闽江河口红树林土壤微生物群落对互花米草入侵的响应

采用磷脂脂肪酸标记法(PLFA)研究外来入侵植物互花米草对闽江河口湿地红树林土壤微生物群落结构的影响,并探讨其主要影响因素。结果表明:从3种不同植被群落土壤(红树林群落MC、红树林-互花米草混生群落MS、互花米草群落SC)共检测到22种PLFA生物标记,MS土壤微生物PLFA生物标记总量明显高于其他植被群落,3种植被群落土壤理化性质和酶活性的变化趋势为:MCMSSC,表明互花米草入侵后土壤微生物量增加,而理化性质和酶活性均有明显下降,红树林湿地土壤质量发生了明显退化。3种植被群落土壤中含量最高的PLFA生物标记是16:0,16:1w7c,9Me15:0w,18:1w12c。土壤中特征微生物相对生物量存在明显差异,细菌分布量最大,其次是真菌和放线菌,原生动物分布量最小。群落多样性指数呈相似规律,MS土壤微生物类群多样性指数均小于MC,表明互花米草入侵后土壤微生物群落多样性指数均有下降。通过主成分分析,基本能区分出3种不同植被群落微生物群落的特征。土壤理化性质、酶活性间存在相关性,有机碳、全氮、蔗糖酶、过氧化氢酶与革兰氏阴性菌、放线菌呈显著或极显著正相关。研究结果表明互花米草入侵在一定程度上具有影响红树林群落土壤营养代谢循环的潜力,特别是关于碳、氮、磷等的循环及酶活性,改变部分有利于自身生长的土壤环境相关的微生物类群含量,竞争有利环境,迅速扩张实现入侵。     

清澜港红树林湿地典型群落类型沉积物活性有机碳组分分布特征

滩涂海岸红树林生态系统通常具有较高的土壤养分,尤其是沉积物有机碳含量。海南岛红树林种类丰富且生长较好,通过对红树林沉积物有机碳组分的基础研究有利于提高对红树林湿地固碳能力的评估精度,加深对海洋蓝碳的认识。以清澜港红树林5种典型群落类型为对象,比较分析表层土壤(0—10 cm)总有机碳(TOC)、微生物生物量碳(MBC)、易氧化有机碳(EOC)、可溶性有机碳(DOC)含量差异及其与土壤因子之间的相关性。结果表明：(1)不同群落类型间,土壤TOC、MBC、DOC和EOC含量均值分别为66.76 g/kg、177.08 mg/kg、25.49 mg/kg和2.34 g/kg。对比发现,土壤TOC在角果木群落中含量最高,但各群落间无显著差异;土壤MBC在不同群落间存在显著差异,其中角果木群落和杯萼海桑群落显著高于榄李群落;土壤DOC在不同群落间存在显著差异,其中海莲群落和角果木群落显著高于其余群落;土壤EOC在不同群落间存在显著差异,其中角果木群落显著高于海莲群落和正红树群落。(2)活性有机碳各个组分占总有机碳的比例均值大小依次为EOC>MBC>DOC。土壤EOC、MBC、DOC的...     

Vegetation changes induced by dam construction in a tropical estuary: the case of the Mánamo river,Orinoco Delta (Venezuela)

This study documents the increased distribution of mangrove communities into the oligohaline regions of the Mánamo river as a consequence of a dam constructed in 1965. The dam caused a major change in the discharge regime of the water, stopping the annual floodings and allowing an extensive upriver intrusion of saline waters. Penetration of salt water from the sea due to the daily tides, that would be observed only during the dry season, occurs now throughout the year.Three sites were chosen along the upper, middle and lower river course. The evolution of site geomorphology and vegetation was evaluated over 3 periods, from 1932 to 1996, using aerial photographs and recent field surveys. Soil and plant samples were taken in the mangrove communities of two sites nearer to the river mouth along 100 m transects inland from the river fringe. The influence of sea water in soils was measured by the concentration of Na, Mg, Cl and SO4 in the interstitial soil water. In plants, the impact of soil salinity was determined by the concentration of Na, K, and Mg in mature leaves.The geomorphological processes created new habitats (sand bars) for aquatic and terrestrial vegetation. In the middle and lower river course tidal penetration of sea water due to lower river discharge salinized the soil, allowing mangrove establishment. This occurred mainly in the open sand bars or in areas with sparse herbaceous vegetation. The ion content was higher in the down river site and also higher in the subsoils compared with the topsoils. The apparent expansion rate of a plant community dominated by a mangrove species (Rhizophora mangle) increased from 1 ha yr–1 prior to the regulation of water flow, to 6–7 ha yr–1 after the river closure. The dam influences the entire Mánamo river basin, affecting the distribution of halophytic species along the river fringes.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

