| 15 Oct 2025
2022 drought consequences on nutrient dynamics in forest soil solutions of a declining spruces plot in the Strengbach catchment (Vosges Mountains, France)
Abstract. 2022 was the hottest and driest year ever recorded in France, including within the Strengbach catchment, a Critical Zone Observatory (http://ohge.unistra.fr) located in a forested watershed of the Vosges Mountains and characterized by declining Norway spruce (Picea abies) stands. During and following the summer drought of 2022, an unusual chemical signature was detected in soil solutions, marked by elevated concentrations of K+, Ca2+, Mg2+, NO3-, NH4+, Al3+, and Dissolved Organic Carbon (DOC) with significant variations of fluorescence indices (HIX, BIX and FI). Thanks to interdisciplinary monitoring of soil solution chemistry, the impacts of drought on biogeochemical processes – and more broadly, on forest soil fertility – are now better understood. The 2022 drought induced (1) lower mineral dissolution, (2) reduced plant nutrient uptake, (3) increased concentrations in throughfall (4) biological stress on soil microfauna, leading to organic matter accumulation during the dry period and subsequent release upon rewetting, (5) disruption of the nitrogen cycle, with ammonium accumulation during drought followed by intense nitrification after rainfall resumed, and (6) acidification of the soil solution, enhancing the desorption of both nutrient cations and toxic Al3+. Drought affects forest soil reactivity and fertility through physical (water deficit), chemical (nutrient leaching and acidification), and biological (vegetation and microbiota stress) mechanisms. The decline in soil fertility during and after drought is especially concerning for forest ecosystems already subject to nutrient deficiency, such as those in the Strengbach catchment. Understanding these drought-induced biogeochemical disturbances is essential for predicting ecosystem responses to extreme climatic events, whose intensity and frequency are expected to increase in the Vosges Mountains under ongoing climate change.
