Carbon additions increase nitrogen availability in northern hardwood forest soils |
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Authors: | P M Groffman |
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Institution: | (1) Institute of Ecosystem Studies, Box AB, Millbrook, NY 12545, USA e-mail: groffmanp@ecostudies.org, Tel.: +1-914-677-5343, Fax: +1-914-677-5976, US |
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Abstract: | The effects of acetate additions to northern hardwood forest soils on microbial biomass carbon (C) and nitrogen (N) content,
soil inorganic N levels, respirable C and potential net N mineralization and nitrification were evaluated. The experiment
was relevant to a potential watershed-scale calcium (Ca) addition that aims to replace Ca depleted by long-term exposure to
acid rain. One option for this addition is to use calcium-magnesium (Mg) acetate, a compound that is inexpensive and much
more readily soluble than the Ca carbonate that is generally used for large-scale liming. Field plots were treated with sodium
(NA) acetate, Na bicarbonate or water (control) and were sampled (forest floor – Oe and Oa combined) 2, 10 and 58 days following
application. It was expected that the addition of C would lead to an increase in biomass C and N and a decrease in inorganic
N. Instead, we observed no effect on biomass C, a decline in biomass N and an increase in N availability. One possible explanation
for our surprising results is that the C addition stimulated microbial activity but not growth. A second, and more likely,
explanation for our results is that the C addition did stimulate microbial growth and activity, but there was no increase
in microbial biomass due to predation of the new biomass by soil fauna. The results confirm the emerging realization that
the effects of increases in the flow of C to soils, either by deliberate addition or from changes in atmospheric CO2, are more complex than would be expected from a simple C : N ratio analysis. Evaluations of large-scale manipulations of
forest soils to ameliorate effects of atmospheric deposition or to dispose of wastes should consider microbial and faunal
dynamics in considerable detail.
Received: 13 March 1998 |
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Keywords: | Carbon Nitrogen Microbial biomass Mineralization Respiration |
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