Windthrow modifies soil solution chemistry and nutrient leaching in the Canadian black spruce boreal forest

Abstract

Soil solution chemistry is directly related to vegetation nutrition and growth in forest ecosystems. However, the impacts of natural disturbances on boreal forest soil solution composition and nutrient fluxes remain unclear. In this study, we explore the effects of a windthrow on soil solution chemistry collected weekly between 2012 and 2018 during the snow-free period at a Canadian black spruce boreal forest site. We show that the windthrow had an important effect on soil solution chemistry within only a few days, inducing much higher NO₃⁻ and NH₄⁺ concentrations and a strong pH drop, persisting up to six years after the disturbance. Following the windthrow, soil solution major ion concentrations (i.e., K⁺, Ca²⁺, Mg²⁺, Mn²⁺, Cl⁻, SO₄²⁻) similarly increased but with various intensities and recovery times. This windthrow also occurred on a site receiving a chronic ammonium nitrate treatment as part of a N deposition simulation experiment, which showed that two decades of N treatment had nearly no impacts on soil solution NO₃⁻ and NH₄⁺ concentrations. Therefore, our results indicate that windthrows could potentially alter the North American boreal forest soil chemistry much more than elevated N deposition corresponding to 200 years of accelerated ambient N deposition. While this finding needs to be supported by larger studies, it clearly highlights the significance of wind disturbances’ impacts on nutrient cycling and calls for more research as windthrow frequency is predicted to increase with global change.