Connecting seas: western Palaearctic continental flyway for water birds in the perspective of changing land use and climate

The western Palaearctic continental flyway that connects the tundra and taiga belts of Russia with north‐west Europe is the major migratory avenue for an estimated 9.3 million herbivorous water birds (swans, geese and ducks). Agricultural practices together with protection measures subsidize the carrying capacity of winter habitats of the birds. Densities of these birds are highest in the Netherlands, where nitrogen (N) inputs to farmland have increased during the last 70 years and became the highest in Europe (>250 kg manure and fertilizer ha^?1 yr^?1). A comparison of population trends of 13 species of avian herbivores reveals generally expanding populations in the past 50 years, with the greatest increases from 1970 to 1990. Populations of the smallest avian herbivores, such as ducks, are either stable or have peaked and are now in decline, whereas numbers of larger herbivores (geese and swans) continue to increase and barnacle and greylag geese now breed in the Netherlands, in addition to northern sites. During the northerly spring migration, stop‐over sites, mostly in the agricultural regions of eastern Europe and Scandinavia, lie between the 3 and 6°C mean daily temperature isotherms in April, temperatures at which grasses start to grow, where flooding of riparian wetlands frequently occurs and fertilizers are applied to farmland. However, the restructuring of agricultural practices in an enlarged EU is likely to affect water bird populations and their migration routes. The reduced use of N in the Netherlands is predicted to constrain population growth, especially of the smallest avian herbivores with their high basal metabolic rates, because of the declining food quality of grass leaves. The introduction of large‐scale farming of oilseed rape, winter cereals, sugar beet and potatoes at the expense of grassland also will adversely affect these birds, whereas larger species are likely to continue exploiting these crops.     

放牧对草地昆虫多样性的影响研究进展

在草地生态系统中,大型草食动物放牧是重要的管理方式之一,对草地生物多样性起着关键的驱动作用。昆虫是草地生态系统中生物多样性的重要组成成分,对生态系统的食物网结构以及其功能与稳定性起着关键作用。已有研究结果表明,大型草食动物与昆虫存在密切联系,放牧对草地昆虫多样性或有正向、或负向、或无明显作用,这依赖于放牧管理方式、昆虫类群以及草地类型。放牧必然通过直接(采食、践踏或粪尿)或间接(植物群落组成或植被结构)作用对昆虫多样性产生显著的影响。当前,关于大型草食动物放牧对草地昆虫多样性影响研究较多,但是,从研究系统性、深入性和延续性来说还存在一定问题。本文在综述国内外对放牧对草地昆虫多样性的影响研究基础上,提出了今后的研究方向,对于理解放牧管理的草地昆虫多样性变化规律,以及为积极探索维持草地昆虫多样性的长期有效的科学管理措施提供理论指导。     

Outbreak of Cronobacter turicensis in European brown hares (Lepus europaeus)

This is the first report of acute deaths in five European brown hares (Lepus europaeus) attributed to mucoid and necrotizing typhlocolitis caused by genetically different Cronobacter (C.) turicensis strains in northeastern Austria. As this opportunistic pathogen is mainly known for causing disease in immunocompromised humans and neonates, this previously unrecognized potential for a spill over from a wildlife reservoir to humans warrants further attention.     

Ecology of eutrophic waterbodies in a coastal grazing marsh

The ecology of a mainly interconnected, complex system of smallwater-bodies on a coastal grazing marsh in the Greater Thames estuary,north-east of London, England, is described. Sixteen sites were sampled on aregular basis over a two-year period while 37 sites were sampled once in Mayto develop a site classification. Most sites were brackish and alkaline but,following re-wetting after drying out, the pH in some water-bodies decreasedsharply (minimum pH 2.7). All sites had high concentrations of phosphorusbut there were large differences; some, with good growths of submergedaquatic macrophytes, having lower phosphorus than other sites, which weredevoid of macrophytes. Internal loading with phosphorus was important.Nitrate levels were low. Waters were mostly turbid, Secchi depths sometimes falling as low as 2cm, while chlorophyll a was very high, indicating extreme hypertrophy.Diatoms and euglenoids were characteristic members of the phytoplankton;cyanobacterial blooms did not occur. The zooplankton was dominated bycopepods, while Cladocera were much less numerous, largely due to predationby shrimps in waterbodies without macrophytes. The classification of siteswas influenced primarily by water depth, some waterbodies drying out, whilephosphorus and turbidity were also important in differentiating sites. Animal guano is the likely cause of the hypertrophic state but livestockgrazing is an essential management tool for grazing marshes. The dredging ofwaterbodies (with removal of sediments from the site) and the instigation ofa flushing regime, requiring a new system of sluices, should reduce nutrientloading and assist the establishment of submerged macrophytes, providingrefuges for cladocerans from predation.     

