Warming, Snow Exclusion, and Soil Type Alter the Timing of Plant and Soil Activity and Associated Nutrient Losses

In seasonally snow-covered ecosystems, changing temperatures and snowpack dynamics under climate change have increased the occurrence and duration of soil temperatures that support microbial activity during plant dormancy. During these periods of microbial activity without plant activity (i.e., plant-microbe asynchronies), soil nutrients that build up are vulnerable to leaching loss, with potentially important consequences for ecosystem productivity. Furthermore, asynchronies likely do not occur uniformly in space; rather, their occurrence may be modulated by subsurface characteristics. Soil texture, for example, moderates biogeochemical cycles and water holding capacity, and could mitigate or exacerbate nutrient losses during plant-microbe asynchronies. Here, we quantified how climate change treatments and soil characteristics alter the synchrony of plant and microbial activity, and the associated impacts on leaching of soil nutrients—carbon, nitrogen, phosphorus—and cations prone to mobilization following environmental perturbation—calcium, magnesium, and aluminum. To do this, we conducted a forest sapling mesocosm experiment that imposed replicated warming and snow exclusion treatments on two soils. To estimate the extent and effect of asynchrony, we measured soil temperature and plant phenology over 2 years to develop an index for asynchrony duration, which we correlated with measured nutrient and cation leachate losses. We found that warming consistently increased the duration of plant-microbe asynchrony, with an average increase of 25% across the experiment. Snow exclusion shortened asynchrony duration by 8% on coarse soils in the second year of the experiment. Climate treatments generally elevated nutrient losses from fine but not coarse soils during asynchronies. Longer asynchronies resulted in increased carbon, nitrogen, and magnesium losses, with variation across time, soil type, and nutrient. Our results demonstrate that longer periods of microbial activity in the absence of plant uptake generally compound nutrient losses, but the magnitude of these losses depends on soil type and individual nutrients.