Local distribution of native and invasive earthworms and effects on a native salamander

North America is home to both native and invasive earthworms acting as ecosystem engineers as they build burrows that can serve as habitat for other species or otherwise alter soil structure, affecting nutrient cycling and other ecosystem processes. Here I determine where and what earthworm species commonly occur in my study area, and compare effects of native and invasive earthworms on the common woodland salamander, Plethodon cinereus, in field surveys and laboratory experiments. The native earthworm Eisenoides carolinensis was the most common earthworm, followed by two invasive species Dendrobaena octaedra and Octolasion tyrtaeum. The presence of O. tyrtaeum was associated with a narrower O-horizon (i.e., organic layer in the soil). Using structural equation modeling to explore direct and indirect pathways of these three most common earthworm species on salamanders, I found O. tyrtaeum occurrence was negatively correlated with nighttime salamander counts, a proxy for total salamander numbers, mediated by negative effects on O-horizon depth and microinvertebrate numbers. In the laboratory, O. tyrtaeum and D. octaedra consumed more leaf litter per gram of earthworm per day than the native E. carolinensis. However, salamanders consumed earthworms and used burrows of all native and invasive species of earthworms similarly. The potential for negative indirect effects of the invasive earthworm O. tyrtaeum on P. cinereus was demonstrated both in the field and laboratory, highlighting that seemingly small differences between native and invasive ecosystem engineers have the potential to significantly alter the effects of these closely related native and invasive organisms.     

Nitrogenous Compounds and Nitrogen Metabolism in the Liliaceae: II. The Nitrogenous Compounds of Leaves of the Genus Tulipa: Environmental Effects on the Composition of Tulipa gesneriana

Because of the predominance of -methyleneglutamine in Tulipagesneriana a quantitative, chromatographic investigation hasbeen made to show the factors which determine the compositionof the alcohol-soluble nitrogen fraction in Tulipa A comparative study of the amino-acids that occur free in theleaves of fourteen different species of Tulipa has been made,-methyleneglutamine varied from as much as 60–70 per cent,of the amino-acid nitrogen down to levels below those whichpermit its chromatographic detection. The effects of temperature during growth and of diurnal variationon the nitrogenous compounds of the leaves of T. getnerianaare described. Excised shoots of T. gesneriana were exposed to light and darknessto affect the balance of protein synthesis and breakdown sothat the concomitant effects on the -methyleneglutamine acidcompounds and other main components of the soluble nitrogenfraction could be determined. Lastly, the relative ease of entry of C¹⁴ from C¹⁴O₂ into thesugars and certain other compounds of T. gesneriana is contrastedwith the relative difficulty with which it enters the -methyleneglutamineof the mature leaves on excised shoots. The occurrence and metabolism of -methyleneglutamine in T. gesnerianaleaves may, therefore, be regarded as additional to and superimposedupon an otherwise typical pattern of nitrogen metabolism: inthese leaves -methylene-glutamine does not assume the role usuallydischarged by glutamine.     

Glycogen-lead relationship in the earthworm Dendrobaena rubida from a heavy metal site

Summary Control individuals contained no lead in the chloragocytes but high -glycogen rosette reserves. Starvation of contaminated earthworms for 4d caused a lead loss and the chloragocytes possessed fewer debris vesicles than those of unstarved worms, suggesting that the debris vesicles may be the route for at least some of the lead loss. No glycogen deposits were observed in the chloragocytes of starved or unstarved earthworms from contaminated soil. Maintenance of contaminated earthworms in potting compost caused lead losses similar to those sustained by starvation, but the chloragocyte cytoplasm possessed -glycogen reserves. Specimens maintained in lead-spiked potting compost showed lead levels similar to those of earthworms taken directly from contaminated soil. No -glycogen accumulations were observed under this enriched regime.Although the possible interference of lead in carbohydrate metabolism is discussed, the results do not wholly support metabolic inhibition by lead. It is hypothesised that lead sequestration is energy-demanding and that in the absence of an energy-rich diet glycogen stores fail to accumulate. In the presence of an organic-rich medium, elevated lead levels preclude glycogen formation, because of the high sequestration-demand, but at lower lead levels -glycogen deposits occur if a high organic diet is available.     

