Why does nitrogen addition to forest soils inhibit decomposition?

• Enrichment of forest soils with inorganic nitrogen (N) tends to inhibit oxidative enzyme expression by microbes and reduces plant litter and soil organic matter decomposition rates. Without further explanation than is currently presented in the scientific literature, we argue that upregulation of oxidative enzymes seems a more competitive response to prolonged N enrichment at high rates than the observed downregulation. Thus, as it stands, observed responses are inconsistent with predicted responses. In this article, we present a hypothesis that resolves this conflict. We suggest that high rates of N addition alter the competitive balance between enzymatic lignin mineralisation and non-enzymatic lignin oxidation. Using metatransciptomics and chemical assays to examine boreal forest soils, we found that N addition suppressed peroxidase activity, but not iron reduction activity (involved in non-enzymatic lignin oxidation). Our hypothesis seems positioned as a parsimonious and empirically consistent working model that warrants further testing.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Markvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Soil Science (hsv//eng)

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

Nyckelord

Lignin decomposition

Soil carbon cycling

Nitrogen fertilisation

Brown and white rot fungi

Oxidative zymes

Fenton reaction

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