Effect of eight benthic diatoms as feed on the growth of red abalone (Haliotis rufescens) postlarvae

The growth rate of abalone post larvae of Haliotis rufescens fed ad libitum with a benthic monoalgal diatom culture maintained as monocultures on a semi-commercial scale, was evaluated and correlated with the biochemical composition of the diatoms. The cell size (7.0 × 4.0 μm to 21.0 × 7.5 μm), protein percentage (7.42% to 13.66%), and ash content (49.03% to 59.61%) were different among diatom strains; lipid percentage, nitrogen free extract, and energy content (Kcal g⁻¹) were similar among diatom strains. The values of essential and non-essential amino and fatty acids composition differed among diatom strains. Differences in the abalone shell length and orthogonal analyses revealed postlarval growth was dependent on the quality of the food source. Postlarvae abalone displaying the longest shell lengths were fed Nitzschia thermalis var. minor and Amphiprora paludosa var. hyalina (1,712.0 ± 61 μm and 1,709 ± 67 μm, respectively), followed by Navicula incerta (1,413.3 ± 43 μm). The fatty acid content of benthic diatoms and abalone growth rate were not correlated.     

Isolation and structural characterisation of two antibacterial free fatty acids from the marine diatom, <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

One solution to the global crisis of antibiotic resistance is the discovery of novel antimicrobial compounds for clinical application. Marine organisms are an attractive and, as yet, relatively untapped resource of new natural products. Cell extracts from the marine diatom, Phaeodactylum tricornutum, have antibacterial activity and the fatty acid, eicosapentaenoic acid (EPA), has been identified as one compound responsible for this activity. During the isolation of EPA, it became apparent that the extracts contained further antibacterial compounds. The present study was undertaken to isolate these additional antibacterial factors using silica column chromatography and reverse-phase high-performance liquid chromatography. Two antibacterial fractions, each containing a pure compound, were isolated and their chemical structures were investigated by mass spectrometry and nuclear magnetic resonance spectroscopy. The antibacterial compounds were identified as the monounsaturated fatty acid (9Z)-hexadecenoic acid (palmitoleic acid; C16:1 n-7) and the relatively unusual polyunsaturated fatty acid (6Z, 9Z, 12Z)-hexadecatrienoic acid (HTA; C16:3 n-4). Both are active against Gram-positive bacteria with HTA further inhibitory to the growth of the Gram-negative marine pathogen, Listonella anguillarum. Palmitoleic acid is active at micro-molar concentrations, kills bacteria rapidly, and is highly active against multidrug-resistant Staphylococcus aureus. These free fatty acids warrant further investigation as a new potential therapy for drug-resistant infections.     

Studies on the production of useful chemicals,especially fatty acids in the marine diatom Nitzschia conspicua Grunow

A local marine diatom, Nitzschia conspicua Grunow, was cultured in enriched synthetic seawater using flasks (agitated by magnetic stirring) and a 1.2 l fermenter. Lipids, fatty acids, proteins, carbohydrates and ash of the flask cultures were determined at various stages of growth (day 3, 5, 7, 10, 13, 15 and 17). The fermenter culture was harvested during the stationary phase for similar chemical analyses. N. conspicua attained a higher biomass concentration during the stationary phase when cultured in the fermenter (188 mg dry weight l^–1) than in flasks (140–151 mg dry weight l^–1). However, both systems showed similar specific growth rates based on chlorophyll-a concentration. Appreciable amounts of the essential fatty acids 20:4 (0.6–4.7% total fatty acids) and 20:5 (1.9–4.7% total fatty acids) are present in this diatom. Maximal amounts of these fatty acids were produced after 7 days' growth (i.e. 2 days after the end of the exponential phase). Lipids, fatty acids, proteins, carbohydrates and ash varied with culture age in N. conspicua.author for correspondence     

Biochemical composition of three algal species proposed as food for captive freshwater mussels

