解速率及残余物成分变化在不同生物量密度组间存在一定差异,但总体趋势一致。分解过程中,植物残余物中P、纤维素、木质素含量的变化趋势种间差异较小,总体上P含量先迅速下降后缓慢上升,纤维素含量先下降后趋于稳定,木质素含量先上升后趋于稳定;植物残余物中C、N、半纤维素含量在分解初期种间的变化趋势不同,而分解后期则均为C含量上升,N、半纤维素含量趋于稳定。相关性分析结果表明,总体上,在整个分解周期中,初始N、P含量越大分解越快,初始纤维素、半纤维素、木质素含量、C/N、C/P、木质素/N等越大分解越慢;植物腐解不同阶段的质量指标对分解速率的影响有所不同,在分解前期,残余物中N含量越高分解越快,半纤维素含量、C/N、木质素/N越高,分解越慢,而后期木质素含量越高分解越慢,其它因子影响较小。     

Accumulation properties of As,Cd, Cu,Pb and Zn by four wetland plant species growing on submerged mine tailings

Plants may reduce element leakage from submerged mine tailings by phytostabilisation. However, high shoot concentrations of elements might disperse them and could be harmful to grazing animals. The aim of this investigation was to find out which of the three properties; low-accumulation, root accumulation or shoot accumulation of elements, occur in four of the most common wetland species growing on an old submerged mine tailings and if their properties can be determined by a hydroponic experiment. Above- and below-ground parts of Salix (mixed tissue from S. phylicifolia and S. borealis), Carex rostrata, Eriophorum angustifolium, and Phragmites australis were sampled and analysed for Cd, Cu, Zn, Pb and As. Differences in uptake and translocation properties of the same plant species were observed between field-grown plants and plants grown in hydroponics. These differences were probably due to processes in the soil–root interface. Thus, hydroponic screening studies should not be used to find suitable species for vegetation of wet-covered mine tailings. Most species were found to have restricted translocation of elements to the shoot, i.e. they were root accumulators, and only the shoot concentrations of Salix for Cd and Zn and E. angustifolium for Pb might be toxic to grazing animals. Thus, plant establishment on submerged tailings can be a safe method to stabilise the metals.     

Effects of submergence on the growth of Phragmites australis seedlings

Colonisation by reed seedlings, Phragmites australis (Cav.) Trin. ex Steud. is rare and usually occurs after drawdown and when shallow water prevails. P. australis seeds have high rates of germination but successful colonisation is dependent upon subsequent water depths. We investigated the capacity of young reed plants to resist a 4 weeks submergence stress within a 5 months period, and their subsequent recovery. A pond experiment examined the interactions between submergence depth and the age of the seedlings at submergence. Four submergence treatments were used. In two partial submergence treatments, 50 and 80% of the initial leaf area was submerged. In two total submergence treatments, plants were either submerged at 125% of their initial height with possible subsequent development of emerged leaves, or the water was deepened as they grew to maintain total submergence for 4 weeks. The ages at submergence were 40, 60 and 80 days. Plants were harvested at 5 months. Shoot elongation, biomass allocations to aerial biomass, roots and rhizomes, and photosynthetic activity of aerial leaves were measured. Redox potential was measured for a subsample.Mortality (18.7%) occurred only in the permanent submergence treatment for 40-day-old seedlings. In all treatments, submerged leaves senesced, except the terminal (youngest) leaves of permanently submerged plants. Submergence differentially affected shoot length and biomass, depending upon the intensity of the treatment and the seedling age. The major differences were found between the two partial and two total submergence treatments. Partial submergence (50 and 80%) significantly enhanced biomass accumulation and growth, whereas total submergence largely decreased biomass production and growth in length, with less effect on shoot numbers. The 80-day-old seedlings tolerated submergence better but growth was poorest in medium-aged plants (60-day-old). Increased elongation of the growing internodes of up to 140% was caused by submergence, and photosynthetic activity was enhanced by 85% in emergent leaves of plants initially submerged but allowed to produce emerged leaves during the treatment period.Young P. australis plants require shallow water levels without long lasting submergence to grow and survive. Tolerance to submergence increases with age. These processes contribute to define the conditions for colonisation via seeds in P. australis.     

