Abundance of terrestrial gymnamoebae at a northeastern U. S. site: a four-year study, including the El Niño winter of 1997-1998

ABSTRACT. The abundance, sizes, and when appropriate, diversity of gymnamoebae were documented at approximately monthly intervals for four years (1995–1998) at a grassy, terrestrial site slightly upslope from a freshwater pond. Soil samples were analyzed for viable gymnamoebae using a standard laboratory culturing protocol. The mean density of gymnamoebae based on the total data set was ca. 1,600/g (s.e. ± 190). Minimum densities of gymnamoebae (156/g) occurred in January 1995, and a maximum for the sampling period (5,838/g) occurred in July 1997, when a rainy period followed an extended period of drought. Among the environmental variables monitored (precipitation, soil moisture, organic content, and temperature) only precipitation correlated significantly with abundance of gymnamoebae (r= 0.34 , p = 0.02 ). During the mild, moist El Niño winter of 1997–1998, a larger than usual number of gymnamoebae was recorded at the site (～3,800/g) compared to a mean density of ～900/g for comparable periods in preceding years. The mean sizes were also larger. Since gymnamoebae are increasingly recognized as major members of soil microbial communities enhancing soil fertility through nutrient mineralization, it is important to document environmental variables that influence their abundance and activity in terrestrial ecosystems.     

Densities and Diversity of Gymnamoebae in Relation to Some Inshore Aquatic Habitats at Bermuda

ABSTRACT Densities and diversity of gymnamoebae are reported for three sites at Bermuda. Two are marine sites in Mullet Bay, and the third is a shallow pond (Ferry Reach Park), Bermuda. Site 1 (edge of a small island in Mullet Bay) had higher densities of gymnamoebae (28,761/g sediment) than at a disturbed site 2 (17,597/g), a boat mooring. The diversity was higher, however, at site 2 (H = 4.3) compared to site 1 (H = 3.3). The site 2 species were larger including morphotypes categorized as type 1 (e.g. Mayorella and a reticulate amoeba). The brackish inland pond had higher abundances in the sediments (40.590/g) compared to the marine habitats. However, the diversity was lower (H = 2.7) and it was dominated largely by Vannella and Platyamoeba (categorized as morphotype 4). These data are consistent with findings at continental coastal locations in northeastern USA. Pond sediments generally contain higher densities of gymnamoebae than marine coastal sediments with less organic content. The ratio of type 4 to type 1 amoebae in pond samples is higher than those from coastal sites. The data from Bermuda, an open ocean insular site, provide additional zoogeographic evidence for the generality of these patterns of abundance.     

Seasonal Variability in Abundance and Diversity of Soil Gymnamoebae Along a Short Transect in Southeastern USA

The abundance and diversity of gymnamoebae in three subsoils varying in compaction and water retention along a 1.2 m transect were documented as the local climatic conditions changed from late summer 1999 through mid-summer 2000. The mean density of gymnamoebae for the loose soil (1,655/g) was greater than either the most compact (1,468/g) or moderately compact soil (851/g). Minimum densities occurred in middle and late summer for all soils while significant (F = 38.803, < or = 0.0002) density peaks at 3.212/g occurred in early summer in the most compact soil, 2.928/g in the least compact, and 2,209/g in the moderately compact soil. Limax non-eruptive gymnamoebae (mt 2) correlated (r = 0.49, p < or = 0.016) with moisture while eruptive limax gymnamoebae ( 3) correlated with temperature (r = 0.07, p < or = 0.024), moisture (r = 0.58, p < or = 0.001) and precipitation (r = 0.46, p < or = 0.029). Flattened or discoid amoebae (mt 4) dominated throughout most of the survey, and the two limax groups showed inverse relationships. Chi-square analyses showed significant differences in the numbers of limax eruptive gymnamoebae compared to all other morphotypes on all but one sampling period.     

Effects of aqueous extracts from leaves and leaf litter on the abundance and diversity of soil gymnamoebae in laboratory microcosm cultures

The distribution and abundance of microbiota in soil and litter may be significantly affected by the quality and quantity of localized patches of leaf organic matter. This study examined the relative effects of aqueous extracts of shed autumn leaves from American beech (Fagus grandifolia), sugar maple (Acer saccharum), red oak (Quercus rubra), and white oak (Quercus alba) on the density and diversity of gymnamoebae in laboratory cultures. Overall, the beech leaf extract produced the most growth of gymnamoebae followed by white oak with leaf extracts from maple and red oak producing least growth. Cultures using natural leaf litter from beneath beech trees had higher densities and diversity of gymnamoebae than leaf-litter cultures from a maple-oak stand. Soil microcosms confirmed that beech leaf extracts produced a higher density of gymnamoeba growth when added to soil cultures compared with maple and oak leaf extracts. Protein content, CHN (carbon and nitrogen content), and pH of the leaf extracts were assayed, but these alone were not sufficiently different to account for the effects. A dilution experiment indicated that some other concentration-dependent factor in the extract may produce the effects.     

