Researchers: Land-use Influences Both Topsoil and Subsoil Organic Carbon Distribution

As the largest organic carbon (C) pool in earth’s biosphere, soils play a key role in global carbon cycle. Soil carbon is present in two forms: inorganic and organic. Soil inorganic carbon consists of mineral forms of C. Soil organic carbon (SOC) is present as soil organic matter. 

SOC provides plants with substrate and energy, and is therefore significant to secure the food production for both human kind and animals. It also helps to protect the biodiversity of ecological environment, and thus maintains the soil quality and normal function of the ecosystem. 

Soil organic carbon tends to be concentrated in the topsoil, which led to series of studies on the SOC composition of topsoil. But LI Lanhai and his colleagues at the Xinjiang Institute of Ecology and Geography paid their attention to the effect of land-use on profile distribution of recalcitrant C content, especially the previously ignored subsoil SOC composition.  

“Maintenance and sequestration of SOC are great challenges that humankind must face to address the twin crisis of global change and food insecurity,” said LI. 

LI and his colleagues collected soil samples to a depth of 100 cm from pastures and four major croplands including maize field, wheat field, paddy and apple orchard in the Ili River Valley, northwest China. 

The team investigated the effects of land-use on profile distribution of three types of organic C, namely labile organic C (LOC), semi-labile organic C (SLOC), recalcitrant organic C (ROC), and their relative proportions in total organic C (TOC). 

Their results showed that soil TOC contents of croplands were 20.4–85.2% lower than those of pastures along the soil profile. “This indicates that SOC pool may be decreased by agricultural land-uses,” explained LI. 

Further analysis proved that proportions of each SOC fraction in TOC did not show distinct difference between the two soil layers. This means that land-use types can have influence on SOC fraction in subsoil, according to the study. 

ROC in subsoil is crucial for C sequestration, and should therefore be taken into account when estimating the effect of land-use on SOC kinetic, LI suggested. 

The result of the study was published on Science of The Total Environment, entitled “Land-use impacts on profile distribution of labile and recalcitrant carbon in the Ili River Valley, northwest China”.