Neural Network Cognitive Analysis of Accumulation of Metals by Marigold

Abstract

The article presents the results of assessing the effect of humic acids, taken at a concentration of 250 ppm, on the process of induced phytoextraction of heavy metals from soils selected near Norilsk. Phytoextraction was carried out by different types of marigold plants: Tagetes patula and Tagetes erecta. The studies were carried out in greenhouse conditions under controlled spectral illumination (light culture). The experiment lasted 21 days. A time range of vegetation period was chosen due to a short summer period typical of the study region, where it is more rational to keep records of the systemic removal of toxicants from contaminated soils by several cycles of their sowing/cutting per season, already at the juvenile phase of ontogenesis. For elemental analysis, the method of atomic emission spectrometry with inductively coupled plasma was used. To assess the level of efficiency of metal accumulation, the authors developed and used the original computing neural network CompNN, which allows calculating the cognitive significance index (CSI) based on empirical data on the accumulation of toxicants, both in shoots and roots of plants. The study results showed that the introduction of an organic additive in the form of humic acids into the soil led to inhibition of the growth of the above-ground part of T. patula. As for T. erecta, the rate of accumulation of green plant biomass did not change when humic acids were added. The decrease in the biomass of shoots of T. patula plants is explained by an increase in the accumulation of metals for different experiment variants by 91.6% on average. The content of metals in the shoots of T. erecta under the influence of humic acids, on the contrary, decreased by 17.3% on average. A similar result was also observed in the root zone: the trend of change in the fixation of metals for both plant species was 40.8 and 10.8%, respectively. Calculation of CSI indices also showed that the addition of humic acids in T. patula increases the intensity of metal accumulation from the soil in its biomass in all variants, while in T. erecta, on the contrary, it decreases. The performed cluster analysis demonstrated the fixation of metals in the main buffer zone of plants and also made it possible to isolate nickel into a separate homogeneous series. Based the distribution of this element in the shoots during experiment variants, it was shown that it is closely associated with copper. The correlation coefficients of their accumulation with the CSI index in the shoots of both plants were r = 0.82, 0.87 for Cu and r = 0.87, 0.83 for Ni. The proximity of these values indicates the priority nature of the accumulation of these metals in the plant biomass of marigolds and also characterizes the manifestation of certain interactions between them in contaminated soil by the type of antagonism or synergism.