Density and diversity of protozoa in some arid Australian soils

This is the first extensive study of soil protozoa of arid lands. Twenty-six samples from litters, soils, termitaria, and a cyanobacterial crust, collected from central and south Australian arid lands, were analyzed for numbers and species of gymnamoebae, ciliates, and testacea. Amoebae ranged from 1,000-5,000/g of material, and were two orders of magnitude more abundant than ciliates. Both groups increased in abundance and species richness from bare soils through spinifex to mulga to chenopod vegetations. Testacea ranged 900-5,000/g with similar species richness throughout vegetations, but reached 11,900/g with a doubling of species in a refugium in Kings Canyon. The most prevalent species of amoebae, ciliates, and testacea were taxa associated with ephemeral and disturbed habitats (r-selection). The cyanobacterial crust might be considered a micro-refugium because it contained a number of non-encysting protozoa, including Thecamoeba sp. and Nassula picta, feeding on cyanobacterial filaments. The numbers and species richness of protozoa under shrubs were greater than in bare soils, supporting the resource island hypothesis that desert plants create soil heterogeneity by localizing soil fertility under their canopies.     

Annual Abundances, Diversity and Growth Potential of Gymnamoebae in a Shallow Freshwater Pond

ABSTRACT. Abundance and diversity of gymnamoebae were assessed at monthly intervals for one year in the sediment surface layer of a shallow, highly productive, freshwater pond located in northeastern United States using laboratory culture enumeration techniques. The range in total abundance was 81/ml in January to 1,568/ml in June (spring peak) and 1,813/ml in October (autumn peak). The latter is equivalent to over 1.8 million per liter, one of the highest values reported for gymnamoebae from a freshwater pond. Maximum diversity (H = 3.3) occurred in April, July, and August. The growth potential of the gymnamoebae was determined in laboratory cultures (20° C) containing only the pond water (control culture) and pond water emended with malt-yeast extract and glucose (nutrient culture) using pond water collected in December. The total abundance of gymanmoebae increased from 363/ml in the initial pond water sample to approximately 1,800/ml in each of the culture conditions in the first week. Therafter, abundances reached 5,678/ml (control culture) and 8,016/ml (nutrient culture) by the third week indicating the vigorous growth potential from winter standing stock.     

The density and diversity of gymnamoebae associated with terrestrial moss communities (Bryophyta: Bryopsida) in a northeastern U.S. forest

Moss communities are commonly found in temperate forests and form a nearly continuous understory in some high latitude forests. However, little is known about the microbial component of these communities, especially the non-testate amoeboid protists. Fifty morphospecies of naked amoebae were identified in samples collected at eight sites in a northeastern North American forest. The mean number (+/-SE) of morphospecies found per sample site based on laboratory cultures was 17+/-2.1. The density of amoebae expressed as number/g dry weight of moss ranged from 3.5+/-0.04 x 10(3) to 4.3+/-0.2 x 10(4) and was positively correlated with the moss moisture content (r=0.9, P<0.001, df=26). Densities of gymnamoebae in the moss are generally higher than found in the surrounding soil, but this may be due in part to the greater weight of soil per unit volume compared with moss. The percentage of encysted forms was inversely related to the moisture content of the moss sample.     

根结线虫病土引入秸秆碳源对土壤微生物生物量和原生动物的影响

研究了添加秸秆碳源在连续种植条件下对根结线虫病害严重土壤中微生物生物量和原生动物丰富度的影响. 供试作物为番茄, 设置3个梯度的小麦秸秆添加量\[1N(2.08 g·kg^-1)、2N (4.16 g·kg^-1)和4N(8.32 g·kg^-1)\].结果表明: 添加秸秆碳源对微生物生物量碳、氮和原生动物丰富度具有显著影响,且这种影响呈现为4N>2N>1N>CK.添加秸秆碳源对原生动物群落结构也具有显著影响,各处理鞭毛虫、肉足虫和纤毛虫的平均比例分别为36.0%、59.5%和4.5%.在相同秸秆添加量下,土壤微生物量碳氮、微生物碳氮比和原生动物丰富度随种植年限的延长而提高.     

