Carbon mineralization potential in response to land use change

Background/Question/Methods

Soil plays a key role in the global carbon cycle. It contains 1500 Pg of organic carbon in the upper 0-100 cm. Little changes in soil carbon stock will lead to substantial impacts on the concentration of atmospheric CO₂. Land use change is one of important factors impacting soil organic carbon.  The aim of this study is to determine how different land use impact soil carbon mineralization potential.

The study site was conducted at the Semi-Arid Climate and Environment Observatory of Lanzhou University (35^◦57’N, 104^◦09’E). This study site includes four land use types [fenced grassland (FG), grazing grassland (GG), fallow cropland (FC), cultivated cropland (CC)]. The grasslands were restored from cropland since the past 20 years, and the fenced grassland was fenced from October 2005. Soil samples were taken in May, 2008, at 0-10, 10-20, 20-30 cm depths, respectively. The experiment was carried out using incubation method under laboratory conditions.

Results/Conclusions

Our results showed that the temporal changes in CO₂ release were similar in all land use types. A rapidly carbon mineralization occurred  during the first 8 day for all land use types, and followed by a steady and slower carbon mineralization rates. Carbon mineralization in the 0-10 cm soil layer exhibited higher rates than that in the 10-20 and 20-30 layer for all land use types (P<0.05).   The C mineralization rates were significantly higher in grasslands than in croplands only at 0-10cm layer (P<0.01). However, there were no significant differences between FG and GG, or between FC and CC.

      The total amount of CO₂ released during the 64 days incubation ranged from 179.5 to 474.3 mg C·kg^-1 soil in the grasslands, and from 157.2 to 254.6 mg C·kg^-1 soil in the croplands. That equals to 3%-5.7% of total organic carbon in the grasslands and 1.7%-3.5% in croplands.  The amount of CO₂ released decreased with depth in the four land use types. The amount of CO₂ released in grasslands were significantly higher than in croplands at 0-10 and 10-20 cm layers (p<0.05). Our results suggest that soil carbon release in grasslands is more than that in croplands, probably resulting from changes in soil microbial community, SOM quality, and environmental factors.