Ecosystem linkages revealed by experimental lake-derived isotope signal in heathland food webs

Cross-ecosystem movement of nutrients and biomass can have important effects on recipient systems. Emerging aquatic insects are subsidies to terrestrial ecosystems and can influence foodweb interactions in riparian systems. In a 2-year field experiment, we simulated aquatic insect deposition by adding adult midge carcasses (150?g dry mass m^?2 year^?1) to 1-m² heathland plots at a site with low natural midge deposition. We established four levels of midge-addition treatments and measured stable isotopes (??¹³C and ??¹⁵N) in plants and arthropods within each treatment. We used a multiple-source isotope Bayesian mixing model to estimate the terrestrial versus aquatic contribution to the diets of arthropods. Aquatic resources were incorporated into plant, detritivore, and predator biomass. Detritivorous Collembola showed the greatest difference in isotope values (+3??? ??¹⁵N and +4??? ??¹³C) between midge-addition and reference treatments. Isotope values of small spiders followed the same trend of enrichment as Collembola while other arthropods (mites and large spiders) were only enriched after 2?years of midge addition. Although predator diets did not change, they became isotopically enriched via their likely prey (Collembola). Plants also had elevated ??¹⁵N (+1???) in midge-addition treatments. The time required and amount of midge-derived C and N detected varied and depended on trophic position. Midge-derived nutrients were no longer present in arthropod biomass in the year following midge addition. Aquatic insect carcasses can be rapidly incorporated into terrestrial food webs in nearshore habitats, and repeated inputs can be detected at multiple trophic levels, thus highlighting the importance of the detrital pathway for aquatic to terrestrial cross-ecosystem subsidies.     

The Roots of Carnivorous Plants

Carnivorous plants may benefit from animal-derived nutrients to supplement minerals from the soil. Therefore, the role and importance of their roots is a matter of debate. Aquatic carnivorous species lack roots completely, and many hygrophytic and epiphytic carnivorous species only have a weakly devel-oped root system. In xerophytes, however, large, extended and/or deep-reaching roots and sub-soil shoots develop. Roots develop also in carnivorous plants in other habitats that are hostile, due to flood-ing, salinity or heavy metal occurance. Information about the structure and functioning of roots of car- nivorous plants is limited, but this knowledge is essential for a sound understanding of the plants’ physiology and ecology. Here we compile and summarise available information on: (1) The morphology of the roots. (2) The root functions that are taken over by stems and leaves in species without roots or with poorly developed root systems; anchoring and storage occur by specialized chlorophyll-less stems; water and nutrients are taken up by the trap leaves. (3) The contribution of the roots to the nutrient supply of the plants; this varies considerably amongst the few investigated species. We compare nutrient uptake by the roots with the acquisition of nutri-ents via the traps. (4) The ability of the roots of some carnivorous species to tolerate stressful conditions in their habitats; e.g., lack of oxygen, saline conditions, heavy metals in the soil, heat during bushfires, drought, and flooding     

富营养化水体生物净化效应的研究进展

水体富营养化治理已成为当今世界性难题,解决水体富营养化问题的关键是调控水生生态系统结构,使其恢复自然、健康和稳定的水生生态系统功能,提高水生生态系统的生物净化能力,水生高等植物及水生植被是水生生态系统中最重要的初级生产者,它们个体大、生长周期长、吸取和储存营养物质的能力强,保持和恢复一定数量的水生植物种群可抑制浮游植物的生长,提高系统的生物多样性,使水生生态系统结构更加稳定,水生动物在水生生态系统物质和能量循环中处于十分重要的地位,浮游动物和底栖动物可直接捕食浮游植物,控制浮游植物的数量;而改变鱼类种群结构可提高浮游动物的生物量,从而间接控制浮游植物的大量繁殖,达到治理水体富营养化的目的,我国的生物净化研究还处于起步阶段,今后在水生高等植物及水生植被生物净化的关键技术及优化水产养殖新模式技术研究方面有待提高,这将对我国水体富营养化治理及水体可持续利用有着重要的意义。     

