A 13CO2 Enrichment Experiment to Study the Synthesis Pathways of Polyunsaturated Fatty Acids of the Haptophyte Tisochrysis lutea

The production of polyunsaturated fatty acids (PUFA) in Tisochrysis lutea was studied using the gradual incorporation of a ¹³C-enriched isotopic marker, ¹³CO₂, for 24 h during the exponential growth of the algae. The ¹³C enrichment of eleven fatty acids was followed to understand the synthetic pathways the most likely to form the essential polyunsaturated fatty acids 20:5n-3 (EPA) and 22:6n-3 (DHA) in T. lutea. The fatty acids 16:0, 18:1n-9 + 18:3n-3, 18:2n-6, and 22:5n-6 were the most enriched in ¹³C. On the contrary, 18:4n-3 and 18:5n-3 were the least enriched in ¹³C after long chain polyunsaturated fatty acids such as 20:5n-3 or 22:5n-3. The algae appeared to use different routes in parallel to form its polyunsaturated fatty acids. The use of the PKS pathway was hypothesized for polyunsaturated fatty acids with n-6 configuration (such as 22:5n-6) but might also exist for n-3 PUFA (especially 20:5n-3). With regard to the conventional n-3 PUFA pathway, Δ6 desaturation of 18:3n-3 appeared to be the most limiting step for T. lutea, “stopping” at the synthesis of 18:4n-3 and 18:5n-3. These two fatty acids were hypothesized to not undergo any further reaction of elongation and desaturation after being formed and were therefore considered “end-products”. To circumvent this limiting synthetic route, Tisochrysis lutea seemed to have developed an alternative route via Δ8 desaturation to produce longer chain fatty acids such as 20:5n-3 and 22:5n-3. 22:6n-3 presented a lower enrichment and appeared to be produced by a combination of different pathways: the conventional n-3 PUFA pathway by desaturation of 22:5n-3, the alternative route of ω-3 desaturase using 22:5n-6 as precursor, and possibly the PKS pathway. In this study, PKS synthesis looked particularly effective for producing long chain polyunsaturated fatty acids. The rate of enrichment of these compounds hypothetically synthesized by PKS is remarkably fast, making undetectable the ¹³C incorporation into their precursors. Finally, we identified a protein cluster gathering PKS sequences of proteins that are hypothesized allowing n-3 PUFA synthesis.     

Solubility and uptake of heavy metals from a Swedish soil

Samples of the surface layer (Ap) and of grass, collected from: (1) grass ley fertilized in the normal way; (2) permanent pasture fertilized in the normal way; and (3) permanent pasture treated with large amounts of sewage sludge five years earlier, were analysed for Mn, Zn, Cu, Cr, Co, Ni, Pb, and Cd.The soil samples were extracted with: (1) distilled water saturated with CO₂; (2) 1 M neutral ammonium acetate; (3) ammonium acetate + acetic acid, pH 4.75; and (4) 2 M nitric acid on a waterbath. The efficiency of these extractants differed greatly and, in relative values, was: 1 for H₂O + CO₂, 3.4 for NH₄OAc, 20.7 for NH₄OAc + HOAc, and 343 for 2 M HNO_3- The dissolving effects of the extractants differed markedly with the kind of element.Grass from the field treated with sewage sludge showed much higher contents of Mn and Zn and somewhat higher contents of Cu and Pb than grass from the untreated field. The levels of Cr, Co, Ni, and Cd were practically uninfluenced by the treatment. Grass from a field close to a highway accumulated large amounts of air-borne Pb and Cd during the summer.It is concluded that the total contents of heavy metals in soils have only limited importance for the uptake by plants. Weak extractants therefore give better information about the plant-available amounts in soils.     

The role of neutral salts in the ion exchange between acid precipitation and soil

Theory and experimental results have shown that neutral salts in the precipitation or supplied to the ground by other means reduce the acidification of soils by acid precipitation. This salt effect is caused by the cation exchange occurring after the entry of the rain water into the soil.The acid components of precipitation consist of H₂SO₄, HNO₃ and HCl and of NH₄⁺ after nitrification in the soil. The magnitude of the salt effect depends on the relative bonding energy of H₃O⁺ and of Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺ in the soil as well as on the concentrations of H₃O⁺ and the above cations in the precipitation. The salt effect may be considerable in very acid soils. It decreases with rising pH to become very small or negligible in neutral soils, chiefly due to the increasing bonding energy of H₃O⁺ in this direction.The adverse effect of acid precipitation, therefore, is likely to be less in very acid soils, such as podsols, than in slightly acid and neutral soils with low buffering capacity against pH change. Soil texture and calcite content are very important factors in this respect as fine material and calcite increase the buffering.     

Stable carbon and nitrogen isotopic evidence for ecotonal coupling between boreal forests and fishes

Abstract— As a result of water turbulence effects on boundary layer diffusion resistance and carbon isotopic discrimination, the δ¹³C values (ratios of ¹³C: ¹²C) of attached algae may often overlap those of terrestrial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic animals. The present study used a dual isotope approach (δ¹³C and δ¹⁵N) to refine measurements of the incorporation of allochthonous organic matter into freshwater fishes. The dependence of five species of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Shield lakes are, therefore, not isolated from their surrounding riparian forests in terms of carbon flow as present day timber management guidelines erroneously assume, but instead exhibit a measurable degree of ecotonal land-water coupling. As a result, clearcut logging of riparian forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a forest harvesting strategy.     