The influence of leaf litter on zooplankton in floodplain wetlands: changes resulting from river regulation

1. The loss of input of leaf litter through clearing of riparian vegetation may result in significant changes to aquatic ecosystems. River red gums (Eucalyptus camaldulensis) surrounding floodplain wetlands in the Murray–Darling Basin, Australia, contribute large quantities of leaf litter, but the quality of this resource may change depending on the timing of inundation. 2. We used experimental mesocosms to test the hypotheses that zooplankton would have a greater abundance with an input of leaf litter and that fewer zooplankton would emerge from egg banks in cleared than forested wetlands. The experiment was carried out in summer/autumn and in spring to test a third hypothesis that zooplankton would respond to changes in the timing of wetland inundation as a result of river regulation. 3. In summer/autumn, leaf litter reduced zooplankton abundance by 89% at the beginning of the experiment through its influence on water quality. Only a few taxa (Polyarthra spp., Colurella spp. and the cladoceran Family Moinidae) responded positively to leaf litter when water quality improved later in the experiment, indicating a switch in the role of leaf litter from a non‐trophic to a trophic pathway. 4. In spring, microcrustaceans emerged in smaller numbers from sediment sourced from cleared compared to forested wetlands, reflecting different communities in these two wetland types and/or disturbances to the sediment that interfere with emergence. 5. Although leaf litter appears not to be an important resource for zooplankton in floodplain wetlands, riparian clearing may have lasting effects on future emerging zooplankton communities. Additionally, river regulation may have considerable impacts on the influence of leaf litter on zooplankton, which has implications for the management of floodplain river systems.     

喀斯特森林常见树种倒木分解对土壤真菌群落组成及分布规律的影响

倒木是森林生态系统的重要组分,其分解调控着土壤的养分循环,同时也影响着土壤微生物群落结构。但目前鲜见关于倒木分解对土壤微生物群落影响方面的报道。选取贵州茂兰喀斯特常绿落叶阔叶混交林中处于轻、中和重度腐烂等级的狭叶润楠（Machilus rehderi）、枫香（Liquidambar formosana）、青冈栎（Cyclobalanopsis glauca）和圆果化香（Platycarya longipes）4种常见树种倒木为研究对象,以距倒木外围的3个不同水平距离（10cm、30cm和50cm）的土壤样品为实验材料,分析倒木树种、腐烂等级和距离对土壤真菌种类及多样性的影响。结果表明：1）喀斯特森林4种树种倒木所影响土壤真菌群落在门级分类上主要为子囊菌门、担子菌门和毛霉门,优势属有Mortierella spp.、Phlebia spp.、Pluteus spp.和Chaetomium spp.等;2）倒木的树种对土壤真菌群落相对丰度的影响有差异,圆果化香倒木下的土壤真菌丰富度Chao1指数显著高于青冈栎;3）随腐烂程度加深,4种树种倒木下的土壤真菌群落多样性呈显著增加趋势;4）土壤真菌群落丰度随着距倒木距离的增大（10-50cm）变化明显,如狭叶润楠影响的Pluteus spp.、Mortierella spp.和Ganoderma spp.,枫香的Chaetomium spp.,圆果化香的Mortierella spp.和青冈栎的Phlebia spp.和Oliveonia spp.等。本研究量化了喀斯特森林倒木所影响的土壤真菌群落组成及分布规律,在一定程度上为倒木分解与土壤微生物群落之间的作用机制的深入探索提供了科学依据。     

