Ladislav Holík

The role of cytokinins, ethephon, and chlorocholine chloride in the native proteolytic activity of forest soils

PurposePlant growth-promoting rhizobacteria (PGPRs) synthesizes and exports phytohormones which are called plant growth regulators (PGRs). These PGRs may play a regulatory role in plant growth and development. PGRs are organic substances that influence physiological processes of plants at extremely low concentrations. The objective of this study was to find out whether three PGRs, cytokinins, ethephon, and chlorocholine, have a stimulatory or inhibitory effect on the activity of native proteases in soil.Materials and methodsA revised methodology was used to determine soil protease activity, where TRIS-HCl buffer was replaced with demineralized water. This is described as native protease activity as its activity is not affected by chemicals. The aim was to approximate the protease response to cytokinins in the native soil environment. The native soil proteolytic activity was determined spectrophotometrically.Results and discussionThe present paper shows that cytokinin, ethephon, and chlorocholine chloride negatively affect the native proteolytic activity of forest soils with the exceptions of the organic and organomineral horizons of European beech (Fagus sylvatica L.) on a rendzic Leptosol. In addition, 6-benzylaminopurine stimulates the native proteolytic activity of the organic horizon of pedunculate oak (Quercus robur L.). A negative effect of cytokinins on the soil proteolytic activity can decrease the rate of organic matter decomposition. The results provide soil biochemists with an insight into the roles of rhizospheric substances on soil microbial activity.ConclusionsThis work has shown that cytokinins and PGRs inhibit the activity of native soil proteases in most of the studied forest sites. Results describe the effect of rhizospheric compounds on the activity of soil microorganisms, with potentially significant implications for the nitrogen cycle in forest soils.

Seasonal dynamics of arginine ammonification in forest soils of Norway spruce pure stands under different silvicultural practices

Abstract Effects of seasonal dynamics and silvicultural practice on ammonification of arginine, one of the proteinogenic amino acids, were assessed in surface organic H-horizon of three Norway spruce pure stands in medium altitudes (600 - 660 m a.s.l.). Contents of ammonium ions NH4+ measured monthly in the field and contents of NH4+ after laboratory incubation of these samples with arginine were taken as dependent variables in ANOVA and in linear regression model using generalised linear model. The aim of the analyses was to determine the significance of decomposition of this amino acid in H-horizon of forest soils and to determine categorical and continuous predictors which influence intensity of the ammonification. Laboratory experiments confirmed its close link to seasonal dynamics, as well as to forest management; however the last mentioned was firstly found as less significant when compared within whole season. As regards to seasonal dynamics in forest soils, the highest amount of ammonium ion was released in May and the lowest in July. As regards to the silvicultural practice applied, more ammonium ion was released under mature spruce monoculture, especially in August and May; in the young stands, the method of thinning had no effect on the ammonium ion release. However, the arginine ammonification was found to be influenced by ammonium nitrogen content (slight, less significant negative correlation) and by soil water content (stronger positive significance), especially in the stand with thinning from below. This was concluded to be caused by changes in stand microclimate in function of the silvicultural practice.

Effect of salicylic acid on protease and urease activity in soils under Norway spruce pure stands

This study tested the hypothesis that soil protease and urease activity is inhibited by salicylic acid. This was tested in soils from spruce monocultures of different ages and treated by different forest management methods at the Rajec-Němcice Ecosystem Station. Surface organic H-horizons from three study plots were sampled: a mature spruce monoculture of 105 years and two young spruce monocultures of 33 years, one of which was thinned from above and the other thinned from below. Statistically significant differences between the measured values confirm that young stands are sensitive to the presence of 2-hydroxybenzoic acid as a phytotoxic substance. The results of this study do not conclusively show whether the effect of salicylic acid on protease activity inhibition increases when the protease activity itself is high. The impact of salicylic acid on soil urease activity was not clearly evident either.