| Oxygen is an key factor in maintaining biological function, is the fundamental guarantee of human life on earth, is also an important component of the atmosphere. Photosynthesis of terrestrial green vegetation is the main source of oxygen for the atmosphere. The amount of oxygen in the atmosphere directly affects the atmospheric quality. With the C-FIX model in this study, we simulated the Net Ecosystem Productivity (NEP) from the Normalized Difference Vegetation Index (NDVI), temperature, radiation, and CO2 concentration. Following the principle of the carbon-oxygen balance, annual oxygen productions of global terrestrial vegetation in 2001,2004,2007,2010, and 2012 were spatially estimated in ARCGIS, ERDAS, FORTRAN and their influencing factors were analyzed via model simulation. The results showed that:(1) The total annual oxygen production of global terrestrial vegetation is 176.811×109 t from 2001 to 2012, vegetation oxygen production per unit area is 1219.288 t/km2. Monthly oxygen production of global terrestrial vegetation is in the range of 9.651-25.554×109t, monthly oxygen production per unit area is in the range of 62.356-189.357 t/km2. Oxygen production of terrestrial vegetation on all continents, the primacy of South America, average is 50.189×109t, followed by Africa, Asia, and about 40×109 t, while in North America, Europe, Oceania were lower than 20×109 t; Continents oxygen production per unit area order changes slightly, ranking first in South America, the mean value is 2830.131 t/km2, followed by Africa, Oceania, Europe, which were valued at more than 1200 t/km2, and oxygen production per unit area in Asia and North American were lower than 1000 t/km2.(2) Spatial distribution of unit area oxygen production of global terrestrial vegetation were similar from 2001 to 2012, the average correlation coefficient is 0.945, and distribution trend of decreasing gradually from equatorial to polar regions. Among them, high oxygen production value of terrestrial vegetation mainly distributed in parts of Southeast Asia, Central Africa, Southern America and northern South America, the amount of oxygen production unit area in 4000 t/km2 or more; While oxygen productions of the Sahara desert in Africa, West Asia, South Chile of southern America, China's Taklimakan desert and Greenland were close to zero. Monthly oxygen production of global terrestrial vegetation change significantly over months, January July spatial distribution of oxygen production in high value areas gradually moved north from the southern hemisphere to the northern hemisphere; August-December high oxygen production areas were moved from the northern hemisphere to the southern hemisphere.(3) Interannual change of oxygen production of global terrestrial vegetation was decreased and then increased trend, but was not significantly increased during 2001-2012. Compared with 2001, vegetation oxygen production increased 8.216×109t in 2012, with an average annual growth rate of 0.389% and annual variation coefficient of 0.023. Oxygen production on all continents showed an increasing trend from 2001 to 2012, North America, Europe increased significantly, while Asia, South America, Oceania and Africa didn't increase significantly. Spatial distribution of oxygen production variation were obvious from 2001 to 2012, reduction region and increased regional of oxygen production were distributed in the southern hemisphere and the northern hemisphere, increased area, reducing area, did not change the percentage of the the world's land mass were 51.782%,28.614%,19.604%, increased area is to reducing area of 1.8 times.(4) Terrestrial vegetation changes lead to global oxygen production decreased slightly, while climate change (temperature and solar radiation), changes in CO2 concentration in the atmosphere increased oxygen production of global terrestrial vegetation. Among them, the increase in atmospheric CO2 concentration is the main cause of changes in global oxygen production. In all continents, vegetation change is the dominant factor in Asia, but the dominant factor in North America, South America, Oceania, Africa were changes in CO2 concentration and climate change as the main reason in Europe. |
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