Structure and species distribution in Coringa mangrove forest,Godavari Delta,Andhra Pradesh,India

Coringa mangrove forest is located in the Godavari delta, Andhra Pradesh, India. The mangrove community consisted of more than 13 species of mangrove and other plants in the present study area. The following three dominant mangrove plants,Avicennia marina, Excoecaria agallocha andSonneratia apetala were found to be present on the banks of a major channel of the Godavari river running through the forest. The structure and species distribution of mangrove, in the Channel Nagathana Kalaya has been described. The area behind the belt consisting ofAcanthus ilicifolius andMyriostachya wightiana is generally colonized byE. agallocha andA. marina. The zone has been called theAvicennia andExcoecaria zone. Adjacent to this zone species likeAegiceras corniculatum andA. officinalis were the common species. In the flat clayey soil,Suaeda maritima was found to grow. In areas of high elevation, devoid of inundation of tidal seawater during the high tidal period, species such asM. wightiana andAcanthus were found to colonize both the banks of the channels.An analysis of species diversity, indicated a definite trend in the distribution of mangrove from the mouth of the estuarine region to the inland waters.The levels of atmospheric pollutants such as sulphur dioxide (SO₂), oxides of nitrogen (NO_x), ammonia (NH₃) and suspended particle matter (SPM) were within the legal limits.     

Hydrologic and mechanical control for an invasive wetland plant, <Emphasis Type="Italic">Juncus ingens</Emphasis>, and implications for rehabilitating and managing Murray River floodplain wetlands,Australia

Wetlands are prone to increased invasion by plant species following changes in hydrologic regime, leading to shifts in plant community composition and potentially ecosystem function and health. In this paper, the ecology and potential control of Juncus ingens, a native wetland plant in the Murray-Darling Basin of south-eastern Australia, is investigated. J. ingens has benefited from altered Murray River hydrologic conditions by expanding its range and invading seasonally-flooded grassland and riparian habitats along the Murray River. Here results of complementary glasshouse and field research of seedling and mature J. ingens growth and resilience as influenced by hydrologic regime (moist, saturated, partial inundation and when possible, complete inundation) and mechanical control (i.e., clipping) are presented. A moist hydrologic regime (soil held at field capacity) resulted in the most vigorous seedlings (13.9–73.0% more total biomass), while saturated conditions (flooding maintained level with the soil surface) resulted in the most vigorous mature J. ingens (14.1–98.4% more total biomass). Seedling mortality was greatest under complete and prolonged inundation (60% fatal with remaining 40% showing severe stress), conditions suspected to have limited prior invasion but which currently occur infrequently as a result of reduced flooding magnitude. Clipping was fatal for nearly all seedlings regardless of hydrologic regime but was only fatal for mature plants if coupled with prolonged inundation. Coupling ground-level clipping with strategic flooding may be the most effective means for controlling current populations of J. ingens and limiting further invasion, promoting re-colonisation by displaced species and rehabilitating the health of Barmah Forest and similar Murray River floodplain wetlands.     

漳江口红树植物群落周转对大型底栖动物群落结构的影响

在城市化的背景下,探明不同大型底栖动物群落对植物群落变化的响应,对红树林生态系统的健康评价和退化生态系统的修复具有重要意义。以福建漳江口国家级红树林自然保护区为研究对象,揭示红树植物群落周转对不同大型底栖动物群落结构（蟹类和软体动物）的影响,并分析其与环境参数的关联性。结果表明：在1.6 km的地理尺度上,漳江口红树林湿地的环境变化较大,表现出7.19个环境梯度。在此地理尺度的环境梯度上,红树植物群落由5种红树植物组成,其平均周转率为76%;软体动物群落由12种软体动物以模块化和非随机的方式聚集,其平均周转率为83%,并随红树植物群落周转出现显著非线性增加,盐度和老鼠簕（Acanthus ilicifolius）周转是其主要影响因素;蟹类群落则由20种蟹类以更高的模块化和非随机的方式分散,平均周转率为89%,并随红树植物群落周转而呈线性增加,主要受pH和白骨壤（Avicennia marina）周转的影响。研究揭示了大型底栖动物与植物群落和环境之间的关系,为城市化背景下红树林生态系统的保护和恢复提供基础资料。     