To identify potential diets for rearing captive freshwater mussels, the protein, carbohydrate (CHO), and lipid contents of two green algae, Neochloris oleoabundans, Bracteacoccus grandis, and one diatom, Phaeodactylum tricornutum, were compared at different growth stages. The fatty acid and sterol composition were also identified. Protein was greatest (55–70%) for all species at late log growth stage (LL), and declined in late stationary (LS) growth. CHO was greatest at LS stage for all species (33.9–56.4% dry wt). No significant change in lipid levels occurred with growth stage, but tended to increase in N. oleoabundans. Mean lipid content differed significantly in the order: N. oleoabundans > P. tricornutum > B. grandis. Total fatty acids (TFA) were higher at LS stage compared to other stages in the two green algae, and stationary stage in the diatom. Mean unsaturated fatty acids (UFA) as %TFA was significantly higher in N. oleoabundans than the other species. The green algae contained high percentages of C-18 polyunsaturated fatty acids (PUFAs), while the diatom was abundant in C-16 saturated and mono-unsaturated fatty acids and C-20 PUFA fatty acids. Growth stage had no effect on sterol concentration of any species. B. grandis showed significantly higher sterol levels than the other species except P. tricornutum at S stage. B. grandis was characterized by predominantly ⁵, C-29 sterols, while N. oleoabundans synthesized ^5,7, ^5,7,22 , and ⁷, C-28 sterols. P. tricornutum produced primarily a ^5,22, C-28 sterol, and a small amount of a ^7,22, C-28 sterol.     

Host-recognition kairomone from Sogatella furcifera for the parasitoid Anagrus nilaparvatae

A kairomone produced by the rice white-backed planthopper Sogatella furcifera (Horvath) for the mymarid egg parasitoid Anagrus nilaparvatae Pang et Wang was investigated. Eggs, female and male adults, nymphs, exuvia, honeydew, nymph-damaged plants and plants with S. furcifera eggs all elicited searching behavior in the parasitoid. Eggs, female adults and plants with eggs were the most attractive, while exuvia and honeydew evoked the weakest responses. The active compound(s) from S. furcifera female adults, nymphs and plants with eggs could be effectively extracted with methanol, acetone, n-hexane, ethyl ether and dichloromethane. Isolation of the active chemical(s) in three solvent extracts, the acetone and n-hexane extracts of S. furcifera female adults, and the acetone extract of S. furcifera nymphs, was accomplished by thin-layer chromatography. Only one fraction was active and had the same chemical properties in the three solvent extracts. Infra-red analysis of this fraction revealed a kind of ester with saturated and unsaturated fatty acids, which was previously found to be active in the same compound as the extracts from the nymphs and female adults of the rice brown planthopper, Nilaparvata lugens (Stål), and identified as palm oil. The results are discussed in relation to host location by A. nilaparvatae.     

Comparison of fatty acid composition of bacterial and protozoal fractions in rumen fluid of sheep fed diet supplemented with sunflower, rapeseed and linseed oils

