Effect of pH and dissolved organic matter on the abundance of nirK and nirS denitrifiers in spruce forest soil
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Acid N depositions in the Bohemian Forest during the second half of the last century caused enormous soil acidification which led to the leaching of essential nutrients including nitrates. We investigated the effect of dissolved organic matter (DOM) and pH on the abundance of 16S RDNA, nirK and nirS gene copies in four spruce forest sites. Soil samples for molecular based quantification (qPCR) were taken from the organic litter and humus layers. The amounts of dissolved organic carbon (DOC) and dissolved nitrogen (DN) were much lower in highly acidified soils. We found a strong correlation between nirK denitrifiers and the amount of available P (r = 0.83, p < 0.001), which suggested a higher nutrient sensitivity of this group of denitrifying bacteria. Additionally, we found that correlations between the amount of nirK denitrifiers and DOC and pH are exponentional showing two important threshold values, being 4.8 mol kg−1 and 5, respectively. The amount of nirK denitrifiers rapidly decreased below these values. The amount of nirK and nirS denitrifiers was higher in the organic litter horizon than the organic humus horizon at all sampling sites.
KeywordsDissolved organic matter Available phosphorus nirK and nirS denitrifiers Acid forest soil N depositions qPCR
This study was supported by the Czech Science Foundation, project 526/08/0751 and 206/07/1200 and the project MSM 6007665801. We acknowledge the laboratory and field assistance provided by our colleagues and students. We also thank the authorities of NP Šumava and The Jizera Mountains for permission to study the spruce forest ecosystems. We thank our American colleague Dr. Keith Edwards for language correction.
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