薄荷化感物质的作用及其初步分离

以小麦(Triticum aestivum)、青菜(Brassica chinensis)和萝卜(Raphanus sativus)3种作物为受体，对薄荷(Mentha Haplocalyx)化感物质的作用进行了研究．结果表明：薄荷根分泌物显著促进小麦幼苗和幼根的生长，显著抑制青菜幼苗和幼根生长，显著促进萝卜幼苗而抑制其幼根生长．薄荷地上部分水浸液显著抑制青菜、萝卜的种子萌发和幼苗、幼根的生长；萝卜比青菜更敏感，幼根比幼苗更敏感；随着化感物质浓度的降低，抑制作用逐渐减弱、消失，甚至转变为促进作用．水浸液经氯仿、石油醚萃取后，剩余水相浓度变小、水势升高，但其抑制作用反而更加强烈．这说明，这种极其强烈的抑制作用不是低水势而是化感物质造成的；而且，剩余水相的抑制作用被同样具有抑制作用的石油醚相和氯仿相组分所削弱。即化感组分之间存在拮抗作用．剩余水相经大孔树脂进一步分离得到的3个组分都极显著地促进青菜幼苗的生长．这表明，水相强烈的抑制作用是由起极显著促进作用的3个组分的混合物产生的，且排除了水势降低的影响．但组分2显著抑制青菜、萝卜种子的萌发和幼根的生长．图2表4参26     

黄瓜根分泌物中化感物质的鉴定及其化感效应

作物生长过程中能从根系分泌释放出化感物质,此类物质被认为是引起连作障碍的重要因子。为进一步明确黄瓜(Cucumis sativus L.)根分泌物中化感物质与其连作障碍间的关系,采用GC-MS分析法,鉴定了XAD-4吸附树脂收集黄瓜水培液所获得根分泌物化感物质的种类,并考察了根分泌物对黄瓜种子胚根伸长及鉴定出的酚酸类化感物质对黄瓜枯萎病菌菌丝生长的影响。结果表明:黄瓜根分泌物中化感物质主要有苯甲酸、对羟基苯甲酸,香草酸,阿魏酸,苯丙酸等苯甲酸的衍生物。根系分泌物酸性、中碱性组分对黄瓜胚根伸长都有抑制作用,其中酸性组分抑制作用更加明显。42h内,质量浓度低于50mg·L-1时,酚酸对枯萎病菌菌丝生长有刺激作用,而高于50mg·L-1时,对菌丝生长有抑制作用。随处理时间延长,枯萎病菌对酚酸物质的耐受性增强,对高质量浓度酚酸的生长抑制作用表现不明显。本研究为从根际微生态角度揭示连作障碍机理积累了重要数据。     

黄花菜根浸提液对耐抽薹生菜化感作用的初步研究

为了解黄花菜浸提液的化感作用,本实验采用不同浓度黄花菜根浸提液对耐抽薹生菜的种子萌发、根长、茎长和幼苗鲜重的影响.结果表明,经黄花菜根浸提液处理后的生菜种子其发芽率和发芽指数随浸提液浓度的升高而显著降低,并且对生菜幼苗根的抑制作用强于对其幼苗茎的抑制作用.高浓度黄花菜根浸提液对生菜种子胚根和幼苗的生长表现出较强的抑制作用,而低浓度黄花菜根浸提液表现出促进作用.图4,表3,参14.     

