Saturday, 15 July 2006

Some Aspects of Soil Enzyme Activity Application.

Evgenia V. Dadenko, Rostov State University, B. Sadovaya str., 105, Rostov-on-Don, 344006, Russia

The major parameters of soils fertility are their biological properties. Among these special emphases is given to the enzyme activity. Some researches established that the activity of soil enzymes can be an additional diagnostic index of soil fertility and its changes as a result of human activity. Application of enzyme activity as a diagnostic index promotes high sensivity to external effects, simplicity of definition and low error of experience. Use of enzyme activity parameters in the diagnostic purposes is limited because of insufficient development of methodical approaches of their application. At carrying out an experiment it is important to rule out the possibility of distortion received results and conclusions because of methodical mistakes. Activity of all biological processes has seasonal dynamics. During long-term researches and selecting of terms of sampling, it is necessary to take into account seasonal variation in the enzyme activities. Often laboratory analyses are not carried out immediately after sampling. Therefore, it is important to study the question of enzyme activity stability. The purpose of the present research was to study seasonal variation in the enzyme activities in soils of South of Russia. The effects of storage conditions and terms of storage on the enzyme activities were also assessed. We have analyzed the activity of catalase, dehydrogenase and invertase. In our investigation we have analyzed enzyme activities of ordinary chernozem, southern chernozem, chestnut soil, alkali soil, solonchak, brown forest soil and grey forest soil. Soils were sampled from sites in different districts of the South of Russia in 1999-2005. Enzymatic activity is changeable during the vegetation season. The character of changes is different in different years. Seasonal variation in the enzyme activities was greater in the arable horizon than in the virgin one. Dynamics of catalase activity was higher than invertase activity. Invertase activity correlates with the humus content, which is a stable and poorly varying parameter. There was no connection of enzyme activities maxima with certain seasons. In different years differences in the rate of enzyme activity were no significant in spring and autumn months. The maximal distinctions were established in the summer. Hence, seasonal dynamics needs to be taken into account at monitoring of soils. Therefore, it is essential to carry out long-term researches at the same time. For chernozems of the South of Russia this is May - June or September - the periods of the minimum variation of enzyme activity. Features of enzyme activity changes in different storage conditions of soil samples were determined. The effects of air-dry, refregiratid and frozen storage on activities of enzymes were assessed The activity of catalase was reduced by all researched samples. In various soils changes had similar character. In two months of storage its activity was leveled, reached one level - 40-50 % from initial. Changes of catalase activity of the South of Russia soils were minimal in the natural - damp samples stored in conditions of low positive temperatures. Field-moist storage was best for preserving the original catalase activity. During initial periods of storage, were revealed increase of invertase, and then its reduction. Activity of dehydrogenase appeared as the most dynamical parameter. A general prediction of the storage behavior of samples could not be made because of the variability of changes shown by the individual soils. Storage in a refrigerator (4C) appeared to be most satisfactory for retaining dehydrogenase activities. Were established the fact of significant reduction in enzyme activity during long-term storage. During 7 year storage catalase and invertase activity was decreased on 45-85 % and 30-80 % accordingly. For 50 years of samples storage catalase activity practically completely was decreased. Similar character of enzyme activity changes at storage of samples of various horizons in various conditions was established. Reduction in invertase activity in the first weeks of storage is more significant, than decrease in catalase activity. After long storage of soil samples in various conditions activities of enzymes were leveled. We have considered different storage conditions of soil samples from the point of view of preservation of distinctions in activity of enzymes between various soils. Distinctions of enzyme activities in the South of Russia soils were kept on initial periods of storage, irrespective of a way of storage of samples.

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