Changes in the Levels of Free Amino Acids in Various Regions of Cuscuta during Growth

The angiospermous plant parasite Cuscuta derives reduced carbonand nitrogen compounds primarily from its host. Free amino acidsalong Cuscuta vines in three zones, viz., 0 to 5 cm, 5 to 15cm, and 15 to 30 cm, which in a broad sense represent the regionof cell division, cell elongation and differentiation and vasculartissue differentiation respectively, were quantitatively estimated.The free amino acid content was the highest in the 0 to 5 cmregion and progressively decreased along the posterior regionsof the vine. The haustorial region showed the lowest contentof free amino acids. In general, the free amino acid contentin samples collected at 7 p.m. was found to be higher than thatin the samples collected at 7 a.m. Three basic amino acids,histidine, the uncommon amino acid -hydroxyarginine, and arginineconstituted more than 50% of the total free amino acids in allthe zones studied except the haustorial region. Aspartic acidand glutamic acid constituted the major portion in the acidicand neutral fraction of amino acids. Glutamine, asparagine,threonine, and serine were eluted together and occurred in substantialamounts. -Hydroxyarginine constituted the largest fraction inthe cut end exudate of Cuscuta and presumably appeared to bethe major form of transport amino acid. -Hydroxyarginine wasalso a major constituent of the basic amino acids in Cuscutavines parasitizing host plants from widely separated families,suggesting that this amino acid is a biosynthetic product ofthe parasite rather than that of the hosts. Also, U-¹⁴C argininewas converted to -hydroxyarginine by cut Cuscuta vines, suggestingthat -hydroxyarginine is synthesized de novo from arginine byCuscuta. (Received March 30, 1987; Accepted June 7, 1988)     

Local-scale correlates of native and non-native earthworm distributions in juniper-encroached tallgrass prairie

European and Asian earthworms have invaded much of North America with profound impacts to soils, plant communities, and animal populations. However, few studies have assessed local-scale correlates of earthworm distributions, and most invasive earthworm research has occurred in northern forests. Additionally, despite several studies showing facilitative relationships between invasive earthworms and invasive plants, no research has assessed a potential facilitative interaction between earthworms and woody plants encroaching into prairies. We conducted the first assessment of factors influencing local-scale distributions of native and non-native earthworms for the U.S. Great Plains in a tallgrass prairie-woodland mosaic experiencing eastern redcedar (Juniperus virginiana) encroachment. We documented both native and non-native earthworms, including non-native species from Eurasia (Aporrectodea spp.) and South America (Family Ocnerodrilidae). Native and non-native earthworm distributions were strongly correlated, yet local-scale predictors of distribution also differed between the groups. Native earthworms were more likely to occur near roads and in areas with moist soils. Contrary to expectation, we found no evidence that non-native earthworms occurred more frequently in areas with eastern redcedar-encroachment; instead, non-native earthworms were most likely to occur in tallgrass prairie. Our results suggest that, within prairies and woodlands of the Great Plains, native and non-native earthworms occur most frequently near roadways and in locations with moist soil. Because the few approaches for controlling invasive earthworms are only likely to be feasible on a small scale, findings from such local-scale studies are important for directing management to reduce earthworm impacts on biodiversity and ecosystem services.     

A comparative study of gut microbiota profiles of earthworms fed in three different substrates

The gut microbiome of earthworms has a complex interdependence with the host. When the soil minerals pass through earthworm’s gut, they may affect the gut microbiota. To gain insight into the response of gut microbiota to the passed minerals, we fed earthworm (Eisenia fetida) on nutrient-poor soil and ore powder, and used high throughput sequencing to characterize the earthworm intestinal microbial community to find evidence for a core bacterial community of the E. fetida. The results showed that earthworms’ gut maintained a core microbiome that appeared in all samples. These core microbiota may play a significant role in a species’ environmental interactions. The composition of intestinal microbiomes varied with substrates. The earthworm guts from two nutrient-poor substrates had similar microbial communities and they were different from nutrient-rich substrate. Proteobacteria and Bacteroidetes were more abundant in the gut of earthworms kept on a nutrient-poor substrate such as ore powder or mineral soil than in the gut of earthworms kept in organic-rich compost soil; some of these microorganisms may help earthworms survive in nutrient-poor substrates.     

