Variations in diurnal and seasonal net ecosystem carbon dioxide exchange in a semiarid sandy grassland ecosystem in China's Horqin Sandy Land

[摘要] Grasslands are major terrestrial ecosystems in arid and semiarid regions, and they play important roles in the regional carbon dioxide ( CO 2 ) balance and cycles. Sandy grasslands are sensitive to climate change, yet the magnitudes, patterns, and environmental controls of their CO 2 flows are poorly understood for some regions (e.g., China's Horqin Sandy Land). Here, we report the results from continuous year-round CO 2 flux measurements for 5 years from a sandy grassland in China's Horqin Sandy Land. The grassland was a net CO 2 source at an annual scale with a mean annual net ecosystem CO 2 exchange (NEE) of 49  ±  8  g C m - 2 yr - 1 for the years for which a complete dataset was available (2015, 2016, and 2018). Annual precipitation had the strongest effect on annual NEE; grassland carbon sequestration increased with the increasing precipitation since NEE depended on annual precipitation. In the spring, NEE decreased (i.e., C sequestration increased) with increasing magnitude of effective precipitation pulses, total monthly precipitation, and soil temperature ( T soil ). In the summer, NEE was dominated by the total seasonal precipitation and high precipitation pulses ( >  20  mm ). In the autumn, NEE increased (i.e., C sequestration decreased) with increasing effective precipitation pulses, T soil , and near-surface soil water content (SWC) but decreased with increased SWC deeper in the soil. In the winter, NEE decreased with increasing T soil and SWC. The sandy grassland was a net annual CO 2 source because drought decreased carbon sequestration by the annual plants. Long-term observations will be necessary to reveal the true source or sink intensity and its response to environmental and biological factors.

[学科分类] 大气科学