Competition and facilitation in multispecies plant-herbivore systems of productive environments

We develop a multispecies plant-herbivore model to explore how plant competition for light and the selectivity of herbivores affect abundance patterns of plants and herbivores along productivity gradients. The model considers a small and a tall plant species, a generalist herbivore, and a selective herbivore. The selective herbivore feeds only on the small plant species. In the absence of the generalist herbivore, the tall plant species becomes increasingly dominant with increasing productivity, and the small plant and its selective herbivore disappear. The model shows that generalist herbivores can facilitate selective herbivores by suppressing competition for light. This favours the small plant species, and thereby the selective herbivores. The model predictions are qualitatively consistent with field studies of multispecies plant-herbivore systems.     

Importance of grazing and soil acidity for plant community composition and trait characterisation in coastal dune grasslands

Question: Does grazing by large herbivores affect species composition or community‐wide variation in plant functional traits? Location: Dune grasslands at the Belgian coast. Methods: Plant cover and soil data were collected in 146 plots that were randomly selected at 26 grazed and ungrazed grassland sites. Plant community composition was assessed by Detrended Correspondence Analysis and mean values of plant trait categories were calculated across the plots. Results: Differentiation of plant composition and community‐wide plant trait characteristics was largely determined by grazing, soil acidity and their interaction. In ungrazed situations, a clear floristic distinction appears between acidic (non‐calcareous) and alkaline (calcareous) grasslands. In grazed situations, these floristic differences largely disappeared, indicating that grazing results in a decrease of natural variation in species composition. At higher soil pH, a larger difference in plant community composition and community‐wide plant traits was observed between grazed and ungrazed plots. In ungrazed situations, shifts in plant functional traits along the acidity gradient were observed. Conclusions: Grazing is responsible for shifts in plant community composition, and hence a decrease in plant diversity among grasslands at opposing acidity conditions in coastal dune grasslands. Therefore, care should be taken when introducing grazing as a system approach for nature conservation in dune grasslands as it may eliminate part of the natural variation in plant diversity along existing abiotic gradients.     

滨海盐沼湿地有机碳的沉积与埋藏研究进展

滨海盐沼湿地有着较高的碳沉积速率和固碳能力,在缓解全球变暖方面发挥着重要作用,而盐渍土壤是滨海盐沼湿地碳收支研究中最大的有机碳库,研究其碳沉积与埋藏对于理解滨海湿地碳收支有着重要的意义.本文从滨海盐沼湿地土壤有机碳的来源、土壤有机碳库与沉积速率、盐沼湿地有机碳的埋藏机制、全球变化与滨海盐沼湿地碳封存等几方面对滨海盐沼湿地有机碳沉积与埋藏的相关研究进行综述.今后研究应侧重:1)加强对控制滨海盐沼湿地碳储存变异的基本因素的迸一步研究;2)对测量滨海盐沼湿地沉积物碳储量和沉积碳埋藏速率的方法进行标准化;3)对潮汐影响下滨海盐沼湿地碳与邻近生态系统之间的横向交换通量进行量化;4)探明全球变暖的影响和生产力的提高是否可以抵消因呼吸增强而造成的有机碳降解速率的升高.确定固碳速率变化驱动因子,理解气候变化和人类活动对碳埋藏的影响机制,有助于提升我国滨海盐沼湿地的固碳能力.     

Vegetation patch dynamics in rangelands: How feedbacks between large herbivores,vegetation and soil fauna alter patches over space and through time

Aim

Large herbivore grazing is a popular conservation management tool to promote vegetation structural diversity of rangelands. However, vegetation patch dynamics, that is, how patches of grazing-defended tall vegetation and grazer-preferred short lawns shift over space and time, is poorly understood. Here, we describe a new conceptual framework for patch dynamics within rangelands, combining theories of classical cyclical succession, self-organization and multitrophic feedbacks between grazers, vegetation and bioturbating soil fauna.

