Land use change is one of the most important factors strongly affecting soil organic C (SOC) stocks and dynamics on earth. Land use changes can induce shifts in plant functional diversity and community structure, which lead to differences in plant litter compounds and thus modify SOC decomposition and storage. However, the effects of land use changes on Tibetan grasslands remain unknown.

Dr. QIAO Na of Xishuangbanna Tropical Botanical Garden (XTBG) and researchers from Institute of Geographic Sciences and Natural Resources Research conducted a study to clarify the effects and mechanisms of land use change on SOC dynamics and stocks in these Kobresia grasslands on the Tibetan Plateau.

During microbial decomposition, the light isotope (e.g., C and N) is respired, and the heavy isotope (e.g., C and N) is assimilated into biomass that is subsequently deposited in the soil organic matter. Consequently, isotopic enrichment occurs and reflects increased decomposition of soil organic matter. Therefore, the researchers combined direct measurements of SOC with soil δ¹³C and δ¹⁵N as well as microbial biomass C and N contents to analyze the mechanisms of C and N losses. To achieve more detailed information regarding the effects of land use on SOC, they analyzed soil samples at 5-cm intervals up to 30-cm depth, including ¹³C, δ¹⁵N, bulk density, microbial C, and N contents in three land use types (Kobresia pasture, Elymus pasture, and cropland). 

   The researchers found that land use changes strongly affected the surface layer, because greater difference in SOC, microbial biomass, soil δ¹³C, and soil bulk density were mostly observed in the top 5-cm depth. Furthermore, land use change from grasslands to agricultural uses could cause soil C loss and the magnitude of the C loss depended on the land use types, e.g., conversion to cropland (10 %) led to more C losses than Elymus pasture (1.6 %).

  The researchers thus concluded that the conversion of montane Kobresia grasslands to cropland decreases C stocks, while the C stocks were unchanged after conversion to Elymus pasture.

   The study entitled “Land use change decreases soil carbon stocks in Tibetan grasslands” has been published online in Plant and Soil.

Key words

Grassland, soil organic carbon, conversion, land use, total nitrogen, δ¹³C, δ¹⁵N

Contact

QIAO Na

Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China