Searching for the perfect surface area normalizing term - a comparison of BET surface area-, geometric surface area- and mass-normalized dissolution rates of anorthite and biotite

Dissolution rates were calculated for a range of grain sizes of anorthite and biotite dissolved under far from equilibrium conditions at pH 3, T = 20 degrees C. Dissolution rates were normalized to initial and final BET surface area, geometric surface area, mass and (for biotite only) geometric edge surface area. Constant (within error) dissolution rates were only obtained by normalizing to initial BET surface area for biotite. The normalizing term that gave the smallest variation about the mean for anorthite was initial BET surface area. In field studies, only current (final) surface area is measurable. In this study, final geometric surface area gave the smallest variation for anorthite dissolution rates and final geometric edge surface area for biotite dissolution rates. (c) 2005 Published by Elsevier B.V.

Does reactive surface area depend on grain size? Results from pH 3, 25 circle C far-from-equilibrium flow-through dissolution experiments on anorthite and biotite

Laboratory determined mineral weathering rates need to be normalised to allow their extrapolation to natural systems. The principle normalisation terms used in the literature are mass, and geometric- and BET specific surface area (SSA). The purpose of this study was to determine how dissolution rates normalised to these terms vary with grain size. Different size fractions of anorthite and biotite ranging from 180-150 to 20-10 mu m were dissolved in pH 3, HCl at 25 degrees C in flow through reactors under far from equilibrium conditions. Steady state dissolution rates after 5376 h (anorthite) and 4992 h (biotite) were calculated from Si concentrations and were normalised to initial- and final- mass and geometric-, geometric edge- (biotite), and BET SSA. For anorthite, rates normalised to initial- and final-BET SSA ranged from 0.33 to 2.77 X 10(-10) mol(feldspar) m(-2) s(-1), rates normalised to initial- and final-geometric SSA ranged from 5.74 to 8.88 X 10(-10) mol(feldspar) m(-2) s(-1) and rates normalised to initial- and final-mass ranged from 0.11 to 1.65 mol(feldspar) g(-1) s(-1). For biotite, rates normalised to initial- and final-BET SSA ranged from 1.02 to 2.03 X 10(-12) mol(biotite) m(-2) s(-1), rates normalised to initial- and final-geometric SSA ranged from 3.26 to 16.21 X 10(-12) mol(biotite) m(-2) s(-1), rates normalised to initial- and final-geometric edge SSA ranged from 59.46 to 111.32 x 10(-12) mol(biotite) m(-2) s(-1) and rates normalised to initial- and final-mass ranged from 0.81 to 6.93 X 10(-12) mol(biotite) g(-1) s(-1). For all normalising terms rates varied significantly (p <= 0.05) with grain size. The normalising terms which gave least variation in dissolution rate between grain sizes for anorthite were initial BET SSA and initial- and final-geometric SSA. This is consistent with: (1) dissolution being dominated by the slower dissolving but area dominant non-etched surfaces of the grains and, (2) the walls of etch pits and other dissolution features being relatively unreactive. These steady state normalised dissolution rates are likely to be constant with time. Normalisation to final BET SSA did not give constant ratios across grain size due to a non-uniform distribution of dissolution features. After dissolution coarser grains had a greater density of dissolution features with BET-measurable but unreactive wall surface area than the finer grains. The normalising term which gave the least variation in dissolution rates between grain sizes for biotite was initial BET SSA. Initial- and final-geometric edge SSA and final BET SSA gave the next least varied rates. The basal surfaces dissolved sufficiently rapidly to influence bulk dissolution rate and prevent geometric edge SSA normalised dissolution rates showing the least variation. Simple modelling indicated that biotite grain edges dissolved 71-132 times faster than basal surfaces. In this experiment, initial BET SSA best integrated the different areas and reactivities of the edge and basal surfaces of biotite. Steady state dissolution rates are likely to vary with time as dissolution alters the ratio of edge to basal surface area. Therefore they would be more properly termed pseudo-steady state rates, only appearing constant because the time period over which they were measured (1512 h) was less than the time period over wich they would change significantly. (c) 2006 Elsevier Inc. All rights reserved.