Above- and belowground competition between two submersed macrophytes

Several studies have shown that submerged macrophytes provide a refuge for zooplankton against fish predation, whereas the role of emergent and floating-leaved species, which are often dominant in eutrophic turbid lakes, is far less investigated. Zooplankton density in open water and amongst emergent and floating-leaved vegetation was monitored in a small, eutrophic lake (Frederiksborg Slotssø) in Denmark during July–October 2006. Emergent and floating-leaved macrophytes harboured significantly higher densities of pelagic as well as plant-associated zooplankton species, compared to the open water, even during periods where the predation pressure was presumably high (during the recruitment of 0+ fish fry). Zooplankton abundance in open water and among vegetation exhibited low values in July and peaked in August. Bosmina and Ceriodaphnia dominated the zooplankton community in the littoral vegetated areas (up to 4,400 ind l^?1 among Phragmites australis and 11,000 ind l^?1 between Polygonum amphibium stands), whereas the dominant species in the pelagic were Daphnia (up to 67 ind l^?1) and Cyclops (41 ind l^?1). The zooplankton density pattern observed was probably a consequence of concomitant modifications in the predation pressure, refuge availability and concentration of cyanobacteria in the lake. It is suggested that emergent and floating-leaved macrophytes may play an important role in enhancing water clarity due to increased grazing pressure by zooplankton migrating into the plant stands. As a consequence, especially in turbid lakes, the ecological role of these functional types of vegetation, and not merely that of submerged macrophyte species, should be taken into consideration.     

Effects of elevated CO2, temperature and N fertilization on nitrogen fluxes in a temperate grassland ecosystem

The soil nitrogen cycle was investigated in a pre‐established Lolium perenne sward on a loamy soil and exposed to ambient and elevated atmospheric CO₂ concentrations (350 and 700 μL L^?1) and, at elevated [CO₂], to a 3 °C temperature increase. At two levels of mineral nitrogen supply, N– (150 kgN ha^?1 y^?1) and N+ (533 kgN ha^?1 y^?1), ¹⁵N‐labelled ammonium nitrate was supplied in split applications over a 2.5‐y period. The recovery of the labelled fertilizer N was measured in the harvests, in the stubble and roots, in the macro‐organic matter fractions above 200 μm in size (MOM) and in the aggregated organic matter below 200 μM (AOM). Elevated [CO₂] reduced the total amount of N harvested in the clipped parts of the sward. The harvested N derived from soil was reduced to a greater extent than that derived from fertilizer. At both N supplies, elevated [CO₂] modified the allocation of the fertilizer N in the sward, in favour of the stubble and roots and significantly increased the recovery of fertilizer N in the soil macro‐organic matter fractions. The increase of fertilizer N immobilization in the MOM was associated with a decline of fertilizer N uptake by the grass sward, which supported the hypothesis of a negative feedback of elevated [CO₂] on the sward N yield and uptake. Similar and even more pronounced effects were observed for the native N mineralized in the soil. At N–, a greater part of the fertilizer N organized in the root phytomass resulted in an underestimation of N immobilized in dead roots and, in turn, an underestimation of N immobilization in the MOM. The 3 °C temperature increase alleviated the [CO₂] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots. In conclusion, at ambient temperature, the N cycle was slowed down under elevated [CO₂], which restricted the increase in the aboveground production of the grass sward, and apparently contributed to the sequestration of carbon belowground. In contrast, a temperature increase under elevated [CO₂] stimulated the soil nitrogen cycle, improved the N nutrition of the sward and restricted the magnitude of the soil C sequestration.     

Local and regional disturbances associated with the invasion of Chesapeake Bay marshes by the common reed <Emphasis Type="Italic">Phragmites australis</Emphasis>

