Neutral Lipid Fatty Acid Research Articles

Variation in trophic niches of oribatid mites in temperate forest ecosystems as indicated by neutral lipid fatty acid patterns

Shifting of trophic niches of soil microarthropods may allow them to adapt to changing resource conditions as induced by global change processes. However, the capability of microarthropods to shift their trophic niches is little studied. Whereas some studies based on stable isotopes (15N/13C) point to distinct and narrow trophic niches, others indicate that trophic niches are plastic. Here, we investigated shifts in trophic niches of oribatid mites (Oribatida, Acari), a major soil detritivore microarthropod group, due to forest management, i.e., plantation of beech and spruce forests in Central Europe, using neutral lipid fatty acid (NLFA) markers. Due to differential microbial communities, we expected a fungi-based diet of oribatid mites in beech forest, but more bacterial contributions to the diet in spruce forest. Supporting these hypotheses, NLFA markers indicated that the trophic niches of each of the studied oribatid mite species differed between beech and spruce forests and shifted from feeding predominantly on litter and fungi in beech forest to more intensively feeding on bacteria in spruce forest. Oribatid mite species with the most pronounced differences in trophic niches included Achipteria coleoptrata, Eupelops hirtus, Eupelops plicatus and Liacarus xylariae, which had been classified as primary or secondary decomposers in previous studies. Overall, the results indicate that the ability of oribatid mite species to colonize different habitats and ecosystems is due to their ability to adjust their diet, i.e., to trophic plasticity. Changes in trophic niches in each of the studied oribatid mite species suggest that detritivores in soil may better cope with future changes in environmental conditions and associated changes in resource composition than species above the ground.

Vineyard management system affects soil microbiological properties

Aim: The aim of this study was to investigate the effects of integrated (INT), organic (ORG) and biodynamic (BD) management systems with similar C- and N-inputs on soil microbiology in a viticultural long-term field trial.Methods and results: Within the systems comparison, soil samples were taken 10 years after conversion, throughout the growing season. To gather information about microbial community structure, the activity of five soil enzymes was measured, and phospholipid fatty acids (PLFA) and neutral lipids fatty acids (NLFA) profiles were analysed accompanied by comprehensive soil analysis. pH associated with BD was significantly higher compared to INT soil. Copper and N-min values in INT were significantly lower compared to the organic systems. BD and ORG were characterised by a higher b-D-glucosidase and urease activity and a higher abundance of fungi and bacteria. INT had larger quantities of mycorrhizae indicator NLFAs.Significance and impact: Results from this study contribute to a better understanding of the microbial community structure and nutrient cycling under organic and biodynamic viticulture.

The importance of diet-related effects of the antibiotic ciprofloxacin on the leaf-shredding invertebrate Gammarus fossarum (Crustacea; Amphipoda)

Antibiotics may constitute a risk for aquatic detritivorous macroinvertebrates (i.e., shredders) via waterborne and dietary antibiotic exposure. In addition, antibiotics can alter the food quality for shredders mediated by shifts in leaf-associated decomposer (i.e., aquatic fungi and bacteria) communities. However, little is known about the relative importance of the waterborne and dietary effect pathway. Therefore, we followed a tiered testing approach aimed at assessing the relative importance of these effect pathways. We employed the antibiotic ciprofloxacin (CIP) and the shredder Gammarus fossarum as model stressor and test species, respectively. In a first step, we assessed the short-term waterborne toxicity of CIP using survival and leaf consumption of G. fossarum as response variables. Alterations in the leaf-associated decomposer community, which may be reflected by their palatability, were assessed using food choice assays. Finally, we conducted a 2 × 2-factorial experiment over 24 days assessing the pathways individually and combined using energy processing (i.e., leaf consumption and feces production), growth and energy storage (i.e., neutral lipid fatty acids) as variables. Short term waterborne exposure indicated low toxicity with LC50 and EC50 values of 13.6 and 6.4 mg CIP/L, respectively. At the same time, shredders did not prefer any leaf material during the food choice assay. However, the fungal community was significantly affected in the highest CIP-treatments (0.5 and 2.5 mg/L) suggesting an altered food quality for shredders. This assumption is supported by the results of the long-term assay. At 0.5 mg CIP/L, gammarids’ leaf consumption, growth and energy storage were increased when subjected via the dietary pathway, which was linked to changes in the leaf-associated microbial community. Our data highlight the importance of dietary effect pathways for effects on shredders, potentially impacting energy dynamics in detritus-based stream ecosystems.

