Effects of drought on nitrogen turnover and abundances of ammonia-oxidizers in mountain grassland

[摘要] Future climate scenarios suggest an increased frequency of summer droughtperiods in the European Alpine Region. Drought can affect soil nitrogen (N)cycling, by altering N transformation rates, as well as the abundances ofammonia-oxidizing bacteria and archaea. However, the extent to which droughtaffects N cycling under in situ conditions is still controversial. The goalof this study was to analyse effects of drought on soil N turnover andammonia-oxidizer abundances in soil without drought history. To this end weconducted rain-exclusion experiments at two differently managed mountaingrassland sites, an annually mown and occasionally fertilized meadow and anabandoned grassland. Soils were sampled before, during and after drought andwere analysed for potential gross rates of N mineralization, microbial uptakeof inorganic N, nitrification, and the abundances of bacterial and archaealammonia-oxidizers based on gene copy numbers of the amoA gene (AOBand AOA, respectively).

Drought induced different responses at the two studied sites. At the managedmeadow drought increased NH₄⁺ immobilization rates andNH₄⁺ concentrations in the soil water solution, but led to areduction of AOA abundance compared to controls. At the abandoned site grossnitrification and NO₃⁻ immobilization rates decreased duringdrought, while AOB and AOA abundances remained stable. Rewetting had onlyminor, short-term effects on the parameters that had been affected bydrought. Seven weeks after the end of drought no differences to controlplots could be detected. Thus, our findings demonstrated that inmountain grasslands drought had distinct transient effects on soil nitrogencycling and ammonia-oxidizers, which could have been related to a nichedifferentiation of AOB and AOA with increasing NH₄⁺ levels.However, the effect strength of drought was modulated by grasslandmanagement.

[学科分类] 地球化学与岩石