流域水质管理系统构建的理论、方法和实践

随着工农业的发展及乡村都市化 ,淡水资源的短缺成为全球性的问题。淡水资源的短缺 ,一方面是对淡水需求量增加 ,供不应求。另一方面是水体水质恶化 ,水资源退化。保护淡水资源是一项持久性的艰巨任务 ,其中水资源管理工具评价预测各种管理措施对水资源的影响 ,是必不可缺少的。工业和生活废水对水体的点源污染问题 ,早在2 0世纪 2 0年代就被意识到 ,并开展了一些水资源的保护和管理研究工作。自 192 5第一个水质数学模型Ｓｔｒｅｅｔｅｒ Ｐｈｅｌｐｓ[1] 用于模拟水环境中ＢＯＤ和ＤＯ的动态变化研究以来 ,出现了许多水质模型并用于河流、…     

Floral phenotypic plasticity as a buffering mechanism in the globeflower–fly mutualism

A buffering mechanism in co-evolutionary relationships could be to display phenotypic plasticity in response to environmental changes. In the nursery pollination mutualism between the European globeflower and its exclusive fly pollinators, adults feed and mate in flowers, and larvae develop feeding on seeds. Flower number and size influence fitness for both partners, and large flowers attract more flies. We tested floral plasticity in plants from two contrasting environments: a high-altitude heath and low- and intermediate-altitude meadow forests. High-altitude plants have single flowers, while meadow-forest plants sometimes have multiple flowers. Plants were grown for 3 years in a garden and supplied with eight times more nutrients than available in natural soils, given to controls. During the experiment, over 90% of all plants with excess nutrients flowered, while in controls, 40% (high-altitude) to 75–78% (meadow-forest) plants flowered. Excess nutrients stimulated 30% larger flowers, and in meadow-forest plants flower number increased 4.5–5 times. Flower number was only doubled in high-altitude plants. High-altitude plants displayed less plasticity, and possibly, a different genetic strategy involving meristem limitation.     

Managing water quality with aquatic macrophytes

The principal sources of water for human use are lakes, rivers, soil moisture and relatively shallow groundwater basins. Water quality in lakes and reservoirs is subjected to the natural degradation, processes of eutrophication and the impacts of human activities. Water quality problems can often be as severe as those of water availability but less attention has been paid to them, particularly in developing countries. Currently additional sustainable ways to mitigate the degradation of water quality are being researched all over the world. Phytoremediation is one of the serious efforts towards the sustainability. Most of the aquatic macrophytes are naturally occurring and well adapted for their surroundings. Aquatic macrophytes have the capability to remove excessive nutrient load from the water that otherwise cause eutrophication of the water body. Aquatic macrophytes absorb nutrient mineral ions from water column and influence metal retention indirectly by acting as traps for particulate matter, by slowing the water current and favoring sedimentation of suspended particles. Aquatic macrophytes also reduce sediment resuspension by offering wind protection. The use of aquatic macrophyte for treatment of wastewater to mitigate variety of pollution level is one of the most researched issues all over the world. Aquatic plant species are very specific for the uptake of nutrients. Owing to this specificity, the selection of the aquatic plant species is one of the skilled tasks prior to the design of a water treatment facility. An effort has been made in this review to cover the most researched aquatic flora for mitigation purposes and their possible use in a mesocosm as the selection of an appropriate aquatic plant specie reduce the time and cost of the treatment processes.     

The number and kinds of embryo-bearing plants which have become aquatic: a survey

The extant embryo-bearing plants (mosses, ferns and seed plants) have an aquatic ancestor or ancestors. Today they dominate the terrestrial vegetation of the world. Embryo-bearing plants which now live in water have, for a second or even third time, re-invaded water. Aquatic species are found in 440 genera from 103 families of embryo-bearing plants. This survey attempts to find out how often the Event of evolving from land back to water has taken place among the living plants of today. Analysing the morphological and phylogenetic affinities of all aquatics at taxonomic levels from divisio to varieties of species indicate the Event has taken place, at least 222 times but it could have happened 271 or even more times (bryophytes 10–19 times, ferns seven times, seed plants 205–245 times). Aquatic plants have evolved from often very different genetic and ecological backgrounds. Also, they have evolved at different times; some old ones are aquatic at the level of order or family, while others, more recent, are isolated species in otherwise terrestrial genera or races within species. It is, nevertheless, wonderful that such a large variety of plants have evolved solutions to the single problem of remastering life in water.     