Distributions and Biomass of Benthic Ciliates,Foraminifera and Amoeboid Protists in Marine,Brackish, and Freshwater Sediments

The quantitative importance of ciliates, foraminifers, and amoebae was investigated in marine, brackish, and freshwater sediments from 15 littoral stations. Total protozoan communities were usually dominated by ciliates in term of abundance, while amoebae often dominated in terms of biomass. Applying the biomass‐metabolic rate equation, ciliates, amoebae, and foraminifera were estimated to contribute 66% of the total abundance and 33% of the biomass, but up to 55% of the combined metabolic rate to the micro‐ and meiobenthos in the 15 sediments. Statistical analyses using ciliate data demonstrated: (1) species composition and community structures represented significant differences between freshwater and marine/brackish sediments, and subsequently between temperate and arctic sampling sites; (2) the occurrence of dominant ciliates and their allocation to feeding types indicated that herbivory was the most common feeding strategy in these sediments; (3) multivariate analyses showed all of the tested environmental factors (temperature, salinity, silt/clay, carbon, nitrogen, and chlorophyll a) to be important to varying degrees, but especially the combination of salinity, temperature, and silt/clay. Multiple factor effects or comprehensive influences might be important in regulating the distribution of protozoa in sediments. The importance of protozoa in sediment systems and the potential ecological significance of cysts are discussed.     

三种林下土壤浅剖面有机碳含量研究

对大连棒棰岛丘陵山地橡树、松树和灌木林春季和秋季土壤浅剖面有机碳含量和水含量测定与分析,结果表明,不同植物过程土壤碳含量和水含量有明显差异,松树林土壤碳含量和水含量总体上高于橡树和灌木林土壤,碳含量和水含量分布规律基本一致。相同植物过程土壤碳含量和水含量层次间有显著差异,有机碳含量和水含量分布又随土壤深度加深而呈下降趋势。相同植物过程秋季土壤含碳量和含水量高于春季土壤。     

Colonisation and succession of marine biofilm-dwelling ciliate assemblages on biocidal antifouling and fouling-release coatings in temperate Australia

Ciliate assemblages are often overlooked, but ubiquitous components of microbial biofilms which require a better understanding. Ciliate, diatom and bacterial colonisation were evaluated on two fouling-release (FR) coatings, viz. Intersleek 970 and Hempasil X3, and two biocidal antifouling (AF) coatings, viz. Intersmooth 360 and Interspeed 5640, in Port Phillip Bay, Australia. A total of 15 genera were identified during the 10 week deployment. Intersleek 970 displayed the most rapid fouling by ciliates, reaching 63.3(± 5.9) cells cm^?2. After 10 weeks, all four coatings were extensively fouled. However, the toxicity of the AF coatings still significantly inhibited microbial fouling compared to the FR coatings. On all treatments, colonies of sessile peritrichs dominated the ciliate assemblage in the early stage of succession, but as the biofilm matured, vagile ciliates exerted more influence on the assemblage structure. The AF coatings showed selective toxic effects, causing significant differences in the ciliate species assemblages among the treatments.     

冻融期去根处理对小兴安岭6种林型土壤微生物量的影响

春季冻融期,在小兴安岭的阔叶红松(Pinus koraiensis)林、谷地云冷杉(Picea koraiensis-Abies nephrolepis)林、阔叶红松择伐林、白桦(Betula platyphylla)次生林、红松人工林、兴安落叶松(Larix gmelinii)人工林的去根处理样地和对照样地进行野外取土实验,分析了根去除对上述林型土壤微生物量的影响以及与土壤环境因子的关系。结果表明:冻融循环期间对照样地和去根处理样地的林型、土壤层次、取样时间均显著地影响土壤微生物量碳(MBC)(P0.05),对照样地中各林型的土壤微生物量氮(MBN)差异显著,而去根处理样地中各林型的MBN没有显著差异(P0.05);冻融循环期间去根处理显著地减少了大部分林型及土层(谷地云冷杉林0—10 cm及择伐林外)的MBC,而去根处理对大部分林型及土层(阔叶红松林0—10 cm,谷地云冷杉林和择伐林的10—20 cm除外)的MBN没有显著影响。说明在小兴安岭春季冻融期根系对土壤微生物量的影响不可忽视。     

Shrimp ponds lead to massive loss of soil carbon and greenhouse gas emissions in northeastern Brazilian mangroves