The invasion of wetlands by Phragmites australis is a conservation concern across North America. We used the invasion of Chesapeake Bay wetlands by P. australis as a model system to examine the effects of regional and local stressors on plant invasions. We summarized digital maps of the distributions of P. australis and of potential stressors (especially human land use and shoreline armoring) at two spatial scales: for 72 subestuaries of the bay and their local watersheds and for thousands of 500 m shoreline segments. We developed statistical models that use the stressor variables to predict P. australis prevalence (% of shoreline occupied) in subestuaries and its presence or absence in 500 m segments of shoreline. The prevalence of agriculture was the strongest and most consistent predictor of P. australis presence and abundance in Chesapeake Bay, because P. australis can exploit the resulting elevated nutrient levels to enhance its establishment, growth, and seed production. Phragmites australis was also positively associated with riprapped shoreline, probably because it creates disturbances that provide colonization opportunities. The P. australis invasion was less severe in areas with greater forested land cover and natural shorelines. Surprisingly, invasion was low in highly developed watersheds and highest along shorelines with intermediate levels of residential land use, possibly indicating that highly disturbed systems are uninhabitable even to invasive species. Management strategies that reduce nutrient pollution, preserve natural shorelines, and limit nearshore disturbance of soils and vegetation may enhance the resilience of shorelines to invasion.     

Performance of Saxifraga hirculus L. in North-East Scotland as measured by counts of inflorescences

Summary

Saxifraga hirculus, the yellow marsh saxifrage, is a rare protected species growing in baserich flushes. For conservation, better knowledge is needed on its performance and habitat preferences, hence three colonies in the Cabrach district of Aberdeenshire have been monitored closely over the past eleven years. Additionally observations are reported on flowering at a ‘recovery site’ to which saxifrage Plants have been transplanted.

At one of the natural colonies S. hirculus has clearly increased, at another there has been decline, and at the third so many inflorescences are removed by grazing that the trend could not be decided. The increase, as measured by flowering, was associated with moderately heavy grazing that maintained sward height at about 20–25 cm in summer. The decrease in saxifrage flowering was associated with light grazing and a sward of 35–40 cm height; however drought conditions in 2003 were perhaps responsible, affecting the water table of this colony more than the other colonies due to site topography.

At the third colony water voles (Arvicola amphibious) have been regularly present, and have clear impact on the vegetation around their holes. It is suggested that the voles eat the flowering shoots of the saxifrage.     

Ecology of benthic and epiphytic nematodes in brackish waters

Abundances of benthic nematodes from shallow waters in Tvärminne, Finland and in Ringkøbing Fjord, Denmark averaged 1.2–1.5 10⁶ individuals m^?2. Less than 20 species were found. More than 80% of the individuals were made up by Anoplostoma viviparum, Chromadorita fennica, Axonolaimus spinosus, Daptonema trabeculosum and Sabatieria pulchra. S. pulchra is designated as an anoxybiotic species and is attracted to the root tips of young Potamogeton perfoliatus, whilst A. viviparum and C. fennica are oxybiotic species. Abundance of epiphytic nematodes extracted from submerged macrophytes in the Cladophora-Pilayella belt in the outer archipelago of the Finnish archipelago (July 1978) was estimated to reach 5 · 10⁶ individuals m^?2, equivalent to a biomass of 1.2 g org. C m^?2. Abundance and biomass are smaller in the Potamogeton meadows in the inner archipelago, in littoral algal vegetation of the sea zone, and on sublittoral vegetation. Epiphytic nematode species composition is influenced by salinity and food availability and not by physiognomic types or silt contents of the vegetation in the Baltic Sea, European estuaries and lakes. Dominant species are: Chromadorina bioculata, Punctodora ratzeburgensis, Chromadorita tenuis, Adoncholaimus thalassophygas, Theristus acer, Monhystera parva, M. aff. filiformis and Chromadora aff. nudicapitata. A theory is proposed to explain observed seasonal changes in the species composition of epiphytic and benthic nematodes. During winter months, the submerged vegetation is mostly destroyed, being found as detritus on the sea bottom. Sampling benthic nematodes during winter thus includes epiphytic species living in the detritus. In spring the epiphytic nematodes detect the newly growing vegetation, leave the sea bottom, colonize the submerged vegetation and spend their life there.     