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Aims To quantify pollen–vegetation relationships from saline to freshwater in an estuarine gradient from surface samples of the modern pollen rain, to allow more accurate interpretations of the stratigraphic palynological record. Location Whangapoua Estuary, Great Barrier Island, northern New Zealand. Methods Six transects were laid out along a vegetation sequence running from estuarine mud to freshwater swamp. Along these transect lines, 108 plots were sampled for vegetation and surface sediments from wet sand, mud, plant litter or moss (sand and mud sites are inundated by most tides, other sites less frequently). All sediment samples were analysed for pollen. The relationships between plant species frequency and pollen representation were examined at a community scale using twinspan and ordination analyses, and for individual species using fidelity and dispersibility indices, regression and box‐plot analyses. Results The quantitative relationships between source taxon vegetation frequency and its pollen representation varied between species due to differential pollen production and dispersal. twinspan of the surface pollen samples suggests five vegetation types: (A) mangrove (Avicennia marina); (C) Leptocarpus similis salt meadow; (D) Baumea sedges; (E) Leptospermum shrubland; and (F) Typha/Cordyline swamp forest. The (B) Juncus kraussii community is not represented palynologically owing to the destruction of its delicate pollen grains during acetolysis of samples. Detrended correspondence analysis places these communities on an estuarine‐to‐freshwater gradient. However, pollen assemblages at the seaward end of the salinity gradient are less clearly representative of the associated vegetation than those at the landward end, probably because the open vegetation at the former allows the influx of wind‐ and water‐dispersed pollen from surrounding vegetation. Main conclusions The vegetation pattern (zonation) at Whangapoua is reflected in the pollen rain. When the long‐distance and over‐represented pollen types are excluded, five out of six of the broad vegetation communities can be identified by their pollen spectra. Species with high fidelity and low‐to‐moderate dispersibility indices can be used to identify the vegetation types in the sedimentary sequences. The more open vegetation types at the ‘marine end’ of the sequence tend to be ‘overwhelmed’ by regional pollen, but the nature of the sediments and the presence of discriminatory species (e.g. A. marina, Plagianthus divaricatus, Cordyline australis), even in small amounts, will allow correct identification of the local vegetation represented in sedimentary palynological sequences. A box‐plot analysis indicates that the pollen and spore types A. marina (mangroves), Sarcocornia quinqueflora (salt meadow), P. divaricatus (sedges), Gleichenia (shrubland) and C. australis (swamp forest) are highly discriminatory in relation to vegetation type. These discriminatory palynomorphs help with the interpretation of stratigraphic pollen studies. However, salt marsh vegetation communities in the sediments must be interpreted with caution as the marine sediments are easily affected by erosion, bioturbation and tidal inundation effects.     

柴达木盆地荒漠灌丛群落谱系结构研究

谱系信息是群落生态学和保育生物学研究的主要内容之一。为探究柴达木盆地荒漠灌丛群落谱系结构及其与环境因子的关系,该研究以柴达木盆地荒漠灌丛为对象,基于群落中物种存在与否的物种组成数据,使用R语言中picante软件包计算了灌丛群落谱系多样性指数和谱系结构指数,并且分析了谱系结构指数与年均温度、年均降水以及土壤含水量之间的关系,以揭示柴达木盆地灌丛群落物种之间的亲缘关系和群落生物多样性维持机制。结果表明:(1)柴达木盆地灌丛群落谱系结构与土壤含水量之间存在极显著相关性(P=2.77×10-6),随着土壤含水量的增加,群落谱系结构聚集程度逐渐降低,表现出生境过滤作用逐步减弱,生物间相互作用逐渐加强的变化趋势。(2)群落谱系结构与年均温度、年均降水之间无显著相关性。(3)典型荒漠生境灌丛和河谷(河漫滩)生境灌丛群落的谱系结构差异显著(P0.05),整体上分别表现为谱系聚集状态和谱系发散状态;河谷(河漫滩)生境灌丛群落的谱系多样性显著高于典型荒漠生境灌丛(P0.05)。(4)将群落谱系信息应用在生物多样性保护实践中,发现河谷(河漫滩)生境灌丛群落较典型荒漠生境的灌丛群落可能具有更高的保护价值。研究认为,将群落谱系研究与保育生物学理论结合将会使生物多样性保护策略更加科学有效。     

