Abstract
Soil proteases are involved in organic matter transformation processes and, thus, influence ecosystem nutrient turnovers. Phytohormones, similarly to proteases, are synthesized and secreted into soil by fungi and microorganisms, and regulate plant rhizosphere activity. The aim of this study was to determine the effect of auxins, cytokinins, ethephon, and chlorocholine chloride on spruce forest floor protease activity. It was concluded that the presence of auxins stimulated native proteolytic activity, specifically synthetic auxin 2-naphthoxyacetic acid (16% increase at added quantity of 5 μg) and naturally occurring indole-3-acetic acid (18%, 5 μg). On the contrary, cytokinins, ethephon and chlorocholine chloride inhibited native soil protease activity, where ethephon (36% decrease at 50 μg) and chlorocholine chloride (34%, 100 μg) showed the highest inhibitory effects. It was concluded that negative phytohormonal effects on native proteolytic activity may slow down organic matter decomposition rates and hence complicate plant nutrition. The study enhances the understanding of rhizosphere exudate effects on soil microbial activity and soil nitrogen cycle.
Highlights
Forest Floor of Norway Spruce Stand.Bacteria are ubiquitous organisms distributed unevenly in the soil environment
The naphthoxyacetic acid (NOA) synthetic auxin stimulated native protease activity the most in all studied quantities, with the highest stimulation achieved at 5 μg (16%, 91.22 μg l-tyrosine produced)
Occurring auxins showed generally lower stimulating effect on native soil protease activity with the exception of indole-3-acetic acid (IAA) at the 5 μg quantity (92.36 μg), a stimulating response to the addition of 5 μg IAA was detected in the Oe horizon of the spruce stand
Summary
Bacteria are ubiquitous organisms distributed unevenly in the soil environment. The highest concentrations of bacteria are found around the roots of plants in the so-called rhizosphere [1]. Rhizosphere bacteria can play a key role in the transformation and mobilization of macro- and micronutrients in the soil, improving the nutritional state of plants [2,3]. Phytohormones synthesized and secreted into their surroundings by plant growth-promoting rhizobacteria (PGPR), located in the rhizosphere (close to the plant roots) [4] act as plant growth regulators (PGR). Much like bacteria, can interact with plants in a beneficial way, for example, in the form of mycorrhizal symbiosis [5]
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