Positive feedback in aquatic ecosystems

Aquatic ecosystems offer striking examples of how positive feedback can be integral to the dynamics of complex communities. In particular, microorganisms (bacteria and protozoa) introduce a multitude of positive feedback pathways by rapidly recycling nutrients at the very base of many aquatic food webs. The relatively large magnitude of fluxes being shunted through this 'microbial loop' allows an accumulation of nutrients in localized areas, promotes a general build-up of biomass, and acts as a 'life-support system' in harsh environments. In contrast to customary notions which portray positive feedback effects as undesirable, a reassessment indicates that this 'bootstrapping' can often be advantageous for many organisms.     

Tissue nutrient concentrations in freshwater aquatic macrophytes: high inter-taxon differences and low phenotypic response to nutrient supply

1. The elemental composition and stoichiometry of aquatic plants has often been suggested to reflect the nutrient enrichment of aquatic habitats. However, the relationship is often weak. Moreover, uncertainties remain in the relevance of laboratory derived critical plant tissue nutrient concentrations to maximum yield or growth rates in the field.
2. Aquatic vascular plants and bryophytes, overlying water and sediment samples were collected to test whether freshwater aquatic macrophytes: (i) show tissue nutrient deficiencies when growing in oligotrophic freshwater habitats, and (ii) have strict homeostatic stoichiometry.
3. Plant nutrient concentrations were significantly related to total inorganic nitrogen (or nitrate), total dissolved phosphorus and sediment total phosphorus. However, these relationships were weak. Virtually all the variance in plant tissue nutrient concentrations, however, could be explained by species (taxon) identity.
4. Critical tissue nutrient concentrations for 95% maximum yield or 95% maximum growth rate in aquatic angiosperms, determined from laboratory bioassays, suggested that nutrients should not limit yield in wild aquatic macrophytes. However, there were a substantial number of samples where potential growth rate limitation was possible, particularly due to phosphorus.
5. Strict C : N : P stoichiometric ratios were found for both vascular plants and bryophytes, suggesting little scope for plants as indicators of nutrient enrichment, but provide robust stoichiometric data for studies on ecosystem metabolism and nutrient cycling.     

浮游藻类的化感作用研究进展

化感作用由于在水产上有着巨大的潜力,成为近年来各国的研究热点。本文综述了藻类化感作用的定义、研究方法、化感物质的作用机制、影响因素、化感作用的应用等,并对今后研究方向以及应用前景进行了展望。     

Ecological studies to assess the efficacy of biological control on populations of alligator weed and lippia

Abstract  The risk of non-target effects from biological control agents can be reduced if we can better identify effective agents prior to release. Introducing only those agents with high potential for effective control will reduce the number of agents released and reduce the probability of both direct and indirect non-target impacts. Identifying effective agents requires understanding the roles that resources, disturbances and herbivory play in regulating plant populations under natural field conditions. Here we propose a series of experiments that will contrast the mechanisms of population regulation of two invasive wetland plants, alligator weed ( Alternanthera philoxeroides ) and lippia ( Phyla canescens ), with native congener species, Alternanthera denticulata and Phyla nodiflora . We hypothesise that the native plants will have greater growth rates when nutrients are low and herbivores are present, whereas the introduced plants will exhibit greater growth rates when nutrients are high and herbivores are absent.     

The smallest but fastest: Ecophysiological characteristics of traps of aquatic carnivorous Utricularia

Aquatic Utricularia species usually grow in standing, nutrient-poor humic waters. They take up all necessary nutrients either directly from the water by rootless shoots or from animal prey by traps. The traps are hollow bladders, 1–6 mm long with elastic walls and have a mobile trap door. The inner part of the trap is densely lined with quadrifid and bifid glands and these are involved in the secretion of digestive enzymes, resorption of nutrients and pumping out the water. The traps capture small aquatic animals but they also host a community of microorganisms considered as commensals. How do these perfect traps function, kill and digest their prey? How do they provide ATP energy for their demanding physiological functions? What are the nature of the interactions between the traps and the mutualistic microorganisms living inside as commensals? In this mini review, all of these questions are considered from an ecophysiologist''s point of view, based on the most recent literature data and unpublished results. A new concept on the role of the commensal community for the plants is presented.Key words: aquatic carnivorous plants, bladderwort, bladders, firing, resetting, enzyme secretion, water pumping, microbial commensals     

