Paleo-Progressive Nitrogen Limitation (PNL)
Is nitrogen (N) availability to plants increasing or decreasing over time? Global environmental changes such as N deposition, climate warming and increasing atmospheric CO2 concentrations are driving complex changes in N cycling within ecosystems. The Progressive Nitrogen Limitation (PNL) hypothesis posits that as atmospheric CO2 concentrations increase, plants will become increasingly nitrogen-limited; this will have strong negative impacts on primary productivity of ecosystems worldwide. A global synthesis of stable nitrogen isotope (δ15N) records has been conducted in order to test the progressive nitrogen limitation hypothesis for both recent and ancient periods of increasing atmospheric CO2. Our results, which were published in Nature, demonstrated that long-term declines in N availability are an important but overlooked negative consequence of rising carbon sequestration within biomass. Collaborators on this project include Kendra McLauchlan, and Joseph Craine (Kansas State University) and Joseph Williams (Aberystwyth). New research involving Marc Macias-Fauria will utilise shrub wood δ15N to investigate the potential for nitrogen to limit deciduous shrub growth in the Arctic tundra.