The objective of this study was to investigate effects of oil supplements on the composition of fatty acids (FA), especially of trans11-C18:1 (vaccenic acid, TVA) and cis9, trans11-C18:2 conjugated linoleic acid (c9,t11-CLA), in bacterial (BF) and protozoal (PF) fractions of rumen fluid of sheep that was fractionated centrifugation. Four sheep were fed a diet consisting of meadow hay (960 g dry matter (DM)/day) and of barley grain (240 g DM/day), with sunflower oil (SO), rapeseed oil (RO) or linseed oil (LO) as supplements (60 g/day) in a Latin square design. The oils were used as they are rich in linoleic acid (SO, 533 g/kg of FA), oleic acid (RO, 605 g/kg of FA) and α-linolenic acid (LO, 504 g/kg of FA). Compared to the control (i.e., without oils), oil supplements influenced the concentration of unsaturated (UFA) and saturated fatty acids (SFA). In both BF and PF, the main fatty acids were palmitic and stearic, but PF contained a higher proportion of TVA and c9,t11-CLA than BF. In PF, TVA concentrations, ranked by oil supplement, were SO > RO > LO > Control (174, 150, 118, 74 g/kg of FA, respectively) and the c9,t11-CLA concentrations were RO > SO > LO > Control (59, 51, 27 and 15 g/kg of FA, respectively). Concentrations of c9,t11-CLA in PF were two to three times higher than in BF with all the oil supplements versus the control. Oil treatments impacted the c9,t11-CLA concentration in the fractions, especially SO and RO. The protozoal fraction contained a higher proportion of TVA and c9,t11-CLA than did the bacterial fraction, and dietary addition of SO, RO and LO resulted in a higher incorporation of TVA into both bacterial and protozoal microbial fractions, which probably positively affected TVA flow from the rumen.     

Effect of cobalt ions on the metabolism of some volatile and polar compounds in the marine invertebrates Mytilus galloprovincialis and Actinia equina

The compositions of the volatile and polar fractions from two coexisting Black Sea invertebrates, the mussel Mytilus galloprovincialis and the beadlet anemone Actinia equina, were established. The main metabolites in the volatile fraction from the investigated animals appeared to be methyl esters of fatty acids and fatty aldehydes. In the polar fraction from both animals low concentrations of free acids and nitrogen-containing compounds were obtained. Free carbohydrates were in much higher concentrations in M. galloprovincialis than in A. equina. Some sterols, probably as polar conjugates, were identified mainly in A. equina. Significant changes among all compounds appeared after treatment of both invertebrates with two different concentrations of cobalt ions. The variety of changes in each invertebrate could be due to their different evolutionary status. The effect of cobalt ions was often stronger at medium cobalt-ion concentrations.     

High content of polyunsaturated fatty acids in muscle phospholipids of a fast runner,the European brown hare (Lepus europaeus)

To investigate both seasonal changes and possible intracorporal gradients of phospholipid fatty acid composition, skeletal muscles (n=124), hearts (n=27), and livers (n=34) from free-living brown hares (Lepus europaeus) were analyzed. Phospholipids from both skeletal muscles and heart had a high degree of unsaturation with 66.8±0.63% and 65.7±0.5% polyunsaturated fatty acids, respectively. This is the highest proportion of polyunsaturated fatty acids reported in any mammalian tissue. Polyunsaturated fatty acid content in skeletal muscles was 2.3% greater in winter compared to summer (F_1,106=17.7; P=0.0001), which may reflect thermoregulatory adjustments. Arachidonate (C20:4n-6) showed the greatest seasonal increase (+2.5%; F=7.95; P=0.0057). However, there were no pronounced differences in polyunsaturated fatty acid content between skeletal muscles from different locations in the body (m. iliopsoas, m. longissimus dorsi and m. vastus). Total muscle phospholipid polyunsaturated fatty acid content was correlated with polyunsaturated fatty acid content in triacyglycerols from perirenal white adipose tissue depots (r²=0.61; P=0.004). Polyunsaturated fatty acids were enriched in muscle phospholipids (56.8–73.6%), compared to white adipose tissue lipids (20.9–61.2%), and liver phospholipids (25.1–54.2%). We suggest that the high degree of muscle membrane unsaturation is related to hare-specific traits, such as a high maximum running speed.Abbreviations BMR basal metabolic rate - DPA docosapentaenoic acid - DHA docosahexaenoic acid - FA fatty acid - MUFA monounsaturated fatty acid - PC principal component - PUFA polyunsaturated fatty acid - SFA saturated fatty acid - UI unsaturation index - WAT white adipose tissueCommunicated by: G. Heldmaier     

Fatty acid composition of lipids from mushrooms belonging to the family Boletaceae