植物与土壤微生物在调控生态系统养分循环中的作用

陆地生态系统的地上、地下是相互联系的。植物与土壤微生物作为陆地生态系统中的重要组成部分, 它们之间的相互作用是生态系统地上、地下结合的重要纽带。该文首先介绍了植物在养分循环中对营养元素的吸收、积累和归还等作用, 阐述了土壤微生物对养分有效性及土壤质量具有重要的作用。其次, 重点综述了植物与土壤微生物之间相互依存、相互竞争的关系。植物通过其凋落物与分泌物为土壤微生物提供营养, 土壤微生物作为分解者提供植物可吸收的营养元素, 比如共生体菌根真菌即可使植物根与土壤真菌达到互惠。然而, 植物的养分吸收与微生物的养分固持同时存在, 因而两者之间存在对养分的竞争。通过植物多样性对土壤微生物多样性的影响分析, 以及土壤微生物直接或间接作用于植物多样性和生产力的分析, 探讨了植物物种多样性与土壤微生物多样性之间的内在联系。针对当前植物与土壤微生物对养分循环的调控机制的争论, 提出植物凋落物是调节植物与土壤微生物养分循环的良好媒介, 植物与土壤微生物的共同作用对维持整个生态系统的稳定性具有重要意义。也指出了目前在陆地生态系统地上、地下研究中存在的不足和亟待解决的问题。     

The effect of nutrients on adenine nucleotide levels and the adenylate energy charge ratio in Spartina alterniflora and Spartina patens

Abstract. The response of the adenylate energy charge (AEC) ratio and the adenine nucleotide pools to nutrients was studied in two perennial marsh plant species. Adenine nucleotide levels and the AEC ratio were measured in Spartina patens (Alton) Muhl. plants which were grown in the greenhouse at various nutrient levels as well as in Spartina alterniflora Loisel. transplants removed from the field but maintained in marsh soil amended with different nutrient supplements. In addition, adenine nucleotide concentrations were measured in both species in their natural environment and compared with that of the same species grown in the greenhouse with a complement of nutrients.
The addition of nutrients stimulated an increase in the individual and total adenylate pools and the AEC ratio. Low nutrient levels resulted in extremely reduced adenylate pools. The AEC ratio was significantly affected in some instances, but did not decrease proportionately with the adenine nucleotide level and was typically maintained at values above 0.60. The adenine nucleotide concentrations measured in the leaves of both species were significantly higher in greenhouse-grown plants compared to field plants, but the AEC ratios were not significantly different.
Because the AEC ratio in plants can be significantly affected by nutrient level. AEC response in field investigations should be planned with attention to the potential effect of dissimilar nutrient levels among study sites.     

内生真菌对兰科药用植物种子萌发作用研究进展

兰科植物种子细小,无胚乳,自然条件下需与适宜的内生真菌共生才能萌发。近年来,大量研究结果表明,内生真菌能够为兰科药用植物种子萌发提供必要的碳源、氮源等多种营养物质。本文对内生真菌为兰科药用植物种子提供的营养物质进行总结,并对二者的营养关系进行了综述。     

Does low nutritional quality act as a plant defence? An experimental test of the slow‐growth,high‐mortality hypothesis

Abstract.  1. The slow-growth, high-mortality hypothesis was experimentally tested in this study by investigating the effects of plant quality and natural enemies on leaf-miner growth, performance, and survivorship. Two leaf miners ( Acrocercops albinatella and Brachys tesselatus ) occurring on the turkey oak Quercus laevis were studied using a factorial design that manipulated predation/parasitism pressure and plant nutritional quality.
2. Forty trees were randomly divided into four treatments: (1) control plants (nutrients and natural enemies unaltered); (2) nutrients added, natural enemies unaltered; (3) nutrients unaltered, natural enemies reduced; and (4) nutrients added and natural enemies reduced. Water content, leaf toughness, tannin concentration, and foliar nitrogen were quantified monthly for each plant, and mine growth and survivorship were assessed by tracing mines on a 2–3-day interval and by following the fates of 50 mines per species per treatment combination.
3. Fertilised plants exhibited significantly higher amounts of nitrogen, but no significant differences among treatments were observed for water content, leaf toughness, and tannin concentration. These results only partially support the slow-growth, high-mortality hypothesis, as mines were significantly smaller and developed faster on fertilised plants, but neither fertilisation nor natural enemy exclusion significantly affected mine survivorship or mortality caused by natural enemies.     