An invasive wetland grass primes deep soil carbon pools

Understanding the processes that control deep soil carbon (C) dynamics and accumulation is of key importance, given the relevance of soil organic matter (SOM) as a vast C pool and climate change buffer. Methodological constraints of measuring SOM decomposition in the field prevent the addressing of real‐time rhizosphere effects that regulate nutrient cycling and SOM decomposition. An invasive lineage of Phragmites australis roots deeper than native vegetation (Schoenoplectus americanus and Spartina patens) in coastal marshes of North America and has potential to dramatically alter C cycling and accumulation in these ecosystems. To evaluate the effect of deep rooting on SOM decomposition we designed a mesocosm experiment that differentiates between plant‐derived, surface SOM‐derived (0–40 cm, active root zone of native marsh vegetation), and deep SOM‐derived mineralization (40–80 cm, below active root zone of native vegetation). We found invasive P. australis allocated the highest proportion of roots in deeper soils, differing significantly from the native vegetation in root : shoot ratio and belowground biomass allocation. About half of the CO₂ produced came from plant tissue mineralization in invasive and native communities; the rest of the CO₂ was produced from SOM mineralization (priming). Under P. australis, 35% of the CO₂ was produced from deep SOM priming and 9% from surface SOM. In the native community, 9% was produced from deep SOM priming and 44% from surface SOM. SOM priming in the native community was proportional to belowground biomass, while P. australis showed much higher priming with less belowground biomass. If P. australis deep rooting favors the decomposition of deep‐buried SOM accumulated under native vegetation, P. australis invasion into a wetland could fundamentally change SOM dynamics and lead to the loss of the C pool that was previously sequestered at depth under the native vegetation, thereby altering the function of a wetland as a long‐term C sink.     

基质养分对寄生植物南方菟丝子生长的影响

群落中各营养级的相互作用在群落结构形成中起了重要作用.以南方菟丝子(Cuscuta australis R.Br.)和三叶鬼针草(Biden pilosa L.)为研究对象,采用完全随机区组实验设计方法,测定并分析基质养分(不施肥与施肥)对寄生植物生长的影响,探讨寄生植物生物量与寄主生长特性、生物量和光源捕获能力的相关性.结果表明,施肥显著增加寄生植物南方菟丝子的吸器数量、缠绕圈数、相对盖度、营养器官生物量、生殖器官生物量和总生物量,但对生殖器官的生物量比无显著影响.施肥显著增加寄主植物的根、茎、叶生物量和总生物量、叶生物量比、比叶面积和叶绿素含量,但显著降低根冠比与根生物量比.南方菟丝子生物量与三叶鬼针草生物量、叶生物量比、比叶面积以及相对叶绿素含量之间均存在显著正相关,与根生物量比和根冠比存在显著负相关.研究结果表明施肥可以提高寄主植物的光资源捕获能力,将更多地生物量分配至叶等光合机构上,从而促进寄主植物(生产者)的生长,并间接促进寄生植物(初级消费者)的生长.     

Effect of rotational and continuous grazing on vegetation of an upland grassland in the Jizerské hory Mts., Czech Republic

The effect of different grazing regimes on pasture vegetation was studied during the intensive grazing of heifers in the Jizerské hory mountains during 1993–1997. The vegetation was monitored in 3 pairs of permanent 1×1 m plots using a continuous grid of nine 0.33 × 0.33 m subplots. We applied continuous stocking and rotational grazing. Vegetation varied as a result of time and differences between treatments. Several prostrate dicotyledonous species (Trifolium repens, Taraxacum sp.,Bellis perennis andLeontodon autumnalis) increased under continuous stocking. This treatment also promoted the growth of the perennial grassLolium perenne, which was able to cope with frequent defoliation. Tall grasses sensitive to frequent defoliation (Poa trivialis, Holcus mollis, Alopecurus pratensis, Dactylis glomerata andElytrigia repens) were more abundant in rotationally grazed paddocks. Species diversity was not significantly influenced by the different grazing systems. The decrease in the potential sward height under continuous stocking revealed the replacing of tall dominants by lower species. Our results indicate that different grazing systems alter the composition and structure of grassland vegetation. Defining the intensity of grazing under continuous stocking or rotational grazing is complex due to the different stocking rates and the heights of sward during a grazing season. Information about pasture management should therefore involve not only grazing intensity but also the grazing system used.     