The non-polar lipid content and fatty acid (FA) composition of 11 mushroom species of the family Boletaceae were determined. The non-polar lipid content ranged from 2.0 (Leccinum aurantiacum and Boletus erythropus) to 5.4 % (w/w) d.w. (Suillus grevillei) with an average value of 2.9 %. More than 25 different FAs were found in the mushroom lipids. Unsaturated FAs, mainly linoleic and oleic acids, accounted for about 83 % of the total FAs, while palmitic acid was the main saturated FA. Some FAs are identified for the first time in Boletaceae and in higher Basidiomycetes (cis-11,12-methyleneoctadecanoic acid, 7-cis,10-cis hexadecadienoic) or in fungi (cis-11,12-methyleneoctadecanoic acid). There were significant differences (P < 0.05) in the contents of specific FAs between mushroom species.     

Characterization of fatty acid composition in healthy and bleached corals from Okinawa, Japan

Under bleaching conditions, corals lose their symbiotic zooxanthellae, and thus, the ability to synthesize fatty acids (FAs) from photosynthetically derived carbon. This study investigated the lipid content and FA composition in healthy and bleached corals from the Odo reef flat in Okinawa, southern Japan, following a bleaching event. It was hypothesized that the FA composition and abundance would change as algae are lost or die, and possibly microbial abundance would increase in corals as a consequence of bleaching. The lipid content and FA composition of three healthy coral species (Pavona frondifera, Acropora pulchra, and Goniastrea aspera) and of partially bleached and completely bleached colonies of P. frondifera were examined. The FA composition did not differ among healthy corals, but differed significantly among healthy, partially bleached, and completely bleached specimens of P. frondifera. Completely bleached corals contained significantly lower lipid and total FA content, as well as lower relative amounts of polyunsaturated FAs and higher relative amounts of saturated FAs, than healthy and partially bleached corals. Furthermore, there was a significantly higher relative concentration of monounsaturated FAs and odd-numbered branched FAs in completely bleached corals, indicating an increase in bacterial colonization in the bleached corals.     

Identification of lipids in the cuticle of the parasitic nematode Anisakis simplex and the somatic tissues of the Atlantic cod Gadus morhua

The main aim of this work was to assign the cuticular lipids identified in a parasitic nematode and to distinguish those originating from its host. The hypothesis that long-chained fatty acids and sterols are imported by the parasite in the absence of certain enzymes was also tested. The organisms (Anisakis simplex and Gadus morhua) were extracted in petroleum ether and dichloromethane. Matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF) was used to identify unknown components, and electrospray ionization mass spectrometry (ESI/MS) to verify recognized groups of lipids. The lipid classes identified in the surface layer were free saturated and unsaturated fatty acids, triacylglycerols, sterols and non-polar sphingolipids (ceramides, sphingoid bases). The most abundant fraction consisted of fatty acids. The predominant saturated acids were tetradecanoic acid in the petroleum ether extract of A. simplex, hexadecanoic acid in the dichloromethane extract of A. simplex, and also the polyunsaturated octadecahexaenoic and octadecatrienoic acids in both extracts of the parasitic nematode. The mass spectrum revealed the presence of fatty acids with different numbers of carbons, and with odd and even numbers of unsaturated bonds. The MALDI-TOF mass spectrum also identified triacylglycerols (TAGs). The dominant short-chain TAGs were CoCoCy:₁, CoCoPg and Bu0:0B:₆. The majority of TAGs were found in the ether and dichloromethane extracts of A. simplex. Sterols were the least common class of lipids found in the nematode extracts; most likely, this is the fraction that is entirely incorporated from the host organism because of the parasite’s inability to synthesize them. MALDI-TOF also identified non-polar sphingolipids - ceramides and sphingoid bases. The signals due to N-octanoyl-d-erythro-octasphinganine (m/z 288.3) and N-tetranoyl-d-erythro-tetradecasphinganine (m/z 316.4) were dominant on the mass spectra; quite a large number of short-chain non-polar sphingolipids were also identified.     