不同林龄木麻黄林地特有细菌代谢产物及其化感潜力

为揭示土壤微生物代谢产物的组成及其在植物化感作用中的影响机制,采用GC-MS比较分析不同林龄木麻黄林地特有细菌与木麻黄土壤、根、凋落物的代谢产物,并研究木麻黄林地特有细菌发酵液对3种乡土树种青皮、红厚壳和杨叶肖槿种子萌发的影响.结果表明:木麻黄林地特有细菌代谢产物主要为酸、酯、烷、醛、酮、酰胺、酚类、醚类、吡喃、吡啶等有机化合物.以甲醇为萃取剂共萃取出60余种物质,以正己烷为萃取剂共萃取出20余种物质.与木麻黄土壤、根、凋落物浸提液GC-MS结果比较,发现2,4-二叔丁基苯酚、硬脂酸甲酯、1,2,3,4-丁四醇、甘油醚和苯并吡喃5种相同物质,及仅在特有细菌中存在的4-甲基-6-叔丁基苯酚.该物质与土壤浸提液中2,4-二叔丁基苯酚的结构类似,二者可通过烷基取代发生转化.表明木麻黄林地土壤细菌产生的代谢产物可在土壤中积累,或经过转化后进入土壤.木麻黄林地特有细菌发酵液对青皮、红厚壳和杨叶肖槿种子的生物测定结果表明,其发酵液对三种植物种子萌发均具有抑制作用,对青皮种子的抑制作用最为强烈,最低发芽率为25.3%,最强化感效应指数为-0.43.说明土壤细菌代谢产物参与了木麻黄的化感作用.     

植物体中萜类物质化感作用的研究进展

萜类物质主要以挥发油的形式广泛存在于高等植物中,尤以菊科植物含量丰富。萜类是天然物质中种类最多的一类,按结构可分为单萜、双萜、倍半萜、三萜及多萜等,是第二大类化感物质,尤其是单萜和倍半萜化感活性很强。萜类化感物质合成后大多通过植物体挥发或根系分泌等途径进入土壤,从而影响自身及邻近植物的生长。植物体中萜类物质化感作用已成为近年来国内外研究的热点。文章从萜类物质在植物中的分布、积累特点、释放途径及影响因素等方面进行了系统论述,分析了萜类对植物化感作用的机理及特点,总结了近年来该领域所取得的研究成果。文章认为萜类物质具有独特的化感活性,往往在较低的浓度即能表现出很强的抑制作用,影响其释放的内外因素较多,而且因其种类繁多化感作用机制也较复杂。最后指出了萜类物质化感作用研究中存在的关键问题,并对今后的研究方向进行了展望,希望研究者能进一步创新萜类化感物质的收集方法,关注土壤及空气等媒介对萜类物质化感活性的影响,采用多学科交叉的手段深入探索萜类物质的化感机理。     

油菜根系分泌物对不同作物幼苗生长的化感效应

在实验室采用发芽试验的方法研究了油菜Brassicacampestris根系分泌物对小麦、油菜、蚕豆和玉米种子活力、幼苗生长发育及生理生化特性造成的化感效应。结果表明,油菜根系分泌物的化感累加作用对不同作物种子发芽率、幼苗芽长、芽质量、根长、根质量、根系活力以及幼芽过氧化物酶(POD)活性和丙二醛(MDA)含量均具有显著影响,其化感效应对小麦的影响程度最弱,其中对小麦的种子发芽率、幼苗根长、芽干物质量、POD活性和根系活力以及各作物幼芽细胞膜的毒害程度均表现出促进作用,而对小麦幼苗其它生长特性以及油菜、蚕豆和玉米幼苗的所有生长特性均表现为抑制作用,表明油菜根系分泌物对不同作物及不同生长特性的化感效应具有不同的选择性。因此,合理搭配油菜作物的间、套、轮作是其夺取优质、高产栽培的关键技术。     

雪松枝叶挥发性物质的化感作用及其化学成分分析

采用半密闭容器测定法,研究了离体雪松(Cedrus deodara)枝叶挥发性物质对白菜(Brassica pekinensis)、萝卜(Raphanus sativus)、莴苣(Lactuca sativa)种子萌发的化感作用,并对其成分进行了GC-MS分析。结果表明:雪松枝叶的自然挥发物对白菜、萝卜和莴苣的发芽率和干质量影响不显著,但对萌发的芽长产生显著的影响,而挥发油对受体种子的发芽率、发芽指数、萌发的根长以及芽长均产生显著的抑制作用,其中对莴苣的发芽率和发芽指数的抑制效应达到92.85%和96.43%,对白菜种子萌发的根长的抑制效应达到51.3%,表明雪松枝叶的挥发物中存在潜在的化感物质,抑制种子的萌发,且挥发油的化感作用大于自然挥发物。对挥发油和自然挥发性成分分析结果表明,两种方法收集的挥发性气体中均鉴定出大量的萜烯类化合物,其中挥发油中鉴定出37种化合物,84.68%为萜烯类化合物,主要成分为α-蒎烯(24.72%)、β-蒎烯(21.04%)、1-石竹烯(12.42%);自然挥发物中鉴定出22种化合物,52.81%也都是萜烯类化合物,主要成分为α-蒎烯(17.16%)、β-蒎烯(11.53%)、b-侧柏烯(13.06%),两者共有成分15种,均为萜烯类化合物,其中挥发油中的成分含量较高,挥发油中化学成分的种类以及成分含量均大于自然挥发物,这可能是导致挥发油的化感作用大于自然挥发物的一个原因。从成分的分析结果可以看出,萜烯类化合物是雪松挥发性物质的主要成分,因此雪松枝叶挥发物的化感作用可能与其中的萜烯类物质有关。     

