Effects of drought on nitrogen turnover and abundances of ammonia-oxidizers in mountain grassland
Future climate scenarios suggest an increased frequency of summer drought periods in the European Alpine Region. Drought can affect soil nitrogen (N) cycling, by altering N transformation rates, as well as the abundances of ammonia-oxidizing bacteria and archaea. However, the extent to which drought...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-11-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/11/6003/2014/bg-11-6003-2014.pdf |
| Summary: | Future climate scenarios suggest an increased frequency of summer drought
periods in the European Alpine Region. Drought can affect soil nitrogen (N)
cycling, by altering N transformation rates, as well as the abundances of
ammonia-oxidizing bacteria and archaea. However, the extent to which drought
affects N cycling under in situ conditions is still controversial. The goal
of this study was to analyse effects of drought on soil N turnover and
ammonia-oxidizer abundances in soil without drought history. To this end we
conducted rain-exclusion experiments at two differently managed mountain
grassland sites, an annually mown and occasionally fertilized meadow and an
abandoned grassland. Soils were sampled before, during and after drought and
were analysed for potential gross rates of N mineralization, microbial uptake
of inorganic N, nitrification, and the abundances of bacterial and archaeal
ammonia-oxidizers based on gene copy numbers of the <i>amoA</i> gene (AOB
and AOA, respectively).
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Drought induced different responses at the two studied sites. At the managed
meadow drought increased NH<sub>4</sub><sup>+</sup> immobilization rates and
NH<sub>4</sub><sup>+</sup> concentrations in the soil water solution, but led to a
reduction of AOA abundance compared to controls. At the abandoned site gross
nitrification and NO<sub>3</sub><sup>−</sup> immobilization rates decreased during
drought, while AOB and AOA abundances remained stable. Rewetting had only
minor, short-term effects on the parameters that had been affected by
drought. Seven weeks after the end of drought no differences to control
plots could be detected. Thus, our findings demonstrated that in
mountain grasslands drought had distinct transient effects on soil nitrogen
cycling and ammonia-oxidizers, which could have been related to a niche
differentiation of AOB and AOA with increasing NH<sub>4</sub><sup>+</sup> levels.
However, the effect strength of drought was modulated by grassland
management. |
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| ISSN: | 1726-4170 1726-4189 |