Location

We use the cattle-grazed salt marsh of the island Schiermonnikoog, The Netherlands, as a model system. The grazed salt marsh is characterized by distinct tall vegetation patches dominated by the grazing-defended rush Juncus maritimus and grazing-intolerant grass Elytrigia atherica, surrounded by a matrix of grazing lawn (dominated by Festuca rubra).

The Framework

Based on previous observational and experimental studies, we propose a cyclical patch dynamic where plant species composition and structure transitions through four phases: patch initiation (a) occurs when the grazing-defended rush J. maritimus establishes in the grazed lawn. Patch establishment (b) follows when the grazing-intolerant grass E. atherica establishes in the patch due to associational defence by J. maritimus and produces a large amount of litter that attracts the key bioturbating amphipod Orchestia gammarellus. Patch expansion (c) occurs when O. gammarellus activities improve soil properties of the patch, which favours E. atherica growth, leading to E. atherica competitively displacing J. maritimus in the centre of the patch. Patch degeneration (d) follows when cattle enter the enlarged patch to consume E. atherica in the centre, trample the soil, displace O. gammarellus and decrease vegetation cover, opening space for grazing-lawn species to invade. The cycle restarts when remnants of the rush J. maritimus in the degenerated patches (or individuals recently established from seed dispersal) initiate new patches in the grazing lawn.

Synthesis

Our proposed patch-dynamic model provides a means to describe the mechanisms driving vegetation patch dynamics and serves as a foundation for further experimental and observational exploration, not only for this specific system, but more generally for grazed systems worldwide that show patches of typical grazing-defended and grazer-preferred vegetation.     

海岸盐沼湿地土壤硫循环中的微生物及其作用

硫及硫化合物的动态循环是海岸盐沼湿地的重要组成部分,硫酸盐还原菌(SRB)和硫氧化菌(SOB)是推动硫循环的重要微生物。硫酸盐还原菌把硫酸盐还原为硫化物,同时消耗土壤中的有机物质;硫氧化菌把还原性硫化合物氧化为硫酸盐,缓解土壤中硫化物的积累,它们共同维持硫循环的动态平衡。本文综述了海岸盐沼湿地土壤中硫的存在形式、硫的地球化学循环以及在硫循环过程中扮演重要角色的硫酸盐还原菌和硫氧化菌的生物多样性、活性测定方法及其生态学意义等的最新研究进展,并提出了存在的问题及研究展望。     

滨海盐沼湿地有机碳的沉积与埋藏研究进展

滨海盐沼湿地有着较高的碳沉积速率和固碳能力,在缓解全球变暖方面发挥着重要作用,而盐渍土壤是滨海盐沼湿地碳收支研究中最大的有机碳库,研究其碳沉积与埋藏对于理解滨海湿地碳收支有着重要的意义.本文从滨海盐沼湿地土壤有机碳的来源、土壤有机碳库与沉积速率、盐沼湿地有机碳的埋藏机制、全球变化与滨海盐沼湿地碳封存等几方面对滨海盐沼湿地有机碳沉积与埋藏的相关研究进行综述.今后研究应侧重:1)加强对控制滨海盐沼湿地碳储存变异的基本因素的进一步研究;2)对测量滨海盐沼湿地沉积物碳储量和沉积碳埋藏速率的方法进行标准化;3)对潮汐影响下滨海盐沼湿地碳与邻近生态系统之间的横向交换通量进行量化;4)探明全球变暖的影响和生产力的提高是否可以抵消因呼吸增强而造成的有机碳降解速率的升高.确定固碳速率变化驱动因子,理解气候变化和人类活动对碳埋藏的影响机制,有助于提升我国滨海盐沼湿地的固碳能力.     

Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands

Grasslands are subject to considerable alteration due to human activities globally, including widespread changes in populations and composition of large mammalian herbivores and elevated supply of nutrients. Grassland soils remain important reservoirs of carbon (C) and nitrogen (N). Herbivores may affect both C and N pools and these changes likely interact with increases in soil nutrient availability. Given the scale of grassland soil fluxes, such changes can have striking consequences for atmospheric C concentrations and the climate. Here, we use the Nutrient Network experiment to examine the responses of soil C and N pools to mammalian herbivore exclusion across 22 grasslands, under ambient and elevated nutrient availabilities (fertilized with NPK + micronutrients). We show that the impact of herbivore exclusion on soil C and N pools depends on fertilization. Under ambient nutrient conditions, we observed no effect of herbivore exclusion, but under elevated nutrient supply, pools are smaller upon herbivore exclusion. The highest mean soil C and N pools were found in grazed and fertilized plots. The decrease in soil C and N upon herbivore exclusion in combination with fertilization correlated with a decrease in aboveground plant biomass and microbial activity, indicating a reduced storage of organic matter and microbial residues as soil C and N. The response of soil C and N pools to herbivore exclusion was contingent on temperature – herbivores likely cause losses of C and N in colder sites and increases in warmer sites. Additionally, grasslands that contain mammalian herbivores have the potential to sequester more N under increased temperature variability and nutrient enrichment than ungrazed grasslands. Our study highlights the importance of conserving mammalian herbivore populations in grasslands worldwide. We need to incorporate local‐scale herbivory, and its interaction with nutrient enrichment and climate, within global‐scale models to better predict land–atmosphere interactions under future climate change.     

Dry season diets of sympatric ungulates in lowland Nepal: competition and facilitation in alluvial tall grasslands

Based on microhistological analyses of faecal material, we compared the early dry season diets of greater one-horned rhinoceros Rhinoceros unicornis, swamp deer Cervus duvauceli and hog deer Axis porcinus, which inhabit the same alluvial grassland habitat complex in lowland Nepal. Their diets were quite similar, both at the forage category level and within subcategories of graminoids and woody plants. Early successional tall grasses, especially Saccharum spontaneum, were the dominant food of all three species, underlining the key role of the threatened alluvial floodplains in large mammal conservation in South Asia. The two deer species ate significantly more graminoids (>66.5%) than did rhino (45.5%), and although they did not differ in proportions of graminoids, swamp deer ate significantly more late successional tall grasses (Narenga porphyrocoma and Themeda spp.) and short grasses (mainly Imperata cylindrica) than hog deer. The two deer consumed almost equal proportions of woody browse (ca. 10%), significantly less than that of rhino (33.0%). The prediction of the Jarman–Bell hypothesis, that large-bodied herbivores are less selective and subsist on lower quality graminoids than smaller ruminants, was not supported by the data. Based on this and previous studies in the same area we propose a conceptual model where the larger megaherbivores (rhino and elephant Elephas maximus) facilitate the smaller swamp deer and hog deer during the monsoonal growing season, while the smaller and more selective deer species outcompete the larger during the dry season when food is more limited. Owing to the all-year sprouting ability of S. spontaneum, facilitation may occur also in the dry season with low numbers of megaherbivores, thus accentuating competitive exclusion at higher deer densities.     

滨海湿地植被地上生物量遥感反演

盐沼植被生物量是滨海湿地生态系统碳循环研究的重要参数,是湿地生态系统健康评价、资源可持续利用的关键指标,开展盐沼植被地上生物量监测方法研究具有重要意义。目前,遥感技术在湿地生物量监测领域已经得到广泛应用,但反演方法仍以统计模型为主,模型构建需要实测数据支撑,时空拓展性不强。选择江苏盐城丹顶鹤保护区为研究区,基于冠层辐射(PROSAIL)传输模型,通过局部和全局敏感性分析,对模型参数本地化,构建了互花米草地上生物量半经验反演模型,应用于Landsat 8 OLI遥感影像,获得了互花米草地上生物量的时空分布。研究结果表明,利用PROSAIL模型模拟互花米草冠层反射率,叶面积指数(LAI)、叶片干物质含量(Cm)、叶倾角分布参数(LIDF)、等效水厚度(Cw)、叶绿素含量(Cab)、叶片结构参数(N)为高敏感性参数,类胡萝卜素含量(Car)、土壤参数(P_soil)为低敏感性参数;利用不同时刻的遥感影像反演了地上生物量,遥感反演结果与实测数据对比,拟合度R²为0.83,均方根误差(RMSE)为0.43kg/m²,平均相对误差(MRE)为15.7%,精度较高,模型具有较好的时空普适性。研究发展了盐沼植被地上生物量遥感反演方法,解决了以往过于依赖现场实测数据构建反演模型的局限性,该方法可以为研究滨海湿地生态系统碳循环以及准确估算其碳汇潜力提供技术支持。     

The importance of facilitation in the zonation of shrubs along a coastal salinity gradient