Sulphur‐oxidizing and sulphate‐reducing communities in Brazilian mangrove sediments

Mangrove soils are anaerobic environments rich in sulphate and organic matter. Although the sulphur cycle is one of the major actors in this ecosystem, little is known regarding the sulphur bacteria communities in mangrove soils. We investigated the abundance, composition and diversity of sulphur‐oxidizing (SOB) and sulphate‐reducing (SRB) bacteria in sediments from three Brazilian mangrove communities: two contaminated, one with oil (OilMgv) and one with urban waste and sludge (AntMgv), and one pristine (PrsMgv). The community structures were assessed using quantitative real‐time polymerase chain reaction (qPCR), polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE) and clone libraries, using genes for the enzymes adenosine‐5′‐phosphosulphate reductase (aprA) and sulphite reductase (Dsr) (dsrB). The abundance for qPCR showed the ratio dsrB/aprA to be variable among mangroves and higher according to the gradient observed for oil contamination in the OilMgv. The PCR‐DGGE patterns analysed by Nonmetric Multidimensional Scaling revealed differences among the structures of the three mangrove communities. The clone libraries showed that Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria were the most abundant groups associated with sulphur cycling in mangrove sediments. We conclude that the microbial SOB and SRB communities in mangrove soils are different in each mangrove forest and that such microbial communities could possibly be used as a proxy for contamination in mangrove forests.     

Nitrogen pools and soil characteristics of a temperate estuarine wetland in eastern Australia

The nitrogen status of the soil and plant components of an estuarine wetland near Sydney were investigated over 6 months to detect seasonal and spatial changes in nitrogen content. Organic carbon, organic nitrogen and inorganic nitrogen concentrations were measured in the soil at various depths in six vegetation zones across the wetland. Carbon and nitrogen content of the plant biomass were also determined in each of the zones. Soil redox potentials and pH were measured in situ and both were found to vary with depth and inundation frequency. Organic carbon, organic nitrogen and inorganic nitrogen in the soil decreased significantly from the fringe Casuarina forest (1391 g N m^?2) through to the Avicennia mangrove zone (133 g N m^?2). Exchangeable NH₄⁺, NO₃^? and NO₂^? concentrations from less than 1% of the soil nitrogen pool and vary seasonally. The distinctive feature of the mangrove zone is that the plant component of the total nitrogen pool is large (55%). This contrasts with the saltmarsh and fringe communities, where the plant pools are small (15%) in comparison with the soil. These findings are consistent with the hypothesis that mangroves export organic nutrients whereas the saltmarsh and fringe communities act as nutrient sinks.     

Effects of vanillin on the community structures and abundances of Fusarium and Trichoderma spp. in cucumber seedling rhizosphere

Soil microbial communities are crucial to the functioning of agricultural systems but little information is available on the effects of allelochemicals on soil microorganisms in vivo. Cucumber seedlings grown in soil were treated with different concentrations of vanillin (0.02–0.2?μmol/g soil), a phenolic compound with autotoxic activity. The community structures and abundances of Fusarium and Trichoderma spp. in cucumber rhizosphere were analyzed by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis and quantitative PCR, respectively. Results showed that vanillin changed the community structures of Fusarium and Trichoderma spp. Vanillin decreased the number of bands of Fusarium spp., but increased the number of bands, Shannon–Wiener and evenness indices of Trichoderma spp. (p?Fusarium and Trichoderma spp. (p?Fusarium and Trichoderma spp., and that these two microbial groups showed different responses to vanillin.     

