Is Nitrogen Becoming Less Available in Terrestrial Ecosystems?

Nitrogen (N) is both necessary for life and potentially harmful to it, so the amount and distribution of reactive forms of nitrogen around the world is an important matter. While N is often viewed as a pollutant (think fertilizer runoff and ocean dead zones), there are reasons to expect that rising atmospheric CO₂ and other global changes are rendering N less accessible to plants and microorganisms. This talk will begin by summarizing the evidence, from sources ranging from pollen chemistry to spectroscopy of cattle manure, that N is indeed becoming less available in many terrestrial ecosystems. N is an essential building block of plant proteins, so the concentration of N in leaves is important for the growth and reproduction of creatures, such as folivorous insects and grazing mammals, that depend on plants for protein. As part of her SESYNC work, Rachel and colleagues have collected a large (almost 100k measurements) and partially crowd-sourced set of foliar N measurements that may reveal global trends in foliar N over time. Analyzing this kind of large and inhomogeneous dataset presents some methodological challenges. In this seminar, she will outline (in as non-technical a manner as possible!) the procedures they are using to maximize the chances of detecting real trends while minimizing the likelihood of false positives. She'll conclude with some reflections on—and questions about—the increasingly large and complex datasets encountered in ecology, and the many concurrent changes the Earth system is undergoing.