鄱阳湖湿地不同土地利用方式下土壤微生物群落功能多样性

于2011年5月分别采集鄱阳湖围垦92、48a和38a的水稻田,退田还湖25a的退耕地以及自然湿地共5个样地的表层土壤,利用Biolog-ECO板技术对土壤微生物群落的单一碳源利用情况进行了测定,并结合群落指数和主成分分析(PCA)对培养72 h土壤微生物群落功能多样性变化进行了分析。结果表明:退耕地和自然湿地土壤微生物群落利用31种碳源的能力较强,来自不同围垦年限的土壤微生物群落利用碳源能力均较弱;且随围垦时间的增长,土壤微生物对碳源的利用能力呈降低的趋势。自然湿地、退耕地与围垦92、38a样地土壤之间存在显著的微生物功能多样性差异;围垦对土壤微生物代谢糖类、羧酸类、氨基酸类物质的影响最为明显。结果提示,围垦改变了湿地土壤微生物群落结构,退田还湖有助于湿地土壤微生物群落结构的恢复。     

湿地植物根系泌氧及其在自然基质中的扩散效应研究进展

湿地植物根系径向泌氧(ROL)是构造根际氧化-还原异质微生态系统的核心要素,其扩散层为好氧、厌氧微生物提供了良好生境并促进其代谢活动,使湿地植物根际成为有机物降解、物质循环及生命活动最为强烈的场所,已有成果证明湿地植物根系ROL的强弱与污染物的去除效果密切相关。因此,开展湿地植物根系ROL及其在自然基质中的扩散效应研究,对于了解湿地植物根系ROL机理及其根际氧环境特征,进而发挥湿地植物的污染去除功能具有十分重要的意义。基于此,首先归纳了湿地植物根系ROL特征及其受影响机制的研究现状,而后从种属差异、时空分布及对微生物的影响等方面对根系ROL在自然基质中的扩散效应国内外研究成果进行了总结,最终根据研究现状与不足对今后的研究方向进行了简要展望。创新之处在于:1)提出影响根系氧供给及氧输送释放通道的环境、生物等因素,阐述了其对根系ROL的影响机制;2)着重阐述了目前研究较少提及的根系ROL扩散效应测定方法。     

三江平原不同湿地类型土壤活性有机碳组分及含量差异

土壤活性有机碳对土壤干扰的反应较快,是土壤有机碳早期变化的敏感性指标。近50年来,三江平原湿地土壤有机碳库受农事活动影响较大。为了探讨不同湿地类型土壤活性有机碳主要组分土壤可溶性有机碳(Dissolved organic carbon,DOC)、微生物量碳(Microbial biomass carbon,MBC)和易氧化有机碳(Easily oxidized organic carbon,EOC)的分布差异及主要影响因子,选择了三江平原洪河自然保护区4种典型的湿地类型(小叶章+沼柳湿地、小叶章湿地、毛苔草湿地和芦苇湿地)为研究对象。分析了不同湿地类型土壤可溶性有机碳,微生物量碳和易氧化有机碳在0—30 cm土层内的分布特征和分配比例及其与有机碳、土壤养分和酶活性指标(蔗糖酶、纤维素酶和过氧化氢酶)之间的相关关系。结果表明:(1)4种湿地类型土壤DOC、MBC和EOC含量均随土层深度的增加而减少。不同湿地类型之间土壤活性有机碳含量在0—30 cm土层内存在显著性差异(P0.05),相对于长期淹水的毛苔草湿地和芦苇湿地而言,未淹水的小叶章+沼柳湿地和小叶章湿地具有较高的DOC,MBC和EOC含量。(2)土壤DOC、MBC和EOC占有机碳比例分别为0.27%—0.63%,1.27%—5.94%和19.63%—41.25%。土壤DOC所占比例呈先增后减的变化趋势,最大的比例均出现在10—20 cm。MBC所占比例在土壤剖面上则未表现出一致的变化规律,而EOC所占比例则随土层深度的增加而逐渐减少。(3)土壤DOC占SOC比例以小叶章湿地最高,MBC和EOC占SOC的比例则以小叶章+沼柳湿地最高。而长期淹水的毛苔草湿地和芦苇湿地则具有更低的DOC,MBC和EOC比例。(4)综合分析表明,4种湿地类型土壤DOC,MBC和EOC两两之间存在极显著相关性关系,它们除了与碳氮比相关性不显著外,与土壤有机碳,全氮,全磷养分和酶活性指标间相关性均达到极显著水平,尤其是与有机碳和全氮的相关性系数更高,此外DOC与纤维素酶,MBC与过氧化氢酶相关性更大。由此可见,土壤碳氮磷养分和酶活性是影响土壤活性有机碳组分分布的重要因素。     