大气CO2浓度增高对不同供氮水平下水稻生长和化感物质释放的影响

利用开放式空气CO2浓度升高(free air carbon-dioxide enrichment,FACE)平台中的水培试验,研究了低氮(LN:10 mg·L-1)和高氮(HN:30 mg·L-1)水平下,大气CO2浓度升高对化感与非化感水稻(Oryza sativa L.)品种的生长、碳氮比(C/N)和化感物质含量的影响,并分析了CO2浓度升高条件下水稻C/N和化感物质含量间的相互关系.结果表明:CO2浓度升高对化感(PI)与非化感水稻品种(秀水)的生长均有极显著促进作用.CO2浓度升高后,LN条件下水稻C/N显著增加,HN条件下则无显著变化.CO2浓度升高后化感水稻品种次生代谢物质含量增加,特征化感物质含量增加,非化感品种的这种变化不显著.化感水稻品种C/N分别与次生代谢物质含量和特征化感物质含量之间呈显著正相关关系.     

不同土壤提取物对人参种子生长的化感效应及其化学组成

采用甲醇提取法提取新林地土、人参根际土以及栽培人参(Panax ginseng)、西洋参(Panax quinquefolius)的老参地土.每种土壤提取物设6个质量浓度梯度,以研究不同土壤提取物在特定质量浓度下对人参种子胚根和胚轴生长的化感效应,每种处理设3次重复.试验结果表明,与对照相比,人参根际土提取物对人参种子生长的化感效应最强,老参地土提取物对人参种子生长的化感效应次之,新林地土提取物对人参种子生长的化感效应最弱.经GC-MS分析,分别从6种土壤提取物中检测到1425种数量不等的化合物组分,其中苯胺类物质、酚酸及其衍生物被报道在其它植物上有化感活性,可能参与对人参种子的生理性毒害作用.     

抑制薇甘菊生长的日本菟丝子化感物质研究

采用制备型高效液相色谱、重结晶等方法从有害植物日本菟丝子（Cuscuta japonica Choisy）的水浸液有机萃取物中分离出能显著抑制薇甘菊（Mikania micrantha H.B.K.）种子萌发的化感物质,并采用核磁共振（1HNMR、13CNMR）法、质谱（MS）法等对其结构进行分析和鉴定。结果表明：能显著抑制薇甘菊种子萌发的日本菟丝子化感物质为桂皮酸（cinnamicacid）和3-苯基丙酸（3-phenylpropanoic acid）。这2种化合物在菟丝子属的植物中属首次分离鉴定。这2种化感物质具有开发为生物源农药（如除草剂）的潜力。研究结果为入侵植物薇甘菊的防治提供了参考依据,也为日本菟丝子的开发利用开辟了一条新途径。     

