Relationship between nitrogen deposition and LUCC and its impact on terrestrial ecosystem carbon budgets in China

Increased nitrogen (N) deposition and land-use and land-cover change (LUCC) have influenced the terrestrial ecosystem carbon budget in China over the past few decades. However, the coupling effects of N deposition and LUCC on the carbon cycle remain unclear. This study first evaluated the effects of LUCC on N deposition based on estimated N deposition data from NO2 column remote sensing data and the GlobeLand30 LUCC dataset, and then assessed the coupling effects of N deposition and LUCC on carbon budgets in China based on a terrestrial ecosystem process-based model. The results showed that the average rate of increase in N deposition in China was 0.35 Tg N yr(-1) (Tg = 10(12) g), which caused net primary production (NPP) and net ecosystem production (NEP) to rise by 92.2 Tg C yr(-1) and 46.9 Tg C yr(-1), respectively. The effects of LUCC reduced N deposition by 0.21 Gg N yr(-1) (Gg = 10(9) g). The land changed from forest to cropland had the greatest rate of increase in N deposition among all types of land-cover change. Changes from cropland to forest slowed the rate of N deposition increase the most. Generally, the change in N deposition resulting from LUCC reduced NPP and NEP by 0.7 and 0.4 Gg C yr(-1), respectively. Compared with the total effects of N deposition on NPP and NEP, N deposition changes caused by LUCC had a limited aggregate effect on the C budget.