Influence of management intensity and environmental conditions on microbiota in biological soil crust and crust-free soil habitats of temperate forests

The microbiota in three distinct terrestrial habitats (biological soil crusts – BSC, crust-adhering soil beneath BSC – trans, and crust-free soil close to BSC – soil) was studied in 33 temperate forest stands differing in management intensity (ForMI). Specific lipid fractions and respective marker fatty acids were used to determine microbial biomass and community structure (phospholipid fatty acids – PLFA), energy reserves (neutral lipid fatty acids – NLFA), and community level lipid profiles (CLLP) of nematodes and enchytraeids. The density and diversity of nematode fauna were additionally determined morphologically. The highest total amounts of PLFA and NLFA occurred in the BSC, followed by soil and trans habitats, indicating stronger effects of habitats than forest management intensity. This corresponds to the distribution pattern of bacterial PLFA that dominated the soil microbiota. The highest nematode population density occurred in the BSC, followed by soil and trans. The BSC was dominated by bacterial feeders and omnivores, while plant feeding nematodes were most frequent in the crust-free soil habitat. The highest biomass of photoautotrophs also occurred in the BSC, followed by the crust-adhering and crust-free soil habitats. Redundancy analysis indicated strong effect of ForMI and total N on soil PFLAs and NFLAs across habitats. The C:N and C:S ratios were important for the separation of NLFAs while P:S accounted for the separation of PLFAs. Bacterial and fungal PLFAs largely separated the microbial community across habitats, and particularly between BSC and trans habitats. The separation of nematodes and enchytraeids by CLLP was less pronounced, and most distinct between the crust-free soil and BSC or crust-adhering soil habitats. Overall, BSC and crust-adhering soil habitats provide different suitability for microbiota, resulting in specifically adapted communities that are shaped by the management intensity and nutrient availability.

Comparison of Fatty Acid Content between New Zealand Grass-Fed and American Grain-Fed Beef Strip Loins Varying in Marbling Level

ObjectivesMarbling impacts eating quality and consumer preference of beef as it intensifies flavor, and improves tenderness and juiciness. Triglycerides are the predominate lipid in beef and are considered neutral fatty acids, whereas polar fatty acids are found in the phospholipid portion of beef. Diet of cattle during the finishing period can impact type and saturation of fatty acids in meat.The objective of this research was to evaluate differences in neutral and polar lipid fatty acid content from grass-fed and grain-fed beef of varying quality grades sourced from New Zealand and the United States, respectively.Materials and MethodsBeef strip loins (n = 200) representing two fed cattle types (n = 100/finishing type: grass-finished and grain-finished) and five different USDA quality grades (n = 20 per quality grade: USDA Standard, Select, Low Choice, “Top” Choice: High and Average Choice, and Prime) were acquired from beef processing facilities in New Zealand (grass-fed) and Nebraska (grain-fed). A face steak was cut from the anterior end of each strip loin for fatty acid analysis. Face steaks (n = 200) were frozen and stored at the Gordon W. Davis Meat Science Laboratory until further fabrication. Samples were thawed for 12 to 24 h, trimmed of subcutaneous fat and connective tissue and ground. The ground sample was frozen in liquid nitrogen and homogenized for fatty acid analysis. Lipids were extracted, fractionated into neutral lipid (NL) and polar lipid (PL), derivatized to fatty acid methyl esters and determined by gas chromatography.Statistical analyses were conducted using the procedures of SAS (Version 9.3; SAS Inst. Inc., Cary, NC). Treatment comparisons were tested for significance using PROC GLIMMIX with α = 0.05.ResultsInteractions of cattle diet × marbling level affected the overall concentrations (mg/g) of NL saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) (P < 0.05). Saturated fatty acid and MUFA NL concentration decreased as marbling level decreased, as grain-fed Prime was higher (P < 0.05) than all other treatments. Grain-finished and grass-finished Standard had the lowest (P < 0.05) SFA and MUFA NL concentration compared to all other treatments. Concentration of PUFA NL was higher (P < 0.05) for grain-finished Prime than grain-finished Top Choice and grass-finished Prime. No difference was found between grain-finished Low Choice and Select and grass-finished Top Choice NL concentration (P > 0.05), however all were higher (P < 0.05) than grass-finished and grain-finished Standard and grass-finished Select. A cattle diet × marbling level interaction affected the overall PL concentrations of SFA and MUFA (P < 0.05), but not PUFA (P > 0.05). Generally, polar fatty acid content increased as marbling increased for SFA and MUFA. Grain-finished PUFA PL concentration was higher (P < 0.05) than grass-finished samples. Additionally, PUFA PL concentration increased as quality grade decreased (P < 0.05).ConclusionIn conclusion, polar and neutral fatty acid content increased with increasing quality grades except for PL polyunsaturated fatty acids. Additionally, grain-finished beef steaks generally contained a higher SFA and MUFA NL concentration than grass-finished beef steaks for all quality grades except Low Choice and Top Choice.