Achieving Open Access to Conservation Science

Conservation science is a crisis discipline in which the results of scientific enquiry must be made available quickly to those implementing management. We assessed the extent to which scientific research published since the year 2000 in 20 conservation science journals is publicly available. Of the 19,207 papers published, 1,667 (8.68%) are freely downloadable from an official repository. Moreover, only 938 papers (4.88%) meet the standard definition of open access in which material can be freely reused providing attribution to the authors is given. This compares poorly with a comparable set of 20 evolutionary biology journals, where 31.93% of papers are freely downloadable and 7.49% are open access. Seventeen of the 20 conservation journals offer an open access option, but fewer than 5% of the papers are available through open access. The cost of accessing the full body of conservation science runs into tens of thousands of dollars per year for institutional subscribers, and many conservation practitioners cannot access pay‐per‐view science through their workplace. However, important initiatives such as Research4Life are making science available to organizations in developing countries. We urge authors of conservation science to pay for open access on a per‐article basis or to choose publication in open access journals, taking care to ensure the license allows reuse for any purpose providing attribution is given. Currently, it would cost $51 million to make all conservation science published since 2000 freely available by paying the open access fees currently levied to authors. Publishers of conservation journals might consider more cost effective models for open access and conservation‐oriented organizations running journals could consider a broader range of options for open access to nonmembers such as sponsorship of open access via membership fees. Obtención de Acceso Abierto a la Ciencia de la Conservación     

Rapid,recurring, structured survey versus bioblitz for generating biodiversity data and analysis with a multispecies abundance model

A bioblitz inexpensively and quickly generates biodiversity data, but bioblitzes are often conducted with haphazard, unreplicated sampling. Results tend to be taxonomically, geographically, or temporally biased, lack metadata, and consist of lists of observed taxa that do not enable further analyses or correction for imperfect detection. A rapid, recurring, structured survey (RRSS) uses a structured sampling design and temporal and spatial replication to survey randomly selected sites on a conservation property. We participated in a loosely structured bioblitz and a subsequent RRSS at Big Canoe Creek Nature Preserve in Springville (St. Clair County), Alabama (USA) to compare observed richness derived from the 2 survey approaches. The RRSS data structure enabled us to fit models that accounted for imperfect detection to estimate abundances, occupancy probabilities, and habitat associations. The loosely structured bioblitz data could not be used in such models. We present a new integrated multispecies abundance model that we applied to avian RRSS data. Our model extension enables estimation for the community, employs data augmentation to estimate the number of undetected species, and incorporates covariates. The RRSS generated a more comprehensive and less biased list of observed taxonomic richness than the loosely structured bioblitz (e.g., 73 vs. 45 bird species and 104 vs. 63 insect families from the RRSS vs. loosely structured bioblitz, respectively). Models fit to the RRSS data identified seasonal patterns in avian community composition and allowed for estimation of habitat–occupancy relationships for insect taxa. The RRSS protocol has potential for broad transferability as a standardized, quick, and inexpensive way to inventory biodiversity and estimate ecological parameters while providing an outreach opportunity.     

Compliance with and ecosystem function of biodiversity offsets in North American and European freshwaters

Land-use change via human development is a major driver of biodiversity loss. To reduce these impacts, billions of dollars are spent on biodiversity offsets. However, studies evaluating offset project effectiveness that examine components such as the overall compliance and function of projects remain rare. We reviewed 577 offsetting projects in freshwater ecosystems that included the metrics project size, type of aquatic system (e.g., wetland and creek), offsetting measure (e.g., enhancement, restoration, and creation), and an assessment of the projects’ compliance and functional success. Project information was obtained from scientific and government databases and gray literature. Despite considerable investment in offsetting projects, crucial problems persisted. Although compliance and function were related to each other, a high level of compliance did not guarantee a high degree of function. However, large projects relative to area had better function than small projects. Function improved when projects targeted productivity or specific ecosystem features and when multiple complementary management targets were in place. Restorative measures were more likely to achieve targets than creating entirely new ecosystems. Altogether the relationships we found highlight specific ecological processes that may help improve offsetting outcomes.     

Some polyphagous Homoptera gain protection from their natural enemies by feeding on the toxic plantsSpartium junceum andErythrina corallodendrum (Leguminosae)

