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

Abstract. Grasslands are major terrestrial ecosystems in arid and semiarid regions, and they play important roles in the regional carbon dioxide (CO2) balance and cycles. Sandy grasslands are sensitive to climate change, yet the magnitudes, patterns, and environmental controls of their CO2 flows are poorly understood for some regions (e.g., China's Horqin Sandy Land). Here, we report the results from continuous year-round CO2 flux measurements for 5 years from a sandy grassland in China's Horqin Sandy Land. The grassland was a net CO2 source at an annual scale with a mean annual net ecosystem CO2 exchange (NEE) of 49 ± 8 gCm-2yr-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 (Tsoil). 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, Tsoil, and near-surface soil water content (SWC) but decreased with increased SWC deeper in the soil. In the winter, NEE decreased with increasing Tsoil and SWC. The sandy grassland was a net annual CO2 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.

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

10.5194/bg-2020-89-supplement ◽

2020 ◽

Author(s):

Yayi Niu ◽

Yuqiang Li ◽

Hanbo Yun ◽

Xuyang Wang ◽

Xiangwen Gong ◽

...

Keyword(s):

Carbon Dioxide ◽

Carbon Dioxide Exchange ◽

Horqin Sandy Land ◽

Sandy Land ◽

Grassland Ecosystem ◽

Ecosystem Carbon ◽

Supplementary Material ◽

Sandy Grassland

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

10.5194/bg-2020-89 ◽

2020 ◽

Author(s):

Yayi Niu ◽

Yuqiang Li ◽

Hanbo Yun ◽

Xuyang Wang ◽

Xiangwen Gong ◽

...

Keyword(s):

Carbon Dioxide ◽

Terrestrial Ecosystems ◽

Soil Heat Flux ◽

Carbon Dioxide Exchange ◽

Co2 Absorption ◽

Horqin Sandy Land ◽

Sandy Land ◽

Environmental Controls ◽

Annual Scale ◽

Sandy Grassland

Abstract. Grassland ecosystems are major components of the terrestrial ecosystems in arid and semiarid regions, and play important roles in the regional carbon dioxide (CO2) balance and cycle. Sandy grasslands are sensitive to climate change, yet the magnitudes, patterns, and environmental controls of their CO2 flows are poorly understood. Here, we report the results from continuous year-round CO2 observations in 5 years from a sandy grassland in the Horqin Sandy Land. The result showed that the sandy grassland was a CO2 source at annual scale (with mean annual net ecosystem CO2 exchange (NEE) of 48.88 ± 8.10 g C m−2 yr−1 in completely year 2015, 2016 and 2018), the total precipitation was the most important factor for NEE. At the seasonal scale, the sandy grassland showed a CO2 absorption during the summer, and in the rest of the seasons, it were all expressed as CO2 release. The main environmental factor of NEE were temperature and soil water content (SWC) in spring, radiation in summer, soil heat flux (SHF) and temperature in autumn, and SWC and temperature in winter. At the diel scale, net radiation (Rn) was the most important factor of NEE in all seasons. The sandy grassland may have been a net annual CO2 source at annual scale because the study site is recovering from degradation, thus vegetation productivity is still relatively low. Therefore, the ecosystem has not yet transitioned to a CO2 sink and long-term observations will be necessary to reveal the true source or sink intensity and its response to environmental and biological factors.

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Effectiveness of shrub planting and grazing exclusion on degraded sandy grassland restoration in Horqin sandy land in Inner Mongolia

Ecological Engineering ◽

10.1016/j.ecoleng.2014.10.004 ◽

2015 ◽

Vol 74 ◽

pp. 164-173 ◽

Cited By ~ 28

Author(s):

Renhui Miao ◽

Deming Jiang ◽

Ala Musa ◽

Quanlai Zhou ◽

Meixia Guo ◽

...

Keyword(s):

Inner Mongolia ◽

Grassland Restoration ◽

Horqin Sandy Land ◽

Sandy Land ◽

Grazing Exclusion ◽

Sandy Grassland

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Biomass Accumulation and Carbon Sequestration in an Age-Sequence of Mongolian Pine Plantations in Horqin Sandy Land, China

Forests ◽

10.3390/f10020197 ◽

2019 ◽

Vol 10 (2) ◽

pp. 197 ◽

Cited By ~ 5

Author(s):

Xiao Zhang ◽

Xueli Zhang ◽

Hui Han ◽

Zhongjie Shi ◽

Xiaohui Yang

Keyword(s):

Carbon Sequestration ◽

Forest Floor ◽

Developmental Stages ◽

Northern China ◽

Stand Age ◽

Horqin Sandy Land ◽

Sandy Land ◽

Carbon Density ◽

Tree Biomass ◽

Ecosystem Carbon

The Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) was first introduced to the southeastern Horqin sandy land in the mid-1950s. Since then, it has been widely planted and has become the most important conifer species in Northern China, providing significant ecological, economic and social benefits. However, its function in sequestering carbon at different developmental stages has been little studied. In this study, twenty plots inventory and destructive sampling of eight trees were conducted in 12-, 19-, 34-, 48- and 58-year-old Mongolian pine stands of China. Allometric biomass equations (ABEs) for tree components were established and used to determine the magnitude and distribution of tree biomass and carbon density. The carbon density of the understory, forest floor and soil was also determined. The ABEs with age as the second variable could simply and accurately determine the biomass of plantation tree branches, foliage and fruit, which were considerably influenced by age. With increasing stand age, the proportion of stem biomass to total tree biomass increased from 22.2% in the 12-year-old stand to 54.2% in the 58-year-old stand, and the proportion of understory biomass to total ecosystem biomass decreased, with values of 7.5%, 4.6%, 4.4%, 4.1% and 3.0% in the five stands. The biomass of the forest floor was 0.00, 1.12, 2.04, 6.69 and 3.65 Mg ha−1 in the five stands. The ecosystem carbon density was 40.2, 73.4, 92.9, 89.9 and 87.3 Mg ha−1 in the 12-, 19-, 34-, 48-, and 58-year-old stands, in which soil carbon density accounted for the largest proportion, with values of 67.4%, 76.8%, 73.2%, 63.4%, and 57.7% respectively. The Mongolian pine had the potential for carbon sequestration during its development, especially in the early stages, however, in the later growth stage, the ecosystem carbon density decreased slightly.

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