Linking lipid transfer with reduced arbuscule formation in tomato roots colonized by arbuscular mycorrhizal fungus under low pH stress.

Arbuscules are the core structures of arbuscular mycorrhizae (AM), and arbuscule development is regulated by environmental stress, e.g., low pH. Recent studies indicate that lipid transfer from plants is essential for AM fungal colonization; however, the role of lipid transfer in arbuscule formation and the dynamics of lipid accumulation in arbuscules under low pH stress are far from well understood. In the symbiosis of tomato and Rhizophagus intraradices under contrasting pH conditions (pH 4.5 vs. pH 6.5), we investigated arbuscule formation, nutrient uptake, alkaline phosphatase activity and lipid accumulation; examined the gene expression involved in phosphate transport, lipid biosynthesis and transfer and sugar metabolism; and visualized the lipid dynamics in arbuscules. Low pH greatly inhibited arbuscule formation, in parallel with reduced phospholipid fatty acids accumulation in AM fungus and decreased P uptake. This reduction was supported by the decreased expression of plant genes encoding lipid biosynthesis and transfer. More degenerating arbuscules were observed under low pH conditions, and neutral lipid fatty acids accumulated only in degenerating arbuscules. These data reveal that, under low pH stress, reduced lipid transfer from hosts to AM fungi is responsible for the inhibited arbuscule formation.

Non-symbiotic soil microbes are more strongly influenced by altered tree biodiversity than arbuscular mycorrhizal fungi during initial forest establishment.

While the relationship between plant and microbial diversity has been well studied in grasslands, less is known about similar relationships in forests, especially for obligately symbiotic arbuscular mycorrhizal (AM) fungi. To assess the effect of varying tree diversity on microbial alpha- and beta-diversity, we sampled soil from plots in a high-density tree diversity experiment in Minnesota, USA, 3 years after establishment. About 3 of 12 tree species are AM hosts; the other 9 primarily associate with ectomycorrhizal fungi. We used phospho- and neutral lipid fatty acid analysis to characterize the biomass and functional identity of the whole soil bacterial and fungal community and high throughput sequencing to identify the species-level richness and composition of the AM fungal community. We found that plots of differing tree composition had different bacterial and fungal communities; plots with conifers, and especially Juniperus virginiana, had lower densities of several bacterial groups. In contrast, plots with a higher density or diversity of AM hosts showed no sign of greater AM fungal abundance or diversity. Our results indicate that early responses to plant diversity vary considerably across microbial groups, with AM fungal communities potentially requiring longer timescales to respond to changes in host tree diversity.

Conversion of rainforest to oil palm and rubber plantations alters energy channels in soil food webs.

In the last decades, lowland tropical rainforest has been converted in large into plantation systems. Despite the evident changes above ground, the effect of rainforest conversion on the channeling of energy in soil food webs was not studied. Here, we investigated community‐level neutral lipid fatty acid profiles in dominant soil fauna to track energy channels in rainforest, rubber, and oil palm plantations in Sumatra, Indonesia. Abundant macrofauna including Araneae, Chilopoda, and Diplopoda contained high amounts of plant and fungal biomarker fatty acids (FAs). Lumbricina had the lowest amount of plant, but the highest amount of animal‐synthesized C20 polyunsaturated FAs as compared to other soil taxa. Mesofauna detritivores (Collembola and Oribatida) contained high amounts of algal biomarker FAs. The differences in FA profiles between taxa were evident if data were analyzed across land‐use systems, suggesting that soil fauna of different size (macro‐ and mesofauna) are associated with different energy channels. Despite that, rainforest conversion changed the biomarker FA composition of soil fauna at the community level. Conversion of rainforest into oil palm plantations enhanced the plant energy channel in soil food webs and reduced the bacterial energy channel; conversion into rubber plantations reduced the AMF‐based energy channel. The changes in energy distribution within soil food webs may have significant implications for the functioning of tropical ecosystems and their response to environmental changes. At present, these responses are hard to predict considering the poor knowledge on structure and functioning of tropical soil food webs.

Salinity can change the lipid composition of adult Chinese mitten crab after long-term salinity adaptation.

