Articles

A laboratory experiment was carried out to investigate the sorption behavior of 2.4-D onto two types of bentonite material: Na-Ca bentonite and organically modified bentonite (HDTMA-Br) using hexadecyltrimethylammonium bromide. The amount of HDTMA-Br was equivalent to the cation exchange capacity of the dominant mineral, montmorillonite, in the bentonites. The results showed that the organically modified bentonite absorbed 4.5 times more 2.4-D compared to the unmodified Na-Ca bentonite, indicating a significantly stronger sorption affinity for the organic cation. This finding suggests that organically modified bentonites may be more effective for the removal of 2.4-D from contaminated soil or water. In the range of pH values between 4 and 6, the sorption sites on the hydrophobic surface of organobentonite were found to have a relatively uniform energy for 2.4-d molecules (Freundlich constant n ≈ 0.8). Hydrophobic interactions were the dominant mechanism for the uptake of 2.4-D at these pH values. The possibility of using HDTMA-bentonite to reduce the mobility of 2.4-D in soils and landscapes, or to create new formulations, should be considered only after a thorough evaluation of the toxic effects of the organoclay on nontarget organisms.

Currently, the physiological and biochemical role of certain groups of phenols that have high biological activity remains poorly understood. Thus, the functions of hydroxycinnamic acids, related to phenylpropanoids, and, in particular, caffeic acid (CA), remain unclear.

The purpose of this work was to study the effect of different concentrations of caffeic acid on barley productivity, both under normal plant development conditions and in the presence of salt stress.

In a series of laboratory experiments using different test cultures and in a growing season on spring barley plants Hordeum vulgare L., the effect of CA was studied. The activity of different concentrations of caffeic acid was determined using several methodological approaches to phytotesting: the express method in Petri dishes; in plastic flat tablets using the applicate method; in conditions of growing plants in aqueous solutions. The vegetation experiment was carried out on gray forest medium-loamy soil with an organic matter content of 3.8%, a slightly acidic reaction of the soil solution (pH_KCl 5.9). NaCl solution (7.5 g×l^–1) was added to the 2–3 leaf phase. Plants were treated with CA foliarly once during the tillering phase. Three concentrations of CA were used in the experiment, based on the results of preliminary laboratory experiments: 100 µM, 50 µM, 10 µM. At the beginning of booting, the barley plants were harvested and soil samples were taken. Potassium, sodium and total nitrogen content were determined in dry plant mass. The flag leaf of plants was used to determine the content of chlorophyll and carotenoids.

According to the results of phytotesting, it was established that for monocotyledonous and dicotyledonous crops the greatest activity is manifested in variants with the lowest concentrations of CA (10 and 25 μM), while higher concentrations of CA (50 and 100 μM) significantly reduce all test indicators. Based on the results of the growing season, it was established that CA does not have a reliable stimulating effect. Under conditions of sodium chloride salinity with the use of a high concentration of CA (100 μM), a slight increase in the potassium content in the soil occurs. The sodium content in the soil decreased with the use of CA. The total plant weight per vessel decreased significantly from 1.25g/vessel to 0.25g/vessel. Without the use of NaCl, CA treatment was not accompanied by significant changes in barley weight. The content of chlorophyll (a and b) in the control variant (1.83 mg×g^–1) was significantly lower compared to their content in the leaves of plants that were treated with CA (4.03 mg×g^–1 — 10 µM and 3.14 mg×g^–1 — 100 µM). Against the background of NaCl, the content of total chlorophyll decreased to 0.24 mg/g, and when plants were treated with CA it increased from 1.26 mg×g^–1 at low concentration (10 µM) and to 2.14 mg×g^–1 at high concentration (100 µM). The use of CA at a concentration of 100 µM was accompanied by an increase in carotenoid content from 0.22 mg×g^–1 to 0.61 and, against the background of salinity, from 0.16 to 0.38 mg×g^–1. Thus, the use of CA for treating plants during the growing season under salinity conditions affects changes in physiological processes, which contributes to their adaptation.

The response of biological activity and the content of labile forms of biogenic elements in peats of different genesis to variation in their moisture content was studied under laboratory conditions. Samples of peat soils of the northern and southern taiga (Tyumen and Moscow regions) were used in this work. A series of manipulation experiments were conducted in which the dynamics of such indicators as basal respiration (BR), microbial biomass carbon, labile carbon and nitrogen content were estimated for different peat types at different moisture levels. The effect of the experiment duration and type on the dynamics of peat properties was also assessed. It was found that all the studied peat samples are characterized by a wide range of moisture content, at which the maximum of biological activity is observed. In general, it is in the range from 20–30% to 80–90% of water–holding capacity (WHC). In this range, no significant relationship is observed between moisture content and BR. In most experiments, a reliable decrease in biological activity was observed only in the "extreme" humidity ranges - less than 20% and more than 90% WHC. It is shown that the nature of the response to moistening is individual, determined by the properties of the sample and depends little on the type of sample preparation. In experiments and model calculations, it is proposed to use the obtained sensitivity coefficient to moisture — W₂₀, which is 1.0‒1.2 in the range of 40‒80% WHC for peat samples of different genesis. Long-term variants of incubation experiments showed a more pronounced response to overmoistening and a reliable decrease in biological activity at high humidity values (more than 80% WHC). This may indicate their better applicability for solving problems of modeling the behavior of ecosystems in the event of a change in the hydrological situation.