SUMMARYRoots and rhizomes were sampled in a three-year-old grass ley during one year using a mesh bag method and soil coring. Samples, collected after different growth periods (1, 2, 3, 4, 5, 6 and 12 months) and at different times of the year, were analyzed for carbohydrates and Klason lignin. Throughout the year the rhizomes contained more non-structural carbohydrates (20 to '^0% of the organic matter) than the roots (1 to 8%). The non-structural carbohydrate content varied over the year with a maximum in autumn and minimum in early spring and sunimer after the first grass cut. Fructan was the predominant constituent in this fraction. Structural carbohydrates and Klason lignin showed relatively small variations over the annual cycle. The ratio between structural carbohydrates and Klason lignin showed little variation with time but differed between roots (1-9) and rhizomes (2-5). The xylose content was higher in the roots than in the rhizomes. Only small changes occurred with time in the relative composition of the structural carbohydrates. This consistency in composition implies that there was a difference between subterranean and aerial parts. In the latter, ageing is characterized by increased lignification and systematic changes in structural carbohydrates owing to the formation of secondary cell walls.

The content of water-soluble substances and starch in the living tree stem at the time of felling influences wood durability during further utilization. The aim of the study was to describe the annual and seasonal fluctuations in the contents of stored carbohydrates and nitrogenous compounds. The contents of soluble sugars, starch, and nitrogen were measured in the outer sapwood (0-15 mm from cambium) of 65-yr-old Scots pine {Pinus sylvestris L.) trees during an annual cycle. To study the influence of growth conditions, samples were taken from different stands in Sweden, in one stand from a control and a fertilized block. The effect of the age of the trees on the content of stored substances was also considered by comparing young (10-15 yrs old) and older trees (40-65 yrs old). Determination of the carbohydrates was carried out using enzymatic analysis. The outer pine sapwood contained a higher content of low-molecular weight sugars during autumn and winter than during spring and summer. Starch content rose at the beginning of the growth period and decreased in autumn. The content of soluble sugars increased towards the cambium on all sampling occasions. Fructose and glucose were dominant sugars in all the stands studied. Seasonal changes of sucrose were different from those of glucose and fructose, in that the sucrose content was already decreasing in February. The variations in the nitrogen content of the sapwood were far smaller than those of the soluble sugars. No significant differences were found between the stands with regard to glucose, fructose and the sum of all three sugars. The fertilized block showed low content of sucrose and nitrogen. It is concluded that seasonal fluctuations are more important with regard to the sugar content than the effect of growth conditions. Data indicate a lower content of soluble sugars and nitrogen in the outermost sapwood of young trees as compared with older trees.

No abstract

Nine laboratories from Denmark, Finland, Norway, and Sweden participated in a collaborative study to evaluate an immunoaffinity column cleanup/liquid chromatographic determination of aflatoxins B and G. Samples of peanut, fig, maize gluten, soya expel-ler, and copra spiked with total aflatoxin concentrations ranging from 1.37 to 28.60 ng/g were distributed. Altogether, 13 samples were analyzed. Of these, 6 were pairs of blind duplicates, 1 was an unknown negative sample containing ¼0.1 ng/g, and 2 were practice samples. A statistical presentation of the results is given. Although the results obtained were individually corrected for recovery, they were lower than expected in most cases. In some cases, the recoveries were unacceptably low, particularly for aflatoxin G2. Relative standard deviations for method repeatability (RSDr) and reproducibility (RSDR) were good but generally better for the peanut and fig samples than for the others. Results were better for aflatoxins B1 and G1 than for aflatoxins B2 and G2. RSDR values varied from 9 to 35%, and RSDR values varied from 17 to 81%. Horwitz ratio values were >2.00 for 1 RSDR value and <1.00 for 23 of the 35 calculated RSDR values.

Assessment of fertilizer nitrogen accumulation in Pinus sylvestris trees and retention in soil by 15 N recovery technique. Accepted Jan. 9, 1989. Scand. J. For. Res. 4:427-442, 1989.The distribution and quantitative recovery of fertilizer N were determined in three 29-to 43-year-old stands of Scots pine, located in western Uppland, Central Sweden. The experimental technique involved was based on the use of 15 N-labelled fertilizer materials and non-trenched microplots of special design. The standard dose of nitrogen applied was 160 kg N ha -1 . The primary topics examined were (1) fertilizer nitrogen accumulation in trees and in the soil system as influenced by nitrogen source, nitrogen application rate, time of application during the growing season, granule size of the nitrogen material, and method of placement, (2) distribution of labelled N within the tree (different organs of the tree), and (3) redistribution of accumulated N in the tree over an observation period of two to three growing seasons. When quantified at the end of the second growing season, the labelled N accumulation in trees, concerning plots treated with calcium nitrate or ammonium nitrate, averaged 36% (SD=7). The accumulation resulting from split doses did not differ significantly from that resulting from a single-dose application, nor did granule size of the nitrogen materials have any significant effect on accumulation. For urea source of nitrogen, the recovery figure was markedly lower, averaging 28% (SD=6). When expressed as a percentage, the accumulation in trees was not significantly different for 40 and 160 kg nitrogen application rates. In one of the experiments application timing during the growing season proved to be an important factor determining the extent of fertilizer nitrogen accumulation in trees. The figures for total recovery of labelled nitrogen in aboveground parts of trees and in soil, when restricting measurements to the forest floor and the 0-32 cm mineral soil, ranged from 46 to 84%, with an average of 60%. The recovery was lowest for a treatment with calcium nitrate, when applied relatively late in the growing season, and highest for a split application of urea. Treatments with urea source of nitrogen were characterized by a high accumulation of immobilized N in the organic LFH layer of the soils. Recovery figures exceeded 82 % for a 40-kg N dose of nitrogen, regardless of the nitrogen source.