The effect of experimental inundation and sediment deposition on the survival and growth of two herbaceous riverbank plant species

Flow and sediment regimes of floodplain rivers around the world have been changed by river regulation and land management, altering the ecological processes structuring riparian plant communities. However, the combined effects of inundation and sedimentation processes on riparian plant survival and growth are poorly understood. The separate and interactive effects of inundation duration and sedimentation depth on survival, growth and vegetative reproduction of two herbaceous clonal river bank plant species, Carex bichenoviana and Calotis scapigera, were investigated in an outdoor laboratory experiment. Plants were grown under three levels of sediment addition and two levels of inundation duration and were harvested after 60 days. Both species survived up to 30 days inundation in the absence of sediment. Growth and vegetative reproduction were increased for C. scapigera, but reduced for C. bichenoviana. Sediment deposition during periods of inundation reduced survival of both species, with C. scapigera unable to survive. Carex bichenoviana survived, but as inundation duration and depth of sediment increased, growth and vegetative reproduction were reduced. Our results indicate sediment deposition during flooding can change the tolerance of riparian plant species to inundation, reducing survival and growth.     

Little evidence for niche partitioning among ectomycorrhizal fungi on spruce seedlings planted in decayed wood versus mineral soil microsites

Ectomycorrhizal fungal (EMF) communities vary among microhabitats, supporting a dominant role for deterministic processes in EMF community assemblage. EMF communities also differ between forest and clearcut environments, responding to this disturbance in a directional manner over time by returning to the species composition of the original forest. Accordingly, we examined EMF community composition on roots of spruce seedlings planted in three different microhabitats in forest and clearcut plots: decayed wood, mineral soil adjacent to downed wood, or control mineral soil, to determine the effect of retained downed wood on EMF communities over the medium and long term. If downed and decayed wood provide refuge habitat distinct from that of mineral soil, we would expect EMF communities on seedlings in woody habitats in clearcuts to be similar to those on seedlings planted in the adjacent forest. As expected, we found EMF species richness to be higher in forests than clearcuts (P ≤ 0.01), even though soil nutrient status did not differ greatly between the two plot types (P ≥ 0.05). Communities on forest seedlings were dominated by Tylospora spp., whereas those in clearcuts were dominated by Amphinema byssoides and Thelephora terrestris. Surprisingly, while substrate conditions varied among microsites (P ≤ 0.03), especially between decayed wood and mineral soil, EMF communities were not distinctly different among microhabitats. Our data suggest that niche partitioning by substrate does not occur among EMF species on very young seedlings in high elevation spruce-fir forests. Further, dispersal limitations shape EMF community assembly in clearcuts in these forests.     

Detrital traits affect substitutability of a range‐expanding foundation species across latitude

Climate‐driven range shifts of foundation species could alter ecosystem processes and community composition by providing different resources than resident foundation species. Along the US Atlantic coast, the northward expanding foundation species, black mangrove Avicennia germinans, is replacing the dominant salt marsh foundation species, marsh cordgrass Spartina alterniflora. These species have distinct detrital attributes that ostensibly provide different resources to epifauna. We experimentally examined how detritus of these species affects decomposition and community composition in different habitat contexts at regional and local scales. First, we manipulated detritus identity (Avicennia, Spartina) at 13 sites across a 5° latitudinal gradient spanning mangrove, mixed marsh‐mangrove and salt marsh habitats. Across latitude, we found that Avicennia detritus decomposed 2–4 times faster than Spartina detritus, suggesting that detrital turnover will increase with mangrove expansion. Epifaunal abundance and richness increased 2–7 times from south to north (mangrove to salt marsh) and were equivalent between Avicennia and Spartina detritus except for crabs, a dominant taxonomic group that preferred Spartina detritus. Second, to examine the whether changing habitat context affected regional patterns, we manipulated detritus identity and surrounding habitat type (mangrove, salt marsh) at a single mixed site, also including inert mimics to separate structural and nutritional roles of detritus. Epifaunal richness was similar between the two detrital types, but crabs were 2–7 times more abundant in Spartina detritus due to its structural attributes. Surrounding habitat type did not influence decomposition rate or community patterns, which suggests that latitudinal influences, not surrounding habitat, drove the regional community patterns in the first experiment. Overall, mangrove expansion could alter epifaunal communities due to the lower structural value and faster turnover of mangrove detritus. As species shift with changing climate, understanding foundation species substitutability is critical to predict community change, but we must account for concomitant environmental changes that also modify communities.     

