This study is led by Drs. Xiaojuan Feng, Chengzhu Liu and Yunpeng Zhao (Institute of Botany, Chinese Academy of Sciences). Wetlands store 600–1000 Gt soil carbon and have the highest soil carbon density among all terrestrial ecosystems, but they are severely threatened by drainage. Recent studies indicate that drainage can promote the formation of metal-bound organic carbon (bound OC) via ferrous iron oxidation, thereby affecting soil organic carbon (SOC) accumulation. However, the response of bound OC to drainage in different types of wetlands remains unclear. To address this knowledge gap, the team conducted a nationwide, pairwise survey of drained wetlands across China that had experienced long-term (15–55 years) artificial drainage. The survey involved replicated pairs (n = 4) of waterlogged vs. drained soils in 32 wetlands (see the first image below), including 18 non- Sphagnum wetlands and 14 Sphagnum wetlands. Combined with literature data, this study compared drainage-induced metallic protection of SOC in Sphagnum vs. non- Sphagnum wetlands and revealed the underlying mechanisms related to SOC preservation under shifting wetland hydrology.
The team found that long-term drainage largely increased metallic protection of SOC (i.e., bound OC%) in non- Sphagnum wetlands due to increased reactive metal (hydr)oxides, but consistently decreased bound OC% in Sphagnum wetlands following replacement of the ‘rust engineer’ Sphagnum by herbaceous plants (see the second image below). Additionally, both SOC and bound OC content decreased in most of the examined soil layers in Sphagnum wetlands after drainage, but increased in most layers of non- Sphagnum wetlands. Improved SOC stock estimates in soil profiles revealed that bound OC increases could compensate for the loss of unbound SOC components in non- Sphagnum wetlands with substantial accrual of reactive metals.
These results suggested that drainage-induced soil carbon stabilization by reactive metals was prevalent in non- Sphagnum wetlands, whereas this mechanism seemed to be weak or absent in the Sphagnum wetlands after drainage. Incorporating this novel mechanism into models will improve prediction of wetland SOC dynamics under shifting hydrological regimes.
See the article:
Metallic protection of soil carbon: Divergent drainage effects in Sphagnum vs. non- Sphagnum wetlands
https://doi.org/10.1093/nsr/nwae17
National Science Review