Rapid acclimation of topsoil physicochemical and biotic properties to experimental climate change

Climate change rapidly alters the conditions which govern the differentiation of soils, with implications for the wide range of indispensable ecosystem functions that soils provide. The ability of soils to perform these functions in the future will depend on how quickly soil physicochemical and biotic properties respond to warming. On the one hand, soil development is a process that takes millennia. On the other hand, soil processes are mediated by chemical and microbial reactions that can be very rapid, potentially altering soil functioning over a period of months to years. In addition, soils are highly diverse depending on parent material and environmental conditions. As a result, simple questions about soil-climate responses remain unanswered: How long does it take for soil to acclimate to a changed climate? And do some soil properties acclimate faster than others?

 

Here, we addressed these questions with a novel approach which combines elevation gradients with soil transplantation experiments. Elevation gradients are used to study the potential long-term effects of climate, because they can control for parent material while allowing soils to acclimate to climate differences between elevations over long periods of time. Transplant experiments across elevation are warming experiments in which the elevational changes in climate across space are used to investigate short-term climatic responses. Based on the assumption of space-for-time, soils at low elevation can represent the expected state of transplanted soils that have fully acclimated to a new climate over longer timescales. Observations across different transplant experiments thereby provide the opportunity to see whether and how quickly short-term changes converge on expected longer-term changes. To this end, we collected topsoils from eleven elevational transplant experiments across the Alps, Scandinavia and the Rocky Mountains which varied in experiment duration between 1-9 years. We analyzed elevational differences and short-term warming-responses of organic matter dynamics (pools and fluxes), organic matter characteristics (e.g. fraction, functional groups, thermal stability), microbial communities (bacteria, fungi) and soil physicochemistry (pH, particle size, weathering products).  

 

We found that short-term responses of soils to warming were mainly in the same direction as expected changes based on elevational differences between soils. Moreover, different types of soil properties acclimated at comparable and rapid paces: Organic matter dynamics had acclimated to warmer climate by up to 57% of expected change (16% on average across sites). Organic matter characteristics had acclimated by up to 74% (14% average), microbial communities by up to 82% (average 14%) and soil physicochemistry by up to 67% (23% average). Acclimation was significantly related to experiment duration for organic matter dynamics, microbial communities and soil physicochemistry. The observed relationships suggest that, with simplistic assumptions, soils would fully acclimate to the experimental climate change within two decades. Based on climate projections, we estimated that the experiments simulated an average cumulative warming of four to five decades. Taken together, we conclude that topsoil properties can respond rapidly to climate change, implying that many soil functions could keep up with climate change without major time lags.