Shade and salinity responses of two dominant coastal wetland grasses: implications for light competition at the transition zone

BackgroundCoastal wetlands are threatened by the increased salinity that may result from sea level rise. Salinity stress alters species zonation patterns through changes in competitive outcome between species differing in salinity tolerance. This study therefore aimed to understand how salinity and light affect two dominant and competing coastal wetland grasses that differ in salt tolerance, height and photosynthetic metabolism.MethodsThe C₄ species Spartina anglica and the C₃ species Phragmites australis were grown at five salinity levels (0, 7, 14, 21 and 28 ppt) and two light fluxes (100 % and 50 % of natural daylight) in an outdoor experimental setup for 102 d with full access to nutrients.Key ResultsSalinity reduced the biomass, height and shoot density of P. australis from 81.7 g dry weight (DW), 0.73 m and 37 shoots per pot at a salinity of 0 ppt to 16.8 gDW, 0.3 m and 14 shoots per pot at a salinity of 28 ppt. Biomass, height and shoot density of S. anglica did not respond or were only slightly reduced at the highest salinity of 28 ppt. High salinity also resulted in a higher tissue concentration of N and P in P. australis. Both species had low ability to acclimate to the lower light flux. Shade acclimation in S. anglica occurred via modest changes in specific leaf area, pigment content and biomass allocation.ConclusionsHigh salinity reduced traits important for light competition and increased the nutrient concentration in P. australis leaf and root biomass, while this was overall unaffected in S. anglica. This is likely to reduce the competitive ability of P. australis over S. anglica for light because at high salinities the former cannot effectively shade the lower-growing S. anglica. Neither species effectively acclimates to shade, which could explain why S. anglica does not occur in the understorey of P. australis at low salinities.     

Phragmites australis and silica cycling in tidal wetlands

Tidal marshes have recently been shown to be important biogenic Si recycling surfaces at the land–sea interface. The role of vegetation in this recycling process has not yet been quantified. In situ and ex situ decomposition experiments were conducted with Phragmites australis stems. In a freshwater tidal marsh, litterbags were incubated at different elevations and during both winter and summer. Biogenic Si (BSi) dissolution followed a double exponential decay model in the litterbags (from ca. 60 to 15 mg g⁻¹ after 133 days), irrespective of season. Si was removed much faster from the incubated plant material compared to N and C, resulting in steadily decreasing Si/N and Si/C ratios. Ex situ, decomposition experiments were conducted in estuarine water, treated with a broad-spectrum antibiotic, and compared to results from untreated incubations. The bacterial influence on the dissolution of dissolved Si (DSi) from P. australis stems was negligible. Although the rate constant for dissolved Si dissolution decreased from 0.004 to 0.003 h⁻¹, the eventual amount of BSi dissolved and saturation concentration in the incubation environment were similar in both treatments. P. australis contributes to and enhances dissolved Si recycling capacity of tidal marshes: in a reed-dominated small freshwater tidal marsh, more than 40% of DSi export was attributable to reed decomposition. As the relation between tidal marsh surface and secondary production in estuaries has been linked to marsh Si cycling capacity, this provides new insight in the ecological value of the common reed.     

Effects of mowing on the composition of Baltic salt-meadow communities

A moving experiment is carried out at eight sites, situated at different levels in a Baltic salt meadow. The plots have been analyzed and mown with a scythe each year in August since 1979. The response of the sites to mowing is expressed as qualitative and quantitative changes in composition of the vegetation. So far, the most distinct changes in composition have been changes in relative importance of species already present in the initial vegetation. The resistance is found to be highest in the upper parts of the geolittoral, and lowest in the Phragmites australis swamp.     

黄河三角洲滨海草甸与土壤因子的关系

黄河三角洲滨海草甸群落的分布和变化与土壤因子密切相关。于2010年6月对黄河三角洲的草甸植被进行了样方调查,并对土壤进行了取样分析。在所调查的67个草本样方中,共出现52种植物。利用典范对应分析(CCA)分析了9种土壤因子与草甸群落分布的关系,结果显示,前两轴总共解释了物种-环境关系方差的46.4%,土壤含水率和电导率对群落分布的影响最大。双向指示种分析(TWINSPAN)将67个样方分为7种群落类型,将其标示在CCA排序图上后,沿第一轴分成三大类群:盐地碱蓬群落→芦苇-盐地碱蓬群落→其他草甸群落,这反映了黄河三角洲滨海草甸群落在盐分梯度上的演替规律。相关分析显示,物种多样性指数与土壤电导率、速效钾和速效磷呈极显著负相关(P<0.01),与pH值呈显著正相关(P<0.05)。解释了黄河三角洲滨海草甸群落与土壤因子的关系和变化规律,对黄河三角洲植被保护和恢复有一定的指导意义。     