Summary Interactions were studied among alkaloid-containing legumes (Erythrina corallodendrum andSpartium junceum) and non-toxic plants (Citrus sinensis, Cucurbita moschata andEuphorbia tirucalli), several polyphagous homopterans,Aphis craccivora (Aphididae),Icerya purchasi, I. aegyptiaca (Margarodidae),Lepidosaphes ulmi (Diaspididae) andPlanococcus citri (Pseudococcidae), and some major natural enemies of these homopterans. Significant reductions in survival due to negative effects of alkaloid containing as compared with non-alkaloidal plants were recorded for the predatorsRodolia cardinalis andChilocorus bipustulatus, but not forCryptolaemus montrouzieri (Coleoptera: Coccinellidae),Chrysoperla carnea (Neuroptera: Chrysopidae) andSympherobius sanctus (Neuroptera: Sympherobiidae). The development time of the larvae or pupae ofR. cardinalis, C. carnea andS. sanctus was longer on the toxic plants than on the non-toxic ones. The percentage of parasitism ofA. craccivora collected from the non-alkaloidal plantsVicia palaestina andMelilotus albus was much higher than that onS. junceum. The parasitoid complexes ofA. craccivora differed between both plant groups. The nutritive value of honeydew ofI. purchasi andA. craccivora, as expressed by the life span ofEncyrtus infelix (Hymenoptera: Encyrtidae) adults, was also investigated. Life spans were significantly longer when the wasps fed on honeydew produced on non-alkaloidal plants (C. sinensis andPittosporum tobira) than on alkaloid containing plants whenI. purchasi — but notA. craccivora — was the producer. It is suggested that the chemical defense ofE. corallodendrum andS. junceum is exploited by polyphagous phytophages to reduce predation. In nature, population growth and density of four of the investigated homopterans are conspicuously high when they developed on the alkaloid containing plant species, and very low on non-alkaloid plants. The efficiency of their natural enemies may be reduced by sequestration of alkaloids (or other toxic plant compounds) or their transfer into excreted honeydew. Therefore it is assumed that a generalist phytophagous homopteran may be protected from its natural enemies, although at different rates of efficiency, if it can safely sequester the host allelochemical when it develops on toxic species within its host range.     

A palaeo-hydrogeological model for arsenic contamination in southern and south-east Asia

An argument is presented in which areas of natural arsenic contamination of modern groundwaters throughout Asia have a common origin. Arsenic originally accumulated in oceanic ferro-manganoan sediments of the eastern Palaeo-Tethys. This was further concentrated through oceanic crustal extinction in what later became the south-east Chinese accreted mineralised terrain. Proto-Himalayan uplift of this area created the palaeo-drainage systems of the Ganges – Brahmaputra, Irrawaddy, Mekong, and Red Rivers, with consequent headwater erosion of arsenic-rich sediments. Their downstream deposition as immature and easily redistributed Neogene sandstones, silts, and iron-rich clays has created secondary and tertiary reservoirs of adsorbed and authigenic arsenic, from which the current arsenic-rich groundwaters have evolved. Considering river basins within the above palaeo-hydrogeological framework provides a basis for assessing the risk of arsenic in groundwater basins of south and south-eastern Asia.     

Sequestration of cucurbitacin analogs by New and Old World chrysomelid leaf beetles in the tribe Luperini

Summary Two South American polyphagous leaf beetles,Diabrotica speciosa andCerotoma arcuata, selectively accumulated the bitter tasting compound 23,24-dihydrocucurbitacin D in their body after ingesting root tissues of cucurbit plants. Similarly, three Asian Cucurbitaceae-feeding specialists in the genusAulacophora were found to sequester the same compound. Cucurbitacin analogs were shown to deter feeding by a bird predator, indicating an allomonal role for these compounds in cucurbitacin-associated chrysomelid leaf beetles both of New and Old Worlds. The strong affinity to cucurbitacins, selective sequestration of the analogs and consequent protection from predators suggested an ecological adaptation mechanism developed in common among these two geographically isolated subtribes in the Luperini.     

