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ŠUMARSKI LIST 7-8/2021 str. 30     <-- 30 -->        PDF

significantly less than the relative values from 2003 and 2004, but that these differences are not the same for all tissue types. These results can be explained by tree metabolism slowing down  and the intensity of photosynthesis during the vegetation dormancy, which results in poorer flow through the conducting tissues and temporary accumulation of 137Cs in the phloem, xylem and root, while on the other hand during the growing season, boosted metabolism and intensive circulation of substances in the relation root - xylem - needles - phloem – root,  the temporary accumulation of 137Cs is seen in the top shoots and needles.
Relationship of 40K and 137Cs activities in the tissues of silver fir – Odnos aktivnosti 40K i 137Cs u tkivima obične jele
Behavior and distribution of cesium in plants and organisms is similar to potassium because these elements are homologous (Shaw and Bell 1991, Robinson and Stone 1992). Research (Lovrenčić et al. 2008) confirms that 137Cs is involved in physiological processes in a similar way as potassium. For this purpose, a 40K distribution was measured simultaneously with that for 137Cs, in the same samples by gamma spectrometric measurement. The scatter plot in Figure 12 shows the ratio of the measured 40K and 137Cs activities in fir tissues (for twigs, needles, rings, bark and cambium). The obtained result is expressed collectively for all tissue types and shows the ratio of measured values for 40K and 137Cs, where each point on the graph represents an arranged pair of values for 40K and 137Cs measured in the same tissue type, sampled at the same time (the same year) and at the same height of an ordinary fir tree (when it was sampled from several heights for some type of tissue). We can observe a large scattering of data, with a linear correlation that is statistically significant (R = 0.4999; with p = 0.000), so this result is not inconsistent with the fact that 40K and 137Cs are homologous isotopes that the plant does not distinguish. The grouping of points from samples of different tissue types can also be observed on the same graph, so it was appropriate to perform the same analysis separately for individual tissue types.
Distribution of 40K and 137Cs in the soil – Distribucija 40K i 137Cs u tlu
While the focus of the research was the distribution of 137Cs activity in the plant tissue of silver fir, we collected composite samples of forest soil at the same site Vrhovine, on which we measured activity of 40K and 137Cs (Bq/kg) by gammaspectrometer in all three sampling years (Table 2). The level of 137Cs activity in the fir forest was much higher in the samples of soil collected in 2003 and 2004 in relation to the activity levels measured on 2017 samples (recalculated on day July 1, 2003 and July 1, 2016). The 40K activity level in 2017 was twice higher as in 2003 and 2004.
Activity of 137Cs in the tissues of silver fir trees – Aktivnost 137Cs u tkivima drveća obične jele
The results of this study showed that the distribution of 137Cs activity within each individual tissue was causally related to the degree of physiological activity in a particular tissue. In the radial distribution, this is reflected in an increased activity value with decreasing age (the maximum activity was observed in the youngest wood rings), while the vertical distribution is reflected in the increased activity correlated to the height of the tree. In the underground part (root samples) the similar dependence was measured in the vegetation period, while during the vegetation dormancy the level of 137Cs activity did not vary significantly with the reduction of the root dimensions. The results of this study show similar dynamics of 137Cs movement in fir tissues (Abies Alba Mill.) as in previous results by Popijač et al. (2004) fifteen years