Seasonal changes of mechanisms maintaining clear water in a shallow lake with abundant Chara vegetation

The study is based on monitoring data on the seasonal variation during four (1996–1999) vegetation periods, as well as long-term summer data on submerged vegetation, nutrients, light, phytoplankton and zooplankton in Lake Krankesjön, a shallow, calcium-rich, moderately eutrophic lake in southern Sweden.The lake has been in the clear water state with abundant submerged vegetation since the end of the 1980s. Somewhat lower summer biomass of submerged macrophytes during 1997 and 1999 indicates a temporary instability of the clear water state. During these 2 years, summer transparency was about 1.2–2.1 m, while concentrations of total phosphorus and chlorophyll (Chl) a were about 26–40 and 8–18 μg l⁻¹, respectively.Summer biomass of submerged macrophytes was higher during 1996 and 1998. In both years, a distinct increase in light availability and decrease in concentrations of nutrients and chlorophyll occurred simultaneously with the development of dense Chara vegetation. Summer values for transparency were about 2.0–2.5 m, while concentrations of total phosphorus and Chl a were about 20–32 and 4–11 μg l⁻¹, respectively.Summer biomass of crustacean zooplankton was below 250 μg l⁻¹ during all 4 years. A peak abundance of Cladocera (mainly Bosmina longirostris) during May or June caused only a short-term reduction in chlorophyll concentrations that was more pronounced in 1997 than in 1996.Measured light attenuation during 1999 was closely correlated with light attenuation calculated from the amount of suspended solids, chlorophyll concentrations, and water colour. Detritus contributed most to the total amount of suspended solids, while chlorophyll was the main contributor to light attenuation.A long-term decrease of the ratios between chlorophyll and total phosphorus suggests that phytoplankton in the clear water state is limited by factors other than total phosphorus concentrations. Increased sedimentation rate, carbon limitation, allelopathy and a lower bioavailable fraction of the total amount of phosphorus are possible explanations, while nitrogen limitation and grazing from zooplankton probably are of minor importance.Possible reasons for the “instability” of the clear water state during 1997 and 1999 are discussed. Unusually high water level as well as cold and windy weather during the spring of 1996–1999 may have caused a slow and late growth of the plants and thus a temporary instability. However, a tendency for an increase in total phosphorus concentrations and sediment accumulation along the wind-protected shores during the clear water state indicate the possibility of a long-term destabilization which contradicts the alternative stable states model.     

外源钙离子对南方菟丝子寄生入侵植物喜旱莲子草效果的影响

外源钙离子可以有效地缓解植物在胁迫下受到的毒害,提高植物组织或细胞抗胁迫的能力。以喜旱莲子草为研究对象,采用完全随机区组的实验设计,研究不同钙离子浓度与南方菟丝子寄生对喜旱莲子草茎生物量的影响,探讨外源钙离子是否可以减少南方菟丝子对喜旱莲子草的损伤。研究表明南方菟丝子寄生对喜旱莲子草的根、茎和叶的生物量具有显著影响,且南方菟丝子寄生与外源钙离子对喜旱莲子草茎和叶的生长具有显著的交互作用。不同浓度的钙离子与南方菟丝子寄生对喜旱莲子草茎生物量存在拮抗的交互作用;而仅8 mmol/L Ca2+与南方菟丝子寄生对喜旱莲子草叶生物量存在拮抗的交互作用。不同浓度钙离子均可以缓减南方菟丝子对喜旱莲子草茎的有害效应,仅8 mmol/L Ca2+可以缓减南方菟丝子对喜旱莲子草根和叶的有害效应。2—6 mmol/L的外源钙离子对南方菟丝子寄生下的喜旱莲子草的丙二醛(MDA)含量无显著影响,但可以显著地降低过氧化物酶(POD)活性,表明低浓度的外源钙离子的添加可以缓减南方菟丝子对喜旱莲子草的寄生胁迫,并体现在生理指标上。