The Chinese mitten crab (Eriocheir sinensis) is an euryhaline crustacean, whose adults migrate downstream to estuaries for reproduction. Lipids are believed to be involved in salinity adaptation during migration. This study investigated the effects of different salinities (0, 6, 12, and 18‰) on the total lipids, neutral lipids, and polar lipids contents, and fatty acid profiles in the gonads, hepatopancreas, and muscles of adult E. sinensis after 40 days of salinity adaptation. The results showed that the males and females from 12‰ treatment had the highest contents of total lipids and neutral lipids in their hepatopancreas and total lipids in the muscles. Notably, salinity had a greater effect on the fatty acid profiles in the hepatopancreas compared to that in the gonads and muscles. The male hepatopancreas treated with 18‰ salinity had the highest percentage of total n-6 polyunsaturated fatty acid (∑n-6PUFA) in both neutral lipids and polar lipids, while the percentage of total n-3 polyunsaturated fatty acid (∑n-3PUFA) in neutral lipids and polar lipids decreased significantly with increasing salinity in males. In females, the 0‰ treatment had the highest percentages of total saturated fatty acids in neutral lipids and polar lipids in the hepatopancreas, while the highest ∑n-3PUFA and ∑n-6PUFA in neutral lipids and polar lipids were detected in the 12‰ treatment group. In conclusion, brackish water could promote the accumulations of total lipids and neutral lipids in the hepatopancreas and change the fatty acid profiles of adult E. sinensis, particularly in the hepatopancreas after long-term salinity adaptation.

Interaction between root hairs and soil phosphorus on rhizosphere priming of soil organic matter

We hypothesized that the rhizosphere priming effect (RPE) of soil organic matter by mutant barley lacking root hairs is dependant on a large network of symbiotic arbuscular mycorrhizal fungi (AMF). We thus predicted that fertilizing with phosphate-P would reduce AMF abundance and, in turn, reduce RPE of mutant barley. We packed microcosms with a P-responsive soil in which we grew mutant barley lacking root hairs as well as wild type barley and narrowleaf plantain, each possessing root hairs. One set of microcosms was fertilized with phosphate-P while another set was not fertilized. The plants were grown in a labelling chamber with 13C-depleted CO2. Soil respiration and δ13C of headspace CO2 were measured after 3, 4 and 5 weeks and RPE was calculated using an isotope mass balance approach. Root hair length was measured and soils were analyzed for the 16:1ω5 neutral lipid fatty acid (i.e. AMF biomarker). AMF abundance was greater, whereas RPE was lower, in mutant barley soil under low-P than under high-P conditions. In the other two plant-types, P had no effect on AMF or on RPE. As our results contradict our prediction, we propose an alternative explanation based on plant N demand under high-P.

Neutral and polar lipid fatty acids in five families of demersal and pelagic fish from the deep Northwest Atlantic

AbstractFatty acids in neutral and polar lipids were used to investigate trophic connections in species from five families of demersal (Rajella fyllae, Malacoraja senta, Alepocephalus bairdii, Borostomias antarcticus) and pelagic fish (Bathytroctes macrolepis, Lampanyctus spp., Chaulidos sloani, Serrivomer beanii) sampled in the deep Atlantic Ocean off Newfoundland, Canada. Lipid extracts were fractionated into neutral, acetone-mobile polar, and phospholipids to separate fatty acids in storage from those in membranes. Multivariate analysis of fatty acids showed that there were greater differences among the three lipid fractions than there were among the species when all fatty acid fractions were considered together. Neutral lipid fatty acids were characterized by monoenes, acetone-mobile polar lipids (AMPL) by C18 polyenes, and phospholipids by 16:0 and DHA. Multivariate analysis of fatty acids in phospholipids showed a strong grouping by taxonomic family (>80% similarity), while the neutral lipid fatty acids showed a weaker grouping by family (72.5% similarity) but groupings that also related to habitat and vertical migration. The neutral lipid data supported the use of 20:1ω9 as a biomarker of calanoid copepods and of 16:1ω7 as a marker of diatoms to determine food web connections in deep-sea fish, but not some other common markers. In addition, correlations with δ15N showed that series of ω6 and ω7 fatty acids were trophically transferred though neutral lipids, especially the essential fatty acid, ARA. Neutral lipids were also reservoirs for essential ω3 fatty acids in demersal species, but the major reservoir for DHA was AMPL and phospholipid in pelagic species.