盐分对湿地甲烷排放影响的研究进展

当前在全球气候变化和人类活动双重作用下,湿地正在或者将要面临着显著的盐分变化形势,尤其是内陆和滨海咸化湿地。湿地是大气甲烷的重要排放源。甲烷排放是甲烷产生、氧化和传输过程综合作用的结果。盐分变化将影响湿地水-土环境,降低植物群落初级生产力和有机物积累速率,改变微生物主导的有机物矿化速率和途径等,进而改变湿地生态系统的结构和功能,影响湿地甲烷产生、氧化、传输和排放系列过程。本文综述了盐分(浓度与组成)对湿地甲烷产生与排放的影响结果,从底物供给、微生物(产甲烷菌和甲烷氧化菌等)数量、活性与群落组成、酶活性、植物、电子受体、p H和氧化还原电位等几个关键方面分析了盐分影响湿地甲烷排放过程的内在机制。在此基础上提出了今后需重点关注的5个方面:1)加强盐分浓度与组成对湿地甲烷产生、氧化、传输与排放影响的系统性、框架性研究;2)深入探讨盐分背景、变化幅度与速率的耦合如何影响湿地甲烷系列过程;3)不同离子组成及其交互效应如何影响湿地甲烷动态过程;4)结合生物学、基因组学及同位素技术等,加强湿地产甲烷菌与甲烷氧化菌与盐分的关系及其响应研究;5)湿地甲烷对盐分变化响应的时空分异规律。     

鄱阳湖南矶山湿地自然保护区的外来入侵植物调查与分析

为了解鄱阳湖南矶山自然保护区外来入侵植物的状况, 从2010 年至2014 年对外来入侵植物的物种种类、分布、传播等进行了调查。结果表明, 南矶山湿地保护区共有外来入侵植物32 种, 隶属于l8 科28 属, 其中菊科最多, 有8 种6 属;其次是苋科, 有4 种3 属, 绝大多数是草本植物;以原产地为美洲的最多, 有15 种, 其中来自北美的有9 种。对保护区造成严重危害的外来入侵植物有5 种, 分别为野燕麦(Avena fatua)、小飞蓬(Conyza canadensis)、野胡萝卜(Daucus carota)、裸柱菊(Soliva anthemifolia)和空心莲子草(Alternanthera philoxeroides), 危害较强的主要有7 种, 危害较轻的有20 种。对外来植物的入侵途径、规律与成因以及对生态环境造成的影响进行了讨论, 并提出了防治对策与建议。     

Waterlogging responses of Schoenoplectus scirpoides (Schrad) Browning (Cyperaceae)

Waterlogging responses of an emergent freshwater macrophyte, Schoenoplectus scirpoides, were investigated by carrying out laboratory and field experiments. Soil cores containing uniform plants of S. scirpoides were subjected to drained, 1/3 flooded, alternately flooded and drained at weekly intervals, and continuously flooded treatments for 6 months. Mean soil redox potential of the drained soil was 225 ± 29 mV and was significantly lower in the other treatments. Total dry biomass, above‐ground biomass and number of culms in the flooded/drained and flooded treatments were significantly higher than those in the drained and 1/3 flooded treatments. Below‐ground/above‐ground biomass ratios were highest in the drained treatment and significantly lower in the waterlogged treatments. Plant height and the growth rate of culms were least in the drained treatment and significantly higher in the other treatments. Culm specific gravity decreased significantly with increase in soil moisture. In the field study, soil redox potentials were moderately reduced in the inland and streamside sites, while culm elongation rate was significantly higher by 94% in the streamside compared with the inland site. Optimum growth occurred under flooded conditions, suggesting that the species could flourish with increasing water intrusion in estuarine areas, as predicted by global climate change.     