The Enzymic Decarboxylation of {gamma}-methyleneglutamic Acid by Plant Extracts

-Methyleneglutamic acid, an acidic amino-acid isolated fromgroundnut plants, was decarboxylated by enzymes present in extractsof Capsicum fruits, barley roots, and tulip leaves, and alsoby intact cells of Clostridium welchii S.R. I2. The amino-acidwas attacked in a similar manner to, but in all cases at a slowerrate than, l-glutamic acid. The nature of the enzyme responsiblefor the decarboxylation of -methyleneglutamic acid was furtherinvestigated using preparations from barley roots (which donot contain the amino-acid) and from tulip leaves (in whichthe amino-acid is normally present, together with larger amountsof its amide form, -methyleneglutamine). The effects of pH,inhibitors, and partial heat denaturation upon the enzyme systemspresent in the barley and tulip extracts indicated that a singleenzyme was responsible for the decarboxylation of both l-glutamicacid and -methyleneglutamic acid. Although the Cl. welchii rapidlydeamidated and then decarboxylated l-glutamine, -methyleneglutaminewas not attacked by the organism.     

{gamma}-Amiobutyric Acid Metabolism in Plants: Part 1. Metabolism in Yeasts

The metabolism of -aminobutyric acid (AB) by two yeasts, Saccharomycescerevisiae and Torulopsis utilis, was investigated. Both yeastsgrew well upon AB as a sole source of nitrogen (N), and thelag phase for Torulopsis was shorter than when provided the N-source. The metabolism of AB by Torulopsis, whichwas associated with an increased O₂ uptake, was adaptive incharacter. The enzyme whose formation was induced by the supplyof AB was a transaminase, which was apparently specific forAB as the amino donor. Small amounts of transaminase were presentin unadapted, -grown cells. The optimum pH, equilibrium constant, Michaelis' constant, and coenzyme requirementwere investigated for the transamination reaction involving-ketoglutaric acid (KG) as amino group acceptor. Succinic semi-aldehyde(SSA) was a product of this transamination reaction.The possibility;that some AB was converted into SSA by a direct oxidative deaminationremained unconfirmed. The further conversion of SSA into succinic acid was establishedusing intact. cells for both yeasts. This oxidation processwas shown to be linked to the reduction of pyridine nucleotidesvising extracts of Saccharomyces as a source of SSA dehydrogenase.Dehydrogenase activity could be ascribed to two separate enzymes,one linked to DPN, and the other utilizing TPN and requiringMg⁺⁺ as an activator. The properties of the former enzyme, whichwas more important quantitatively, were investigated and comparedwith those described in the literature for an aldehyde dehydrogenaseof baker's yeast and for SSA dehydro-genases of Pseudomonas.Torulopsis extracts could catalyse the reduction of SSA to -hydroxybutyricacid (OHB); the OHB dehydrogenase involved required TPNH asa coenzyme. Certain other properties of this enzyme are recorded. The possibility is discussed that AB and SSA act as intermediatesin a metabolic pathway that may form a by-pass of the KG-succinatestage of the tricarboxylic acid cycle.     

Studies on the Growth of Basidiomycetes in Soil

Fructifications of basidiomycetes have been collected at LakenheathWarren, and thirty-nine species have been obtained from fivegrassland soils. The different soils have been found to havedifferent species growing upon them and most species occur onthe alkaline-slightly acid grasslands. Highly acid grasslandat Lakenheath has a poor fungus flora. Studies have been made of the regions in the soil in which themycelia of certain of these basidiomycetes occur, and attemptshave been made to isolate these fungi from soil. Some specieshave been found to inhabit the litter zone rather than the minerallayers of the soil. A few form extensive rhizomorph systemswhich may penetrate deeply into the soil. A few species of ringfungi, such as Marasmius oreades, Psalliota arvensis, and Tricholomanudum, have been found to possess a well-defined mycelial zonein the soil, from which the fungus could be isolated. Profile studies have shown that the mycelial zones of thesespecies contain a restricted population of microfungi, bothfewer species and fewer colonies, as compared with the normalsoil around. Ascomycetes, such as Arachniotus, Chaetomium, Gymnoascus,and Penicillium, have been isolated more frequently from mycelialzones than from normal soil.     