Carbon Investment Required for the Mobilization of Inorganic and Organic Phosphorus Bound to Goethite by an Arbuscular Mycorrhiza (Solanum lycopersicum x Rhizophagus irregularis)

Nutrient supply in phosphorus (P)-limited ecosystems, with most P being associated with secondary minerals, has to rely on efficient nutrient allocation strategies, such as those involving mycorrhizal symbioses. Yet, little is known about the extent of photo-assimilate transfer to the fungal partner, who in turn mobilizes mineral-bound P sources required by the plant. This study aims to explore the carbon (C)–P trade between an arbuscular mycorrhizal (AM) plant and its ability to incorporate P from differently accessible P sources. We compared P uptake rates of AM plants for orthophosphate (OP) and phytic acid (PA), applied to mesocosms in either dissolved form or bound to goethite (α-FeOOH). The design of the mesocosms allowed the plant to only access the P in the fungal compartment via the AM hyphae. We hypothesized the AM plant to invest more C into the symbiosis, if P is present in the less accessible form. To estimate the C budget of the symbiosis, we determined total organic carbon (OC), 16:1ω5c phospholipid fatty acid (PLFA; AM fungi extraradical mycelium), 16:1ω5c neutral lipid fatty acid (NLFA; AM fungi energy storage), and CO2 cumulative respiration in the fungal compartment. A ratio to the total C mobilized into the fungal compartment (OC+CO2 cumulative respiration) and the P incorporated into the AM plant (Total C/P) was calculated to estimate the C investment made by the AM plant into its symbiotic partner. AM plants incorporated P derived from all four P sources exclusively via the mycorrhizal pathway in different amounts and kinetics. The Total C/P ratio was significantly larger for those AM plants accessing the goethite-bound P compounds. They also transferred significantly larger amounts of PLFA and NLFA to their fungal partner, both indicating a larger plant C investment per P taken up. Our data provide first evidence about the ability of an AM plant to incorporate P from an organic source bound to a secondary mineral. The different C investments of AM plants into P allocation from variably available sources suggests a broad nexus between P mining strategies, resource partitioning in soil, and the amounts of C accumulated in terrestrial soils.

Protura are unique: first evidence of specialized feeding on ectomycorrhizal fungi in soil invertebrates

BackgroundEctomycorrhizal fungi (ECM) play a central role in nutrient cycling in boreal and temperate forests, but their role in the soil food web remains little understood. One of the groups assumed to live as specialised mycorrhizal feeders are Protura, but experimental and field evidence is lacking. We used a combination of three methods to test if Protura are specialized mycorrhizal feeders and compared their trophic niche with other soil invertebrates. Using pulse labelling of young beech and ash seedlings we analysed the incorporation of 13C and 15N into Acerentomon gallicum. In addition, individuals of Protura from temperate forests were collected for the analysis of neutral lipid fatty acids and natural variations in stable isotope ratios.ResultsPulse labelling showed rapid incorporation of root-derived 13C, but no incorporation of root-derived 15N into A. gallicum. The transfer of 13C from lateral roots to ectomycorrhizal root tips was high, while it was low for 15N. Neutral lipid fatty acid (NLFA) analysis showed high amounts of bacterial marker (16:1ω7) and plant marker (16:0 and 18:1ω9) fatty acids but not of the fungal membrane lipid 18:2ω6,9 in A. gallicum. Natural variations in stable isotope ratios in Protura from a number of temperate forests were distinct from those of the great majority of other soil invertebrates, but remarkably similar to those of sporocarps of ECM fungi.ConclusionsUsing three in situ methods, stable isotope labelling, neutral lipid fatty acid analysis and natural variations of stable isotope ratios, we showed that Protura predominantly feed on mycorrhizal hyphae via sucking up hyphal cytoplasm. Predominant feeding on ectomycorrhizal mycelia by Protura is an exception; the limited consumption of ECM by other soil invertebrates may contribute to carbon sequestration in temperate and boreal forests.

Comparison of Fatty Acid Content between New Zealand Grass-Fed and American Grain-Fed Beef Strip Loins Varying in Marbling Level