Mangroves of the semiarid Caatinga region of northeastern Brazil are being rapidly converted to shrimp pond aquaculture. To determine ecosystem carbon stocks and potential greenhouse gas emissions from this widespread land use, we measured carbon stocks of eight mangrove forests and three shrimp ponds in the Acaraú and Jaguaribe watersheds in Ceará state, Brazil. The shrimp ponds were paired with adjacent intact mangroves to ascertain carbon losses and potential emissions from land conversion. The mean total ecosystem carbon stock of mangroves in this semiarid tropical landscape was 413 ± 94 Mg C/ha. There were highly significant differences in the ecosystem carbon stocks between the two sampled estuaries suggesting caution when extrapolating carbon stock across different estuaries even in the same landscape. Conversion of mangroves to shrimp ponds resulted in losses of 58%–82% of the ecosystem carbon stocks. The mean potential emissions arising from mangrove conversion to shrimp ponds was 1,390 Mg CO₂e/ha. Carbon losses were largely from soils which accounted for 81% of the total emission. Losses from soils >100 cm in depth accounted for 33% of the total ecosystem carbon loss. Soil carbon losses from shrimp pond conversion are equivalent to about 182 years of soil carbon accumulation. Losses from mangrove conversion are about 10‐fold greater than emissions from conversion of upland tropical dry forest in the Brazilian Caatinga underscoring the potential value for their inclusion in climate change mitigation activities.     

Trophic coupling of the microbial and the classical food web in Lake Baikal,Siberia

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不同植茶年限土壤团聚体及其有机碳分布特征

作为土壤结构的基本单元和土壤肥力的重要组成部分,土壤团聚体对土壤的物理、化学和生物特性均有重要影响。试验选取了雅安市名山区中峰乡生态茶园区12—15a、20—22a、30—33a和50a的茶园,研究其土壤团聚体及其有机碳总量、储量和活性组分的分布特征,探究植茶年限对土壤团聚体及其有机碳分布的影响。结果表明:(1)研究区土壤以2 mm粒级团聚体为主,约为70%—80%,且在0—20 cm土层植茶20—22a土壤团聚体含量最高;(2)茶园土壤团聚体有机碳含量随团聚体粒级的减小而增加,最大值出现在0.25 mm粒级团聚体,且在植茶50a时达最高值,0—20 cm土层团聚体有机碳含量均高于20—40 cm,土壤团聚体水溶性有机碳和微生物生物量碳随植茶年限的延长呈先增加后降低的变化趋势,植茶30—33a时含量最高,且小粒级团聚体水溶性有机碳含量较高而微生物量碳较低;(3)土壤团聚体对有机碳的贡献率约有70%来自2 mm粒级团聚体,团聚体有机碳储量随植茶年限延长呈增加的趋势,不同植茶年限0—20 cm土层各粒级团聚体有机碳储量均高于20—40 cm土层,且以0.25 mm粒级团聚体有机碳储量最高。研究结果在一定程度上揭示了不同植茶年限土壤团聚体及其有机碳的分布特征,可为改善区域土壤质量及实施退耕还茶工程提供理论指导。     

Trophic coupling within the microbial food web: a study with fine temporal resolution in a eutrophic freshwater ecosystem

• 1 The major components of the microbial food web (dissolved organic carbon, bacteria, protozoa, rotifers and algae) of Priest Pot, a small freshwater pond, were investigated over a period of 5 months. Water samples were collected from the epilimnion every 1–3 days.
• 2 Time series analysis helped identify the trophic relationships within the planktonic community. There were strong predator—prey relationships between both ciliates and large rotifers and the total nanoplankton, between rotifers and small ciliates and between the total microzooplankton community and phytoplankton. Small rotifers and small ciliates probably share the same food resources. The major bacterivores in the system could not be identified with our methods. However, our previous results point to a dominating role of nanoplanktonic (2–20 μm) heterotrophic protists as the main grazers of bacteria.
• 3 Rotifers are the major type of metazoan zooplankton in Priest Pot; crustacean zooplankton are absent from the community. Bacterial production probably reaches rotifers via a variety of pathways: there may be a three-step link from bacteria to bacterivorous nanoplankton, to ciliates and then to rotifers. Furthermore, a strong correlation between the nanoplankton and rotifers suggests a direct link between these components, implying a much shorter pathway. Some of the rotifers in the pond can graze directly on bacteria, and many of the larger planktonic organisms (large ciliates and rotifers) are algivores. The latter two predator—prey relationships suggest an efficient transfer of bacterial and primary production to higher trophic levels.