Winter hatching in New England populations of invasive pheretimoid earthworms <Emphasis Type="Italic">Amynthas agrestis</Emphasis> and <Emphasis Type="Italic">Amynthas tokioensis</Emphasis>: a limit on population growth,or aid in peripheral expansion?

Some Asian megascolecid earthworms, e.g. Amynthas agrestis and Amynthas tokioensis, are highly invasive and have only recently been reported from natural ecosystems in the northeastern USA. There, they are annual earthworms that survive the winter as cocoons (an egg in a tough covering). Hatching occurs in mid-April when temperatures rise consistently above 10 °C. In some years, winter temperatures also reach 10 °C during short warming episodes, but hatchlings then are likely to die when temperatures drop again. To test this hypothesis, soil was collected on 7 sampling dates during January–May 2016 at one site in the Champlain Valley, Vermont and extracted for the cocoons. Both hatched and unhatched cocoons were enumerated and identified to species by both size and sequencing of the mitochondrial cytochrome c oxidase I gene (COI). A regression model on the number of unhatched cocoons over time predicted that ~ a quarter (A. agrestis) and ~ a third (A. tokioensis) would hatch before mid-May; no hatchlings were observed. Thus, hatching during warming periods in winter seemingly resulted in high mortality. Such winter hatching, and loss, may increase with climate warming in the region because winter warming periods should become more common. Climate warming could therefore reduce ability of the invasive earthworms to persist in northern habitats. Conversely, rapid hatching when the soil warms in spring could have an ecological benefit by allowing opportunities to expand at the thermal edge of the range as the climate continues to warm.     

Radiomimetic Effect of Cisplatin on Cucumber Root Development: the Relationship between Cell Division and Cell Growth

Cisplatin [DDP, cis-dichlorodiammine platinum (II)], a strongcytostatic and antineoplastic agent, was tested on seedlingsof cucumber Cucumis sativus L. for its general effect on rootdevelopment and its particular effects on root cell divisionand cell growth. DDP was characterized as a radiomimetic compoundsince both DDP (1·3 x 10^-5 M) and -irradiation (2·5-10kGy) drastically and irreversibly stopped development of embryoniclateral root primordia (LRPs) in the radicle by inhibiting bothmitotic activity and cell growth. In 20% of the LRPs of DDP-treatedroots, cells did not divide at all. Dividing cells completedno more than two cell cycles. These effects were specific becausewhen DDP was available to the roots only at the onset of celldivision, cell proliferation and cell growth were similar tothat produced by constant incubation. Neither DDP nor -irradiationaffected non-meristematic cell elongation. It was concludedthat cell growth of meristematic cells is closely related tocell division. However, non-meristematic cell growth is independentof DNA damage. This suggests DDP as a tool to reveal these autonomousprocesses in plants development and to detect tissue compartmentsin mature plant embryos which contain potentially non-meristematiccells.Copyright 1993, 1999 Academic Press Cucumis sativus, cucumber, cisplatin, cell growth, cell elongation, cell division, lateral root, root development     

Production of multiple cytokines by clones of human large granular lymphocytes

Summary LGL in addition to mediating natural killer (NK) activity, can secrete a variety of lymphokines, depending on the stimulus used: interleukin-1 (IL-1), interleukin-2 (IL-2), interferon and (IFN), and B-cell growth factor (BCGF). To define more directly whether cells with NK activity can also secrete one or more cytokines, we obtained clones by limiting dilution assays from highly purified preparations of human LGL and cultured them in IL-2-containing medium for several weeks. All the clones tested spontaneously produced detectable levels of IFN- and 35 of 40 clones (87%) produced higher levels when stimulated with PHA. A smaller proportion (16%) of clones (9 of 54) secreted IL-1 after stimulation with LPS, while 34% of the clones (17 of 49) produced IL-2 in response to PHA stimulation. Cytokine production was associated with both cytotoxic and noncytotoxic clones and did not correlate with their surface phenotype, as has been observed for fresh LGL. The ability to produce IL-1 or IL-2 was not usually found within the same clones following PHA and LPS stimulation, respectively; however two clones produced both IL-1 and IL-2 when stimulated in different experiments, but not at the same time. In addition, two of nine cloned LGL simultaneously produced IFN and IL-1. These results indicate that LGL-derived clones have the ability to produce multiple cytokines, suggesting that the LGL population may play an important immunoregulatory role and may also be capable of self-regulation of cytolytic activity.Abbreviations NK natural killer - LGL large granular lymphocytes - IL-2 interleukin 2 - IFN interferon - IL-1 interleukin 1 - BCGF B-cell growth factor - ADCC antibody-dependent cellular cytotoxicity - PHA phytohemagglutinin A - LPS lipopolysaccharide - FBS fetal bovine serum - MoAb monoclonal antibody - Staph A Staphylococcus aureus protein A - FcR receptor for the Fc portion of Ig     