ObjectivesMarbling impacts eating quality and consumer preference of beef as it intensifies flavor, and improves tenderness and juiciness. Triglycerides are the predominate lipid in beef and are considered neutral fatty acids, whereas polar fatty acids are found in the phospholipid portion of beef. Diet of cattle during the finishing period can impact type and saturation of fatty acids in meat.The objective of this research was to evaluate differences in neutral and polar lipid fatty acid content from grass-fed and grain-fed beef of varying quality grades sourced from New Zealand and the United States, respectively.Materials and MethodsBeef strip loins (n = 200) representing two fed cattle types (n = 100/finishing type: grass-finished and grain-finished) and five different USDA quality grades (n = 20 per quality grade: USDA Standard, Select, Low Choice, “Top” Choice: High and Average Choice, and Prime) were acquired from beef processing facilities in New Zealand (grass-fed) and Nebraska (grain-fed). A face steak was cut from the anterior end of each strip loin for fatty acid analysis. Face steaks (n = 200) were frozen and stored at the Gordon W. Davis Meat Science Laboratory until further fabrication. Samples were thawed for 12 to 24 h, trimmed of subcutaneous fat and connective tissue and ground. The ground sample was frozen in liquid nitrogen and homogenized for fatty acid analysis. Lipids were extracted, fractionated into neutral lipid (NL) and polar lipid (PL), derivatized to fatty acid methyl esters and determined by gas chromatography.Statistical analyses were conducted using the procedures of SAS (Version 9.3; SAS Inst. Inc., Cary, NC). Treatment comparisons were tested for significance using PROC GLIMMIX with α = 0.05.ResultsInteractions of cattle diet × marbling level affected the overall concentrations (mg/g) of NL saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) (P < 0.05). Saturated fatty acid and MUFA NL concentration decreased as marbling level decreased, as grain-fed Prime was higher (P < 0.05) than all other treatments. Grain-finished and grass-finished Standard had the lowest (P < 0.05) SFA and MUFA NL concentration compared to all other treatments. Concentration of PUFA NL was higher (P < 0.05) for grain-finished Prime than grain-finished Top Choice and grass-finished Prime. No difference was found between grain-finished Low Choice and Select and grass-finished Top Choice NL concentration (P > 0.05), however all were higher (P < 0.05) than grass-finished and grain-finished Standard and grass-finished Select. A cattle diet × marbling level interaction affected the overall PL concentrations of SFA and MUFA (P < 0.05), but not PUFA (P > 0.05). Generally, polar fatty acid content increased as marbling increased for SFA and MUFA. Grain-finished PUFA PL concentration was higher (P < 0.05) than grass-finished samples. Additionally, PUFA PL concentration increased as quality grade decreased (P < 0.05).ConclusionIn conclusion, polar and neutral fatty acid content increased with increasing quality grades except for PL polyunsaturated fatty acids. Additionally, grain-finished beef steaks generally contained a higher SFA and MUFA NL concentration than grass-finished beef steaks for all quality grades except Low Choice and Top Choice.

Seasonal dynamics and changing sea level as determinants of the community and trophic structure of oribatid mites in a salt marsh of the Wadden Sea.

Global change processes affect seasonal dynamics of salt marshes and thereby their plant and animal communities. However, these changes have been little investigated for microarthropod communities. We studied the effect of seasonality and changes in sea level on oribatid mites in the natural salt marsh and on artificial islands in the back-barrier environment of the island Spiekeroog (Wadden Sea, Germany). Three zones of the artificial islands were filled with transplanted sods from the lower salt marsh zone and thereby exposed to three different inundation frequencies. We hypothesized that oribatid mite communities will differ along the natural salt marsh vegetation zones [upper salt marsh (USM), lower salt marsh (LSM), pioneer zone (PZ)], which are influenced by different tidal regimes. Accordingly, total oribatid mite densities declined from the USM and LSM to the PZ. Similarly, oribatid mite species compositions changed along the salt marsh transect and also responded to variations in inundation frequency in LSM on artificial islands with typical species of the USM, LSM and PZ being Multioppia neglecta (USM), Hermannia pulchella (LSM), Zachvatkinibates quadrivertex (LSM, PZ) and Ameronothrus schneideri (LSM, PZ). Oribatid mite density in the salt marsh and on the artificial islands was at a maximum in winter and spring; this was due in part to high density of juveniles, pointing to two reproductive periods. We hypothesized that oribatid mite trophic structure changes due to variations in abiotic (e.g., tidal dynamics, temperature) and biotic conditions (e.g., resource availability). Stable isotope (15N, 13C) and neutral lipid fatty acid analyses indicated that oribatid mite species have different diets with e.g., Z. quadrivertex feeding on macroalgae and fungi, A. schneideri feeding on microalgae and bacteria, and Scheloribates laevigatus and M. neglecta feeding on dead organic matter, bacteria and fungi. Overall, the results indicate that oribatid mite species in salt marshes are affected by changes in environmental factors such as inundation intensity, with the effects being most pronounced in species with narrow trophic niches and limited niche plasticity. The results also indicate that oribatid mite communities of the LSM respond little to short-term (one year) changes in inundation frequency.