Factors influencing the dissolution of phosphate rock in a range of high P-fixing soils from Cameroon

A laboratory incubation experiment was conducted to evaluate the soil factors that influence the dissolution of two phosphate rocks (PRs) of different reactivity (Gafsa, GPR, reactive PR; and Togo-Hahotoe, HPR, low reactivity PR) in seven agricultural soils from Cameroon having variable phosphorus (P)- sorption capacities, organic carbon (C) contents, and exchangeable acidities. Ground PR was mixed with the soils at a rate of 500 mg P kg 21 soil and incubated at 30 degrees C for 85 days. Dissolution of the PRs was determined at various intervals using the Delta NaOH-P method ( the difference of the amount of P extracted by 0.5 M NaOH between the PR-treated soils and the control). Between 4 and 27% of HPR and 33 and 50% of GPR were dissolved in the soils. Calcium (Ca) saturation of cation exchange sites and proton supply strongly affected PR dissolution in these soils. Acid soils with pH-(H2O), < 5 (NKL, ODJ, NSM, MTF) dissolved more phosphate rock than those with pH-(H2O) > 5 (DSC, FGT, BAF). However, the lack of a sufficient Ca sink in the former constrained the dissolution of both PRs. The dissolution of GPR in the slightly acidic soils was limited by increase in Ca saturation and that of HPR was constrained by limited supply in protons. Generally, the dissolution of GPR was higher than that of HPR for each soil. The kinetics of dissolution of PR in the soils was best described by the power function equation P At B. More efficient use of PR in these soils can be achieved by raising the soil cation exchange capacity, thereby increasing the Ca sink size. This could be done by amending such soils with organic materials.

Tissue culture propagation alters plant-microbe interactions in tobacco rhizosphere

We have compared properties of roots from different lines (genotypes) of tobacco raised either in tissue culture or grown from seed. The different lines included unmodified plants and plants modified to express reduced activity of the enzyme cinnamoyl-CoA reductase, which has a pivotal role in lignin biosynthesis. The size and structure of the rhizosphere microbial community, characterized by adenosine triphosphate and phospholipid fatty acid analyses, were related to root chemistry (specifically the soluble carbohydrate concentration) and decomposition rate of the roots. The root material from unmodified plants decomposed faster following tissue culture compared with seed culture, and the faster decomposing material had significantly higher soluble carbohydrate concentrations. These observations are linked to the larger microbial biomass and greater diversity of the rhizosphere communities of tissue culture propagated plants.

Dissolution of phosphorus from animal bone char in 12 soils

Heat-treated animal bone char (ABC) has not previously been evaluated for its potential as a phosphorus (P) fertilizer. ABC, Gafsa phosphate rock (GPR) and triple superphosphate fertilizer (TSP) were incubated in 12 soils. Dissolved-P was assessed by extraction with NaOH and bioavailability with the Olsen extractant. The rate of P dissolution from ABC was described almost equally well by the Elovich and Power equations. After 145 days, the fraction of P dissolved ranged from 0 to 73% and to 56% for ABC and GPR, respectively. The most important soil properties determining P dissolution from ABC were pH and P sorption. P dissolution was not significant at soil pH > 6.1 (ABC) and > 5 (GPR) and the lower the pH, the greater the Dissolved-P. Dissolved-P also correlated positively and significantly with inorganic P sorption, measured by the Freundlich isotherm and the P sorption index of Bache and Williams (1971). Soil pH and P sorption index could be combined in multiple regression equations that use readily measured soil properties to predict the potential for ABC dissolution in a soil. Dissolution of P from GPR correlated with soil pH and exchangeable acidity. In comparison with GPR, ABC was a better source of available P, assessed by Olsen-P. In most soils, ABC increased Olsen-P immediately after application, including soils of relatively high pH in which GPR was ineffective. ABC is a P fertilizer of solubility intermediate between GPR and TSP.

Effect of dietary supplementation with selenium-enriched yeast or sodium selenite on selenium tissue distribution and meat quality in beef cattle