绿盲蝽和中黑盲蝽对不同抗性和虫害处理棉花的选择趋性

研究绿盲蝽Apolygus lucorum和中黑盲蝽Adelphocoris suturalis对不同抗性和虫害处理棉花的选择趋性,为棉盲蝽的综合治理提供理论依据。本研究以抗性棉花品种BR-S-10（抗性品种）和感性棉花品种科林08-15（感性品种）,以及绿盲蝽和中黑盲蝽分别危害处理后的该两种棉花植株为试验材料,以纯净空气为空白对照,共成对设置15个气味源组合,采用“Y”型昆虫嗅觉仪室内研究了绿盲蝽和中黑盲蝽对不同抗性和虫害处理棉花的选择趋性。结果表明,绿盲蝽显著选择感性品种、中黑盲蝽危害感性品种和绿盲蝽危害感性品种。中黑盲蝽显著选择绿盲蝽危害感性品种、中黑盲蝽危害感性品种和感性品种。总的来说,两种棉盲蝽趋向于选择敏感棉花品种,抗性棉花品种对供试昆虫有显著趋避性;绿盲蝽显著趋向选择中黑盲蝽危害感性品种和绿盲蝽危害感性品种,中黑盲蝽显著趋向选择绿盲蝽危害感性品种和中黑盲蝽危害感性品种。     

Impact of sarcoglycan complex on mechanical signal transduction in murine skeletal muscle

Loss of the dystrophin glycoprotein complex (DGC) or a subset of its components can lead to muscular dystrophy. However, the patterns of symptoms differ depending on which proteins are affected. Absence of dystrophin leads to loss of the entire DGC and is associated with susceptibility to contractile injury. In contrast, muscles lacking -sarcoglycan (-SG) display little mechanical fragility and still develop severe pathology. Animals lacking dystrophin or -SG were used to identify DGC components critical for sensing dynamic mechanical load. Extensor digitorum longus muscles from 7-wk-old normal (C57), dystrophin- null (mdx), and -SG-null (gsg^–/–) mice were subjected to a series of eccentric contractions, after which ERK1/2 phosphorylation levels were determined. At rest, both dystrophic strains had significantly higher ERK1 phosphorylation, and gsg^–/– muscle also had heightened ERK2 phosphorylation compared with wild-type controls. Eccentric contractions produced a significant and transient increase in ERK1/2 phosphorylation in normal muscle, whereas the mdx strain displayed no significant proportional change of ERK1/2 phosphorylation after eccentric contraction. Muscles from gsg^–/– mice had no significant increase in ERK1 phosphorylation; however, ERK2 phosphorylation was more robust than in C57 controls. The reduction in mechanically induced ERK1 phosphorylation in gsg^–/– muscle was not dependent on age or severity of phenotype, because muscle from both young and old (age 20 wk) animals exhibited a reduced response. Immunoprecipitation experiments revealed that -SG was phosphorylated in normal muscle after eccentric contractions, indicating that members of the DGC are modified in response to mechanical perturbation. This study provides evidence that the SGs are involved in the transduction of mechanical information in skeletal muscle, potentially unique from the entire DGC. muscular dystrophy; eccentric contractions; extracellular signal-regulated kinase 1/2     

Liquid-Tissue Mechanics in Amphibian Gastrulation: Germ-Layer Assembly in Rana Pipiens

