Agriculture and Agri-Food Canada

About: Agriculture and Agri-Food Canada is a facility organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Population & Soil water. The organization has 10921 authors who have published 21332 publications receiving 748193 citations. The organization is also known as: Department of Agriculture and Agri-Food.

Separating Soil Respiration into Plant and Soil Components Using Analyses of the Natural Abundance of Carbon-13

Abstract: In presence of vegetation, the CO 2 -C produced by respiration activity in soils originates from plant C (rhizosphere respiration, R rh ) and from soil C (soil respiration, R s ). Quantitative estimates of the CO 2 produced by each source are required in many studies of C dynamics in the soil-plant system. In this study, we (i) used measurements of the 13 C value of soil CO 2 to separate total soil respiration (R t ) into subeomponents R rh and R, in a maize (Zea mays L.) field under undisturbed conditions and (ii) compared these R rh estimates with values obtained using the root-exclusion approach. The maximum contribution of R rh to total respiration was 45%, observed in August. Estimates of R rh increased from zero 30 d after planting to 2 g CO 2 -C m -2 d -1 70 d after planting, remained relatively constant at that level in August, and then decreased until the end of the growing season. The total C losses as R rh were 17% of the crop net assimilation. Estimates of R s gradually declined from 3.3 g CO 2 -C m -2 d -1 in late June to 1.4 g CO 2 -C m -2 d -1 at the end of the season. Losses of soil C represented 6% of total soil C. Variable values of δ 13 C of the soil CO 2 in the control plot after Day 250 made the technique less reliable late in the season. However, several observations indicated that the approach has potential to provide quantitative estimates of R rh and R,. First, the seasonal pattern of the R rh estimates coincided with that of the plant growth and physiological activity. Second, the cumulated R rh across the growing season agreed well with published data obtained using 14 C labeling techniques. Third, in the maize plot, variation in the estimated R, was closely correlated with changes in soil temperature with a Q 10 of 1.99 (r 2 = 0.87). Finally, the estimates of R rh obtained using the isotopic approach agreed well with those obtained using the root exclusion technique.

Acaricidal properties of Artemisia absinthium and Tanacetum vulgare (Asteraceae) essential oils obtained by three methods of extraction.

Abstract: Essential oils of Artemisia absinthium L. and Tanacetum vulgare L. were extracted by three methods, a microwave assisted process (MAP), distillation in water (DW) and direct steam distillation (DSD), and tested for their relative toxicity as contact acaricides to the twospotted spider mite, Tetranychus urticae Koch. All three extracts of A. absinthium and of T. vulgare were lethal to the spider mite but to variable degrees. The LC50 obtained from the DSD oil of A. absinthium was significantly lower (0.04 mg/cm2) than that of the MAP (0.13 mg/cm2) and DW (0.13 mg/cm2) oil of this plant species. DSD and DW extracts of T. vulgare were more toxic (75.6 and 60.4% mite mortality, respectively, at 4% concentration) to the spider mite than the MAP extract (16.7% mite mortality at 4% concentration). Chromatographic analysis indicated differences in composition between the more toxic DSD oil of A. absinthium and the other two extracts of this plant, indicating that a sesquiterpene (C15H24) compound present in the DSD oil and absent in the other two may enhance the toxicity of the DSD oil. Chemical analysis of the T. vulgare extracts indicated that β-thujone is by far the major compound of the oil (>87.6%) and probably contributes significantly to the acaricidal activity of the oil.

Transitional properties of starch colloid with particle size reduction from micro- to nanometer.

Abstract: High-pressure homogenization was used to disperse starch particles in water and reduce the size from micro- to nanometer. The resultant starch colloids were characterized by particle morphology, mean size, size distribution, and zeta potential. Starch slurries were transformed from a mixture containing sediment, dispersion, and sol, to gel as a result of reduction of the particle size from 3-6mum to 10-20nm under a pressure of 207MPa. Furthermore, this process led to the transition of fluid properties without affecting the crystal structure and thermal stability of starch granules. Viscosity of the colloids increased with an increased number of homogenization passes, accompanied by a decreased particle size, narrower particle size distribution (PSD), and an increased absolute zeta potential, indicating the formation of a suspension or stable gel composed of nanoparticles. Lognormal and two other mathematical functions were established to describe the PSDs and their relationship to the homogenization passes. Hence, an environmentally friendly means of producing starch-based nanoparticles or nanogels with high yields, and predictable size and viscosity properties was presented.

Occurrence of a Hyperglycæmic Factor in the Corpus Cardiacum of an Insect

Abstract: ALMOST two decades have elapsed since Abramowitz et al.1 first reported the occurrence of a ‘diabetogenic’ factor in the sinus gland of a crustacean. To the best of my knowledge the experiments described here are the first to show that a substance with a similar effect occurs in the corpus cardiacum of an insect. The corpus cardiacum was selected for investigation because of its analogy to the sinus glands of Crustacea and its known content of biologically active materials2–4. In view of the recent finding that the main blood sugar in insects is the non-reducing disaccharide trehalose5–7 the effect of corpora cardiaca extracts on both reducing and non-reducing sugars in the blood has been investigated.