     

川西亚高山云杉人工林恢复过程中表层土壤碳动态变化

对川西亚高山云杉原始林及其皆伐迹地上云杉人工林不同演替阶段（22、47和65年）表层（0～30 cm）土壤碳储量及活性有机碳含量进行了分析.结果表明：在0～10、10～20和20～30 cm土层中,土壤总有机碳（TOC）储量分别由22年生云杉人工林的9587、7908和71.55 t·hm^-2减少到65年生云杉人工林的56.12、34.75和31.06 t·hm^-2,且47和65年生云杉人工林各层土壤TOC储量小于原始林（88.08、71.16和64.81 t·hm^-2）;各层土壤易氧化有机碳（EOC）含量分别由原始林的3589、26.91和26.00 g·kg^-1 减少到65年生云杉人工林的20.25、14.50和12.36 g·kg^-1,土壤微生物生物量碳（MBC）含量由原始林的524.44、273.26和257.97 mg·kg^-1减少到65年生云杉人工林的 312.41、186.95和152.18 mg·kg^-1,颗粒态有机碳（POC）含量由原始林的40.23、27.10和19.55 g·kg^-1减少到65年生云杉人工林的12.33、7.31和5.32 g·kg^-1.川西亚高山云杉原始林在转变为人工林后相当长的时间内,土壤有机碳及活性碳一直处于净消耗状态.     

The effects of predation by planktivorous juvenile fish on the microbial food web

The feeding impact of planktivorous fish on microbial organisms is still poorly understood. We followed the seasonal dynamics of the food web in two natural fishponds for two years: one was stocked with planktivorous whitefish while the other had no planktivorous fish. The aim of the study was the simultaneous assessment of the feeding behaviours of planktivorous fish and of bacterivorous meta-/protozooplankters. We hypothesized that in the presence of planktivorous fish there would be fewer metazooplankton, more protozoans and decreased numbers of bacteria. Our results showed that the amount of metazooplankton eaten by the fish was indeed negatively correlated with metazooplankton biomass. The feeding impact of planktivorous fish in shaping the microbial loop was remarkable. The main grazers of bacteria in the fishpond were ciliates, whereas in the pond without fish these were heterotrophic nanoflagellates. In the fishless pond the role of the top predator shifted to the predaceous metazooplankter Leptodora kindtii which controlled the abundance of herbivorous metazooplankters. We found a negative relationship between the number of bacteria and flagellates in the fishless pond, while the number of bacterivorous ciliates was suppressed by predaceous ciliates. Therefore the bacteria-grazing activity was higher in the absence of planktivorous fish.     

轮虫培育池生态系统各有机碳库储量及其日变化

2001年5～6月对辽宁省盘锦光合水产有限公司的两种模式轮虫培育池有机碳库储量及动态进行了研究.结果表明,静水池溶解有机碳（DOC）和颗粒有机碳（POC）库储量平均值分别为5.69±2.90 mg·L^-1和24.56 ± 2.12 mg·L^-1;流水池DOC和POC分别为9.61±3.17 mg·L^-1和24.13 ±2.91 mg·L^-1.流水池和静水池TOC、DOC和POC的比例分别为 1∶0.75∶0.25和1∶0.82∶0.18.POC含量高的池塘DOC含量也较高.流水池的POC、DOC周日变动幅度大,静水池昼夜变动幅度小.流水池POC含量白天(5:00～17:00)升高,静水池降低,夜间(15:00～23:00)两池POC含量均降低.从23:00至次日5:00上升,两池分别在17:00和5:00达到高峰.白天(5:00～17:00) 流水池DOC/POC升高,静水池降低;夜间(17:00～23:00)两池均上升,23:00 至次日5:00则呈下降趋势.     

土地利用方式转变对赣中地区土壤活性有机碳的影响

选取江西省安福县15年撂荒地和3种林地(毛竹林人工林、木荷次生林、杉木人工林),研究土地利用方式改变对土壤有机碳库以及活性有机碳的影响.结果表明：不同样地的土壤总有机碳、微生物生物量碳、热水浸提有机碳和易氧化态碳均表现为毛竹人工林>杉木人工林>木荷次生林>撂荒地;与对照(撂荒地)相比,3种林地的土壤有机碳含量、碳储量及活性有机碳含量均随土壤深度增加而递减,表层富集现象明显;不同土壤活性有机碳的分配比例明显不同,其中,土壤易氧化态碳占总有机碳的比例最大,微生物生物量碳所占比例最小,土壤总有机碳、微生物生物量碳、热水浸提有机碳和易氧化态碳间的相关性均达到极显著水平.后三者表征了土壤中活性较高部分碳的含量,对土地利用方式的响应较敏感,可以作为评价赣中地区土壤质量和肥力的指标之一.