Changes of chemical and nutrient composition of porcine blood during fermentation by <Emphasis Type="Italic">Aspergillus oryzae</Emphasis>

A solid-state fermentation (SSF) of a mixture of porcine blood and wheat bran with a ratio of 8:1 by Aspergillus oryzae was investigated. Water content, pH, crude protein, heme and total iron, free amino acids (FAA) and total fatty acids (TFA) of the fermented mixture were determined at 0, 40, 80 and 120 h, respectively, and protein hydrolysis were analyzed with SDS-PAGE accordingly. The results showed that, during the fermentation, water contents and pH decreased significantly (P < 0.05) from 68.33% to 59.94%, 7.18% to 4.48%, respectively. Heme iron content changed slightly (P > 0.05). With the degradation of large protein molecules, free amino acids in the mixture increased from 872.83 mg l⁻¹ to 11560.94 mg l⁻¹ (P < 0.05). Content of free isoleucine, methionine and cystine, deficient in fresh porcine blood increased (P < 0.05) after fermentation. Percentages of saturated fatty acids such as C14:0, C17:0 and C18:0 in the total fatty acids decreased significantly (P < 0.05), and those of polyunsaturated fatty acids C18:1, C18:2, C18:3, C20:1 and C20:2 increased significantly from 27.06% to 47.90% (P < 0.05). The results indicated that Aspergillus oryzae could ferment porcine blood and bran mixture and change its chemical and nutrient composition.     

The budding bacteria,Pirellula and Planctomyces,with atypical 16S rRNA and absence of peptidoglycan,show eubacterial phospholipids and uniquely high proportions of long chain beta-hydroxy fatty acids in the lipopolysaccharide lipid A

Fatty acids of twelve strains of budding bacteria (Planctomyces and Pirellula spp.), which have atypical 16S rRNA and do not contain peptidoglycan cell walls, were shown to contain typical diacyl polar lipids with no indication of isoprenoid ether lipids suggestive of a relationship with the archaebacteria. The major ester-linked fatty acids of the phospholipids were palmitic, palmitoleic and oleic acids, which are more typical of microeukaryotes than of eubacteria. Lipopolysaccharide lipid A (LPS) was detected; it contained major proportions of long chain normal 3-OH fatty acids (3-OH eicosanoic at 23% and 17% of the total in two strains of Planctomyces, and 3-OH octadecanoic at 18%, and 3-OH palmitic at 11% of the total in one strain of Pirellula). Major portions of long chain 3-OH fatty acids in the LPS are extremely unusual and provide another atypical property of these organisms. Each strain investigated showed a specific total fatty acid composition, reflecting the diversity in 16S rRNA nucleotide catalogues.     

Analysis of whole cellular fatty acids and anastomosis relationships of binucleate Rhizoctonia spp. associated with Ceratobasidium cornigerum

Previous research has demonstrated that whole cellular fatty acids analysis is a useful tool for identifying and establishing taxonomic relationships between anastomosis groups (AGs) and related Rhizoctonia isolates. In this experiment, the composition of fatty acid of 28 isolates of teleomorph genus Ceratobasidium cornigerum, consisting of binucleate Rhizoctonia, AG-A, AG-B(o), AG-C, AG-P, and AG-Q, was evaluated using gas chromatography. Eleven fatty acids identified, i.e., myristic, pentadecanoic, palmitic, 2-hydroxypalmitic, palmitoleic, heptadecanoic, 9-heptadecenoic, stearic, oleic, linoleic, and linolenic acids, were present in isolates of AG-A, AG-B(o), AG-C, AG-P, and AG-Q. The major fatty acids, palmitic, oleic, and linoleic acids, were common in all isolates, constituting 87.1% to 94.7% of the whole cellular fatty acids identified. Isolates within the same AG were closely clustered, whereas isolates from different AGs were clearly and distinctly clustered based on average linkage cluster analysis of whole cellular fatty acids. Principal-component analysis generated from all fatty acids also confirmed the divergent separation of the 5 AGs of binucleate Rhizoctonia.     

