Effect of alder(Alnus glutinosaL. Gaertn.) roots on distribution of proteolytic, ammonifying, and nitrifying bacteria in soil

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Abstract
The aim of this study was to determine the main factor affecting mineralizing and nitrifying bacteria in a riparian bank, where alder ( Alnus glutinosa L. Gaertn., diazotrophic plant), willow (Salix alba L.) and poplar (Populus × hybrida Moench 1–214) were the main species of vegetation. This was investigated by estimating the most probable number of microorganisms in soil samples from roots collected in spring, summer, autumn, and winter. The numbers of the total microbial population and the ammonifying and proteolytic microorganisms were higher in the plant rhizosphere and rhizoplane than in the shaded soil, litter, and root‐free soil under the trees. Nitrifier densities were the lowest around alder roots. Principal components analysis showed that the main factor affecting microorganism density was the rhizosphere of alder trees. Our results suggest that roots favor microorganism colonization (proteolytic and ammonifying microorganisms) and that roots, particularly alder roots, inhibit nitrifying microorganisms.