During amphibian gastrulation, migrating subsurface germ layersmay flow past one another like immiscible viscous liquids inresponse to tissue surface tension forces. We describe heretwo physical tests for liquid-tissue morphogenesis in culturedaggregates of subsurface ectoderm (E), mesoderm (M) and endoderm(N) excised from mid-yolk-plug Rana pipiens gastrulae. (i) Liquidsare coherent substances in which subunits can slip past oneanother to relax internal shear stresses. We find, in cross-sectionsof cell aggregates fixed during compression, that cells withinflattened aggregates are intially deformed, but do, as predicted,gradually reassume their original, undistorted shapes, (ii)Surface tensions ('s) govern ordinary liquid-droplet spreading;e.g., if equal-sized droplets A and B fuse in medium O, B spreadsaround A when _{AO BO}. When pairs of subsurface aggregates arecultured together, N surrounds M and E, and M surrounds E. Tosee if _EO > _MO > _NO. we flatten aggregates with quartzfibers calibrated to measure the force of compression. As predicted,under the same flattening force, E aggregates are rounder thanM aggregates, which are rounder than N aggregates. Furthermore,a second surface tension relationship can account for the autonomousinvolution of M between E and N; and these surface tension relationshipscan also explain the inversion of E, M and N by coated ectodermto produce normal gastrular germ-layer arrangements. We concludethat, combined with active cell shape changes in solid-likesurface cell layers and also with autonomous elongation of dorsallip mesoderm, tissue surface tension control of liquid-tissueflow in subsurface germ layers is a key morphogenetic mechanismin amphibian gastrulation which might be regulated by changesin intercellular adhesiveness.     

Intragenic Hill-Robertson interference influences selection intensity on synonymous mutations in Drosophila

Natural selection influences synonymous mutations and synonymouscodon usage in many eukaryotes to improve the efficiency oftranslation in highly expressed genes. Recent studies of genecomposition in eukaryotes have shown that codon usage also variesindependently of expression levels, both among genes and atthe intragenic level. Here, we investigate rates of evolution(Ks) and intensity of selection (_s) on synonymous mutationsin two groups of genes that differ greatly in the length oftheir exons, but with equivalent levels of gene expression andrates of crossing-over in Drosophila melanogaster. We estimate_s using patterns of divergence and polymorphism in 50 Drosophilagenes (100 kb of coding sequence) to take into account possiblevariation in mutation trends across the genome, among genesor among codons. We show that genes with long exons exhibithigher Ks and reduced _s compared to genes with short exons.We also show that Ks and _s vary significantly across long exons,with higher Ks and reduced _s in the central region comparedto flanking regions of the same exons, hence indicating thatthe difference between genes with short and long exons can bemostly attributed to the central region of these long exons.Although amino acid composition can also play a significantrole when estimating Ks and _s, our analyses show that the differencesin Ks and _s between genes with short and long exons and acrosslong exons cannot be explained by differences in protein composition.All these results are consistent with the Interference Selection(IS) model that proposes that the Hill-Robertson (HR) effectcaused by many weakly selected mutations has detectable evolutionaryconsequences at the intragenic level in genomes with recombination.Under the IS model, exon size and exon-intron structure influencethe effectiveness of selection, with long exons showing reducedeffectiveness of selection when compared to small exons andthe central region of long exons showing reduced intensity ofselection compared to flanking coding regions. Finally, ourresults further stress the need to consider selection on synonymousmutations and its variation—among and across genes andexons—in studies of protein evolution.     

Localization of the carbon in caffeine biosynthesized from N-methyl carbon of {gamma}-glutamylmethylamide in tea plants

1. Localization of carbon in caffeine molecule biosynthesizedfrom the N-methyl carbon of -glutamylmethylamide in tea plantswas observed. ¹⁴C-Caffeine produced from ¹⁴C--glutamylmethylamidewas isolated and degraded. Approximately 26–55% of the¹⁴C was observed in the three methyl carbons in caffeine, withonly 2–3% at the C-2 carbon, 3–7% at the C-8 carbonposition. The amount of ¹⁴C at the C-4, C-5 and C-6 positionswas calculated from the results obtained. 2. The role of the N-methyl carbon of -glutamylmethylamide inthe formation of RNA in tea plants was examined. Incorporationof the N-methyl-¹⁴C of ¹⁴C--glutamylmethylamide into AMP andGMP in RNA was found. These facts indicate that in tea plants, -glutamylmethylamideis metabolized and most of its N-methyl carbon is utilized asa precursor for caffeine formation and little, if any, as aprecursor for nucleic acid formation. ¹ Present address: Department of Agricultural Chemistry, ShizuokaUniversity, Iwata, Shizuoka 438, Japan. (Received February 2, 1972; )     