Carbohydrate synthesis by two Navicula strains isolated from benthic and pelagic mucilages in the Tyrrhenian Sea (Tuscan Archipelago)

Two exopolysaccharide (EPS)-producing strains of the diatom Navicula, were isolated from benthic and pelagic mucilaginous aggregates sampled in the Tyrrhenian Sea and cultured under laboratory conditions. The amount of carbohydrate formed over the growth period and on a per cell basis was quite similar. However, the benthic strain showed a preferential synthesis of the bound (i.e., cellular and capsular) carbohydrate fraction, whereas the pelagic strain preferentially synthesised soluble, polymeric carbohydrates. The polysaccharides released into the medium by the two strains showed the same qualitative monosaccharidic composition, being constituted by two acidic and six neutral sugars. It is suggested that the difference between the benthic and the pelagic strain in the synthesis of bound or soluble carbohydrates may be related to the different role of these compounds in the particular habitats of the strains.     

Studies on (Na + K)-activated ATPase XLIX. Content and role of cholesterol and other neutral lipids in highly purified rabbit kidney enzyme preparation

(1) The neutral lipids and the free and bound fatty acids of a highly purified (Na⁺ + K⁺)-ATPase preparation from rabbit kidney outer medulla have been analysed. (2) On a dry weight basis, the total lipid content is nearly the same as the total protein content, and consists for 66% of phospholipids and for 34% of neutral lipids and free fatty acids. In the latter category cholesterol is the main component (71%). (3) On a molar basis the enzyme preparation contains 382 mol phospholipids, 67 mol free fatty acids, 9, 16 and 12 mol mono-, di- and triacylglycerols, 249 and 19 mol free and esterified cholesterol per mol enzyme. (4) The fatty acid composition of each lipid and of the free fatty acid fraction, present in the enzyme preparation, is reported. (5) All cholesterol and part of the phospholipids can be removed by hexane extraction, leaving 66% of the (Na⁺ + K⁺)-ATPase activity. Oxidation of all cholesterol to cholest-4-en-3-one by cholesterol oxidase leaves 85% of the (Na⁺ + K⁺)-ATPase activity. These results indicate that cholesterol is not essential for (Na⁺ + K⁺)-ATPase activity.     

Metabolism of symmetrical dialkyl ethers by Acinetobacter sp. HO1-N

The growth of Acinetobacter species HO1-N on a homologous series of dialkyl ethers yielded characteristic cellular and extracellular ether fatty acids. Microbial growth on diheptyl ether resulted in the appearance of 7-n-heptoxy-1-n-heptanoic acid as a cellular fatty acid and 2-n-heptoxy-1-acetic acid as the sole extracellular fatty acid. The oxidation of dinonyl ether and didecyl ether by Acinetobacter resulted in the extracellular accumulation of 2-n-nonoxy-acetic acid and 2-n-decoxy-1-acetic acid, respectively. The 16-carbon ether fatty acid, 6-n-decoxy-1-n-hexanoic acid, was identified as a major cellular fatty acid in didecyl ether-grown cells. The extracellular ether fatty acids accumulated in an inverse relationship to the disappearance of the dialkyl ether and appeared to represent end products of metabolism. The carbon and energy required for cellular growth and metabolism resided in the terminal 5-carbons of diheptyl ether, 7-carbons of dinonyl ether and 8-carbons of didecyl ether. Glutarate, adipate, pimelate and suberate were identified from cells grown at the expense of diheptyl, dioctyl, dinonyl and didecyl ether, respectively, suggesting a role for dibasic acids as metabolic intermediates. A new and novel mechanism for the metabolism of symmetrical dialkyl ethers is suggested. Terminal methyl group oxidation of the dialkyl ether results in the formation of an alkoxy-fatty acid followed by an internal carbon-carbon scission reaction 2-carbons removed from the oxygen atom. The resulting endproducts are alkoxyacetic acid and the corresponding dibasic acid.Non-Standard Abbreviations TLC Thin Layer Chromatography - PS-DEGS · PS Diethylene glycol succinate - DHE Diheptyl ether - DOE Dioctyl ether - DNE Dionyl ether - DDE Didecyl ether     