From shallow to deep waters: habitats used by larval lampreys (genus Petromyzon and Lampetra) over a western European basin

Abstract –  Habitat requirements of lamprey ammocoetes (Petromyzon marinus and Lampetra genus) were investigated, for the first time, from shallow to deep waters, at different spatial scales across the Gironde‐Dordogne continuum, thanks to a water suction dredge. Fish‐habitat relationships were assessed through two complementary statistical analyses: habitat‐use curves and habitat suitability models using the Boosted Regression Trees (BRT) technique. Analyses were performed on a small‐size data set that was characterised by the low prevalence of lamprey. The sea lamprey larvae occurred in deeper areas than their Lampetra genus counterparts. ‘Pools’ of 2 m’ depth and more were optimal habitats for the former species. Among the environmental variables retained to model lamprey occurrences, the mesohabitat (a categorical variable) was demonstrated to be highly influential, in terms of fine grain‐size substratum and vegetation cover. These preliminary results suggest that monitoring using the water suction dredge method may contribute to sea lamprey conservation.     

Effects of supplemental alfalfa hay on the digestion of soybean hull-based diets by cattle

We evaluated the optimal level of alfalfa inclusion in soybean hull-based diets. In Exp. 1, 20 Holstein steers (319 kg of BW) were used in a complete block design. Treatments included a soybean hull mix (95.7% soybean hulls, 3% molasses, 0.5% urea, 0.8% mineral mix; DM basis) fed alone (100:0) or with 10.4, 20.7, or 30.9% (DM basis) coarsely chopped alfalfa hay (90:10, 80:20, and 70:30, respectively) or alfalfa alone (0:100). Diets were fed once daily at 1.75% (DM basis) of BW. In some cases, orts were present, which caused DM, OM, and NDF intakes to decrease (linear, P < 0.05) as alfalfa was added to the diets. Digestibilities of DM, OM, and NDF decreased linearly (P < 0.05) as alfalfa was added to the diets, but quadratic responses (P < 0.05) indicated that positive associative effects occurred between soybean hulls and alfalfa. Liquid dilution rates increased (linear, P < 0.05) with alfalfa additions to the diets and also demonstrated positive associative effects between soybean hulls and alfalfa (quadratic, P < 0.05). Solid passage rates were similar for 100:0 and 0:100 but were increased (quadratically and cubically, P < 0.05) when combinations of soybean hulls and alfalfa were fed. In Exp. 2, in vitro NDF digestibilities were measured for soybean hulls, alfalfa, and a blend of 85% soybean hulls and 15% alfalfa, each with no N source or supplemented with casein or urea to ascertain the effects of protein from alfalfa on digestibility. Disappearances were increased (P < 0.05) by addition of urea or casein, but no interactions between substrate and N supplement were observed. Addition of 30% alfalfa to diets consisting primarily of soybean hulls led to positive associative effects on diet digestibility, but alfalfa additions led to increased liquid and solid passage rates, suggesting that the benefit was not a result of slower passage of soybean hulls from the rumen.     

Evaluating Sugarcane Diets for Dairy Cows Using a Digestion Model

To eliminate unnecessary feeding trials, a mechanistic model of sugarcane digestion was used in the search for suitable supplements to improve milk production. Milk production simulated by the model was compared with data observed in four feeding trials published in the tropical literature where crossbred dairy cows were fed sugarcane/urea diets with different types of supplements. The predicted effects of the supplements on the ruminal microbial population, concentrations of ammonia and volatile fatty acids were also compared with the published results in one experiment. The model indicated the nutrient most limiting milk production for the different feeding situations. The addtion of Leucaena to the basal sugarcane/urea improved the availability of amino acids and long-chain fatty acids, with energy becoming the limiting factor. Supplementation with rice bran increased the availability of energy and long-chain fatty acids, but amino acids then became the limiting factor. Supplementation with both Leucaena and rice bran further improved the milk yield, but availability of energy now limited milk production. Supplementation with Leucaena increased milk production more than supplementation with king grass. The main reason for this increase was increased amino acid absorption due to increased microbial outflow. In all feeding situations, the average difference between the predicted milk production and that observed experimentally was 0.57 kg/d (ranging from 0.08 to 1 kg/d).     

Modelling dairy cattle feeding in the South-East region of Brazil

Computer modelling techniques were applied to study the structure of traditional dairy farms in the South-East region of Brazil and to help define research priorities and policies. Animal feeding is considered the principal factor affecting dairy cattle performance in the study. Knowledge of animal nutrition and feed supply from Brazilian and other literature was synthesized in two mathematical models. One model deals with the optimization of resources used in supplementary feeding for dairy cows under grazing; the other predicts dairy cow performance under a range of feeding conditions imposed by changes in the level of supplementation, stocking rate and calving date. Both models are empirical in nature. The modelling approach shows itself to be a useful means of defining research priorities and making recommendations on practical aspects of dairy cow feeding and management.