Effects of shrub encroachment on soil organic carbon in Inner-Mongolian grasslands

Background/Question/Methods

It is still under debate whether or how shrub encroachment in grasslands can change soil organic carbon (SOC). Field evidence is lacking particularly with respect to the vast Mongolian grasslands. Recently, the shrub encroachment has been widely reported for the Inner-Mongolian grasslands, but it is unclear how SOC changes with the shift from grasslands to shrub encroached grasslands (SEGs). In this study, we conducted a field investigation for 48 sites of SEGs and 30 sites of non-shrub encroached grasslands (CGs) across the Inner-Mongolia within an area of 5.3 x 10⁵ km² to examine SOC changes associated with the shrub encroachment in the temperature grasslands.

Results/Conclusions

The results showed that there was a high spatial heterogeneity in SOC, with the SOC content significantly higher within shrub patch than the interspace patch, and this difference was more contrasting in deep-layer soils. Moreover, the SOC density was significantly lower in SEGs than CGs. We also found that the changes of SOC density by shrub encroachment showed no significant correlation with annual precipitation or mean annual temperature. Our study provides first large-spatial scale survey concerning with the shrub encroachment in relation to soil carbon content for the vast temperature grassland, which should provide some insights into our understanding on carbon budget in terrestrial Asia.