Spatial and temporal variations of N_2O emissions from global forest and grassland ecosystems

摘要

A process-based dynamic ecosystem model of TRIPLEX-GHG was used to estimate the spatial and temporal patterns of N_2O fluxes from global forest and grassland ecosystems under the effects of global warming and elevated CO_2 concentrations. From 1992 to2015, the estimated average N_20 emissions from forests and grasslands were 3.62 ± 0.16 Tg N yr~(-1), and 1.40 ± 0.03 Tg N yr~(-1), respectively. Tropical regions made large contributions (83.9% for forests and 74% for grasslands) to the total N_2O budgets, which were due to the larger N_20 flux values and large natural forest and grassland areas. The regional variations in N_2O emissions mainly resulted from the differences in the spatial distributions of climate characteristics, especially the precipitation patterns. In addition, anomalous years when N_2O emissions were relatively low/high were mainly due to the changes in climate patterns, which may have been induced by El Nino/La Nina events with different strengths and frequencies. Soil N_2O emissions from forests showed a positive effect on the atmospheric N_2O concentrations during June to November (R~2: 0.14-0.28), while those from grasslands showed a positive effect during the growing seasons (R~2: 0.17-0.28). Although natural N_2O sources(forests and grasslands in this study) showed slightly increasing trends, with 9.9 Gg N increment per year for forests and 2.1 Gg N increment per year for grasslands, they were not the main contributors to the elevated N_2O concentrations.