Unheard voices: state-making and popular participation in post-Ottoman Iraq

I explore the nature of the particular nation state form that came into being in Iraq during the British Mandate, and in particular its impact on minorities. The Mandate government, and the broader international legal framework, structured state–minority relations in post-Ottoman Iraq in ways that continue to shape Iraqi politics. While sociocultural differences in Iraqi society were given constitutional recognition, this did not lead to the effective protection of minority rights, primarily because the principle of popular participation was not respected. The Mandate legacy in Iraq has been long-lasting, as the mistakes of the past have been reproduced by postcolonial regimes, and thus the state–minority relationship has been locked in a loop of exclusionary politics and securitization.     

CYANOBACTERIAL BUOYANCY REGULATION: THE PARADOXICAL ROLES OF CARBON1

In stratified lakes, dominance of the phytoplankton by cyanobacteria is largely the result of their buoyancy and depth regulation. Bloom-forming cyanobacteria regulate the gas vesicle and storage polymer contents of their cells in response to interactive environmental factors, especially light and nutrients. While research on the roles of nitrogen and phosphorus in cyanobacterial buoyancy regulation has reached a consensus, evaluations of the roles of carbon have remained open to dispute. We investigated the various effects of changes in carbon availability on cyanobacterial buoyancy with continuous cultures of Microcystis aeruginosa Kuetz. emend. Elenkin (1924), a notorious bloom-former. Although CO₂ limitation of photosynthesis can promote buoyancy in the short term by preventing the collapse of turgor-sensitive gas vesicles and/or by limiting polysaccharide accumulation, we found that sustained carbon limitation restricts buoyancy regulation by limiting gas vesicle as well as polysaccharide synthesis. These results provide an explanation for the positive effects of bicarbonate enrichment on cyanobacterial nitrogen uptake and bloom formation in lake experiments and may help to explain the pattern of cyanobacterial dominance in phosphorus-enriched, low-carbon lakes.     

Using Landsat images to map habitat availability for waterbirds in rice fields

Rice fields are an important habitat for waterbirds. Knowledge of the availability of this habitat is important since the reduction in the area of natural wetlands has converted rice fields into vital refuges. This paper presents a method for mapping habitat availability in rice fields according to different waterbirds’ habitat preferences and examining its phenology during the crop cycle. Data from bird censuses carried out in the Doñana rice fields were analysed to determine the habitat preferences of 22 species of waterbird at different stages in the rice production cycle. Discriminant function analysis of seven Landsat images was used to classify paddy field stages. The phenology of habitat availability in rice fields during autumn and winter was examined. Waterfowl and waders preferentially used the ‘flooded’ and ‘mudflats with water’ paddy field stages, respectively, and the ‘rice growing’ and ‘dry’ stages were rejected by waterbirds. The area of preferred habitats within rice fields increased during autumn; subsequently, the area of the ‘flooded’ paddy fields decreased in January, whereas that of ‘mudflats with water’ remained available until March. The automatic classification of paddy field stages with Landsat images allowed habitat availability for different species of waterbirds to be monitored and provides relevant information for understanding behavioural and population responses in waterbirds that use rice fields. After examining the phenology of the availability of habitat and comparing it with dates of arrival and departure of migrant waterbirds, best crop practices could be defined to favour waterbirds (i.e. adjusting harvest, ploughing and flooding dates). Taking into account climatic change and loss of wetlands this method could help in the integration of agriculture and conservation, in particular in areas where there is no remaining natural wetland habitat.