The objective was to determine the concentration of total selenium (Se) and the proportion of total Se comprised as selenomethionine (SeMet) and selenocysteine (SeCys) in post mortem tissues of beef cattle offered diets containing graded additions of selenized enriched yeast (SY) [Saccharomyces cerevisae CNCM I-3060]), or sodium selenite (SS). Oxidative stability and tissue glutathione peroxidase (GSH-Px) activity of edible muscle tissue were assessed 10 d post-mortem. Thirty two beef cattle were offered, for a period of 112 d, a total mixed ration which had either been supplemented with SY (0, 0.15 or 0.35 mg Se/kg DM) or SS (0.15 mg Se/kg DM). At enrollment (0 d) and at 28, 56, 84 and 112 d following enrollment, blood samples were taken for Se and Se species determination, as well as whole blood GSH-Px activity. At the end of the study beef cattle were euthanized and samples of heart, liver, kidney, and skeletal muscle (LM and psoas major) were retained for Se and Se species determination. Tissue GSH-Px activity and thiobarbituric acid reactive substances (TBARS) were determined in skeletal muscle tissue (LM only). The incorporation into the diet of ascending concentrations of Se as SY increased whole blood total Se and the proportion of total Se comprised as SeMet, as well as GSH-Px activity. There was also a dose dependant response to the graded addition of SY on total Se and proportion of total Se as SeMet in all tissues and GSH-Px activity in skeletal muscle tissue. Furthermore, total Se concentration of whole blood and tissues was greater in those animals offered SY when compared with those receiving a comparable dose of SS, indicating an improvement in Se availability and tissue Se retention. Likewise, GSH-Px activity in whole blood and LM was greater in those animals offered SY when compared with those receiving a comparable dose of SS. However, these increases in tissue total Se and GSH-Px activity appeared to have little or no effect in meat oxidative stability.

Effects of dietary supplementation with selenium enriched yeast or sodium selenite on selenium tissue distribution and meat quality in lambs

The objective was to determine the concentration of total selenium (Se) and the proportion of total Se comprised as selenomethionine (SeMet) and selenocysteine (SeCys), as well as meat quality in terms of oxidative stability in post mortem tissues of lambs offered diets with an increasing dose rate of selenized enriched yeast (SY), or sodium selenite (SS). Fifty lambs were offered, for a period of 112 d, a total mixed ration which had either been supplemented with SY (0, 0.11, 0.21 or 0.31 mg/kg DM to give total Se contents of 0.19, 0.3, 0.4 and 0.5 mg Se/kg DM for treatments T1, T2, T3 and T4, respectively) or SS (0.11 mg/kg DM to give 0.3 mg Se/kg DM total Se [T5]). At enrolment and at 28, 56, 84 and 112 d following enrolment, blood samples were taken for Se and Se species determination, as well as glutathione peroxidase (GSH-Px) activity. At the end of the study lambs were euthanased and samples of heart, liver, kidney, and skeletal muscle were retained for Se and Se species determination. Tissue GSH-Px activity and thiobarbituric acid reactive substances (TBARS) were determined in Longissimus Thoracis. The incorporation into the diet of ascending concentrations of Se as SY increased whole blood total Se and the proportion of total Se comprised as SeMet, and erythrocyte GSH-Px activity. Comparable doses of SS supplementation did not result in significant differences between these parameters. With the exception of kidney tissue, all other tissues showed a dose dependant response to increasing concentrations of dietary SY, such that total Se and SeMet increased. Selenium content of Psoas Major was higher in animals fed SY when compared to a similar dose of SS, indicating improvements in Se availability and retention. There were no significant treatment effects on meat quality assessments GHS-Px and TBARS, reflecting the lack of difference in the proportion of total Se that was comprised as SeCys. However, oxidative stability improved marginally with ascending tissue Se content, providing an indication of a linear dose response whereby TBARS improved with ascending SY inclusion.

Systemic gut microbial modulation of bile acid metabolism in host tissue compartments

We elucidate the detailed effects of gut microbial depletion on the bile acid sub-metabolome of multiple body compartments (liver, kidney, heart, and blood plasma) in rats. We use a targeted ultraperformance liquid chromatography with time of flight mass-spectrometry assay to characterize the differential primary and secondary bile acid profiles in each tissue and show a major increase in the proportion of taurine-conjugated bile acids in germ-free (GF) and antibiotic (streptomycin/penicillin)-treated rats.Although conjugated bile acids dominate the hepatic profile (97.0 ± 1.5%) of conventional animals, unconjugated bile acids comprise the largest proportion of the total measured bile acid profile in kidney (60.0±10.4%) andheart (53.0 ± 18.5%) tissues. In contrast, in the GF animal, taurine-conjugated bile acids (especially taurocholic acid and tauro-β-muricholic acid) dominated the bile acid profiles (liver: 96.0 ± 14.5%; kidney: 96 ± 1%; heart: 93 ± 1%; plasma: 93.0 ± 2.3%), with unconjugated and glycine-conjugated species representing a small proportion of the profile. Higher free taurine levels were found in GF livers compared with the conventional liver (5.1-fold; P < 0.001). Bile acid diversity was also lower in GF and antibiotic-treated tissues compared with conventional animals. Because bile acids perform important signaling functions, it is clear that these chemical communication networks are strongly influencedbymicrobial activitiesormodulation, as evidenced by farnesoid X receptor-regulated pathway transcripts. The presence of specific microbial bile acid co-metabolite patterns in peripheral tissues (including heart and kidney) implies a broader signaling role for these compounds and emphasizes the extent of symbiotic microbial influences in mammalian homeostasis.

