Comparison of the impacts of acid and nitrogen additions on carbon fluxes in European conifer and broadleaf forests

• Published in: Environmental pollution (1987) Vol. 238; pp. 884 - 893
• Main Authors: Oulehle, Filip, Tahovská, Karolina, Chuman, Tomáš, Evans, Chris D., Hruška, Jakub, Růžek, Michal, Bárta, Jiří
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2018
• Subjects: Acidity; Bacteria; DOC; Fertilization; Fungi; Hydrolytic enzymes; Nitrogen; Organic carbon; Respiration; Sulphur; Fungi; Organic carbon; Fertilization; Hydrolytic enzymes; DOC; Bacteria; Acidity; Nitrogen; Respiration; Sulphur
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2018.03.081

Increased reactive nitrogen (N) loadings to terrestrial ecosystems are believed to have positive effects on ecosystem carbon (C) sequestration. Global “hot spots” of N deposition are often associated with currently or formerly high deposition of sulphur (S); C fluxes in these regions might therefore not be responding solely to N loading, and could be undergoing transient change as S inputs change. In a four-year, two-forest stand (mature Norway spruce and European beech) replicated field experiment involving acidity manipulation (sulphuric acid addition), N addition (NH4NO3) and combined treatments, we tested the extent to which altered soil solution acidity or/and soil N availability affected the concentration of soil dissolved organic carbon (DOC), soil respiration (Rs), microbial community characteristics (respiration, biomass, fungi and bacteria abundances) and enzyme activity. We demonstrated a large and consistent suppression of soil water DOC concentration driven by chemical changes associated with increased hydrogen ion concentrations under acid treatments, independent of forest type. Soil respiration was suppressed by sulphuric acid addition in the spruce forest, accompanied by reduced microbial biomass, increased fungal:bacterial ratios and increased C to N enzyme ratios. We did not observe equivalent effects of sulphuric acid treatments on Rs in the beech forest, where microbial activity appeared to be more tightly linked to N acquisition. The only changes in C cycling following N addition were increased C to N enzyme ratios, with no impact on C fluxes (either Rs or DOC). We conclude that C accumulation previously attributed solely to N deposition could be partly attributable to their simultaneous acidification. [Display omitted] •Acidification alters soil carbon fluxes in spruce forest.•No effect of nitrogen on soil dissolved organic carbon concentration.•Acidification and nitrogen additions alter enzyme stoichiometry.•Acidification may stimulate soil carbon accumulation. Acidification alters soil carbon fluxes in spruce and beech forests due to the altered soil pH. Limited effect of N addition on soil C cycling in both forest types.