Virginia Institute of Marine Science
Proceedings of the National Academy of Sciences of the United States of America
Terrestrial ecosystem responses to climate change are mediated by complex plant–soil feedbacks that are poorly understood, but often driven by the balance of nutrient supply and demand. We actively increased aboveground plant-surface temperature, belowground soil temperature, and atmospheric CO2 in a brackish marsh and found nonlinear and nonadditive feedbacks in plant responses. Changes in root-to-shoot allocation by sedges were nonlinear, with peak belowground allocation occurring at +1.7 °C in both years. Above 1.7 °C, allocation to root versus shoot production decreased with increasing warming such that there were no differences in root biomass between ambient and +5.1 °C plots in either year. Elevated CO2 altered this response when crossed with +5.1 °C, increasing root-to-shoot allocation due to increased plant nitrogen demand and, consequently, root production. We suggest these nonlinear responses to warming are caused by asynchrony between the thresholds that trigger increased plant nitrogen (N) demand versus increased N mineralization rates. The resulting shifts in biomass allocation between roots and shoots have important consequences for forecasting terrestrial ecosystem responses to climate change and understanding global trends.
Climate change, nitrogen cycling, coastal wetlands, warming
Noyce, Genevieve L.; Kirwan, Matthew L.; Rich, Roy L.; and Megonigal, J. Patrick, Asynchronous nitrogen supply and demand produce nonlinear plant allocation responses to warming and elevated CO2 (2019). Proceedings of the National Academy of Sciences of the United States of America, 116(43), 21623-21628.