Epilithic diatom community response to years of P04 fertilization: Kuparuk River,Alaska (68 N Lat.)

An arctic river was fertilized continuously through the ice-free season with phosphoric acid beginning in 1983. The epilithic diatom community increased in biomass in the first two years in response to the added limiting nutrient (Peterson et al., 1983). The diatom community switched from one dominated by Hannea arcus to one dominated by species of Achnanthes and Cymbella. The immediate responses to the P-addition were decreases in both the Shannon diversity and evenness indices. By the second year, the community diversity increased downriver reaching maximal species richness (110–127 spp). In 1985–1987, the epilithic algal biomass decreased an order of magnitude with both whole-river PO₄ (1985, 1987) and PO₄ + NH₄ addition (1986). In the 5th summer of fertilization, the reduction in biomass was clearly caused by a numerical increase of grazing, refugia-building chironomids (Orthocladiinae, primarily) (Gibeau, 1991; Gibeau, Miller, Hershey, in prep.). We assume the algal biomass reduction in the 3rd and 4th years was similarly caused by grazers with a two year time lag in the numerical response of these monovoltine species. The evenness of the community increased in 1986 as if it might have been grazed; however the number of immigrants was reduced. The community became dominated by Eunotia, Cymbella and Achnanthes, species either fast growing or more prostrate, as the erect species of Hannea Diatoma, and Fragillaria declined. A detrended correspondence analysis of the temporal and spatial diatom samples in species space (186 spp.) showed that the largest variation in the community was between years and less variation was associated with river fertilization. Samples from bioassay tubes run by Peterson et al. (1983) in the Kuparuk River showed P and N + P limitation as found in the river in 1983–84. Like the river samples, the largest change in the diatom community occurred between 15 and 25 day samples, more than that induced by fertilization. Diatoms sampled from all treatments taken at day 25 were more similar to one another than those sampled at day 15. Diatoms colonizing glass slides used in the bioassay tubes were dominated by Achnanthes linearis and Cymbella minuta. Of the 84 species found in bioassays, 26 species were present in all river samples for 4 years. Differences in the communities discriminated by multivariate methods were cause by changes in rare species and abundance patterns of common species.     

Restoration of mangrove plantations and colonisation by native species in Leizhou bay,South China

To examine the natural colonisation of native mangrove species into remediated exotic mangrove stands in Leizhou Bay, South China, we compared soil physical–chemical properties, community structure and recruitments of barren mangrove areas, native mangrove species plantations, and exotic mangrove species—Sonneratia apetala Buch.Ham—between plantations and natural forest. We found that severely degraded mangrove stands could not regenerate naturally without human intervention due to severely altered local environments, whereas some native species had been recruited into the 4–10 year S. apetala plantations. In the first 10 years, the exotic species S. apetala grew better than native species such as Rhizophora stylosa Griff and Kandelia candel (Linn.) Druce. The mangrove plantation gradually affected soil physical and chemical properties during its recovery. The exotic S. apetala was more competitive than native species and its plantation was able to restore soil organic matter in about 14 years. Thus, S. apetala can be considered as a pioneer species to improve degraded habitats to facilitate recolonisation by native mangrove species. However, removal to control proliferation may be needed at late stages to facilitate growth of native species. To ensure sustainability of mangroves in South China, the existing mangrove wetlands must be managed as an ecosystem, with long-term scientific monitoring program in place.