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Microbial Activity of Soil E-mail
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Monday, 02 July 2007

Microbial Activity of Soil


Oleynik A.S.1, Bityutskii N.P.2, Byzov B.A.1

1 Faculty of Soil Science, Moscow Lomonosov State University, Leninskie gory, GSP-2, Moscow, Russia; 2 Saint-Petersburg State University, Staryi Petergoff, Oranienbaumskoe shosse, 2, Saint-Petersburg, Russia

A number of studies have shown that earthworms affect biological activity of soils. In drilosphere, a two-fold increase in the abundance of bacteria was observed. The length of fungal mycelium decreased by one third. The quantity of the total nitrogen, carbon and humidity noticeably increased in comparison with native soil. These features give the basis to believe that earthworms actively participate in turnover of biogenic elements and regulate microbial communities of soil (Tiunov, Scheu, 1999). The aim of this study was to test the hypothesis whether excretes (mucosa and excrement) of earthworms may act as regulator of microbiological activity of soils.

Excretes were obtained by placing 50 worms in 0.5 kg of sterilized sand for 2 days. Then the excretes were extracted from sand with distilled water and added to soddy-podzolic soil. Dynamics of soil respiration and mineral nitrogen were measured. Influence of excretes in quantity equivalent to volume, that comes from one worm in 10 grams of soil (8 µg C/g, 2.5 µg organic N/g and 0,17 µg NH4+/g), led to increased respiration of microorganisms in 2 hours after treating the soil. Emission of CO2 was found to be 2-3 times higher when soil was treated with excretes. Addition of glucose in quantity equivalent to carbon that comes with earthworm excretes did not increase respiration. Considering the small amount of the carbon from the excretes and the fast reaction of the microbial community, it is possible to assume that excretes stimulate respiration of microorganisms on the stressful mechanism. The reaction proceeds and disappears in a day after treating excretes. Dilution removes effect. This means that there is some threshold concentration of substances which cause stressful influence on microbial respiration.

Results of plating have shown that quantitative changes in bacteria and fungi have not occurred, therefore we concluded that worm excretes do not change the structure of microbial community.

We have found for the first time that earthworm excretes stimulated mineralization of compounds of nitrogen in soil. For two days after treating the concentration of NH4+ increased by 19 % and that of NO3- by 2 times. It corresponds to 70 times and 20000 times more ammonium and nitrate ions, respectively, than has come with excretes. The concentration of nitrate ion remained higher even on day 30 of the addition of excretes. Dilution removes the effect. Therefore, there is some threshold concentration of substances, which cause stressful influence. Ammonium chloride added at a concentration equivalent to that of the excretes stimulated nitrification, too. This led us to assume, that earthworm excretes could act as promoter (priming effect) of mineralisation of organic nitrogen and nitrification in soil. Ammonium as the major component of earthworm excretes could stimulate nitrification in soil, causing long-term cumulative effects disproportional to the direct action. Possibly, complex organic substances are utilized through so-called co-metabolism.

Last Updated ( Monday, 02 July 2007 )
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