根系分泌物介导的根际效应及在水体生态修复中的应用潜力

文章主要以根系分泌物为核心, 综述了根系分泌物的分类、发生机理及影响因素; 围绕着植物-土壤-微生物三者的关系, 阐述了根系分泌物介导的植物与植物之间的化感作用、植物与根际微生物之间的协同作用以及植物微生物相互作用对土壤物质循环的影响。水生植物以其生境的特殊性和功能的不可替代性, 对沉积物污染物去除和水体生态修复产生显著的影响。在水体生态问题较为严峻的今天, 充分认识水生植物根系分泌物介导的根际过程将为水生植物生态学和水体生态修复领域的发展提供基础, 并为学科应用潜力的开发提供依据。     

水生观赏植物的调查和研究

水生绿化观赏植物是美化园林水景的重要植物材料,作者通过几年的调查研究和引种栽培,提出了28种(其中荷花含18个品种,睡莲含20个品种)水生绿化观赏植物,同时介绍了20种(其中荷花含6个品种)观赏价值较高的水生绿化观赏植物。     

Herbivory limits the yellow water lily in an overgrown lake and in flowing water

Aquatic macrophytes with floating leaves are often key ecological species that affect entire aquatic ecosystems. Here we describe an investigation of the importance of insect herbivory for population growth and leaf senescence in the yellow water lily (Nuphar lutea). In order to gain a general picture of the importance of herbivory under different conditions, we experimentally manipulated herbivory in a large lily population in natural still water and observed the natural development of 32 smaller populations in flowing water. Herbivory drastically increased leaf senescence, reducing leaf density. In the still water, over one summer, leaf density increased by a factor of 1.23 in the presence of water lily leaf beetles and 1.61 when herbivory was eliminated. In flowing water, population growth was restricted mainly by leaf crowdedness, which limited large dense populations. Herbivory by water lily leaf beetles also had a limiting effect on yellow water lily, again mainly in large dense populations. Small populations supported a lower density of beetles. Previous studies have not addressed population-level responses of vascular plants with floating leaves. Our results suggest that herbivory can result in greater light penetration into the water and reduce “enemy-free space” for aquatic species that find such space in water lily stands. We suggest that the water lily leaf beetle should be considered an “ecological engineer.”     

Biological control of invasive plants through collaboration between China and the United States of America: a perspective

For more than 100 years, classical biological control of invasive plants through screening, introducing and releasing of host-specific natural enemies from native regions has been regarded as one of the promising approaches to the management of invasive plants. Many invasive plants in the United States of America are native to China, and vice versa. China and the USA also share a number of invasive plant species, including water hyacinth (Eichhornia crassipes), alligator weed (Alternanthera philoxeroides) and cordgrass (Spartina spp.). Collaboration between the two countries on biological control benefits both the nations by reciprocal opportunities to research and exchange natural enemies, by exchanging information on common invasive species, and by providing training for students and professionals. Here we review the history of collaboration between China and the US on biological control of more than 20 invasive plants. Current collaborative projects associated with four plant species, Polygonum perfoliatum L., Trapa natans L. Pueraria montana (Lour.) Merr. var. lobata and Ailanthus altissima (Mill.) Swingle, are also covered. We prioritize 14 invasive plants as targets for future collaborative biological control based on information on their importance in introduced areas, natural enemy records, and their potential biocontrol risk to introduced ecosystems. They are: Ampelopsis brevipendunculata, Celastrus orbiculatus, Dioscorea oppositifolia, Euonymus alata, Euonymus fortunei, Ligustrum sinense, Melia azedarach, Paulownia tomentosa, Sapium sebiferum and Ulmus pumila for the US, as well as Spartina alterniflora, Ambrosia artemisiifolia, Ambrosia trifida and Solidago canadensis for China. In addition, we emphasize that we must very carefully consider any potential non-target effect when we intend to introduce and release new natural enemies. We anticipate that the high priority both countries have placed on control of invasive plants will stimulate increasing collaboration on biological control.