Looking for hotspots of nitrogen cycling in an alpine-subalpine watershed: the search continues

Background/Question/Methods Since there is little quantitative information on the location of nitrogen cycling hotspots across landscapes, this project was designed to identify hotspots and develop testable hypotheses about their function. In this study, I employed two common techniques to measure soil N cycling rates. To measure inorganic N availability within the soil, I deployed ion exchange resin bags at 366 locations for one year. To measure net N mineralization and net nitrification, I conducted two-week in situ buried bag incubations at 205 locations during the peak growing season. I identified hotspots within these datasets using a mathematical definition of hotspots that quantifies deviations from the normal distribution. Results/Conclusions Higher values of inorganic N availability were observed within the tree-covered areas, suggesting that some ecological feature associated with the trees leads to higher N cycling rates. These ecological features might include different rates of primary production than herbaceous areas, conifer-specific tissue chemistry effects on soil, or the deeper snow depth in tree-covered areas, which can affect atmospheric inputs of N. The high levels of variation across the landscape for these N cycling rates suggests that a complex interaction of localized biotic and abiotic factors may be responsible for hotspot occurrence.