Question: What are the interactive roles of abiotic stress and plant interactions in mediating the zonation of the shrub Tamarix chinensis along a salinity gradient? Location: Yellow River estuary (37°46′N, 119°09′E), northeast China. Methods: We surveyed the zonation of T. chinensis along a salinity gradient and quantified its salt tolerance using a pot experiment. In two field experiments, we transplanted T. chinensis seedlings into salt marsh, transitional zone and upland habitats, manipulated neighbours and quantified survivorship and biomass to examine neighbour effects. We also quantified vegetation effects on abiotic conditions in each zone. Results: Tamarix chinensis dominated the transitional zone, but was absent in upland and salt marsh habitats. In the pot experiment, T. chinensis grew well in freshwater treatments, but was inhibited by increasing salinity. Field experiments revealed that competition from neighbours limited T. chinensis growth in the uplands, while T. chinensis transplants were limited, with or without neighbours, in the salt marsh by high soil salinity. In the transitional zone, however, T. chinensis transplants performed better with than without neighbours. Vegetation removal significantly elevated soil salinity in the transitional zone, but not in other zones. Conclusions: Competition, facilitation and abiotic stress are all important in mediating the zonation of T. chinensis. Within its physiological stress tolerance range, or fundamental niche, it is limited by plant competition in low salinity habitats, and facilitated by neighbours in high salt stress habitats, but cannot survive in salt marshes having salinities above its salt stress tolerance limit. Our results have implications for understanding the relationships between facilitation and stress gradients.     

盐城海滨湿地盐沼植被及农作物下土壤酶活性特征

在盐城海滨湿地盐沼植被和农田内采集土壤样品,测定了4种土壤酶(脲酶、转化酶、过氧化氢酶和碱性磷酸酶)的活性,分析了盐沼植被、农作物及土壤理化因子对土壤酶活性的影响。结果表明:由海滨湿地滩涂围垦形成的各类农田其土壤酶活性较高,且均高于湿地盐沼植被;湿地盐沼植被下4种土壤酶活性均高于无植被生长的光滩,且不同类型植被间土壤酶活性差异显著;4种酶的活性大小总体表现为大豆(Glycine max)地棉花(Gossypium hirsutum)地玉米(Zea mays)地互花米草(Spartina alterniflora)滩白茅(Imperata cylindrica var.major)滩碱蓬(Suaeda salsa)滩光滩。相关分析表明,4种土壤酶之间及其与土壤有机碳、全氮均表现出显著正相关,而与土壤盐分、pH值之间存在显著负相关。海滨湿地盐沼植被的发育扩展不仅增加了土壤中的养分含量,也提高了土壤酶活性。     

互花米草入侵对滩涂湿地甲烷排放的影响

在浙江省台州市附近滩涂湿地设置3个不同互花米草入侵密度梯度,即仅有本土植物样地、互花米草与本土植物混生样地和互花米草单优群落样地,研究互花米草入侵对滩涂湿地CH₄排放的影响.结果表明: 3个样地CH₄排放通量为0.68～5.88 mg·m^-2·h^-1,CH₄排放通量随着互花米草入侵梯度的增加而显著升高,互花米草单优群落样地CH₄排放通量分别为本土植物样地和混生样地的8.7和2.3倍.互花米草入侵显著提高了产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量、土壤有机碳含量和土壤pH,降低了土壤全氮含量.CH₄排放通量与土壤全氮呈显著负相关,与产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量和土壤pH呈显著正相关.互花米草的入侵提高了滩涂湿地植物群落生物量和土壤pH,促进了产甲烷菌数量和产甲烷潜力,从而提高了滩涂湿地的CH₄排放.     

Genetic polymorphism of sorbitol dehydrogenase in the brown hare and the distribution of the variation in Central Europe

A genetic polymorphism of sorbitol dehydrogenase (SDH; EC 1.1.1.14) for two allozymes is demonstrated in the brown hare (Lepus europaeus) by means of horizontal starch gel electrophoresis. Segregation analysis was performed in a sample of four matings with 12 offspring and confirmed the genetic hypothesis: two alleles at an autosomal locus. The calculated gene frequencies in the brown hare breed studied areSdh ^a =0.712 andSdh ^b =0.288. The distribution of the polymorphism in free-ranging brown hare populations from Austria, Czechoslovakia, Hungary, and Poland is described.This research was supported by a grant from the Fonds zur Förderung der Wissenschaftlichen Forschung, Austria (project P6767B).