A Further Study on Parasitism of the Diatom Fragilaria crotonensis Kitton by Chytridiaceous Fungi in Culture

Further detailed experiments under laboratory conditions havebeen carried out using clones of Fragilaria crotonensis Kitton.Two morphologically distinct types (rod- and flared-cell forms)were investigated in relation to their infection by a chytridreferred to as species 3. The pathogenicity of the chytrid Rhizophydiumfragilariae Canter towards four newly isolated clones of F.crotonensis was also studied. The results in general confirmedthat clones of the diatom composed of flared-type cells werecompatible with the development and increase of species 3 butremained more or less resistant to R. fragilariae. In contrast,rod-celled type clones showed exactly the opposite host parasiterelationships. Further study has shown that slight differencesin susceptibility towards a particular chytrid can occur withindiatom clones of similar morphological type. The presence ofhypersensitive algal cells was noted in relation to parasitismby both fungi. Some observations are recorded on the developmentof mucilage around filaments of the Fragilaria clones. Fragilaria crotonensis Kitton, Rhizophydium fragilariae Canter, chytrid, diatom, culture, parasitism, hypersensitivity, mucilage envelope     

Influence of Earthworm Invasion on Redistribution and Retention of Soil Carbon and Nitrogen in Northern Temperate Forests

We analyzed soil organic matter distribution and soil solution chemistry in plots with and without earthworms at two sugar maple (Acer saccharum)–dominated forests in New York State, USA, with differing land-use histories to assess the influence of earthworm invasion on the retention or loss of soil carbon (C) and nitrogen (N) in northern temperate forests. Our objectives were to assess the influence of exotic earthworm invasion on (a) the amount and depth distribution of soil C and N, (b) soil ¹³C and ¹⁵N, and (c) soil solution chemistry and leaching of C and N in forests with different land-use histories. At a relatively undisturbed forest site (Arnot Forest), earthworms eliminated the thick forest floor, decreased soil C storage in the upper 12 cm by 28%, and reduced soil C:N ratios from 19.2 to 15.3. At a previously cultivated forest site with little forest floor (Tompkins Farm), earthworms did not influence the storage of soil C or N or soil C:N ratios. Earthworms altered the stable isotopic signature of soil at Arnot Forest but not at Tompkins Farm; the alteration of stable isotopes indicated that earthworms significantly increased the loss of forest floor C but not N from the soil profile at Arnot Forest. Nitrate (NO₃^–) concentrations in tension and zero-tension lysimeters were much greater at Tompkins Farm than Arnot Forest, and earthworms increased NO₃^– leaching at Tompkins Farm. The results suggest that the effect of earthworm invasion on the distribution, retention, and solution chemistry of soil C and N in northern temperate forests may depend on the initial quantity and quality of soil organic matter at invaded sites.     

线性和指数回归方法对土壤呼吸CO2扩散速率估算的影响

 理论上,土壤呼吸通量的量值可以通过观测土壤呼吸CO₂扩散速率(&#601;c/&#601;t)计算得到。但是为获得&#601;c/&#601;t,通常须允许土壤呼吸箱内CO₂浓度升高,因此,如何估算外界大气CO₂浓度条件下的&#601;c/&#601;t是土壤呼吸观测技术的关键,关系到观测结果的准确性。通常&#601;c/&#601;t的估算会受土壤表层大气CO₂扩散梯度(即土壤呼吸箱内CO₂扩散梯度和大气CO₂浓度昼夜变化)的影响。目前,线性回归方法是土壤呼吸观测中估算&#601;c/&#601;t的基本方法。然而,常用的线性回 归方法会低估&#601;c/&#601;t,而指数回归方法则可以准确地估算&#601;c/&#601;t。夜间&#601;c/&#601;t的变化与大气CO₂ 浓度之间存在非常明显的负相关关系。夜间土壤表层大气CO₂扩散梯度的减小导致线性回归方法明显低估&#601;c/&#601;t。&#601;c/&#601;t的昼夜变化过程存在明显的非对称性现象,而指数回归方法可以更好地描述&#601;c/&#601;t昼夜变化的非对称性响应。