Climate change has the potential to alter the cycling and availability of nitrogen in terrestrial ecosystems which would, in turn, mediate the effects of climate change on ecosystem structure and function. The rate and magnitude of climate change also vary geographically, with certain regions of the globe, such as the arctic, experiencing accelerated rates of climate change compared to the global average. To understand how climate change might impact nutrient availability in alpine ecosystems across the globe, we deployed resin strips that absorb soil nutrients available for root uptake in a network of climate change experiments established at high and low elevation sites in ten mountain ranges around the globe. This network used open-top warming chambers to simulate the direct effects of climate change by shifting abiotic conditions as well as a dominant species removal treatment, representing the indirect impact of climate change that occurs as plant communities shift in response to a changing climate. Using this experimental framework, we not only reveal the impact of climate change on the plant-available pools of nutrients, but also investigate the degree to which the existing characteristics of an ecosystem, such as climate and plant community structure, mediate the impact of climate change on nutrient cycling.
Results/Conclusions
By using resin strips to quantify the plant-available nutrient pool across our global climate change experiment network, we found substantial geographic variation in both nitrate (p < 0.001) and ammonium levels (p < 0.001) between global locations, with significant differences in nutrient availability even between high and low elevation sites within the same mountain range (nitrate by elevation: p = 0.002, ammonium by elevation: p < 0.001). While the climate change treatments simulating both the direct and indirect effects of climate change had no discernible impact on ammonium availability (p = 0.307), we found that the interaction between elevation and climate change treatment did have a significant impact on plant-available nitrate levels (p < 0.001). Taken together, these results reveal that climate change might affect certain nitrogen transformations more so than others. Processes that control nitrate availability, such as denitrification, might be more sensitive to abiotic changes than processes related to ammonium pools. In general, our results indicate that nutrient availability in alpine ecosystems globally are highly correlated with the abiotic and biotic characteristics that shape each unique ecosystem, with no clear patterns of nutrient availability across elevational gradients emerging.