Possible causes of high species diversity in tropical Australian freshwater macrobenthic communities

A total of 133 benthic macroinvertebrate species was recorded in four permanent freshwater lagoons (billabongs) and a stream riffle in the Magela Creek catchment, Northern Territory, Australia. 101 species were lentic in occurrence. Each billabong supported at least as many species as larger tropical and Australian temperate lakes, and was an exception to the species-poor status of Australian lentic macrobenthic communities. > 98% of the total benthic biomass was contributed by a mussel species; the remaining species' combined standing crop was an order of magnitude lower than in other lentic systems, further highlighting the diversity of the Magela benthos. Rarefaction (removal of organisms) and predictable environmental heterogeneity, both related to monsoonal variations in flow and water quality, were probably important determinants of the high diversity of these communities.     

Applications of minirhizotrons to understand root function in forests and other natural ecosystems

Minirhizotrons have proved useful to understand the dynamics and function of fine roots. However, they have been used comparatively infrequently in forests and other natural plant communities. Several factors have contributed to this situation, including anomalous root distributions along the minirhizotron surface and the difficulty of extracting data from minirhizotron images. Technical and methodological advances have ameliorated some of these difficulties, and minirhizotrons have considerable potential to address some questions of long standing interest. These questions include more fully understanding the role of roots in carbon and nutrient cycling, rates of root decomposition, responses to resource availability and the functional significance of interactions between plant roots and soil organisms. Maximizing the potential for minirhizotrons to help us better understand the functional importance of fine roots in natural plant communities depends upon using them to answer only those questions appropriate to both their inherent strengths and limitations.     

Biodiversity of soil biota and plants in abandoned arable fields and grasslands under restoration management

The currently widespread abandoning of agricultural land use in Western Europe offers new opportunities for ecological restoration and nature conservation. This is illustrated for abandoned arable fields and for permanent grasslands cut for hay after the cessation of fertilizer application. Although initiated by a sudden reduction of nutrient input to the system, the changing nutrient supply from the soil is considered to be the main driving force of succession. The soil nutrient supply is affected by soil organisms, both directly (root symbionts and herbivores) and indirectly (nutrient mineralization from dead organic matter). It is argued that because of the close association of changes in species diversity with changes in the functioning of ecosystems, biodiversity has to be studied in an ecosystem ecology context.     

The Høylandet area – patterns and processes of a pristine boreal-subalpine ecosystem – a synopsis

The research activities on soil–freshwaterinteractions and freshwater biotic structure andprocesses in the Høylandet area during the years 1986–89are presented in this issue ofHydrobiologia. The 9 papers cover a range of topicsfrom physiochemical gradients and processes in soilsand freshwaters to selected aspects of freshwaterbiotic community structure and temporal variability.This synopsis aims (a) to present an overview of majorfindings, (b) to interpret the results in the contextof air pollution effects and (c) to outlinesuggestions for future research activities inHøylandet. The area has a sub-oceanic climate varyingfrom 1100 to 2200 mm of precipitation normallyoriginating from unpolluted airmasses from the NorthAtlantic. It is chemically dominated by sea salts, haslow concentrations and low deposition of mineralacids. The catchment geology is variable and complexand consists mainly of various granites and gneisses.The soils are undisturbed ancient soils,primarily iron podzols associated with forests, orintact histosols with strong organic characterassociated with mires, often quite acidic.They are sensitive because occurrence of predominantlyinsoluble unstable Al-complexes may leach out ifexposed to anthropogenically acidified soil drainagewater and turn up as toxic inorganic aqueous Al insurface runoff. Small amounts of locally generatednitrogen compounds are mostly retained in thecatchment. The water qualities of these Høylandetsites are run by inputs of sea salts, hydrologicalprocesses including dilution of the base flow, orlateral surface or overland flow and in-catchmentprocesses. Relative to affected areas, it appears thatthe inputs and catchment processes are in balance,i.e., that the inputs of strong acid anions, hydrogenions and sea salts are equilibrated by internalweathering and other processes and integrated withinapparently intact biogeochemical cycles. The overallresult is that these soils remain a net source ofalkalinity to the runoff. These results are confirmedby regional studies of water quality both at low andhigh flow which show that the humus and ionic contentof the water decreased with elevation, headwatersbeing more dominated by sea salts and dilutionprocesses. Excess sulphate concentrations are low, andfew if any sites appear anthropogenically acidified,the most acid pHs reflecting presence of natural weakorganic acids.The resulting surface water quality allows a diverseaquatic fauna and flora with representatives of manyacid-sensitive groups. The fish fauna consists ofself-reproducing salmonid populations with normaldemography and ecological interactions. Despite highin-lake mortality, both brown trout and Arctic charrexhibited normal age-class compositions, with noindication of the recruitment failure or highpost-spawning mortality commonly observed inacid-stressed situations. The zooplankton and benthos in the lakesare inhabited by populations of several acid sensitivespecies, like Daphnia spp and Gammaruslacustris, and with dominance of mayfly species ofthe genus Baetis in the stream fauna. Thediatom flora includes many species which are rare orabsent in acidified waters. The observed gradients indiversity and biomass seem dominated by localenvironmental conditions which reflect natural ratherthan man-made processes. The pristine nature of thearea also emerges from the paleoecological studies inLake Røyrtjønna which show that the low acidity ofthis lake evironment has persisted from preindustrialtill present times. Suggestion for future researchactivities in Høylandet are outlined.     

