Impacts of nitrogen enrichment on ecosystem productivity and GHG emission: A comparative study between China and USA

Abstract:

As the major producers in the agricultural sector, the largest consumers of Nitrogen (N) fertilizer and fossil fuels (only two countries represented 37.61% of global N fertilizer consumption and 39.91% of global fossil fuel consumption), and top two greenhouse gas (GHG) emitters in the world, China and the United States (U.S.) are both facing great challenges of N enrichment which decreases ecosystem productivity and increases GHG emissions. However, there is a lack of comparing study and comprehensive analysis that reveal the differences and similarities in magnitudes and spatiotemporal patterns of these ecological consequences induced by excess N and the mechanisms behind the changes. Through the approach of process-based ecosystem modeling driven by explicit and long-term input datasets (from 1900 to 2016, including climate, atmospheric CO₂ concentration, N fertilization, N deposition, manure application, land use land cover, rotation type, and geographical information), we examine the individual and combined impacts of N fertilization, N deposition, and manure application on terrestrial ecosystem productivity and three major GHG (CO₂, N₂O, CH₄) emissions simultaneously in both countries. We further investigate the coupled effects between N enrichment and climate change on ecosystem productivity and GHG emissions. This study will improve our mechanistic understandings of the various responses of ecosystem productivity and three GHGs to N enrichment in China and the U.S. respectively. The result will also indicate that for each country it is crucial and urgent to develop effective but unique mitigation practices related to N input, although they share many similar characters in economic activities.