Connecting organic to mineral: How the physiological state of an ecosystem-engineer is linked to its habitat structure

The honeycomb worm Sabellaria alveolata is capable of building extensive bioconstructions, including what are currently considered Europe’s largest biogenic reefs. The size and volume of these bioconstructions, however, vary greatly, such that not all habitats engineered by S. alveolata may be easily identified as reefs. Given that European environmental legislation protects marine habitats that are classified as “reefs”, it is important to identity a clear set of definition criteria. Furthermore, quantifiable and unequivocal criteria are also needed to evaluate the ecological (health) state of these reefs, in order to best monitor and protect them. Here we propose new terminology to describe the physical appearance of these bioconstructions and attempt to link these physical criteria to the physiological state of the tube-building polychaete. We tested whether a bioconstruction displaying outward signs of growth is built by “healthy” worms devoid of physiological stress by analysing three macromolecules (carbohydrates, proteins, lipids), four polar lipid fatty acids, six neutral lipid fatty acid markers and three metabolic enzymes (citrate synthase, catalase and superoxide dismutase). The worms were sampled in bioconstructions of different “Type” (veneer vs. hummock), “Phase” (progradation vs. retrogradation), and “Shore Level” (high shore vs. low shore) at Champeaux in Mont-Saint-Michel Bay, France. Our results show that worms sampled in retrograding reefs (i.e. displaying signs of erosion and colonisation by epibionts such as oysters or mussels), were less physiologically stressed than worms sampled in prograding bioconstructions, possibly due to lower intraspecific competition and hence greater food availability. We therefore suggest management measures should encompass the whole mosaic of biogenic construction Types and Phases. We propose the inclusion of the polar lipid fatty acid arachidonic acid, in combination with the activity of two metabolic enzymes, citrate synthase and superoxide dismutase, as the three key biochemical markers to consider for quantitative information on the physiological state of this particular ecosystem engineer. Our results also revealed the influence of both sex and size on fatty acid and enzyme levels, highlighting the importance of taking into account both these variables when sampling and subsequently pooling individuals by sex and size category for laboratory analyses. Once seasonal and site variation have been addressed, these biochemical indicators could be examined in parallel with S. alveolata bioconstruction physical criteria as part of a European-wide protocol for monitoring ecological status in this potential reef habitat.

Warming increased feeding of a root-chewing insect at the soil surface and enhanced its damage on a grass

Air and soil warming influences both plants and root herbivorous insects, but how warming alters their interactions is largely unknown. Because both the intensity of herbivory and plant susceptibility to the herbivory depend on temperature, it is difficult to predict the effects of insect herbivory on plant growth under warming. To analyse changes in belowground plant-insect interaction due to warming, we conducted a pot experiment using one grass species, Lolium perrene, and one beetle grub Anomala cuprea. Temperature (17 °C or 20.3 °C), presence or absence of a grub, and presence or absence of organic matter (OM) on the surface of the potted soil were manipulated. OM at the soil surface is an important resource for grubs, and contains neutral lipid fatty acids (NLFA) that can serve as a bacterial marker. NLFAs can be used as a tracer to determine whether grubs had fed upon OM, so we evaluated the consumption and vertical movement of a grub in response to warming. In the absence of grubs, plant biomass increased with warming, but was not affected by the OM treatment. In the presence of grubs, plant biomass was significantly decreased. Moreover, the interaction term between the temperature and grub treatments was significant, demonstrating that grub damage was more severe under warmer conditions. Grub mortality was not affected by any treatment. The bacterial NLFAs in a grub were significantly more detectable when OM was added relative to those without OM, and the amount increased with warming treatments. This suggests that the grub fed near the soil surface under both temperature conditions, but increased consumption rates under the warmer condition. The mean relative soil moisture content in the warmer conditions was significantly lower than that in the control conditions. OM additionally increased soil moisture, but it had no effect on herbivory damage, suggesting that plant susceptibility to herbivory was not attributable to soil moisture. These results show the importance of biological-context dependency of warming on a plant. Temperature changes will alter the root-herbivore interactions not by changing the plant susceptibility to herbivory but by increasing the consumption of the grub.

Unveiling community patterns and trophic niches of tropical and temperate ants using an integrative framework of field data, stable isotopes and fatty acids.