Chemical composition of lipophylic compounds from the body surface of unfed adult Ixodes persulcatus ticks (Acari: Ixodidae)

Chemical compositions of ethereal extracts of the body surface of unfed male and female Ixodes persulcatus ticks (Acari: Ixodidae) were studied by gas chromatography using mass-spectrometric detection. More than 100 different organic compounds were detected. The predominant components were saturated fatty hydrocarbons, saturated and unsaturated fatty acids, aldehydes, squalene, cholesterol and cholesterol derivatives. A number of compounds found in I. persulcatus are known as components of pheromones or constituents of dermal gland secretions in tick species of the genus Amblyomma: nonanoic acid, saturated fatty acids having from 14 to 16 carbons, and squalene. Saturated fatty aldehydes have not been reported previously as body surface components of hard ticks. Substituted phenols were not found in the extracts, although they are known as common components of sex and attraction–aggregation–attachment pheromones in Amblyomma ticks. With a few exceptions (henicosanal, 2,4-holestadiene and two unidentified cholesterol derivatives), there was no marked difference in composition of surface components between male and female I. persulcatus. The possible role of the different chemical groups in communication between I. persulcatus ticks is discussed.     

野生露珠杜鹃林不同分解层的土壤化感潜力

探明野生杜鹃群落不同层次土壤浸提物的化学成分及其含量差异,为阐明杜鹃群落天然更新障碍与化感作用之间的关系提供基础数据,从化学生态学角度解释群落天然更新障碍的原因。通过种子发芽试验,比较凋落物层(L层)、腐殖质层(H层)和土壤表层(S层)浸提液对自身种子萌发的化感效应,采用内标法结合气相色谱-质谱(GC/MS)联用等技术鉴定土壤浸提液所含的有机化合物。(1)种子发芽试验显示,露珠杜鹃不同土壤层浸提液的化感效应不同。L层的抑制作用最为强烈,其浸提液显著抑制自身种子的萌发。H层和S层对自身具有一定的抑制作用,与对照相比不显著;(2)鉴定了不同层次土壤浸提液中所含的有机化合物,L层、H层和S层均检测出31种组分,其中相对含量大于5%的组分分别有6、8和8种。L层浸提液主要化感成分为丙三醇和棕榈酸,分别达到总量的19.56%和19.17%;H层主要化感成分为2-羟基丙酸和棕榈酸,分别达到总量的14.05%和12.48%;S层土壤浸提物的主要化感成分为棕榈酸和2-羟基乙酸,分别达到总量的14.91%和12.79%。野生露珠杜鹃不同土壤浸提物的化感物质含量以L层最高,L层作为群落土壤化感物质的主要来源;从化感物质组分来分,长链脂肪酸和有机酸类是H层和S层主要的化感物质种类,长链脂肪酸类和醇类是L层主要的化感物质种类。杜鹃群落林下土壤中存在的化感物质可能是其天然更新障碍的重要原因之一。     

Dicarboxylic and Fatty Acid Compositions of Cyanobacteria of the Genus Aphanizomenon

The occurrence of dioic, hydroxy, branched, and unsaturated fatty acids in cyanobacteria of the genus Aphanizomenon growing in different freshwater lakes has been studied. Unusual dicarboxylic (from 4.52 to 7.14%) and other fatty acids were identified by gas chromatography/mass spectrometry (GC/MS).