Inventory Of Chinese Grasslands Carbon Storage And Greenhouse Gases Emission

Grassland, as the second largest terrestrial ecosystem in China, is of crucial importance for the stability of China's ecosystem. On the background of Global Warming and Climate Change, the dynamic of grassland ecosystem would affect the world more than the local area. How to control the greenhouse gas (GHG) emission has become one of the most important things for human beings due to it's a main factor contributing the global climate change. Ecosystem is a huge complex system. Meanwhile, the GHG emission is closely linked with the soil carbon pool. Therefore, to obtain a clear comprehension of so complicated ecosystem under unknown climate change background is not only good for the protection of the ecosystem and its stable functions but also good for us to find the weakness of the ecosystem so that we can optimize the management practice accordingly. In this paper, we took the whole grassland ecosystem as our research subject and extracted the carbon sequestration, GHG emission and their interrelations with current agricultural practice of grassland in China by modeling the biogeochemical processes in the ecosystem.The result indicates, as the second largest terrestrial ecosystem, the grassland has a large amount of carbon storage and has been playing an important role in the stability of whole China's terrestrial ecosystem. The sequestrations of the grassland carbon and the soil organic carbon are 2.1 GtC and 12.4 GtC, respectively. The grassland of China accounts for 8% of the global grassland area and deposits 7.5% of plant carbon,4.9% of soil carbon and 5% of the total carbon, respectively, of the world. The modeled result also indicate that currently the grassland is in a period of carbon sequestration with an increase of 71±4 Tg C y-1, and the large underground carbon pool, which showed quite obviously in alpine steep and alpine meadow, is one significant portion of China grassland carbon storage. A total carbon deposition with 48.26±9.54 per y (68% of total carbon deposition) for montane grassland region, which accounts for 51% of the total grassland area revealed by our research. From this perspective, montane grassland region has a great potential to sequestrate carbon. The total carbon sequestration of grassland increased from 2000 to 2007; however, there was a decrease trend of temperate grassland storage appearing in west of Mongolia, north of Xinjiang and west of Qinghai-Tibetan plateau highland.N2O is the only non-carbohydrate one of 3 main GHG but its global warming potential is 297 times as CO2's. Current agricultural practice is one main source of N2O increase. N2O emissions in different types of grassland, in China differ from each other. The emissions are 0.23,0.11 and 0.39 kg N ha-1 y-1,respectively for Temperate Grassland, Montane grasslands, Tropical/subtropical grasslands. Grassland in China with a total area of 3.37 billion hectares emitted 76.5 GgN of N2O which equivalent to 9.71 Tg CO2 and counterbalanced 14% of the carbon sequestration of grassland. From 2000 to 2007, a growing tendency appeared for the N2O emission of the whole grassland area. Climate change has played a relative important role on it. Grassland in China suffered an intensive disturbance of human in the last years, which should draw attentions in our future research on the emission mode of N2O of grassland.Although grassland is a methane sink from current research, the amount of sequestration is small with a rate of 226 thousand tons per year. The average methane flux is about 0.95±0.77 Kg C ha-1 y-1 which equivalent to 565 tons of CO2-C and is far smaller than the net sequester rate of CO2 210.62±48.76 Kg C ha-1 y-1. The results suggested that increase the carbon sequestration and reduce N2O emission are priority task in the grassland region.