Abstract
Liming can counteract acidification in forest soils, but the effects on soil C and N pools and fluxes over long periods are less well understood. Replicated plots in an acidic and N-rich 40-year-old Norway spruce (Picea abies) forest in SW Sweden (Hasslöv) were treated with 0, 3.45 and 8.75 Mg ha−1 of dolomitic lime (D0, D2 and D3) in 1984. Between 1984 and 2016, soil organic C to 30 cm depth increased by 28 Mg ha−1 (30% increase) in D0 and decreased by 9 Mg ha−1 (9.4% decrease) in D3. The change in D2 was not significant (+ 2 Mg ha−1). Soil N pools changed proportionally to those in soil C pools. The C and N changes occurred almost exclusively in the top organic layer. Non-burrowing earthworms responded positively to liming and stimulated heterotrophic respiration in this layer in both D2 and D3. Burrowing earthworms in D3 further accelerated C and N turnover and loss of soil. The high soil C and N loss at our relatively N-rich site differs from studies of N-poor sites showing no C and N loss. Earthworms need both high pH and N-rich food to reach high abundance and biomass. This can explain why liming of N-rich soils often results in decreasing C and N pools, whereas liming of N-poor soils with few earthworms will not show any change in soil C and N. Extractable nitrate N was always higher in D3 than in D2 and D0. After 6 years (1990), potential nitrification was much higher in D3 (197 kg N ha−1) than in D0 (36 kg N ha−1), but this difference decreased during the following years, when also the unlimed organic layers showed high nitrification potential. Our experiment finds that high-dose liming of acidic N-rich forest soils produces an initial pulse of soil heterotrophic respiration and increases in earthworm biomass, which together cause long-term declines in soil C and N pools.
Highlights
Increasing atmospheric deposition of nitrogen (N), sulfur (S) and protons (H+) affected many areas in Europe and North America during the three decades following World War II and resulted in soil acidification, nutrient imbalances in trees and forest decline (Schulze and others 1989; Ericsson and others 1993; Linder 1995; Prietzel and others 2006)
Our experiment finds that high-dose liming of acidic N-rich forest soils produces an initial pulse of soil heterotrophic respiration and increases in earthworm biomass, which together cause long-term declines in soil C and N pools
After 1990, the D0 plots showed increased nitrification potential despite low pH(H2O) in the FH and 0–5 cm mineral soil layers in 2009 and 2016. These results indicate the presence of acid-tolerant nitrifiers, which may have benefitted from the higher abundance of NH4–N during the aging of the forest stand
Summary
Increasing atmospheric deposition of nitrogen (N), sulfur (S) and protons (H+) affected many areas in Europe and North America during the three decades following World War II and resulted in soil acidification, nutrient imbalances in trees and forest decline (Schulze and others 1989; Ericsson and others 1993; Linder 1995; Prietzel and others 2006). Swedish soils turned out to be affected by soil acidification, and reinvestigation of coniferous forest soils in southern Sweden showed decreasing pH values of 0.3– 1.0 units between 1927 and 1982–1984 (Hallbacken and Tamm 1986). Tree growth often remained unchanged in limed spruce, pine and fir stands (Huttl and Zottl 1993; Lundstrom and others 2003a; Børja and Nilsen 2009, Ouimet and Moore 2015). There were examples of increased growth after liming in productive stands of Norway spruce in Sweden
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