Effect of pH and dissolved organic matter on the abundance of nirK and nirS denitrifiers in spruce forest soil

Abstract

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.

Effects of nitrogen deposition and fertilization on N transformations in forest soils: a review

“…Despite the fact that 16 years of reduced N deposition in spruce forest soil increased NH 4 + availability but did not affect denitrification genes ), Levy-Booth et al (2014) still pointed out that the abundance of certain denitrification genes (napA, nirS, nirK, and nosZ) in forest soils will increase with increasing total N and NH 4 + concentrations through exogenous N input if soil pH, moisture, and organic C favor or facilitate denitrification. In a highly acidic spruce forest soil, Bárta et al (2010) found that there were exponential correlations between the amount of nirK denitrifiers and DOC and pH, showing two important threshold values being 4.8 mol kg −1 and 5, respectively, and below these two values, the amount of nirK denitrifiers decreased rapidly. Therefore, decreased soil pH and C availability may mitigate the stimulation of N deposition and fertilization on denitrification in forest ecosystems (Šimek et al 2002), which may provide explanations for the reversed trends in denitrification (N 2 O emission) of forest soils over time under fertilization (Aronson and Allison 2012;Bengtsson and Bergwall 2000).…”

“…In addition, they found that the richness and diversity of genes involved in the decomposition of starch (~12 %), hemicellulose (~16 %), cellulose (~16 %), chitin (~15 %), and lignin (~16 %) were also significantly reduced by experimental N deposition. Lots of studies have proven that increased N deposition to forest ecosystems has led to soil acidification (Fluckiger and Braun 1998;, which may also affect the activities of soil microbes and C availability (Bárta et al 2010;Fang et al 2004). For instance, in a highly acidic spruce forest soil, the amounts of dissolved organic C (DOC) and dissolved N were found to be very low (Bárta et al 2010).…”

“…Lots of studies have proven that increased N deposition to forest ecosystems has led to soil acidification (Fluckiger and Braun 1998;, which may also affect the activities of soil microbes and C availability (Bárta et al 2010;Fang et al 2004). For instance, in a highly acidic spruce forest soil, the amounts of dissolved organic C (DOC) and dissolved N were found to be very low (Bárta et al 2010). It is well accepted that mycorrhizal fungi exert strong controls over belowground C allocation in forest ecosystems, greatly affecting microbial turnover in the rhizosphere (Janssens et al 2010;Kuzyakov and Xu 2013;Lilleskov et al 2001Lilleskov et al , 2002Tietema 1998;Treseder 2008).…”

“…At site level, the denitrifier community activity and denitrification processes may be greatly influenced by soil moisture and O 2 partial pressure (Gundersen et al 2012;Pilegaard et al 2006;Russow et al 2009), organic C and soil pH (Bárta et al 2010;Gundersen et al 2012;Levy-Booth et al 2014;Pilegaard et al 2006), and oxidation capacity (OXC) (Zhang et al 2009). In addition, the accessibility of NO 3 − ions to denitrifiers on soil particles can also exert an influence on denitrification (Bengtsson and Bergwall 2000).…”

Contrasting denitrifier communities relate to contrasting N2O emission patterns from acidic peat soils in arctic tundra

“…Copy numbers of nirS outnumbered nirK by 2 to 3 orders of magnitude in both acidic peat soils ( Table 5), indicating that nirS-rather than nirK-type denitrifiers were associated with denitrification in acidic peat soils. Indeed, nirS abundance in spruce forest soil was positively correlated with decreasing pH from 6.1 to 3.7, whereas nirK abundance was negatively correlated (Barta et al, 2010). Such data suggest that low pH and high moisture contents might favor nirS-type rather than nirK-type denitrifiers in acidic peat soils and highlight differences in detected nitrite reductase gene containing denitrifier communities of cryoturbated and unturbated peat soils.…”