不同土壤培肥措施下农田有机物分解的生态过程

通过在河北曲周实验站的田间试验,研究了4种不同土壤培肥措施条件下农田生态系统中几种主要土壤生物随有机物分解的变化规律、有机物的分解及其主要影响因素。研究结果表明：除土壤线虫外,其他几种主要的土壤生物的分布规律基本上是堆肥区〉原貌区〉对照区〉化肥区,与施入的有机物（小麦秸秆）的分解规律一致。在受人为扰动的堆肥区、化肥区和对照区土壤中,细菌占绝对优势,而在未开垦的原貌区中,真菌起着重要作用。 在有机物分解初期,土壤微生物能比较快地迁移到秸秆表面,秸秆表面的生物数量最多的是细菌,随着细菌的数量增加,原生动物数量亦呈现增加趋势,蚯蚓数量增多,而线虫的数量则减少。而有机物分解后期,真菌的数量逐渐减少,蚯蚓的数量也呈下降趋势,有机物的分解速度减慢。通过灰色关联度分析,9种外界因素（生物因素和环境因素）对小麦秸秆分解作用的相对重要程度排序：土壤温度（0．844）〉蚯蚓（0．777）〉真菌（0．764）〉全氮（0．754）〉线虫（0．753）〉有机质（0．742）〉细菌（O．738）〉原生动物（0．693）〉土壤含水量（0．661）,其中土壤温度和蚯蚓是影响土壤有机物分解的最重要的两个因素。     

Trampling and Spatial Heterogeneity Explain Decomposer Abundances in a Sub-Arctic Grassland Subjected to Simulated Reindeer Grazing

Mammal grazing is composed of three mechanisms—removal of foliar tissue (defoliation), return of nutrients via dung and urine (fertilization), and trampling. To evaluate the relative role of these mechanisms in the effect of reindeer grazing on soil biota in northern grasslands, we subjected experimental plots in a sub-arctic alpine meadow to defoliation, fertilization (using NPK-solution), simulated trampling, and their factorial combinations once a year from 2002 to 2004 and measured the response of plants and decomposers (including microbes, nematodes, collembolans, and enchytraeids) in 2004. Trampling affected both plant and decomposer communities: the coverage of the moss Pleurozium schreberi and the sedge Carex vaginata, as well as the abundance of collembolans and enchytraeids were reduced in trampled plots. Trampling and fertilization also interacted significantly, with fertilization increasing the abundance of bacteria and bacterial-feeding and omnivorous nematodes in trampled plots only, and trampling decreasing fungal biomass in non-fertilized plots only. Defoliation had no overall effects on plants or decomposers. Nematode genera were not affected by the experimental treatments, but nematode and plant communities were significantly associated, and all decomposer biota, except collembolans, were strongly affected by the spatial heterogeneity of the study site. Our results indicate that trampling may have larger and defoliation and fertilization smaller roles than anticipated in explaining reindeer grazing effects in sub-arctic grasslands. However, even the effects of trampling seem to be outweighed by the spatial heterogeneity of decomposer abundances. This suggests that in sub-arctic grasslands spatial variation in abiotic factors can be a more important factor than grazing in controlling soil biota abundances. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author contributions  LIS was involved in planning of the study, fieldwork, lab work, analysis, and wrote the article with contributions from all other authors; JM and MMK conceived the study and contributed to the data analyses; MMK further contributed to the field work and JM refined the final appearance of the text; JO started and was responsible for managing the field experiment, collecting the plant data and gave advice on statistical analysis.     

寒武纪早期宽川铺生物群中圆管螺化石显微结构及显微谱学分析

陕南寒武系底部宽川铺组不仅保存了大量的小壳化石,还以磷酸盐化的方式立体保存了多种软躯体动物的胚胎和成体化石,为研究早期动物矿化模式、个体发育方式以及动物躯体构型的早期辐射过程提供了非常关键的信息。然而宽川铺生物群的研究大多聚焦于化石系统分类及亲缘关系探索,对生物群的沉积背景、埋藏过程和保存模式的分析甚少。本文以宽川铺生物群的核心产出层位——陕西省西乡县大河镇宽川铺组下部磷质碎屑灰岩为研究对象,对其中的一类管状化石圆管螺及其围岩进行了显微结构学和显微谱学综合分析,获得了化石显微结构和关键结构对应的元素、矿物成分等信息,讨论了管状化石圆管螺的埋藏过程和保存模式,并在此基础上对其生物学特征进行了初步探讨。该研究对理解宽川铺生物群的埋藏机制提供了新的线索。     

陕西宁强埃迪卡拉纪晚期高家山生物群中黄铁矿化化石的成岩及风化过程

陕南埃迪卡拉纪晚期的高家山生物群中部分化石以黄铁矿化三维立体保存软躯体管状化石为主要特征。对野外识别出的具有不同风化程度的3类粉砂岩进行了详细的手标本特征对比和扫描电子显微镜测试对比研究。锥管虫（Conotubus）的化石成岩学特征表明黄铁矿最先沉淀,随后方解石充填于黄铁矿留下的空隙或空腔中。这些化石所经历的第一期风化作用相对较弱,保留了大量的原始化石成岩学信息;第二期风化作用则可能形成于一个氧化条件较强的环境中。