Initial responses of soil chemical properties to simulated warming in Norway spruce (Picea abies (L.) H.Karst.) stands in the Western Carpathians

[Display omitted] •A soil warming experiment in a Norway spruce stand for 476 days was performed.•Warming negatively influenced the stability of the soil organic matter.•Simulated warming increased dissolved organic carbon and nitrogen concentrations.•Warming increased soil pH and ammonium nitrogen of the soil organic matter.•The changes may contribute to reduced resilience of Norway spruce stands to warming. The present-day decline observed in Norway spruce stands in the Western Carpathians is particularly worrying given the large forest area of this species. Relatively little attention has been paid to the contribution of soil chemistry to the Norway spruce decline in the context of global warming. We conducted a field experiment to simulate warming for almost 500 days in the Western Carpathians, in a mature Norway spruce stand. Soil samples were collected approximately every 3 months from the organic and mineral topsoil horizons. Total carbon, total nitrogen, pH, dissolved organic carbon (DOC), total dissolved nitrogen (TDN), nitrate (NO3-N), and ammonium (NH4-N) nitrogen concentrations were estimated. Warming caused increase in DOC, TDN, NH4-N, and pH in organic horizon, as well as increased pH in mineral topsoil. A trend for increasing total carbon and total nitrogen concentrations in the warmed organic horizon was observed. Increased concentrations of DOC and TDN may be associated with decrease in SOM stability or increase in production of biomass of the understory vegetation or soil microbial activity. Increased pH in warmed soil may be associated with the increased NH4-N and may contribute to the decrease in soil ability to adsorb DOC. We conclude that soil warming negatively stimulates soil organic matter stability, resulting in higher concentrations of easy migrating labile forms, mostly organic acid anions. Observed changes may contribute to the deterioration of Norway spruce stands.