BackgroundThe use and partitioning of trophic resources is a central aspect of community function. On the ground of tropical forests, dozens of ant species may be found together and ecological mechanisms should act to allow such coexistence. One hypothesis states that niche specialization is higher in the tropics, compared to temperate regions. However, trophic niches of most species are virtually unknown. Several techniques might be combined to study trophic niche, such as field observations, fatty acid analysis (FAA) and stable isotope analysis (SIA). In this work, we combine these three techniques to unveil partitioning of trophic resources in a tropical and a temperate community. We describe patterns of resource use, compare them between communities, and test correlation and complementarity of methods to unveil both community patterns and species’ niches.MethodsResource use was assessed with seven kinds of bait representing natural resources available to ants. Neutral lipid fatty acid (NLFA) profiles, and δ15N and δ13C isotope signatures of the species were also obtained. Community patterns and comparisons were analyzed with clustering, correlations, multivariate analyses and interaction networks.ResultsResource use structure was similar in both communities. Niche breadths (H′) and network metrics (Q and H2′) indicated similar levels of generalization between communities. A few species presented more specialized niches, such as Wasmannia auropunctata and Lasius fuliginosus. Stable isotope signatures and NLFA profiles also indicated high generalization, although the latter differed between communities, with temperate species having higher amounts of fat and proportions of C18:1n9. Bait use and NLFA profile similarities were correlated, as well as species’ specialization indices (d′) for the two methods. Similarities in δ15N and bait use, and in δ13C and NLFA profiles, were also correlated.DiscussionOur results agree with the recent view that specialization levels do not change with latitude or species richness. Partition of trophic resources alone does not explain species coexistence in these communities, and might act together with behavioral and environmental mechanisms. Temperate species presented NLFA patterns distinct from tropical ones, which may be related to environmental factors. All methods corresponded in their characterization of species’ niches to some extent, and were robust enough to detect differences even in highly generalized communities. However, their combination provides a more comprehensive picture of resource use, and it is particularly important to understand individual niches of species. FAA was applied here for the first time in ant ecology, and proved to be a valuable tool due to its combination of specificity and temporal representativeness. We propose that a framework combining field observations with chemical analysis is valuable to understand resource use in ant communities.

Influence of smallholder farm practices on the abundance of arbuscular mycorrhizal fungi in rural Zambia

While the effects of row crop agriculture on arbuscular mycorrhizal (AM) fungi have been studied in temperate climates, much less is known about the consequences of methods employed by smallholder farmers in Africa. We compared soils from 12 small farms in rural eastern Zambia with soil from nearby grasslands (control) to assess microbial abundances, including AM fungi, using phospholipid and neutral lipid fatty acid (PLFA/NLFA) analyses. We also measured soil pH, soil organic matter, and key nutrients, and categorized farms to link microbial abundances with agricultural practices including: low and high input cultivation, conservation farming, and agroforestry. Soil organic matter was significantly greater in grassland (control) soils, compared to any of the farms. Concentrations of N, P, and K were greater in farm soils compared to grassland soil. Extra-radical AM fungal biomass was significantly greater in grassland soils compared to farms, and grasslands contained more than double the total microbial biomass compared to any farm. Our results indicate agricultural practices in Zambia are negatively affecting AM fungi as well as other soil microbes. However, conservation farming shows promise in facilitating AM fungal recovery, with potential long-term benefits for soil stability via hyphal exudates and physical entanglement.

Effects of storage and handling on neutral lipid fatty acid profiles of two woodlice (Isopoda, Crustacea) species differing in size

Neutral lipid fatty acid (NLFA) analysis is a promising tool to investigate energy fluxes and basal resources of soil animal communities. This study aimed at investigating the effect of common handling and storage procedures in soil animal ecology on the NLFA composition and marker NLFAs. First, we tested the effect of the method of killing (by freezing and by drowning in diethylene glycol mixed with water; 1:1) on NLFA composition of the woodlouse Oniscus asellus. Additionally, we inspected the effect of two reference methods (direct freezing at −20 °C and storage in methanol at −80 °C with evaporating methanol prior to lipid extraction) after 4 and 12 months on the NLFA profile of O. asellus. We investigated the effect of the collection solution used in heat extraction of soil animals (water and glycol), storage fluids (saltwater, glycerine, ethanol and methanol) and storage time (4 and 12 months) on NLFA composition and common marker NLFAs of two Isopoda species differing in body size. The NLFA composition and marker fatty acids (FAs) did not differ between the methods of killing and between the two reference treatments but the amount of saturated FAs and the saturated-to-unsaturated FA ratio generally increased after 12 months indicating oxidation processes. Generally, the collection solution was of minor importance, whereas storage fluid and storage time strongly affected NLFA patterns. The NLFA profile of the larger species O. asellus was affected by storage in methanol and ethanol and to some extent in saltwater, while the NLFA profile of the smaller Trichoniscus pusillus was affected by each of the treatments. Notably, however, marker FAs of O. asellus and T. pusillus were not significantly affected by storing in glycerine even after 12 months in O. asellus. Therefore, if animals need to be stored prior to NLFA analysis for sorting and identification, storage in glycerine is advisable.