Differential effects of thyroid hormone manipulation and ß adrenoceptor agonist administration on uncoupling protein mRNA abundance in adipose tissue and thermoregulation in neonatal pigs

We have shown that there is significant disparity in the expression of uncoupling proteins (UCP) 2 and 3 between modern-commercial and ancient-Meishan porcine genotypes, commercial pigs also have higher plasma triiodothyronine (T(3)) in on the first day of life. T(3) and the sympathetic nervous system are both known to regulate UCPs in rodents and humans; their role in regulating these proteins in the pig is unknown. This study examined whether thyroid hormone manipulation or administration of a selective beta3 adrenoceptor agonist (ZD) influenced plasma hormones, colonic temperature and UCP expression in adipose tissue of two breeds of pig. To mimic the differences observed in thyroid hormone status, piglets from Meishan and commercial litters were randomly assigned to control (1 ml/kg water), T(3) (10 mg/kg) (Meishan only), methimazole (a commonly used antithyroid drug) (50 mg/kg) (commercial only) or ZD (10 mg/kg) oral administration for the first 4 days of postnatal life. Adipose tissue UCP2/3 mRNA abundance was measured on day 4 using PCR. T(3) administration raised plasma T(3) concentrations and increased colonic temperature on day 4. UCP3 mRNA abundance was higher in Meishan, than commercial piglets (p = 0.042) and was downregulated following T(3) administration (p = 0.014). Irrespective of genotype, ZD increased UCP2 mRNA abundance (Meishan p = 0.05, commercial p = 0.03). Expression of neither UCP2 nor 3 was related to colonic temperature, regardless of treatment. In conclusion, we have demonstrated a dissociation between thyroid hormones and the sympathetic nervous system in the regulation of UCPs in porcine adipose tissue. We have also suggested that expression of adipose tissue UCP2 and 3 are not related to body temperature in piglets.

Influence of porcine genotype on the abundance of thyroid hormones and leptin in sow milk and its impact on growth, metabolism and expression of key adipose tissue genes in offspring

Neonatal mortality is greater in commercial porcine genotypes, compared with the ancient Meishan breed that rapidly lay down adipose tissue; this may be related to hormones, such as triiodothyronine (T3) or leptin. Leptin is present in maternal milk; however, the extent to which this supply provides the neonate with leptin is unknown, but may play a role in growth and development. We investigated whether thyroid hormones and leptin concentrations in maternal milk differed between genotypes; and whether this influenced piglet concentrations or expression of genes involved in adipose tissue regulation. Eight Meishan and six commercial sows were entered into the study and milk samples from the day of parturition to day 4 postpartum was taken daily. The median birth weight piglet in each litter had a daily venous blood sample taken and was euthanised on day 4. Gene expressions of IGF-I, IGF-binding protein 3 (IGFBP-3), peroxisome proliferators activated receptor (PPAR) and glucocorticoid receptor (GR) were measured in adipose tissue using real-time PCR. T3 was increased in Meishan milk, but not in piglet plasma. Milk thyroxine was similar between breeds but commercial piglet levels were significantly higher. Leptin was higher in commercial sow milk throughout the study. Milk leptin was strongly correlated to plasma leptin during the first postnatal days and also to organ and body weight in Meishan piglets that also had significantly higher expression of GR, but not IGF-I, IGFBP-3 or PPAR. In conclusion, we have found a significant disparity in the provision of thyroid hormones in Meishan and commercial sow’s milk. These changes are not always translated to plasma concentrations of hormone in the piglet. Leptin appears to have a stronger role in growth and development in the Meishan genotype compared with commercial; along with the increased GR expression, this may also represent a potential mechanism behind the rapid accumulation of adipose tissue in Meishan piglets.