Threats to intact tropical peatlands and opportunities for their conservation

Large, intact areas of tropical peatland are highly threatened at a global scale by the expansion of commercial agriculture and other forms of economic development. Conserving peatlands on a landscape scale, with their hydrology intact, is of international conservation importance to preserve their distinctive biodiversity and ecosystem services and maintain their resilience to future environmental change. We explored threats to and opportunities for conserving remaining intact tropical peatlands; thus, we excluded peatlands of Indonesia and Malaysia, where extensive deforestation, drainage, and conversion to plantations means conservation in this region can protect only small fragments of the original ecosystem. We focused on a case study, the Pastaza‐Marañón Foreland Basin (PMFB) in Peru, which is among the largest known intact tropical peatland landscapes in the world and is representative of peatland vulnerability. Maintenance of the hydrological conditions critical for carbon storage and ecosystem function of peatlands is, in the PMFB, primarily threatened by expansion of commercial agriculture linked to new transport infrastructure that is facilitating access to remote areas. There remain opportunities in the PMFB and elsewhere to develop alternative, more sustainable land‐use practices. Although some of the peatlands in the PMFB fall within existing legally protected areas, this protection does not include the most carbon‐dense (domed pole forest) areas. New carbon‐based conservation instruments (e.g., REDD+, Green Climate Fund), developing markets for sustainable peatland products, transferring land title to local communities, and expanding protected areas offer pathways to increased protection for intact tropical peatlands in Amazonia and elsewhere, such as those in New Guinea and Central Africa which remain, for the moment, broadly beyond the frontier of commercial development.     

Effects of Controlled Fire and Livestock Grazing on Bird Communities in East African Savannas

Abstract: In East Africa fire and grazing by wild and domestic ungulates maintain savannas, and pastoralists historically set fires and herded livestock through the use of temporary corrals called bomas. In recent decades traditional pastoral practices have declined, and this may be affecting biodiversity. We investigated the effects of prescribed fires and bomas on savanna bird communities in East Africa during the first and second dry seasons of the year (respectively before and after the rains that mark the onset of breeding for most birds). We compared abundance, richness, and community composition on 9‐ha burned plots, recently abandoned bomas, and control plots in the undisturbed matrix habitat over a 3‐year period. Generally, recently burned areas and abandoned bomas attracted greater densities of birds and had different community assemblages than the surrounding matrix. The effects of disturbances were influenced by interactions between primary productivity, represented by the normalized difference vegetation index, and time. Bird densities were highest and a greater proportion of species was observed on burned plots in the months following the fires. Drought conditions equalized bird densities across treatments within 1 year, and individuals from a greater proportion of species were more commonly observed on abandoned bomas. Yearly fluctuations in abundance were less pronounced on bomas than on burns, which indicate that although fire may benefit birds in the short term, bomas may have a more‐lasting positive effect and provide resources during droughts. Several Palearctic migrants were attracted to burned plots regardless of rainfall, which indicates continued fire suppression may threaten their already‐declining populations. Most notably, the paucity of birds observed on the controls suggests that the current structure of the matrix developed as a result of fire suppression. Traditional pastoralism appears critical to the maintenance of avian diversity in these savannas.     

Cost‐effective conservation of an endangered frog under uncertainty

How should managers choose among conservation options when resources are scarce and there is uncertainty regarding the effectiveness of actions? Well‐developed tools exist for prioritizing areas for one‐time and binary actions (e.g., protect vs. not protect), but methods for prioritizing incremental or ongoing actions (such as habitat creation and maintenance) remain uncommon. We devised an approach that combines metapopulation viability and cost‐effectiveness analyses to select among alternative conservation actions while accounting for uncertainty. In our study, cost‐effectiveness is the ratio between the benefit of an action and its economic cost, where benefit is the change in metapopulation viability. We applied the approach to the case of the endangered growling grass frog (Litoria raniformis), which is threatened by urban development. We extended a Bayesian model to predict metapopulation viability under 9 urbanization and management scenarios and incorporated the full probability distribution of possible outcomes for each scenario into the cost‐effectiveness analysis. This allowed us to discern between cost‐effective alternatives that were robust to uncertainty and those with a relatively high risk of failure. We found a relatively high risk of extinction following urbanization if the only action was reservation of core habitat; habitat creation actions performed better than enhancement actions; and cost‐effectiveness ranking changed depending on the consideration of uncertainty. Our results suggest that creation and maintenance of wetlands dedicated to L. raniformis is the only cost‐effective action likely to result in a sufficiently low risk of extinction. To our knowledge we are the first study to use Bayesian metapopulation viability analysis to explicitly incorporate parametric and demographic uncertainty into a cost‐effective evaluation of conservation actions. The approach offers guidance to decision makers aiming to achieve cost‐effective conservation under uncertainty.